University of Khartoum Faculty of Medicine Postgraduate Medical Studies Board

THE EXPERIENCE OF CONTACT LENS WEAR AMONG SUDANESE PATIENTS

By Dr. Musa Suliman El Khidir M.B.B.S (U. of Gezira)

A thesis submitted in partial fulfillment for the requirement of the degree of Clinical MD in Ophthalmic Surgery and Medicine 2003

Supervisor Dr. Abd El Rahman Diab Mohamed M.B.B.CH (Ain Shams University) M.O.S.M (U of K)

‫)ﺳﺒﺤﺎﻧﻚ ﻻ ﻋﻠﻢ ﻟﻨﺎ إﻻ ﻣﺎ ﻋﻠﻤﺘﻨﺎ إﻧﻚ أﻧﺖ اﻟﻌﻠﻴﻢ‬ ‫اﻟﺤﻜﻴﻢ(‬

‫ﺻﺪق اﷲ اﻟﻌﻈﻴﻢ‬ ‫ﺳﻮرة اﻟﺒﻘﺮة‬ ‫ﺁﻳﺔ رﻗﻢ )‪(32‬‬

To my family And friends … With love … Musa

CONTENTS SUBJECT

PAGE

- Acknowledgement - Abstract (English) - Abstract (Arabic) - Abbreviations - List of tables - List of figures

i ii iv vi vii viii

CHAPTER ONE Introduction & Literature Review Objectives

1 42

CHAPTER TWO Materials and Methods

43

CHAPTER THREE Results

47

CHAPTER FOUR Discussion Conclusion Recommendations References Appendix

73 82 83 85

ACKNOWLEDGEMENT

I am extremely grateful to my supervisor Dr. A/Rahman Diab, the assistant Prof. of ophthalmology, U of K for his supervision, constant support, criticism, wise guidance and encouragement.

I am greatly indebted to Prof. E. E. Tabidi for help and cooperation and without whom this work would not have been completed. I would also like to thank Mr. Hassan Ali for the data analysis. I would also like to express my gratitude to Miss. Shereen for typing and organizing this work. I wish to acknowledge the help and constructive comments made in preparation of this work, namely by Dr. Waly Eldin and Dr. Anas Jabir. I would also like to thank may patients for cooperation and help and without whom this work would not have come into reality. I also wish to express my sincere thanks to my family for their patience and unlimited support. Finally, I remain indebted to all who took part in this work.

ABSTRACT

Objectives: To determine the indications and difficulties of contact lens wear (CLW) in Sudanese patients. Methods : Background: This study was conducted in a private contact lens clinic during the period January 2003 until August 2003. Eighty patients (160 eyes) were included in a descriptive cross-sectional study. A

questionnaire

designed

containing

all

necessary

information was completed. Refraction and complete ocular examination were performed for each patient. Contact lens trial was performed after which the appropriate contact lens (CL) was chosen. The patients were then given all necessary instructions concerning lens manipulation and asked to come for follow up after one month where refraction and slit lamp examination were routinely carried out. Lens position, movement and fit were checked. The patients were then seen at 3-months interval. Student t-test and Chi-squared analysis were used.

Results : The major indication of CLW was ‘visual’ of which anisometropia was the commonest, 21 patients (26.2%). Others were simple myopia 16 patients (20.0%), high myopia 11 patients (13.6%) and myopic astigmatism, high hypermetropia and hypermetropic astigmatism one patient each (1.3%). Other indications were: 1- Therapeutic: Keratoconus (KC) nine patients (11.2%), surgical aphakia six patients (7.5%), corneal irregularities two patients (2.5%) and protective, albinisms and bullous keratopathy one patient each (1.3%). 2- Cosmetic: Microphthalmos one patient. Thirty-five patients (43.7%) had no difficulty with CLW. Most of those who had difficulty with CLW found them expensive 17 patients (21.3%). Nine patients (11.3%) suffered from lens spoilage, four patients (5.0%) found them intolerable, three patients (3.7%) found them difficult to use and three patients found them to be tedious. Conclusion: The major indication of CLW in Sudan was visual among which anisometropia was the commonest. Difficulties of CLW

were minor and insignificant and mostly related to the cost of CL services.

‫ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ‬

‫ﻣﻠﺨــﺺ اﻟﺪراﺳــﺔ‬ ‫هﺬﻩ اﻟﺪراﺳﺔ أﺟﺮﻳﺖ ﻓﻲ ﻋﻴﺎدة ﺧﺎﺻﺔ ﻟﻠﻌﺪﺳﺎت‬ ‫اﻟﻼﺻﻘﺔ ﻓﻲ اﻟﻔﺘﺮة ﻣﺎ ﺑﻴﻦ ﻳﻨﺎﻳﺮ ‪2003‬م وﺣﺘﻰ‬ ‫أﻏﺴﻄﺲ ‪2003‬م‪.‬‬ ‫اﻟﻐﺮض‪:‬‬ ‫ﺗﺤﺪﻳﺪ اﻟﺪواﻋﻲ واﻟﻤﺸﺎآﻞ ﻻﺳﺘﺨﺪام اﻟﻌﺪﺳﺎت‬ ‫اﻟﻼﺻﻘﺔ ﻓﻲ اﻟﻤﺮﺿﻰ اﻟﺴﻮداﻧﻴﻴﻦ‪.‬‬ ‫اﻟﻄﺮق‪:‬‬ ‫ﺗﻢ ﻓﺤﺺ ‪ 160‬ﻋﻴﻨًﺎ ﻟـ ‪ 80‬ﻣﺮﻳﻀًﺎ‪ .‬أﺧﺬت آﻞ‬ ‫اﻟﻤﻌﻠﻮﻣﺎت اﻟﻼزﻣﺔ ﻋﻦ ﻃﺮﻳﻖ اﺳﺘﺒﻴﺎن‪ .‬أﺟﺮي آﺸﻒ‬ ‫اﻟﺒﺼﺮ وآﺸﻒ آﺎﻣﻞ ﻟﻠﻌﻴﻦ ﻟﻜﻞ ﻣﺮﻳﺾ‪ .‬ﺑﻌﺪ ذﻟﻚ ﺗﻢ‬

‫اﺧﺘﻴﺎر اﻟﻌﺪﺳﺔ اﻟﻼﺻﻘﺔ اﻟﻤﻨﺎﺳﺒﺔ ﻟﻠﻤﺮﻳﺾ ﺣﺴﺐ‬ ‫ﺣﺎﻟﺘﻪ‪ .‬أﻋﻄﻲ اﻟﻤﺮﻳﺾ اﻟﺘﻌﻠﻴﻤﺎت اﻟﻼزﻣﺔ ﻟﻠﺘﻌﺎﻣﻞ ﻣﻊ‬ ‫اﻟﻌﺪﺳﺔ اﻟﻼﺻﻘﺔ وﻃﻠﺐ ﻣﻨﻪ اﻟﺤﻀﻮر ﻟﻠﻤﺮاﺟﻌﺔ ﺑﻌﺪ‬ ‫ﺷﻬﺮ ﻟﻤﺮاﺟﻌﺔ آﺸﻒ اﻟﻨﻈﺮ وﻓﺤﺺ آﺎﻣﻞ ﻟﻠﻌﻴﻦ‬ ‫ﻟﻤﺮاﻗﺒﺔ وﺿﻊ وﺣﺮآﺔ اﻟﻌﺪﺳﺔ‪ .‬ﺑﻌﺪ ذﻟﻚ ﻃﻠﺐ ﻣﻦ‬ ‫اﻟﻤﺮﻳﺾ اﻟﺤﻀﻮر ﻟﻠﻤﺮاﺟﻌﺔ آﻞ ‪ 3‬أﺷﻬﺮ ﻣﺎﻟﻢ ﻳﻜﻦ‬ ‫هﻨﺎك أﺳﺒﺎب أﺧﺮى ﻟﻠﺤﻀﻮر ﻗﺒﻞ ﻣﻮﻋﺪ اﻟﻤﺮاﺟﻌﺔ‪.‬‬ ‫اﻟﻨﺘﺎﺋﺞ‪:‬‬ ‫اﻟﺪاﻋﻲ اﻟﺮﺋﻴﺴﻲ ﻻﺳﺘﺨﺪام اﻟﻌﺪﺳﺎت اﻟﻼﺻﻘﺔ آﺎن‬ ‫ﻷﻏﺮاض إﺑﺼﺎرﻳﺔ وهﻲ‪ :‬ﻻ ﺗﺴﺎوي اﻟﺤﺎﻟﺔ اﻹﺑﺼﺎرﻳﺔ‬ ‫ﺑﺎﻟﻌﻴﻨﻴﻦ )‪) (%26.2‬وﺟﻮد ﻓﺮق آﺒﻴﺮ ﺑﻴﻦ اﻟﻌﻴﺐ‬ ‫اﻻﻧﻜﺴﺎري ﻟﻠﻌﻴﻨﻴﻦ(‪ ،‬ﻗﺼﺮ اﻟﻨﻈﺮ اﻟﺒﺴﻴﻂ )‪، (%20‬‬ ‫ﻗﺼﺮ اﻟﻨﻈﺮ اﻟﻮﺧﻴﻢ )اﻟﻤﺮﺿﻲ( )‪ ، (%13.6‬ﻗﺼﺮ‬ ‫اﻟﻨﻈﺮ اﻟﻼ ﻧﻘﻄﻲ )‪ ، (%11.2‬ﻃﻮل اﻟﻨﻈﺮ اﻟﻮﺧﻴﻢ‬ ‫وﻃﻮل اﻟﻨﻈﺮ اﻟﻼ ﻧﻘﻄﻲ )‪ (%1.3‬ﻟﻜﻞ‪.‬‬

