Swathy G. et al. / IJPPDR / 3(1), 2013, 32-44.

e-ISSN: 2249-7625 Print ISSN: 2249-7633

International Journal of

Pharmacy Practice & Drug Research www.ijppdr.com

A REVIEW ON GLAUCOMA - GROUP OF OCULAR DISORDERS * *

G. Swathy, 1K. Sakthivel, 2P.S. Divya, 3M. Nishanthi

Saastra College of Pharmaceutical Education & Research, Nellore, Andhara Pradesh, India. 1 Periyar College of Pharmaceutical Sciences for Girls, Trichy, Tamilnadu, India. 2 Anna university, Mandaiyur, Tamil Nadu, India. 3 Sri Venkateswara College of Pharmacy, R.V.S Nagar, Chittoor, Andhra Pradesh, India.

ABSTRACT Glaucoma is slow progressive form of blindness, taking many years to develop. It is thought that you need to lose about 30% of the axons of the optic nerve before it starts to affect your vision. This loss is irreversible. Hence, in the early stages of the disease, the patient may have no problems with their vision. In the intermediate to late stages, the peripheral / side vision is affected as you lose more axons. In advanced stages, the central / reading vision is affected. More often than not, the disease is more advanced in one eye than the other. The present mainly focused on etiology, epidemiology, classification, risk factors, diagnosis and current treatment of Glaucoma. Keywords: Glaucoma, Etiology, Epidemiology, Classification, Risk Factors, Diagnosis. INTRODUCTION Glaucoma has been declared to be the second common cause of blindness in adult population in India. Experts estimate that half of those affected by glaucoma may not know they have it because there are normally no symptoms during the early stages of the disease. Worldwide, glaucoma affects close to 67 million people. Glaucoma is called ―the sneak thief of sight,‖ because it often has no symptoms until permanent visual damage has occurred. Although it can be treated, currently there is no cure. Vision lost to glaucoma cannot be regained, and untreated glaucoma leads to blindness [1]. Glaucoma is a life long disease and it is fundamental that the therapeutic approach is tailored to the needs of each individual patient. The aim of glaucoma therapy is to reduce the level of IOP, in the hope that this will slow down the rate of progressive optic nerve damage. Ultimately, the objective is to allow the patient to maintain useful vision throughout their life, while minimizing the risks of therapy [2]. The glaucoma are a group of ocular disorders that lead to an optic neuropathy characterized by changes in the optic nerve head (optic disk) that is associated with loss of visual sensitivity and field. Increased intraocular pressure

(IOP), a traditional diagnostic criterion for glaucoma, is thought to play an important role in the pathogenesis of glaucoma, but is no longer a diagnostic criterion for glaucoma. Two major types of glaucoma have been identified: open angle and closed angle. Open-angle glaucoma accounts for the great majority of cases. Either type can be a primary inherited disorder, congenital, or secondary to disease, trauma, or drugs, and can lead to serious complications. Both primary and secondary glaucoma may be caused by a combination of open-angle and closed-angle mechanisms [3]. EPIDEMIOLOGY Open-angle glaucoma is the second leading cause of blindness, affecting up to 3 million individuals in the United States and up to 60.5 million individuals worldwide by 2010. It is estimated that by 2010, 135,000 persons in the United States, and about 4.5 million in the world, will have bilateral blindness. The prevalence rate varies with age, race, diagnostic criteria, and other factors. In the United States, open angle glaucoma occurs in 1.5% of the population older than 30 years of age, 1.3% of whites and 3.5% of blacks. The incidence of open-angle glaucoma increases with increasing age. The incidence of the disease

Corresponding Author:- G. Swathy Email : [email protected]