‫اﻟﺪواﻋﻲ اﻷﺧﺮى‪:‬‬ ‫‪ (1‬ﻋﻼﺟﻴﺔ وهﻲ ‪ :‬اﻟﻘﺮﻧﻴﺔ اﻟﻤﺨﺮوﻃﻴﺔ‬ ‫)‪ ، (%11.2‬اﺳﺘﺌﺼﺎل اﻟﻌﺪﺳﺔ اﻟﺒﻠﻮرﻳﺔ اﻟﺠﺮاﺣﻲ‬ ‫)‪ ، (%7.5‬ﻋﺪم اﻧﺘﻈﺎم ﺳﻄﺢ اﻟﻘﺮﻧﻴﺔ )‪، (%2.5‬‬ ‫اﻋﺘﻼل اﻟﻘﺮﻧﻴﺔ اﻟﻔﻘﺎﻋﻲ وﺣﻤﺎﻳﺔ اﻟﻘﺮﻧﻴﺔ )‪(%1.3‬‬ ‫ﻟﻜﻞ‪.‬‬ ‫‪ (2‬ﺗﺠﻤﻴﻠﻴﺔ وهﻲ ‪ :‬ﺻﻐﺮ ﺣﺠﻢ اﻟﻌﻴﻦ )‪.(%1.3‬‬ ‫وﺑﺪراﺳﺔ اﻟﺼﻌﻮﺑﺎت اﻟﺘﻲ ﺗﻮاﺟﻪ ﻣﺴﺘﺨﺪﻣﻲ اﻟﻌﺪﺳﺎت‬ ‫اﻟﻼﺻﻘﺔ وﺟﺪ أن ‪:‬‬ ‫‪ 35‬ﻣﺮﻳﻀًﺎ )‪ (%43.7‬ﻟﻴﺴﺖ ﻟﺪﻳﻬﻢ ﻣﺸﺎآﻞ ﻓﻲ‬ ‫اﺳﺘﺨﺪام اﻟﻌﺪﺳﺎت اﻟﻼﺻﻘﺔ‪ .‬أآﺜﺮ هﺬﻩ اﻟﻤﺸﺎآﻞ‬ ‫هﻲ ﺛﻤﻨﻬﺎ وﺛﻤﻦ ﺧﺪﻣﺎﺗﻬﺎ اﻟﺒﺎهﻆ ‪ 17‬ﻣﺮﻳﻀًﺎ‬ ‫)‪ 9 ، (%21.3‬ﻣﺮﺿﻰ‬

‫)‪(%11.3‬‬

‫ﻋﺎﻧﻮا ﻣﻦ ﺗﺨﺮﻳﺐ اﻟﻌﺪﺳﺎت ‪ 4 ،‬ﻣﺮﺿﻰ )‪(%5‬‬ ‫وﺟﺪوا اﻟﻌﺪﺳﺎت ﻣﻬﻴﺠﺔ ﻟﻠﻌﻴﻦ و ‪ 3‬ﻣﺮﺿﻰ‬ ‫)‪ (%3.7‬وﺟﺪوهﺎ ﻣﻤﻠﺔ‪.‬‬

‫اﻟﺨﻼﺻﺔ‪:‬‬ ‫وﺟﺪ أن أآﺜﺮ دواﻋﻲ اﺳﺘﺨﺪام اﻟﻌﺪﺳﺎت اﻟﻼﺻﻘﺔ‬ ‫ﻓﻲ اﻟﺴﻮدان هﻮ اﻻﺑﺼﺎرﻳﺔ وأآﺜﺮهﺎ ﻋﻠﻰ اﻹﻃﻼق هﻮ‬ ‫ﻻ ﺗﺴﺎوي اﻟﺤﺎﻟﺔ اﻹﺑﺼﺎرﻳﺔ ﺑﺎﻟﻌﻴﻨﻴﻦ‪.‬‬ ‫ﻣﺸﺎآﻞ اﺳﺘﺨﺪام اﻟﻌﺪﺳﺎت اﻟﻼﺻﻘﺔ ﺑﺴﻴﻄﺔ وﻏﻴﺮ‬ ‫ﺧﻄﻴﺮة ﺟﻠﻬﺎ ﻣﺮﺗﺒﻂ ﺑﺜﻤﻨﻬﺎ وﺛﻤﻦ ﺧﺪﻣﺎﺗﻬﺎ‪.‬‬

ABBREVIATIONS 12-R-HETE

12-R-Hydroxyeicosatetraenoic

CL(s)

Contact Lens (es)

CLW

Contact Lens Wear

CLWs

Contact Lens Wearers

D

Dioptre

Dk

Oxygen Permeability

EOZ

External Optical Zone

GPC

Giant Papillary Conjunctivitis

HCLWs

Hard Contact Lens Wearers

HEMA

Hydroxyethyl Methacrylate

HM

Ha n d M o v e m e n t

HMP

Hexose Monophosphate

KC

Keratoconus

KTEH

Khartoum Teaching Eye Hospital

NAD

No Abnormality Detected

pH

Hydrogen Ion Concentration

PL

Perception of Light

PMMA

Polymethylmethacrylate

RGP

Rigid Gas Permeable

SCLWs

Soft Contact Lens Wearers

U.K

United Kingdom

U.S.A

United States of American

UVR

Ultraviolet Radiation

VA

Visual Acuity

LIST OF TABLES No. of table

Subjects

Page

Age distribution among the study population Table (3.1)

Table (3.2)

Table (3.3)

Table (3.4)

Table (3.5)

Table (3.6)

Table (3.7) Table (3.8) Table (3.9)

Table (3.10)

53 Distribution of the study population according to duration of contact lens wear Distribution of uncorrected V.A among the study population Distribution of corrected V.A with glasses among the study population Distribution of corrected V.A with contact lenses among the study population Indications of contact lens wear among the study population Difficulties of contact lens wear among the study population Difficulties in relation to type of contact lens Difficulties in relation to duration of contact lens wear Fundal abnormalities in relation to corrected V.A with contact lenses

60

65

66

67

68

69 70 71

72

LIST OF FIGURES No. of figure Figure (3.1)

Figure (3.2)

Figure (3.3)

Figure (3.4)

Figure (3.5)

Figure (3.6)

Figure (3.7)

Figure (3.8)

Figure (3.9)

Figure (3.10)

Subjects

Page 54

Sex distribution among the study population Distribution

of

the

study

population

55

study

population

56

according to residence Distribution

of

the

according to occupational environment Distribution

of

the

study

population

57

population

58

according to the affordability Distribution

of

the

study

according to the educational status Type of contact lens worn among the study

59

population Regularity of contact lens wear among the

61

study population Presenting complaint of the study population Fundal

abnormalities

among

the

study

population Ocular motility defects among the study population

62

63

64

1. INTRODUCTION & LITERATURE REVIEW 1.1 Anatomy and physiology of the cornea and related structures: 1.1.1 The cornea:The transparent cornea forms the anterior one-sixth of the eyeball. Seen from the front it is elliptical in shape. Approximate measures are about 10.6 mm vertically and 11.7 mm horizontally. Posteriorly, it is concave and circular, measuring about 11.7 mm in diameter. It is thinnest at its centre, the optical centre, measuring about 0.5 to 0.6 mm and thickest at the periphery measuring about 0.7 mm. The anterior and posterior radii of curvature are about 7.7 mm and 6.9 mm, respectively (1,2). The cornea, with a refractive index of 1.38, is the main structure responsible for refraction of light entering the eye, separating air, with a refractive index of 1.00, from the aqueous humour, with a refractive index of 1.33

(1, 3)

. Accurate measurement of the corneal shape is

important to understand the optical characteristics of an individual eye and in the fitting and optics of CLs (4). The cornea has five layers: epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium(1).

The pre- corneal tear film: It is a thin layer covering the anterior surface of the cornea. Functionally, it provides a smooth optical surface and lubrication for the cornea, protects the epithelium from air-borne contaminants and provides natural immunity to infectious agents through secretory immunoglobulins.

A major proportion of tears is drained from palpebral fissure through the nasolacrimal duct and a smaller volume lost through evaporation from the ocular surface. Tear ingredients include various electrolytes, metabolites, proteins, enzymes and lipids. The anterior-most layer is the lipid or oily layer, and is derived from the meibomian glands. It retards evaporation of tears and prevents their overflow. The middle aqueous or lacrimal layer is the thickest and is secreted by the lacrimal glands. The posterior mucus layer is derived from conjunctival goblet cells, and it provides a smooth wettable surface for the aqueous layer by reducing the surface tension. CLs gain adherence to the cornea by means of the surface tension of tear film. The lens is in contact with the tear film on its posterior surface and is covered by the tear film on its anterior surface (5).

The epithelium: It is the anterior-most layer of the cornea and is several cell layers thick. It is approximately 50 micron thick. The functions of the epithelium are two-folds: 1-

To form a barrier between the external environment and stroma.

This barrier is formed by the tight junctions between the epithelial cells (zonula occludens), which serve as a semi-permeable highly resistant membrane. This barrier prevents movement of fluid from the tears into the stroma and also protects the cornea and

intraocular structures from

infections by pathogens. Over night rigid lens wear causes hypoxia and increases the permeability of the cornea and this impairs the barrier’s function (6). 2-

To form a smooth refractive surface on the cornea through

interaction with the tear film. The microvilli and microplica on the surface of the most superficial cells are covered with a glycocalyx that interacts

with the tear film, thereby increasing the ability of the cornea to become wet and form the smooth optical surface required for clear vision(7).

Bowman’s layer: It is an acellular layer and about two microns thick. When injured, a fibrous scar tissue is laid down and a permanent opacity results(7).

The stroma: Constitutes 90% of corneal thickness and is approximately 450 micron thick. Stromal fibrils, about 200 layers, have a relatively high degree of spatial order and an interfibrillar spacing. These together with the absence of blood vessels have been implicated as the basis of corneal transparency. Moreover, the interaction among the stromal proteoglycans, the collagen fibril distribution and stromal iron and water are of major importance in maintaining the corneal transparency. The latter may be disturbed by CLW (7).

Descemet’s membrane: Secreted by the endothelium and is approximately three microns at birth and 10 microns in adulthood. It does not adhere strongly to stroma, and can be surgically dissected as a sheet(7).

The endothelium: It is a single layer of about 500,000 cells. With pathologic cellular damage or substantial reduction in cell density to a critical count of approximately 400 to 700 cells/mm2, the endothelial capability becomes overwhelmed, and chronic stromal oedema can ensue. The main physiologic functions of the endothelium are to maintain an effective barrier from the aqueous humour, to maintain the metabolic pump, and ultimately, to maintain the corneal transparency. The integrity of the endothelial cell junctions establishes the barrier and is of the utmost importance in controlling endothelial metabolic pump which is controlled by Na+/ K+ ATPase located in the lateral membrane(7).

Corneal innervation and sensitivity: The epithelium is one of the most highly innervated structures in the body. Sensitivities are 300 to 600 times that of the skin (7). Sensory innervation of the cornea occurs primarily through the ophthalmic division of the trigeminal nerve, which inserts into the posterior portion of the globe as the long ciliary nerves and a portion of the short ciliary nerves through the ciliary ganglion. The limbal region is supplied by fibers passing anteriorly within the suprachoroidal space. These fibers branch to form circumferential plexus near the limbus corresponding to areas of cold sensitivities. Branches travel anteriorly to innervate the adjacent conjunctival and limbal epithelium. Branches from the plexus occur as 60 to 70 nerve fibers; radially enter the mid stromal

cornea. Most fibers loose their myelin sheaths about three mm within the cornea. These bare nerve endings sub-serve both touch and pain (8). The sensitivity of the cornea is maximal apically with a considerable drop at the limbal conjunctiva, and minimal at the fornix. It increases again at the lid margin. CLW decreases corneal sensitivity because of oxygen deprivation and, presumably, the mechanical effect. Sensitivity recovers after their removal (7).

Corneal metabolism: The corneal epithelium primarily uses glucose and glycogen for energy production. Glucose reaches the cells by diffusion from the aqueous humour, perilimbal vessels and from the tear liquid

(7,8)

.

Glycogen, stored in cells, is rapidly depleted under stress, such as hard CLW or trauma. Glucose is metabolized primarily by anaerobic glycolysis; however, up to 35% of glucose enters the hexose monophosphate shunt (HMP). The HMP shunt converts hexoses to pentoses required for nucleic acid synthesis and produces the reduced form of nicotinamide-adenine dinucleotide phosphate (NADPH), a highenergy reducing agent required for fatty acid synthesis. Glucose may also enter the sorbitol pathway, which produces sorbitol and fructose. The epithelium receives its oxygen from the atmosphere under open eye conditions. Under aerobic conditions, pyruvate from glycolysis can enter the tricarboxylic (Krebs) cycle, and under hypoxic conditions (such as during CLW), is converted to lactate which is transported from the cells to maintain an intracellular pH at 7.3 to 7.4. Lactate can not diffuse across the apical barrier and builds up in the stroma. This is associated with anoxia of cells, leading to epithelial oedema. The

acidification of extra-cellular fluid may interfere with cellular metabolism and mitosis, leading to epithelial thinning and erosion. Under conditions of hypoxia or inflammations, arachidonic acid is metabolized through the cytochrome P 450 system with the production of two eicosanoids: 1-

12 (R)- hydroxyeicosatetraenoic acid (12 -R- HETE) which has the

potential to diffuse from the epithelium to the endothelium and inhibit the Na+/K+ ATPase and the endothelial metabolic pump, ultimately causing endothelial polymegathism and corneal swelling. 2-

12 (R) - hydroxyeicosatrienoic acid (12 -R- HETrE) which can

serve as a chemo-attractant and induce stromal neovascularization. CLs that do not fit well or have low oxygen permeability can lead to hypoxia. The lactate plus the 12 (R) HETE produced by the epithelium during CLW can also have an adverse effect on the structure and function of the corneal endothelium. Most contact lens wearers (CLWs) have polymegathism of the corneal endothelium. The endothelium utilizes the same carbohydrates metabolism pathway as the epithelium. The transport function requires oxidative activity. Atmospheric oxygen is the primary source of oxygen. Interruption of this supply by low-oxygen transmissibility CLs will result in a shift to anaerobic metabolism, a concurrent increase in lactic acid and carbon dioxide and a drop in stromal pH. In addition, this hypoxia can stimulate epithelial production of 12 (R) HETE already mentioned. Acute reversible changes seen with hypoxia include stromal swelling, endothelial dysfunction and blebbing (8).

1.1.2 The conjunctiva: Is a thin mucus membrane that lines the eyelids and is reflected at the superior and inferior fornices onto the anterior surface of the globe. The

conjunctival epithelium is continuous with the epidermis of the skin at the lid margin and with the corneal epithelium at the limbus (1). The three geographical zones of the conjunctiva are the tarsal, forniceal and bulbar conjunctiva. The tarsal conjunctiva is firmly adherent to the tarsus. It is rich in capillaries, venules and lymphatics which may nourish the cornea when the lids are closed (7). The bulbar conjunctiva is freely movable and towards the limbus fuses with Tenon’s capsule. Glands of Krause are found in the fornices. These, together with glands of Wolfring within or above the tarsus, provide the base line secretion of tears under sympathetic nervous system control. Lymphocytes and plasma cells as well as lymphoid aggregates are also found in the fornices, especially the inferior. Specialized areas of conjunctiva are the medially located plica semilunaris, which is very rich in goblet cells, and the caruncle (5, 9).

1.1.3 The Eyelids: Are specialized motile skin folds covered on the outside by keratinizing surface epidermis and inside by non-keratinizing conjunctival epithelium. The lid contains four layers: 1-

The outermost skin with scant subcutaneous tissue.

2-

The circular oriented orbicularis striated muscle.

3-

The densely fibrous tarsus and enclosed meibomian glands.

4-

The innermost layer of tightly adherent tarsal conjunctiva. The eyelids protect the eye from injury and excessive light by their closure. They also assist in distribution of tears over the anterior surface of the eyeball and their exit into the drainage system (1).

1.1.4 The lacrimal system: Is divided into secretory and excretory parts: The secretory system: The lacrimal gland is an exocrine gland and is divided into two groups: 1-

The main lacrimal gland which resides in the superotemporal orbit and is

divided by the levator aponeurosis into a larger orbital and a smaller palpebral lobe. It has about 12 secretory ducts that open in the superotemporal portion of the conjunctival fornix.

2-

The accessory lacrimal glands of Wolfring and Krause and are termed the basal

secretors, as they do not possess direct secretory motor fibers. Other basal secretors are the sebaceous glands (meibomian and Zeis) and the mucus glands (goblet cells) (9).

The excretory system: Tears secreted from the lacrimal gland spread over the surface of the globe by two processes: eyelid movement and gravity. Much of the tear fluid lies in strips (rivus lacrimalis) along the lid margins against the cornea. The tears then collect in the lacrimal lake at the medial aspect of the conjunctival fornix. They then pass by capillary attraction into the lacrimal puncta and canaliculi. Aided by the lacrimal pump mechanism and gravity, fluid then passes into the common canaliculus and the lacrimal sac. Regurgitation is prevented by the simultaneous closure of the ampulla of each canalliculus. Fluid continues downward into the nasolacrimal duct, emptying into the inferior meatus of the nose under the inferior turbinate bone (7).