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in patients 80 years of age is 3% in whites and 5% to 8% in blacks. The incidence of closed-angle glaucoma varies by ethnic group, with a higher incidence in individuals of Inuit, Chinese, and Asian- Indian descent. Incidence rates of 1% to 4% have been reported in these populations [4]. ETIOLOLGY OF GLAUCOMA  In the normal eye, the IOP is maintained by the exact balance between the continuous production of aqueous humour (by the ciliary body) and its drainage (by the trabecular meshwork and underlying Canal of Schlemn).  The aqueous drainage channels are located circumferentially around the periphery of the iris where it meets the edge of the cornea, in an area known as the "angle of the anterior chamber". This fluid then drains into the venous system around the eye, and from there, back into the systemic circulation.  Although there is a small diurnal fluctuation in the IOP, it essentially remains constant due to the balance between aqueous production and drainage. The population-based average level is measured at 21 mmHg or less.  It is thought that IOP pressure damages the optic nerve by mechanical means. More recently, however, vascular and rheological factors have been shown to affect optic nerve perfusion, metabolic factors and structural components of the optic nerve. New concepts in glaucoma suggest that other risk factors may eventually be defined, and therapeutic approaches to these may be developed.  Progressive optic neuropathy characterized by specific morphological changes (optic disc cupping) resulting in acquired loss of retinal ganglion cells (RGCs) and RGC axons.  The RGCs die by apoptosis (programmed cell death)  RGC death leads to peripheral visual field loss. Glaucoma- Optic Nerve Damage Elevated IOP ↓ Mechanical back pressure ↓ On the junction of optic nerve/retina ↓ Reduce the blood supply to the optic nerve ↓ Loss of blood supply (< in pOBF) ↓ Ischemia ↓ RGC cell loss [6] CLASSIFICATION OF GLAUCOMA Glaucoma can be classified in a number of ways – anatomical, pathophysiological, age of onset and

genetics. From a pathophysiological view point, glaucoma can be divided into [7] 1) Pediatric/ Congenital 2) Acquired a. Primary i. Open angle ii. Closed angle – acute or chronic b. Secondary i. Open angle e.g. pseudoexfoliation, pigment dispersion, steroids, trauma ii. Closed angle e.g. rubeosis diabetes c. Low-tension The 4 most common glaucoma conditions in our community are  primary open angle glaucoma  primary closed angle glaucoma  low tension glaucoma  secondary glaucoma Pediatric/Congenital glaucoma: The Pediatric glaucoma's consist of congenital glaucoma (present at birth), infantile glaucoma (appears during the first three years), juvenile glaucoma (Age three through the teenage or young adult years), and all the secondary glaucoma’s occurring in the pediatric age group. Congenital glaucoma is present at birth and most cases are diagnosed during the first year of life. Sometimes symptoms are not recognized until later in infancy or early childhood. Primary Open-angle Glaucoma (also called chronic open angle): In open-angle glaucoma, the aqueous humor is unable to drain out of the eye. For unknown reasons, the trabecular meshwork (the eye's filtration area) does not function normally, the pressure in the eye increases, and the optic nerve is damaged. This is the most common form of glaucoma, and is seen in up to 70 % of all glaucoma patients. Symptoms a) Asymptomatic (as moderately elevated IOP usually causes no symptoms but the IOP is still high enough to cause glaucomatous optic neuropathy) b) Loss of part of their visual field cf tunnel vision c) Blindness in one or both eyes (advanced optic nerve damage) d) Genetic factors are important and therefore the family history should be considered. Signs a) Open angle b) Elevated IOP c) Glaucomatous optic nerve cupping

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d) May have visual field loss.

a. 

Primary Angle Closure Glaucoma This form of glaucoma may present in an acute form, in which there is a sudden, dramatic rise in IOP, or in its chronic form, in which there is a gradual elevation of IOP. As aqueous builds up behind the iris, it pushes it forward. In patients with narrow angles, the trabecular meshwork can become blocked, leading to acute angle closure glaucoma. In others, the iris causes damage or sticks to part of the trabecular meshwork, gradually closing the drainage angle, leading to a gradual rise in the IOP.

Primary angle closure suspect (PACS) patients IOP is normal but is at risk of developing damage to the drainage angle b. Primary angle closure (PAC)  patients developing raised IOP due to damage to the drainage angle but no damage to the optic nerve. c. Primary angle closure glaucoma (PACG)  patients developing optic nerve damage ie glaucoma from the raised IOP Acute primary angle closure has replaced acute ACG, symptomatic angle closure has been replaced intermittent angle closure glaucoma and PACG has replaced chronic ACG.