1.2 Contact lenses: 1.2.1 Definition: CLs are prosthetic devices worn in apposition of the cornea as optical correcting lenses (10, 11). They have the same index of refraction as the cornea and become covered with corneal tear film, thus eliminating the corneal curvature and become effectively a new cornea (8, 12). 1.2.2 The history of contact lenses (13): Optical principles: The first of the several well-defined periods of development hinges on theorizing about the optics of neutralization of the corneal surface in water. This period begins by Leonardo da Vinci whose actual work appears to consist of the construction of a large transparent globe intended to form a model of the human eye. This globe being filled with water, into which the observer immersed his face, resulted in the optical neutralization of the observer’s corneas. Rene Descartes (1637) used an elongated water-filled tube to enlarge the size of the retinal image. The contribution of Thomas Young (1801) provided the

immediate stimulus leading to the first optical correction of astigmatism by Airy (1827), and in turn triggered the now famous speculation by sir. John Herschel (1845).

Early practical trials: This began with the work of Fick (1888). Galezowsky (1886) put forward an idea that a gelatine disc might be applied to the cornea immediately following cataract extraction. This disc was to be impregnated with cocaine and sublimate of mercury which would provide corneal anaesthesia to relieve post-operative pain and an antiseptic cover to prevent infection. This suggestion has been quoted by Mann (1938), and was the first use of a soft and hydrophilic lens and the forerunner as a dispenser of ophthalmic medication. Also, the work of F. Müller consisted of the supplying of a protective contact device and does not appear to have been intended primarily as a visual aid. This contribution has been described by Nissel (1965). In 1889, the inaugural thesis of August Müller of Glabdach, ‘Spectacle lenses and corneal lenses’ incorporates the first known use of the expression “corneal lenses”. Simultaneously, Eugene Kalt in Paris was investigating corneal lenses in the treatment of K.C. This may regard as laying down the groundwork, which has led to consideration of the CL as a mean of myopia control. In addition to recommending the use of CL for KC, Fick suggested their potential usefulness in aphakia, as prosthetic/ cosmetic lenses and also postulated the use of pinhole CLs. Thus by 1890 the foundation had been laid for correction of visual errors, protection of the exposed cornea, remoulding of corneal shape, neutralization of corneal irregularities and the use of CLs as an applicator of ophthalmic drugs. There was lack of ability to ensure both good tolerance and good vision by the majority of CLWs. This was because of the limited understanding of detailed topography, of physiology of the anterior segment of the eye and of its response to the CL. Fick stressed the need for sterilization dextrose solution by boiling before using it to insert CLs. He also pronounced on the need for careful disinfection of the lenses. Dar (1892) of Pairs recommended the use of physiological saline solution. Over the period from about 1895 until around 1930, the choice lay between the blown glass lenses produced by the firm of Muller’s of Wiesbaden and the ground glass CLs. The use of CLs to retain a corneal graft in position during healing has been attributed by Mann (1938) to de Weckers in 1900. Ideas progressed on the use of CLs in K.C and the classic form of the ground glass Zeis lens began to emerge. Koeppe (1918) developed CLs for gonioscopy and for slit-lamp microscopy of the fundus.

Contact lens solutions: Obrig and Salvatori (1957) tried buffered solutions. Joseph Dallos (1930s) set out to conserve the tear reservoir and to allow for its interchange by fresh tears, possibly using a loose fitting scleral zone. Norman Bier (1982) worked in fenestration of scleral lenses in 1944.

Acrylic contact lenses: Several plastic scleral lenses which predate the introduction of polymethylmethacylate (PMMA) have been described by Sabell (1980). The final introduction of the all acrylic moulded lenses in the U.S.A. by Obrig laboratories and of acrylic lathe-turned performed lenses by the firm of C.W. Dixey in the U.K., led not only to easier lens modification, but also opened the way to the development of successfulness of CLs. Also, Obrig modified the existing cold dental alginates to produce the first specifically ophthalmic impression material and discovered the value of cobalt blue light for viewing fluorescein solution behind the CL.

Glass and acrylic corneal lenses: For some time after 1948 corneal lenses were believed to have originated with those devised by Tuohy and Woehlk. These have been described by Bier (1957). However, Obrig and Salvatori (1957) and Graham (1959) have put forward the evidence of the attempted use of corneal lenses from as early as 1888. These glass corneal lenses may have been of value for experimental work and/or as aids to eye surgery. Successful development of corneal lenses was the development of PMMA around 1936 and its introduction as a CL material around 1938 by Obrig and Dixey.

Soft lenses and rigid gas-permeable corneal lenses(RGP): Dreifus (1978) has reviewed the early work leading to the announcement of hydrophilic plastics for medical applications and their toxicity to intraocular tissue and effect of hydrogel lenses on corneal metabolism. In 1988, Messrs Johnson and Johnson introduced the first disposable extended wear soft lens system. The great obsession of the 1970s has been the importance of oxygen to the corneal well being

questioned by Dallos (1980). The advent of hydrogel lens turned thoughts towards the possibility of diffusion of oxygen through lens material itself. This stimulated the development of, first high water content materials, and more lately, of ultra-thin lens in lower water content material. Towards the end of 1970s, the growing of the RGP corneal lens gained popularity. Purification of hydrogel material to eliminate intrinsic toxicity and lens design to eliminate many of the early problems is reached by huge research expenditure and governmental departments in U.K. and U.S.A. and other countries in order to safeguard the public from various potential hazards.

1.2.3 Structure of Contact lenses: Historically, glass was used exclusively for some years and it was conventional for lenses to be individually ground. When PMMA began to replace glass in the 1940s, it was because of its toughness, optical properties and physiological inactivity coupled with ease of processing by existing turning techniques. There had been many attempts to find alternative materials until the class of polymers known as hydrogels was discovered(7).

1.2.3.1 The nature of polymeric materials: Polymers that have been used as CL materials are thermoplastics, synthetic elastomers, hybrid rigid “gas-permeable” materials and hydrogels.

1-Thermoplastics: These are the group of polymers capable of being shaped or moulded under the application of heat and pressure, but at room temperature are fairly rigid. Foremost among this group is PMMA, the most widely used CL material till the early

1970s. Properties are optical clarity, processability, toughness and ease of sterilization. On the other hand, the rigidity and virtual impermeability to oxygen are disadvantages producing discomfort and preventing the material from being used for anything other than daily wear(14).

2-Synthetic elastomers: These are flexible and capable of being compressed or stretched and when the deforming force is removed, they instantaneously return to their original shape. Properties are intermediate between those of thermoplastics and hydrogels. Thus, they possess to a degree the toughness of the former and the softness of the latter. Unfortunately, they produce polymers with hydrophobic surfaces(14).

3-RGP materials: These combine to a degree the ease of preparation of PMMA and the oxygen permeability of silicon rubber. Siloxanyl methacrylate co-polymers are the basic formulation of many RGP lenses in use today. Recently, materials containing fluorocarbon with greatest transmissibility and improved resistance to deposits and wettability gained popularity (10).

4-Hydrogels: These are hydrophilic polymers plasticized by water that they absorb and have good oxygen transmission. They can be conveniently described as soft, elastic and water-containing gels. Examples are HEMA-containing materials and silicon rubber lenses (14).

1.2.3.2 Lens parameters: CLs have four parameters in common with all conventional lenses: posterior surface curvature (base curve) anterior surface curvature (power curve), diameter and power (15).

1.2.3.3 Classification of contact lenses:Modern CLs are classified as rigid (hard) or non- rigid (soft) according to the type of material of which they are made (10). Also as corneal or scleral according to the eye tissue that supports their

periphery (15). Rigid lenses are essentially

corneal, their overall size being less than that of the cornea. Non-rigid soft lenses extend 1.5 to 2 mm beyond the limbus (10).

1.2.3.4 Contact lens design:The optical area of the posterior surface is described as the internal optical zone (IOZ). In addition to optical criteria, three optical fitting goals should be kept in mind in selecting the posterior lens surface shape; It should 1- barely clear the central cornea, 2- minimize localized corneal compressive forces created by the mismatch between the lens surface and the non-conic peripheral cornea and 3- elevate the periphery of the lens to enable its edge to glide over the following peripheral cornea during blinking –initiated lens excursion. The optical portion of the front surface of a CL is known as the external optical zone (EOZ).Its curvature is determined by the power needed to correct the eye's refractive error and to neutralize the power introduced by the tear lens. Cylinders can also be incorporated on the front surface of a lens to correct residual astigmatism and on the back surface to improve its fitting relationship with a toric cornea. In most cases, a toric back surface introduces unwanted astigmatism, which

must then be compensated for by an anterior surface astigmatic correction. This type of lens design is called bitoric. Rigid CLs can be described as having a single-cut or lenticular design. A single-cut CL has a single spherical front surface. In contrast, a lenticular lens is designed with its optical correction in the centre and a non-optical peripheral zone known as a carrier. A lenticular design may be chosen to improve comfort and centration. For example, using a non-optical carrier for a high-minus lens correction reduces the thickness of the lens peripherally and minimizes upper lid margin sensation. On the other hand, using a carrier with a plus power lens reduces the centre thickness and bulk by making the EOZ smaller. Equally important, a carrier can be shaped to enhance the fitting action of the upper lid during the opening phase of the reflex blinking and to provide better lens centration and movement than a single-cut plus power lens which, on most corneas, tends to slide down and remain in an inferior position(15).

1.2.3.5 Measuring and inspecting contact lenses:The power is measured by one or other type of focimeter. Modern focimeters, either optical or electronic, measure the posterior vertex power, by placing the lens on the CL adapter of the focimeter(15). Test lenses of known power are used to provide a calibration curve for the particular instrument. Soft lenses should be dried by lint or by paper tissue and given perhaps 10 seconds before being placed on the focimeter. Other lens parameters include the several dimensions: overall diameter, diameter of its various zones both posterior and anterior and the radii of curvature of these as well as lens thickness. Overall diameter is simply estimated by ruler or by simple band measuring device and, if there is blending between one zone and the next, more sophisticated methods may be needed. Radii of curvature can be measured in various ways. The radiuscope is simply a low-power microscope, in which a convex lens is situated between a point source and a reflecting surface that is being measured so that it focuses an image at the surface itself. Keeping the distance between the lens and source fixed both are approached to the reflecting surface so that at one position the reflected image is focused at the same place as the source. The distance both lens and source have had to

move equals the radius of curvature of the surface. This method applies particularly to hard lenses. An alternative curvature measuring technique for either type of lens is to use a keratometer with an attachment that incorporates a 45-degree mirror. This simply reflects the image of the mires on the horizontally placed CL. Other methods for soft lenses involve estimation by simple mechanical or by ultrasonic apparatus of the sagittal depth. Laser interfermometry is also used. Some methods for lens thickness measurement are essential and it is estimated by one of the many gauges available. Other features of importance are best carried out by simple estimation by the naked eye or by loupe or slit-lamp magnification. These include optics and surface quality as well as the very important features of edge design, ideally rounded and being neither too sharp nor too blunt(10).

1.2.3.6 Optics of contact lenses:CL correction differs considerably from spectacle correction because of the following: 1-

The contribution made by the liquid (tear) lens which neutralizes about 90% of

the anterior surface of corneal astigmatism, the remaining 10% being corrected by the back surface of cornea. Thus, any remaining uncorrected astigmatism (residual astigmatism), is essentially due to the crystalline lens. 2- The effect of radius changes on back vertex power of the contact lens / liquid lens system. The fluid lens is changed by 0.25 D for every 0.05 mm radius of curvature different between the base curve of the CLs and the central curvature of cornea. 3- The difference between the total and corneal astigmatism. The total astigmatism equals the front surface corneal astigmatism plus the back surface corneal astigmatism plus the crystalline lens astigmatism (16). The advantages of CLs over spectacle correction are: 1-

Cosmetic: indeed most CLs worn today are prescribed for this reason. An

observer sees the eyes looking their normal size - smaller than with spectacles for a hypermetrope and bigger for a myope. Ugly appearances due to the prismatic effects and surface reflexions of spectacle lenses are also removed (16). 2-

Field of vision: because they are closer to the entrance of the pupil and lack

frames, they provide a larger field of vision (15). By comparison the clear field of view

of the spectacle wearer is limited by the size and vertex distance of the spectacle lens and restricted to about 80%. In the CLWs it is about 100% (16). 3-

Image size: the vertex distance of the corrective lens affects the size of the

retinal image. It may be more physiological in CLWs thus facilitating binocularity in anisometropes and unilateral aphakes

. CLs create larger retinal images in myopes

hypermetropes (15).

and smaller ones in 4-

(10)

Oblique aberrations: as CLs remain almost centred in all directions of gaze,

wearers suffer minimum from the effects of oblique aberrations. These being oblique astigmatism, coma, distortion, transverse chromatic aberrations and curvature of field. By contrast to spectacle lens wearers viewing objects through their periphery. 5-

Being bathed in tears, CLs are not subject to “misting up” as are spectacle

lenses in humid or other climatic conditions (10).

1.2.4 Indications and contraindications of contact lens wearing: 1.2.4.1 Indications: Indications of CLW fall into three categories: visual (refractive), therapeutic and cosmetic.

1.2.4.1.1 Visual: These comprise all types of refractive errors (ametropia) in which parallel rays of light do not come to a focus upon the light sensitive layer of the retina and may be due to one or more of the following conditions: a-

Abnormal length of the globe – too long in myopia, too short in hypermetropia

(axial ametropia). b-

Abnormal curvature of the refracting surfaces of the cornea or lens – too strong a

curvature in myopia, too weak in hypermetropia (curvature ametropia). c-

Abnormal refractive indices of the media (index ametropia). In index myopia the

refractive index, either of the cornea, the aqueous or of the lens is too high, and that of the vitreous may be too low. In index hypermetropia the opposite conditions are operative, and the error is high when the lens is absent. d-

Abnormal position of the lens – displacement forwards in myopia, backwards in

hypermetropia (17,18).

1- Myopia (or short-sight): Is that form of refractive error wherein parallel rays of light come to a focus in front of the retina when the eye is at rest. Axial myopia is the commonest, although curvature myopia occurs commonly as a factor in astigmatism. In simple myopia there are no degenerative changes in the fundus, and a degree of 5 to 6 D. may be attained in adolescence. In the rare developmental myopia, a degree of 10 D may be attained, but progression is rare. In pathological myopia, the main factor is a genetic developmental defect, which affects the whole of the posterior segment, but may be racial (10). Refractive change appears in childhood, usually at the age of 5 to 10 years (10,19), and increases steadily up to 25 years or beyond, finally amounting to 15 – 25 D or more. The degenerative changes in the fundus do not appear until later in life, becoming marked at about the fifth decade. Two typical ophthalmoscopic appearances are seen in high myopia – a myopic crescent in the disc and central fundus changes described as chorioretinal myopic degeneration. Changes in the peripheral retina may occur and may lead to retinal detachment. Degenerative changes in the vitreous are common and give rise to vitreous opacities and large floaters. These degenerative changes are among the most common causes of visual disability. Indistinct distant vision may be the only symptom of low myopia, and rarely headache. In high myopia, there is, in addition, discomfort with near work, floaters and scotomas. There may be an apparent convergent squint. Prognosis: low or moderate degrees (up to 6 D) have good prognosis unless occurring before the age of 7 years because, if so, myopia progresses up to 15 D or more, accompanied by degenerative changes in the fundus and defects of vision (12). Moreover, childhood myopia may be associated with strabismus and amblyopia, an occult eye disease (such as K.C or lens subluxation) or an occult systemic disease (20). Contact lens correction: Soft or RGP lenses may be used. For simple myopes, they have the added advantage of cosmetic and for high myopes; a superior optical correction can be attained. The problem of very high minus lenses is the peripheral edge thickness that may create discomfort or excessive superior lid grab. This can displace the optical

centre of the lens, causing degradation of vision. Modification of lens design is important (21). CLs give larger retinal images, accommodation needed is more, convergence increased and eyes have to move more than with

spectacles (22).

2- Hypermetropia (or far-sight): Is that form of refractive error wherein parallel rays of light come to a focus behind the retina when the eye is at rest. It is by far the commonest of all refractive errors, and in fact forms a stage in normal development. At birth all eyes are hypermetropic to the extent of 2.5 to 3.0D. In the first decade of life, hypermetropia decreases rapidly, remaining in about 50% of the population after the age of 20 years(10). Axial hypermetropia is a chief factor with curvature hypermetropia occurring as a factor in astigmatism and index hypermetropia in old age. It rarely exceeds 12 D(12). Pathological hypermetropia occurs due to flattening of the posterior pole and displacing the retina forward in the macular region as with orbital and intraocular tumours or inflammatory lesions (10). Symptoms: in the young may be a symptomatic. Older patients, with decreasing amplitude of accommodation, may experience headache, asthenopia as well as blurred distant vision. Near vision is decreased at an early age (18). Ophthalmoscopically, the fundus may exhibit no abnormality, but may have a peculiar sheen, shot-silk retina. The optic disc may resemble neuritis, pseudopapillitis (10)

.

Contact lens correction: For high hypermetropes, usually elderly aphakes, the problem of high plus lenses is its weight. In geriatrics, the lid is inelastic resulting in less lid grab and so the lens may drop inferiorly. This may be overcome by modification of lens design. High plus lenses are also thick and oxygen transmission through the central area is therefore reduced, resulting in corneal oedema. When RGP lenses are used, a higher Dk, or permeability value, material is to be used. For soft lenses, a material with higher water content may be needed. Sometimes it is necessary to reduce the time of wear. CLs give the opposite effects that of myopia (21).