Acute Angle Closure Glaucoma Some people have anatomically narrow angles that are susceptible to sudden closure. This is more common in patients who are long sighted, and is commonly seen in the Asian population.

Secondary glaucoma It can be open or closed-angle, and results from some other eye disorder or medical problem, such as inflammation, a tumor, or trauma. Forms of secondary glaucoma include:

Symptoms Angle closure results in severe elevation in IOP causing sudden loss of vision, severe pain, with patients commonly complaining of headache often associated with nausea and vomiting. These people have intermittent angle closure glaucoma and should be referred. However, about 60% have no warning symptoms.

Pigmentary glaucoma – a form of the disease in which pigment granules from the iris flake off into the aqueous humor and clog the trabecular meshwork. Pseudoexfoliation syndrome – a form in which a white material appears to flake off the lens of the eye and block eye fluid flow. It is very common in some populations around the world.

Signs The eye is usually red and inflamed with corneal haze (due to oedema) and a mid-dilated, poorly reactive pupil. The IOP is usually > 60mmHg.

Intermittent Angle Closure Some patients with narrowing of their drainage angles experience early warning symptoms such as episodic headaches, intermittent blurred vision and haloes or rainbow colors around lights. This is due to acute episodic rises in IOP from intermittent blockage of the drainage system of the eye. Chronic Angle Closure Glaucoma In this condition, there is a more gradual closure of the anterior chamber angle, with a slow elevation of IOP pressure resulting in a similar pattern of optic nerve damage and visual field loss as seen in POAG. NEW CLASSIFICATION FOR ANGLE CLOSURE GLAUCOMA Recently, the classification of angle closure glaucoma (ACG) has changed and is based on the natural history of the disease. Over time, the patients angles become closed, which causes the IOP to rise, that leads to damage to the optic nerve. The ISGEO classification is as follows

Neovascular glaucoma – abnormal blood vessels block the fluid drainage channels of the eye, resulting in increased eye pressure. Some factors that cause the abnormal blood vessel growth include: diabetes, blocked arteries in the neck causing insufficient blood supply to the head, and blocked blood vessels in the back of the eye (retina). Irido corneal endothelial syndrome (ICE) - Cells from the back surface of the cornea form scars that connect the iris to the cornea and block the drainage angle. Traumatic glaucoma - Contusion or penetrating injury to the eye can disturb the normal anatomy of the angle of the anterior chamber and predispose to glaucoma. Low-tension glaucoma It is also known as Normal tension glaucoma or normal pressure glaucoma. In this type of glaucoma the optic nerve is damaged even though intraocular pressure (IOP) is not very high. Those at higher risk for this form of glaucoma are people with a family history of normal tension glaucoma, people of Japanese ancestry, and people with a history of systemic heart disease, such as irregular heart rhythm. Normal tension glaucoma is usually detected after an examination of the optic nerve.

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Other Types of Glaucoma: Glaucoma associated with intraocular hemorrhage The intraocular hemorrhage may lead to an acute open angle glaucoma due to the obstruction of trabecular meshwork by hemorrhagic debris, lysed RBC S, macrophages filled with hemoglobin and debris and ghost RBCS . Postoperative glaucoma Marked elevation of intraocular pressure may occur as a complication of intraocular surgery. Glaucoma associated with intraocular tumors Intra ocular tumors like melanomas retinoblastoma may cause secondary glaucoma.

and

Obstructive glaucoma It is a broad term encompassing all types of secondary glaucoma wherein the angle of the anterior chamber or the trabeculum is blocked. Toxic glaucoma It may be found in patients of epidemic dropsy and is characterized by headache, colored halos, normal or deep anterior chamber and marked elevation of intraocular pressure associated with generalized edema of the body. Aphakic (or) Pseudophakic glaucoma It is the commonest form of secondary glaucoma. This term employed to describe a secondary rise of IOP after cataract surgery and can be attributed to the surgery or its complication [9-11]. RISK FACTORS FOR GLAUCOMA Everyone is at risk for glaucoma. However, certain groups are at higher risk than others. People at high risk for glaucoma should get a complete eye exam, including eye dilation, every one or two years. The following are groups at higher risk for developing glaucoma. African-Americans Glaucoma is the leading cause of blindness among African-Americans. It is six to eight times more common in African-Americans than in Caucasians. People Over 60 Glaucoma is much more common among older people. You are six times more likely to get glaucoma if you are over 60 years old. Family Members with Glaucoma The most common type of glaucoma, primary open-angle glaucoma, is hereditary. If members of your immediate family have glaucoma, you are at a much higher risk than the rest of the population.

Family history increases risk of glaucoma four to nine times. Hispanics in Older Age Groups Recent studies indicate that the risk for Hispanic populations is greater than those of predominantly European ancestry, and that the risk increases among Hispanics over age 60. Asians People of Asian descent appear to be at some risk for angle-closure glaucoma. angle-closure glaucoma accounts for less than 10% of all diagnosed cases of glaucoma. Otherwise there is no known increased risk in Asian populations. Steroid Users Some evidence links steroid use to glaucoma. A study reported in the Journal of American Medical Association, March 5, 1997, demonstrated a 40% increase in the incidence of ocular hypertension and open-angle glaucoma in adults who require approximately 14 to 35 puffs of steroid inhaler to control asthma. This is a very high dose, only required in cases of severe asthma. Eye Injury Injury to the eye may cause secondary open-angle glaucoma. This type of glaucoma can occur immediately after the injury or years later. Blunt injuries that ―bruise‖ the eye (called blunt trauma) or injuries that penetrate the eye can damage the eye’s drainage system, leading to traumatic glaucoma. The most common cause is sports-related injuries such as baseball or boxing. Other Risk Factors Other possible risk factors include:  high myopia (nearsightedness)  diabetes  hypertension  Central corneal thickness less than .5 mm.  Farsightedness (hyperopia), which is seeing distant objects better than close ones (Farsighted people may have narrow drainage angles, which predispose them to acute [sudden] attacks of angle-closure glaucoma [12]. GLAUCOMA SCREENING & DIAGNOSIS Diagnosis of Glaucoma Individuals at high risk for glaucoma should have a dilated pupil eye examination at least every two years. Eye doctors use several tests to detect glaucoma, these tests include: Tonometry

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It measures the pressure inside the eye. Examples of tonometers include:  The air puff or noncontact tonometer emits a puff of air. Eye pressure is measured by the eye’s resistance to the air.  The applanation tonometer touches the eye’s surface after the eye has been numbed, and measures the amount of pressure necessary to flatten the cornea. This is the most sensitive tonometer, but a clear, regularly-shaped, cornea is needed for it to function properly.  The electronic indentation method measures pressure by directly contacting anesthetized eyes with a digital penlike instrument. In Pupil dilation, special drops temporarily enlarge the pupil so that the doctor can better view the inside of the eye. Visual field testing It measures the entire area seen by the forwardlooking eye to document straight-ahead (central) and/or side (peripheral) vision. It measures the dimmest light seen at each spot tested. Each time a flash of light is perceived, the patient responds by pressing a button. Visual acuity test It measures sight at various distances. While seated 20 feet from an eye chart, the patient is asked to read standardized visual charts with each eye, with and without corrective lenses. The universally used standard for assessment of visual acuity is the Snellen's Test Types [13]. Pachymetry It uses an ultrasonic wave instrument to help determine the thickness of the cornea and better evaluate eye pressure. Ophthalmoscopy It allows the doctor to examine the interior of the eye by looking through the pupil with a special instrument. This can help detect damage to the optic nerve caused by glaucoma. Gonioscopy It allows the doctor to view the front part of the eye (anterior chamber) to determine if the iris is closer than normal to the back of the cornea. This test can help diagnose closed-angle glaucoma. Optic nerve imaging It helps document optic nerve changes over time. All four techniques are painless and non-invasive. A doctor will determine which method(s) to use.Nerve imaging techniques include  Stereo optic nerve photographs  Scanning laser polarimetry (GDx)

 

Confocal scanning laser ophthalmoscopy (Heidelberg Retinal Tomograph or HRT) Optical coherence tomography (OCT) [15].