3- Astigmatism: Is that condition of refractive error wherein a point focus of light can not be formed in the retina. Curvature astigmatism is usually congenital. Direct (with the rule) astigmatism in which the vertical curve is greater than the horizontal, is the commonest error, and is due to upper lid pressure upon the eye. This type is present in about 70% of children at the age of 4 years and in 95% at the age of 7. With age it tends to decrease or even reverse itself to an inverse astigmatism with the vertical curvature less than the horizontal (indirect, against-the-rule). Acquired astigmatism can be caused by corneal deformity as a result of diseases such as K.C, inflammations, ulcerations and trauma (including surgery for cataract). Lid lumps such as chalazia and neoplasms can also induce astigmatism. Curvature astigmatism of the lens, as in lenticonus and decentration (as in trauma), can also occur. Index astigmatism occurs physiologically in the lens due to the difference in refractive index in various sectors. In gross cataract, it may cause polyopia. The two types of astigmatism are: regular, where the two principal meridians are at right angle and irregular when they are not at right angle. Regular astigmatism may be classified as: 1-

Simple: where one of the foci falls upon the retina, the other may fall in front

or behind, myopic or hypermetropic astigmatism, respectively. 2-

Compound: where either of the foci lies in front or behind the retina,

compound myopic or hypermetropic astigmatism, respectively. 3-

Mixed: where one focus is in front and the other is behind the retina (10). Symptoms of lower astigmatism ( 0.3 mm) occur in the upper tarsal conjunctiva and may be associated with mucus discharge. The aetiology of GPC is multifactorial and begins with the formation of deposits on the surface of the lens. The constant trauma of the blinking lid rubbing on the surface of the lens exposes the deposits to the conjunctival lymphatic system. The antigens associated with the deposits incite an immune response in the conjunctiva. Symptoms are exacerbated by anything that increases contact of the deposits with the tarsal conjunctiva - increased number of deposits, increased size of the lens and increased wearing time, especially overnight wear. GPC is treated by reducing the amount of contact between the deposits and conjunctiva. This can be accomplished by minimizing wearing time, optimal lens hygiene as well as lens selection regarding material and fit. RGP lenses are necessary in recalcitrant cases. Topical mast cell stabilizers may be of use, and topical steroids can be used but with caution (30).

3-Contact lens induced-superior limbic kerato-conjunctivitis : It is an immunologic hypersensitivity reaction caused by thiomersal preservative

(23)

. Typical symptoms are foreign body sensation, photophobia, tearing

and itching. Signs are conjunctival thickening, erythema and variable amount of

fluorescein staining of the superior bulbar conjunctiva and superior cornea. In advanced cases, vascularization and punctate epitheliopathy may extend inferiorly to the visual axis with reduction in VA. Treatment consists of discontinuation of CLW until the epithelium returns to normal and symptoms resolve. Refitting with a better fitting lens, using preservativefree solution with hydrogen peroxide disinfecting system, or switching to RGP lenses may permit a resumption of CLW (30).

1.2.5.4 Corneal epithelial complications: 1- Mechanical epithelial defects: Manipulation of a CL during insertion and removal can traumatize the epithelium, creating painful abrasions of variable shapes and sizes. These will usually heal quite rapidly with simple lubrication or patching. Debris trapped under a CL or a chip or tear in its edge can produce dramatic curvilinear abrasions. Removal of the debris or replacement of the damaged lens is all that is needed to treat this problem. Punctate epithelial erosions are common. Three staining patterns are characteristic of rigid lenses: central, peripheral and 3 and 9 o’clock. If a lens is too flat for the particular cornea, it may produce central punctate staining. A steep cornea such as in K.C where the lens rubs on the tip of the cone is a typical example. A lens that is too steep for the cornea can produce peripheral punctate staining pattern - often in a superior arcuate shape, and so does a poorly moving lens or one with a large optical zone. The most common staining pattern occurs between the lens and limbus in the interpalpebral fissure (at 3 and 9 o’clock), and is caused by the CL lifting the lid away from the cornea resulting in poor tear stability and subsequent drying of the cornea. This is often exacerbated by an incomplete blink. A small amount of 3 and 9 o’clock staining is benign, but persistent epithelial erosions can lead to Déllen formation, neovascalarization and pseudopterygium or Salzmann’s nodule formation. This type of punctate epitheliopathy is alleviated by decreasing the distance from the lens to limbus with a larger lens, reducing edge lift with a thinner edged lens or steeper fit, or refitting with a lens that sets under the upper lid (alignment fit). Punctate staining by soft lenses is not as common as with rigid lenses, but can occur. Soft lenses that cause excessive desiccation can cause an inferior central or inferior arcuate pattern. Usually, these patients will have minor symptoms of mild

irritation or slightly decreased vision. Refitting with a higher water content lens or a RGP lens will usually eliminate this problem. Epithelial splitting, a common finding in soft contact lens wearers (SCLWs), and is often overlooked as it is usually asymptomatic and may be covered by the upper lid. They are horizontal, linear, white, faintly staining epithelial defects in the superior cornea, asymptomatic during lens wear but produce mild foreign body sensation after lens removal. They usually heal after the lenses have been out for 24 hours, and refitting with RGP lenses prevents recurrences (30).

2- Chemical (toxic) epithelial defects: Various CL chemical solutions can produce a range of epithelial defects from marked erosions to less extensive punctate defects. Surfactant cleaning solutions that are left on the lens after cleaning will usually cause immediate pain, redness, photophobia and tearing upon lens insertion. These symptoms typically disappear after one or two days. If hydrogen peroxide is placed on the eye, it can cause intra- and subepithelial gas bubbles. These have a dramatic appearance and can cause significant, but usually temporary, vision loss. They resolve without permanent sequelae within minutes to hours. However, hydrogen peroxide can cause permanent refractive change by altering the shape of the cornea. Enzyme cleaner and chemical disinfection solutions can cause more subtle and intermittent punctate epithelial defects. Removal of the offending agent, the use of preservative-free solutions and proper use of hydrogen peroxide disinfection will usually solve this problem (30).

3- Hypoxic epithelial defects: Mild hypoxia produces epithelial oedema and temporary blurred vision, which may take several hours after removal of the lenses while severe hypoxia results in epithelial cell death and desquamation with classic central defects. Chronic hypoxia produces a variety of more subtle effects, epithelial microcysts and vacuoles, superficial neovascularization, decreased central sensitivity and increased bacterial adherence to epithelial cells, resulting in microbial keratitis (30).

4- Tight lens syndrome:

A CL can occasionally become tightly adherent to the eye and produce marked, diffuse stromal inflammation secondary to acute hypoxia. Pain, photophobia, injection and tearing are acute and severe. There may be punctate epithelial erosions, stromal oedema and infiltrates and a significant anterior chamber reaction. While these may resolve shortly after removal of CLs, the stromal oedema and infiltrates may take a few days to disappear. A short course of topical steroids will speed the resolution of symptoms (30).

5- Superficial immunologic reactions: A variety of chemicals in CL solutions can elicit superficial toxic or immune reactions. The preservative thiomersal, which is now rarely used, produces a keratoconjunctivitis in as many as 10% of CLWs. Early symptoms are mild foreign body sensation and conjunctival hyperaemia. The findings are punctate epithelial erosions and a mixed follicularpapillary hypertrophy. Other preservatives and disinfectants can produce similar pathology. Following correct diagnosis, most of these are easily treated using techniques such as recommending lid hygiene, altering the lens fit or material, changing care regimen and use of anti-allergic drops (30).

1.2.5.5. Corneal stromal complications: 1-Sterile infiltrates: These are caused by immunologic reaction to bacterial toxins (as staphylococcus) from colonized CLs. They are usually small (0.1- 0.2 mm), multiple, peripheral, relatively painless and not associated with endothelial plaques or significant anterior chamber reaction. They may be round, oval or arcuate and may underlie either an intact epithelium or a small epithelial defect. They tend to resolve with no loss of vision, leaving behind only a faint scar in the anterior stroma after a short course of topical steroids or simple elimination of CLs(30).

2- Bacterial keratitis: It is an uncommon, but potentially devastating, complication of CLW. Extended wear have higher incidence of bacterial keratitis than daily wear CLs

(30,45,46,47)

. The risk in disposable lens wearers is increased to daily wear of soft or RGP lenses (30,48,49,50). The primary risk factor for developing CL induced bacterial keratitis is

sleeping with the lenses (51). Daily CLW and high oxygen permeable lenses do not significantly alter the mucosal defences of the outer eye that function to eliminate organisms from the conjunctival sac and prevent infection(52,53). CLs, especially over-night rigid lenses, cause breaks in the epithelium allowing direct access of pathogens, which may be present on lids, in tears or adherent to the CL and to the corneal stroma. A variety of both gram-positive and gramnegative organisms, most commonly Pseudomonas aeruginosa, staphylococcus aureus and staphylococcus epidermis, have been isolated(54). Symptoms are acute (within 24 hours) and include pain, photophobia, tearing, purulent discharge and reduced vision. A whitish to yellow stromal infiltrate may develop under an epithelial defect. However, infection can be established within the corneal epithelium without initially producing an ulcer (55). This may progress to stromal necrosis and perforation. There may be an associated endothelial plaque, anterior chamber inflammation and/or hypopyon. Treatment is by broad-spectrum antibiotics such as a combination of fortified cephalosporin and aminoglycoside while waiting for culture results and gram-strain (30).

3-Amoebic keratitis: Acanthamoeba, a protozoan that is widely found in nature and has been isolated from random samples of soil and water, can gain access to CL solutions and CLs. From any of these sources Acanthamoebal attachment to silicon hydrogel lenses is significantly greater than to the conventional hydrogels, possibly due to an inherent characteristic of the polymer or a side effect of the surface treatment procedure to which the lenses are exposed (56). Tap water, a common source of acanthamoeba contamination, should never be used to rinse, store or make saline solution for CL storage (57). Rigid CL and CL cases should only be washed with boiled tap water and preferably hot(30). Symptoms often take several days or weeks before the patient seeks attention. They include foreign body sensation, blurred vision and redness. Pain may

be severe and is often out of proportion to clinical findings. Corneal findings include epithelial defects, ring infiltrates and prominent corneal nerves with perineuritis(30). The diagnosis can be made by positive cultures on blood agar containing Ecoli. Bacteria probably support acanthamoeba contamination and allow them to feed (58)

. Treatment is difficult due to the ability of the organism to assume a cyst stage,

which may lie dormant in the corneal stroma for months. Traditionally, topical therapy with propamidine (Brolene) with or without concomitant polyhexamethylene beguanide (PHMB) was utilized with variable success. Topical neomycin, meconazole, clotrimazole and oral ketoconazole were also used. Topical neomycin polymyxin B- gramicidin (Neosporin) and Brolene were tried successfully (59). Penetrating keratoplasty may be required to eradicate the infection, although recurrences are common (30).