NEW WAYS TO MEASURE INTRAOCULAR PRESSURE Certain new instruments also developed to measure IOP. They are  The ocular response analyzer provides measurements of corneal biomechanics, including corneal hysteresis. Intraocular pressure readings from the ocular response analyzer have correlated well with Goldmann applanation tonometry and seem to be independent of corneal thickness in non glaucoma patients;  Dynamic contour tonometry also appears to give pressure readings that are independent of corneal thickness.  Rebound tonometry is convenient, can be used without topical anesthesia and appears to correlate well with Goldmann tonometry; however, pressure readings from rebound tonometry are not independent of corneal properties.  Proview phosphene tonometer appears to decrease patient anxiety regarding their glaucoma; however, studies have not been supportive of its accuracy [16]. Drugs That May Induce or Potentiate Increased Intraocular Pressure 1. Open-angle glaucoma        

Ophthalmic corticosteroids (high risk) Systemic corticosteroids Nasal/inhaled corticosteroids Fenoldopam Ophthalmic anticholinergics Succinylcholine Vasodilators (low risk) Cimetidine (low risk)

2. Closed-angle glaucoma  Topical anticholinergics  Topical sympathomimetics  Systemic anticholinergics  Heterocyclic antidepressants  Low-potency phenothiazines  Antihistamines  Ipratropium  Benzodiazepines (low risk)  Theophylline (low risk)  Vasodilators (low risk)  Systemic sympathomimetics (low risk)  Central nervous system stimulants (low risk)  Serotonin selective reuptake inhibitors  Imipramine

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     

Venlafaxine Topiramate Tetracyclines (low risk) Carbonic anhydrase inhibitors (low risk) Monoamine oxidase inhibitors (low risk) Topical cholinergics (low risk) [17].

GOALS OF THERAPY The primary purpose of therapy is to enhance the patient’s quality of life by preserving vision and minimizing adverse therapeutic effects. Goals that support therapeutic purpose include stabilizing ON/retinal nerve fiber status and visual fields; controlling IOP; and educating and involving the patient in disease management. TREATMENT STRATEGIES All current treatment modalities aim to reduce IOP. Finding an IOP range that allows for stabilization of visual fields and ON/retinal nerve fiber status is often a process of trial and error. The upper limit of that range is referred to as the target pressure. The clinician assumes pretreatment IOP resulted in optic neuropathy and endeavors to reduce initial IOP target pressure by at least 20%. Once therapy is initiated, IOP measurement and ON assessment guide therapeutic adjustments. Present options for managing glaucoma include pharmacologic therapy and surgical modalities such as laser trabeculoplasty and filtering or cyclodestructive surgery. Each has associated benefits and risks, and patient-specific factors and preferences must be considered when selecting appropriate initial therapy. Therapies may be combined to achieve treatment goals. Topical medications are an effective first approach in many patients, although laser trabeculoplasty may be an acceptable option. In some patients, filtering surgery may be preferred initially. Pharmacologic Management of Glaucoma Medications used to manage POAG decrease IOP by two primary mechanisms, decreasing AH production or increasing AH outflow (through either the conventional or unconventional pathways). Glaucoma is a chronic disease—there is no cure, and medical management must be continued throughout a person’s life. Currently, prostaglandin analogues and betablockers are the most frequently used topical medications. Sympathomimetics, topical and oral carbonic anhydrase inhibitors, and cholinergics are used to a lesser degree. Adverse effects or inadequate clinical response may necessitate a therapeutic change, while drugs with different mechanisms of action may be used in combination to maximize IOP reduction [18]. ALTERNATIVE MEDICINES