1.2.5.6 Corneal endothelial complications: CLWs have altered endothelial cell morphology as variation in cell size (polymegathism) and variation in cell shape (polymorphism). Also, wearers of all lens types were found to have a small decrease in endothelial cell density, for unknown reasons (30).

1.2.5.7 Corneal keratometric complications: 1-Corneal wrapage: Prolonged CLW may produce gradual and unpredictable changes in contour of the cornea (wrapage), typically irregular astigmatism. It commonly occurs with hard lenses, but can also occur with soft lens wear. The corneas will usually regain a stable and regular shape after discontinuation of CLs, but it may take weeks or even months (30).

2-Contact lens-induced keratoconus: It is suggested that long-term CLW can produce K.C in susceptible individuals (23, 30, 60).

OBJECTIVES This study aims to lightening out the experience of contact lens wear in Sudan from a practical point of view. Objectives of the study were:

1- To determine indications of contact lens wear in Sudanese patients.

2- To specify difficulties of contact lens wear in Sudan.

2- MATERIALS AND METHODS 2.1. Settings: In this study 160 eyes of 80 patients of both sexes were studied during the period January 2003 until August 2003. Patients were either referred by ophthalmologists from all-over Sudan or came by their own.

2.2. Study area: This study was conducted in a private contact lens clinic in Eltagwa mosque clinics complex to the north of Khartoum Teaching Hospital-Khartoum State.

2.3. Study design: A descriptive cross-sectional study.

2.4. Inclusion and exclusion criteria: All patients arriving at the clinic during January 2003 until August 2003 were included in the study. Patients wearing CLs for less than one month or had been abroad part of the wearing time were excluded from the study.

2.5. Procedures: 2.5.1. The questionnaire: Was pre-coded and contained information concerning personal data and history of systemic or ocular diseases. It also contained type of CL worn, duration and regularity of wear.

A full ocular examination was performed by the author for each patient. The author also assisted in performing refraction and CL trials.

2.5.2. Research materials: The following materials were used in the study: - Snellen’s chart and trial set. - Torch. - Loupe. - Slit lamp. - Direct ophthalmoscope. - Keratometer

- Contact lens trial set. - Eye

drops

(topical

anaesthesia,

tropicamide). - Fluorescein and cotton buds. - Ultraviolet light.

2.5.3. Contact lens trial: 1) Motivations of the patient were thoroughly discussed. 2) VA and refraction were done routinely. 3) Eye examination: i. External : using a torch, loupe and slit lamp. ii. Internal : pupillary dilatation using tropicamide

1%

was

done

for

all

patients and the posterior segment examined

using

a

direct

ophthalmoscope. 4) Keratometry reading, which was a guide for selecting the first lens and very important for the follow up was done. Power of the lens was determined by its curvature and in determining the first lens, the meridian with the flattest keratometric reading was chosen

so that the power of the lens would be 0.5 D less, e.g. 8.2 x 180° 42 D - 8.1 x 90°

41 D

here the meridian with the flattest reading is the horizontal one, thus the power of the lens will be 42 – 0.5 = 41.5 D. 5) Checking the fit: i. Corneal lenses: after instillation of topical anaesthetic, fluorescein and ultraviolet light were used to note the fit. • If it is green at the centre and blue at periphery, it is a steep lens. • If it is blue at the centre and green at periphery, it is flat. • If it is greenish blue at the centre and very green at periphery, it is correct.

ii. Soft lenses: here only white light was applied to note movement of the lens when the patient blinks. • If it is a quick rapid movement, it is a flat lens. • If there is no movement, it is steep. • If it moves moderately, it is correct. 6)

The patients were seen after one month, then at three-months intervals.

2.6. Data analysis: Data collected in this study was entered into computer SPSS using both student t test and Chisquared analysis to 95% significance level.

2.7. Limitations of the study: 1- In Sudan CL clinics are few and they are private clinics. 2- The only CL clinic belonging to the Ministry of Health was established in K.T.E.H research department. It was excluded as a study area for the following reasons: a. Shortage of facilities. b. The patient was seen once to decide whether he/she was in need for CLs or not according to the improvement of VA. c. No follow up for the cases, because they were referred to the

market (private clinics) to obtain their CLs which were not available in the hospital.

2.8. Ethical considerations: A verbal consent was taken from each patient included in the study.

3. RESULTS 3.1. Socio-demographic data: 3.1.1. Age (years) distribution among the study population: There were nine patients (11.1%) in the age group (7-16),

22 patients (27.5%) in the age group

(17-26), 26 patients (32.6%) in the age group (27-36), 11 patients (13.8%) in the age group (37-46) and 12 patients in the age group (47-70) [Table 3.1]. 3.1.2. Sex distribution among the study population: Twenty three patients (28.7%) were males and 57 patients (71.3%) were females [Figure 3.1]. 3.1.3. Distribution of the study population according to residence: Sixty seven patients (83.8%) were from Khartoum State and 13 patients (16.2%) were from other States [Figure 3.2]. 3.1.4. Distribution of the study population according to occupational environment: All the patients were working in-doors. Sixty three of them (78.8%) were working in closed

environments (offices) and 17 (21.2%) in open environment (at home) [Figure 3.3]. 3.1.5. Distribution of the study population according to the affordability: Sixty eight patients (85.0%) could afford CLs easily and 12 patients (15.0%) could afford them with some difficulty [Figure 3.4]. 3.1.6. Distribution of the study population according to the educational status: Two patients (2.5%) were illiterate, nine patients (11.3%) were at primary school level, 24 patients (30.0%) at secondary school level, 34 patients (42.5%) at university level and 11 patients (13.7%) at postgraduate level [Figure 3.5]. 3.2. Contact lenses: 3.2.1. Type of contact lens worn among the study population: Seventy one patients (88.8%) were SCLWs and nine patients (11.2%) were hard contact lens wearers (HCLWs) [Figure 3.6].

3.2.2. Distribution of the study population according to duration of contact lens wear: Twenty two patients (27.5%) were wearing CLs for less than one year, 13 patients (16.2%) for (1-5) years, 17 patients (21.3%) for (6-10) years and 28 patients (35.0%) were wearing CLs for more than 10 years [Table 3.2]. 3.2.3. Regularity of contact lens wear among the study population: Seventy seven patients (96.2%) were regular wearers and three patients (3.8%) were irregular wearers [Figure 3.7]. 3.3. Presenting complain of the study population: Sixty five patients (81.2%) had no complain, seven patients (8.7%) had itching, five patients (6.3%) had blurring of vision, two patients (2.5%) had foreign body sensation and one patient (1.3%) presented with seeing floaters [Figure 3.8]. 3.4. Ocular examination: 3.4.1. Fundal abnormalities among the study population:

One hundred and three eyes (71.0%) showed no fundal

abnormalities,

36

eyes

(24.8%)

showed

chorioretinal myopic degeneration, two eyes (1.4%) showed typical retinitis pigmentosa, one eye (0.7%) had coloboma of the optic disc and choroid and three eyes (2.1%) were not visible [Figure 3.9]. 3.4.2.

Ocular

alignment

defects

among

the

study

population: Seventy seven patients (96.2%) had straight eyes and three patients (3.8%) had concomitant squint [Figure 3.10]. 3.5. Visual acuity: 3.5.1. Distribution of uncorrected V.A among the study population: The recorded uncorrected V.A was No PL, HM, 1/60, 3/60, 6/60, 6/36, 6/24, 6/18, 6/12, 6/9 and 6/6 for two eyes (1.4%), three eyes (1.9%), 37 eyes (23.1%), 27 eyes (16.9%), 46 eyes (28.8%), 18 eyes (11.3%), seven eyes (4.4%), five eyes (3.1%), one eye (0.6%), one eye (0.6%) and 13 eyes (8.1%), respectively [Table 3.3]. 3.5.2. Distribution of corrected V.A using glasses:

The recorded V.A corrected with glasses was ≤ 6/60, 6/36, 6/24, 6/18, 6/12, 6/9 and 6/6 for 10 eyes (6.2%), 25 eyes (15.6%), 14 eyes (8.8%), 17 eyes (10.6%), 18 eyes (11.3%), 13 eyes (8.1%) and 31 eyes (19.4%), respectively [Table3.4]. 3.5.3. Distribution of corrected VA using contact lenses: The best corrected V.A obtained with CLs was 3/60, 6/36, 6/24, 6/18, 6/12, 6/9 and 6/6 for one eye (0.7%), four eyes (2.8%), four eyes (2.8%), 11 eyes (7.6%), 15 eyes (10.3%), 27 eyes (18.6%) and 81 eyes (55.8%), respectively [Table 3.5]. 3.6. Indications of contact lens wear among the study population: Indications

of

CLW

were

anisometropia

21

patients (26.2%) simple myopia 16 patients (20.0%), high myopia 11 patients (13.6%), high hypermetropia one patient (1.3%), myopic astigmatism and KC nine patients each (11.2%), surgical aphakia six patients (7.5%), corneal irregularities two patients (2.5%), hypermetropic

astigmatism,

bullous

keratopathy,

protective, albinism and microphthalmos one patient each (1.3%) [Table 3.6]. 3.7. Difficulties of contact lens wear:

Thirty five patients (43.7%) had no difficulties with CLW, 17 patients (21.3%) found them expensive, three patients (3.7%) found them difficult to use, three patients found them difficult to get, three patients found their use tedious, four patients (5.0%) found them intolerable, five patients (6.3%) suffered from lens deposits, and two patients (2.5%) suffered from lens loss [Table 3.7].

3.8. Difficulties in relation to type of contact lens: Thirty five wearers (43.7%) had no difficulty, two of them (2.5%) were HCLWs and 33 (41.2%) were SCLWs. Two HCLWs and

15 SCLWs (18.7%)

found CLs expensive. One HCLW (1.3%) found difficulty in getting them. Nine SCLWs (11.2%) found difficulty with using lenses. One HCLW and two SCLWs thought that wearing lenses was tedious. Two HCLWs (2.5%) and two SCLWs (2.5%) found them irritating. One HCLW (1.3%) and four SCLWs (5.0%) suffered from lens deposits, two SCLWs (2.5%) suffered from lens loss and two SCLWs (2.5%) suffered from lens damage [Table 3.8]. 3.9. Difficulties in relation to duration of contact lens wear: Out of the 22 (27.5%) CLWs for less than one year, five patients (6.2%) had no difficulty, three patients (3.7%) found them expensive, three patients found difficulty in getting them, one patient (1.3%) found their use to be tedious, one patient lost his lens and one patient suffered from lens damage. The thirteen patients (16.3%) who were CLWs for 1-5 years, five of them (6.2%) had no difficulty, two patients (2.5%) found them expensive, one patient

(1.3%) found their use difficult, one patient found their use intolerable two patients suffered from lens deposits, one patient lost his lens and one patient suffered from lens damage. The seventeen patients (21.2%) who were CLWs for 6-10 years, 10 of them (12.5%) had no difficulty, five patients (6.2%) found them expensive and two patients (2.5%) found them intolerable. Twenty eight patients (35.0%) were CLWs for more than 10 years, 15 of them (18.7%) had no difficulties,

seven

patients

(8.7%)

found

them

expensive, two patients (2.5%) found them to be tedious, one patient (1.3%) found them irritating and three patients (3.7%) suffered from lens deposits [Table 3.9]. 3.10. Fundal abnormalities in relation to V.A corrected with contact lenses: One hundred and three eyes (71.0%) had no fundal abnormalities. Thirty six eyes (24.8%) had myopic chorio-retinal degeneration, corrected V.A with CLs was 6/18, 6/12, 6/9 and 6/6 for seven eyes (4.8%), five eyes (3.4%), 16 eyes (11.0%) and eight eyes (5.5%), respectively.

Two eyes (1.4%) had typical retinitis pigmentosa corrected to 6/6. One eye (0.7%) had coloboma of the optic disc, retina and choroid and corrected to 6/36. One patient (0.7%) was a case of bullous keratopathy corrected to 3/60 [Table 3.10].

Table (3.1) : Age distribution among the study population:

Age group (years)

No

%

7-16

9

11.1

17-26

22

27.5

27-36

26

32.6

37-46

11

13.8

47-70

12

15.0

Total

80

100

Figure (3.1) : Sex distribution of the study population:

28.70%

71.30%

Male Female

Figure (3.2) : Distribution of the study population according to residence:

16.20% Khartoum Other States

83.80%

Figure (3.3) : Distribution of the study population according to occupational environment:

21.20% Closed places Open places

78.80%

Figure (3.4) : Distribution of the study population according to the affordability:

15% Can afford easily Can afford with difficulty 85%

Figure (3.5) : Distribution of the study population according to the educational status:

45.00% 40.00% 35.00% 30.00% 25.00%

42.50%

20.00% 30%

15.00% 10.00% 5.00%

13.70%

11.30% 2.50%

0.00% Illiterate

Primary school

Secondary school

University

Post-university

Figure (3.6) : Type of contact lens worn among the study population:

11.20% Soft Hard 88.80%

Table (3.2) : Distribution of the study population according to duration of CLW:

Duration of CLW (years)

No

%

10

28

35.0

Total

80

100

Figure (3.7) : Regularity of CLW among the study population:

1 0.8

96.20%

0.6 0.4 0.2 0

3.80%

Regular wearers

Irregular wearers

Figure (3.8) : Presenting complaint of the study population:

0.9

81.20%

0.8 0.7 0.6 0.5 0.4 0.3 0.2

8.70%

0.1

6.30%

2.50%

1.30%

0

No complaint

Itching

Blurring of vision

Foreign body sensation

Seeing floaters

Figure (3.9) : Fundal abnormalities among the study population:

0.8

71.00%

0.7 0.6 0.5 0.4 24.80%

0.3 0.2 0.1

1.40%

0.70%

2.10%

0 NAD

Myopic degenration

Retinitis pigmentosa

Disc & choroid coloboma

Not visible

Figure (3.10) : Ocular alignment defects among the study population:

3.80% Straight eyes Concomitant squint 96.20%

Table (3.3) : Distribution of uncorrected V.A among the study population:

V.A

No of eyes

%

No PL

2

1.3

H.M

3

1.9

1/60

37

23.1

3/60

27

16.9

6/60

46

28.8

6/36

18

11.3

6/24

7

4.4

6/18

5

3.1

6/12

1

0.6

6/9

1

0.6

6/6

13

8.0

Total

160

100

Table (3.4) : Distribution of corrected V.A with glasses among the study population:

Corrected V.A

No of eyes

%

≤ 6/60

10

6.2

6/36

25

15.6

6/24

14

8.8

6/18

17

10.6

6/12

18

11.3

6/9

13

8.1

6/6

31

19.4

Total

128

100

Table (3.5) : Distribution of corrected V.A with contact lenses among the study population:

V.A

No of eyes

%

≤ 6/60

1

0.7

6/36

4

2.8

6/24

4

2.8

6/18

11

7.6

6/12

15

10.3

6/9

27

18.6

6/6

81

55.8

Total

143

100

Table (3.6) : Indications of CLW among the study population:

Indications

No

%

Anisometropia

21

26.2

Simple myopia

16

20

High myopia

11

13.6

Myopic astigmatism

9

11.2

K.C.

9

11.2

Unilateral aphakia

6

7.5

Corneal irregularities

2

2.5

High hypermetropia

1

1.3

Hypermetropic astigmatism

1

1.3

Bullous keratopathy

1

1.3

Protective

1

1.3

Albinism

1

1.3

Microphthalmos

1

1.3

Total

80

100

Table (3.7) : Difficulties of CLW among the study population:

Difficulties

No

%

No difficulty

35

43.7

Expensive

17

21.3

Difficult to use

9

11.3

Lens deposits

5

6.3

Intolerable

4

5.0

Not available

3

3.7

Tedious

3

3.7

Lens loss

2

2.5

Lens damage

2

2.5

Total

80

100

Table (3.8) : Difficulties in relation to type of contact lens:

Difficulties

Type of lens

Total

Hard

Soft

No difficulties

2

33

35

Expensive

2

15

17

Difficult to use

0

9

9

Lens deposits

1

4

5

Intolerable

2

2

4

Not available

1

2

3

Tedious

1

2

3

Lens loss

0

2

2

Lens damage

0

2

2

Total

9

71

80

X2 : 12.056 P value : > 0.149

Table (3.9) : Difficulties in relation to duration of CLW:

Duration

of

No

Expensive

CLW (years) difficulty

Not

Difficult

available

to use

Tedious

Intoler

Lens

Lens

Lens

able

deposits

loss

damage

Total

< 1 yr

5

3

3

8

1

0

0

1

1

22

1-5

5

2

0

1

0

1

2

1

1

13

6-10

10

5

0

0

0

2

0

0

0

17

> 10

15

7

0

0

2

1

3

0

0

28

Total

35

17

3

9

3

4

5

2

2

80

X2 : 46.622 P value : < 0.004

Table (3.10) : Fundal abnormalities in relation to corrected V.A with contact lenses: (n=145 eyes) V.A Fundal abnormalities

No improvement

Total

3/60

6/36

6/24

6/18

6/12

6/9

6/6

with lenses NAD

0

0

3

2

4

9

12

73

103

Myopic degeneration

0

0

0

0

7

5

16

8

36

Retinitis pigmentosa

0

0

0

0

0

0

0

2

2

Coloboma of disc & choroid

0

0

1

0

0

0

0

0

1

Not visible

2

1

0

0

0

0

0

0

3

Total

2

1

4

2

11

14

28

83

145

X2 : 98.384 P value :