Homeopathic Remedies: Herbs Proponents of homeopathic medicine believe that symptoms represent the body’s attack against disease, and that substances which induce the symptoms of a particular disease or diseases can help the body ward off illness. Holistic Treatments Holistic medicine is a system of health care designed to assist individuals in harmonizing mind, body, and spirit. Some of the more popular therapies include good nutrition, physical exercise, and self-regulation techniques including meditation, biofeedback and relaxation training. While holistic treatments can be part of a good physical regimen, there is no proof of their usefulness in glaucoma therapy. Eating and Drinking Some studies have shown that significant caffeine intake over a short time can slightly elevate intraocular eye pressure (IOP) for one to three hours. However, other studies indicate that caffeine has no meaningful impact on IOP. To be safe, people with glaucoma are advised to limit their caffeine intake to moderate levels. Studies have also shown that as many as 80% of people with glaucoma who consume an entire quart of water over the course of twenty minutes experience elevated IOP, as compared to only 20% of people who don’t have glaucoma. Since many commercial diet programs stress the importance of drinking at least eight glasses of water each day, to be safe, people with glaucoma are encouraged to consume water in small amounts throughout the day. Good Nutrition The ideal way to ensure a proper supply of essential vitamins and minerals is by eating a balanced diet. Some of the vitamins and minerals important to the eye include zinc and copper, antioxidant vitamins C, E, and A (as beta carotene), and selenium, an antioxidant mineral. Bilberry An extract of the European blueberry, bilberry is available in some health food stores. It is most often advertised as an antioxidant eye health supplement that advocates claim can protect and strengthen the capillary walls of the eyes, and thus is especially effective in protecting against glaucoma, cataracts, and macular degeneration. Physical Exercise There is some evidence suggesting that regular exercise can reduce eye pressure on its own, and can also have a positive impact on other glaucoma risk factors including diabetes and high blood pressure.

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Regular exercise may be a useful addition to the prevention of visual loss from glaucoma, but only your eye doctor can assess the effects of exercise on your eye pressure. Yoga and Recreational Body Inversion The long-term effects of repeatedly assuming a head-down or inverted position on the optic nerve head (the nerve that carries visual images to the brain) have not been adequately demonstrated, but due to the potential for increased IOP, people with glaucoma should be careful about these kinds of exercises. Glaucoma patients should let their doctors know if yoga shoulder and headstands or any other recreational body inversion exercises that result in head-down or inverted postures over extended periods of time are part of their exercise routines. Self-Regulation Techniques The results of studies regarding changes in IOP following relaxation and biofeedback sessions have generated some optimism in controlling selected cases of open-angle glaucoma, but further research is needed. However, findings that reduced blood pressure and heart rate can be achieved with relaxation and biofeedback techniques show promise that non-medicinal and non-surgical techniques may be effective methods of treating and controlling open-angle glaucoma. Medical Marijuana Advocates of medicinal marijuana cite evidence that hemp products can lower intraocular pressure (IOP) in people with glaucoma. However, these products are less effective than safer and more available medicines. Most research regarding marijuana use took place before some current medications with fewer side effects were available. The high dose of marijuana necessary to produce a clinically relevant effect on IOP in the short term requires constant inhalation, as much as every three hours. The number of significant side effects generated by long-term oral use of marijuana or long-term inhalation of marijuana smoke makes marijuana a poor choice in the treatment of glaucoma, a chronic disease requiring proven and effective treatment. Currently, marijuana is designated as a Schedule I drug (drugs which have a high potential for abuse and no medical application or proven therapeutic value). The only marijuana currently approved at the Federal level for medical use is Marinol, a synthetic form of tetrahydrocannabinol (THC), the most active component of marijuana. It was developed as an antiemetic (an agent that reduces nausea used in chemotherapy treatments), which can be taken orally in capsule form. The effects of Marinol on glaucoma are not impressive [19-21].

GLAUCOMA SURGERY There are many glaucoma surgeries, and variations or combinations of those surgeries, that facilitate the escape of excess aqueous humor from the eye to lower intraocular pressure, and a few that lower IOP by decreasing the production of aqueous. Procedures that facilitate of aqueous humor 1. Laser trabeculoplasty 2. Iridotomy 3. Iridectomy 4. Filtering procedures: penetrating vs. non-penetrating 5. Other surgical procedures 6. Canaloplasty 2. Procedures that decrease production of aqueous humor Procedures that facilitate outflow of aqueous humor Laser trabeculoplasty Laser trabeculoplasty (LTP) is the application of a laser beam to burn areas of the trabecular meshwork, located near the base of the iris, to increase fluid outflow. LTP is used in the treatment of various open-angle glaucomas. The two types of laser trabeculoplasty are argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). Selective laser trabeculoplasty is newer technology that uses a Nd:YAG laser to target specific cells within the trabecular meshwork and create less thermal damage than ALT Iridotomy An iridotomy involves making puncture-like openings through the iris without the removal of iris tissue. It is typically used to decrease intraocular pressure in patients with angle-closure glaucoma. A laser peripheral iridotomy (LPI) is the application of a laser beam to selectively burn a hole through the iris near its base. Iridectomy An iridectomy, also known as a corectomy or surgical iridectomy, involves the removal of a portion of iris tissue. Filtering procedures: penetrating vs. non-penetrating Filtering surgeries are the mainstay of surgical treatment to control intraocular pressure. An anterior sclerotomy or sclerostomy is used to gain access to the inner layers of the eye in order to create a drainage channel from the anterior chamber to the external surface of the eye under the conjunctiva, allowing aqueous to seep into a bleb from which it is slowly absorbed. Filtering procedures are typically divided into either penetrating or non-penetrating types depending upon whether an intraoperative entry into the anterior chamber occurs. Penetrating filtering surgeries are further subdivided into guarded filtering procedures, also known as protected, subscleral, or partial thickness filtering

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procedures (in which the surgeon sutures a scleral flap over the sclerostomy site), and full thickness procedures . Non-penetrating filtering surgeries do not penetrate or enter the eye's anterior chamber. There are two types of non-penetrating surgeris: Bleb-forming and viscocanalostomy. Bleb forming procedures include ab externo trabeculectomy and deep sclerectomy. Viscocanalostomy is also an ab externo, major ocular procedure in which Schlemm's canal is surgically exposed by making a large and very deep scleral flap.

and the anterior chamber. A cyclogoniotomy is a surgical procedure for producing a cyclodialysis, in which the ciliary body is cut from its attachment at the scleral spur under gonioscopic control. A ciliarotomy is a surgical division of the ciliary zone in the treatment of glaucoma.

Other surgical procedures Goniotomy and trabeculotomy are similar simple and directed techniques of microsurgical dissection with mechanical disruption of the trabecular meshwork. Laser goniotomy is also known as goniophotoablation and laser trabecular ablation. Tube-shunt surgery or drainage implant surgery involves the placement of a tube or glaucoma valves to facilitate aqueous outflow from the anterior chamber. Trabeculopuncture uses a Q switched Nd:YAG laser to punch small holes in the trabecular meshwork with . Goniocurretage is an "ab interno" (from the inside) procedure that used an instrument "to scrape pathologically altered trabecular meshwork off the scleral sulcus". A surgical cyclodialysis is a rarely used procedure that aims to separate the ciliary body from the sclera to form a communication between the suprachoroidal space

Procedures that decrease production of aqueous humor Certain cells within the eye's ciliary body produce aqueous humor. A ciliary destructive or cyclodestructive procedure is one that aims to destroy those cells in order to reduce intraocular pressure.  Cyclocryotherapy, or cyclocryopexy, uses a freezing probe.  Cyclophotocoagulation, also known as transscleral cyclophotocoagulation, ciliary body ablation, cyclophotoablation, and cyclophototherapy, uses a laser.  Cyclodiathermy uses heat generated from a high frequency alternating electric current passed through the tissue,  Cycloelectrolysis uses the chemical action caused by a low frequency direct current [22].

Canaloplasty Canaloplasty is a nonpenetrating procedure utilizing microcatheter technology.

Table 1. Number of people with OAG, 2010 Europe China India Africa Latin America Japan SE Asia Middle East World

Total OAG 10,693,335 8,309,001 8,211,276 6,212,179 5,354,354 2,383,802 2,116,036 1,440,849 44,720,832

% World OAG 23.9 18.6 18.4 13.9 12.0 5.3 4.7 3.2

Total OAG 12,397,352 11,733,463 11,076,123 8,040,780 7,559,113 3,039,376 2,749,598 2,043,721 58,639,527

% World OAG 21.1 20.0 18.9 13.7 12.9 5.2 4.7 3.5

Table 2. Number of people with OAG in 2020 [5] Europe China India Africa Latin America SE Asia Japan Middle East World

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Table 3. Categories of Visual Impairment [14] Category Corrected VA- better eye 0 6/6-6/18 1