End of Lecture, You Will Be Able To. Hard and Soft Contact Lenses for Astigmatism. Toric Market. When Soft Versus GP Toric? Who Are Better Candidates?
End of Lecture, You Will Be Able To… Hard and Soft Contact Lenses for Astigmatism Jeffrey J. Walline, OD PhD The Ohio State University College of Opto...
End of Lecture, You Will Be Able To… Hard and Soft Contact Lenses for Astigmatism Jeffrey J. Walline, OD PhD The Ohio State University College of Optometry
Toric Market
• • • • • •
Determine good candidates for toric lenses Determine most appropriate toric lens Differentiate soft toric stabilization techniques Assess soft toric fits: power, rotation Know GP toric options Empirically fit GP toric lenses
When Soft Versus GP Toric? • Soft toric • Can’t tolerate GP lens • Corneal toricity ≠ refrac ve as gma sm • Example • K Readings: 43.00 / 44.00 @ 090 MC • Refraction: ‐2.00 ‐3.00 X 180 20/15
• Example • K Readings: 42.00 / 44.00 @ 090 MC • Refraction: ‐3.50 ‐1.50 X 045 20/15 •
Nichols, et al. Contact Lens Spectrum Jan 2014
When Soft Versus GP Toric?
Who Are Better Candidates?
• GP
• Both: Poor VA with spherical lens • Soft: GPs difficult to fit or not tolerated
• Corneal toricity = refractive astigmatism • Poor vision with soft toric • Poor fit with spherical GP
• ATR astigmatism, discomfort, 3‐9 staining
• 3‐9 staining • Excessive bearing
• Spectacle blur • Reduce flexure
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Who Are Worse Candidates?
What Affects Fit of Soft Toric Lens?
• Cylinder greater than sphere
• Gravity • Surface tension / tear film quality • Lid / lens interaction
• Example • ‐4.00 ‐6.00 X 090 • +0.25 ‐3.50 X 180
• Oblique cylinders • Example
• Watermelon seed effect • Powers in each meridian
-2.00
-4.25
Lens interact w/ thick meridian and rotate lens temporally
• Lens should settle ~15 mins • Assume first trial will have no rotation
• Typically no choice; may consider steeper first
• Power • • • •
Trials rarely have exactly what you need Use power cross and vertex each meridian If limited cylinder power, adjust sphere If cylinder power not available, lower power
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Fit Assessment • Centration (coverage) • Movement • Orientation • • • •
Assessing Rotation Same as spherical lenses
• Bottom of lens • As you look at lens • Nasal (must indicate eye) • Right • Counter‐clockwise
Rotation must be consistent Wait until lens settles Assess re‐orientation Assess rotation
OD
• Don’t guess!
Assessing Rotation
Measuring Rotation
• Bottom of lens • Nasal (must indicate eye) • Right • Counter‐clockwise
Measuring Rotation
OD
Measuring Rotation
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Measuring Rotation
Measuring Rotation
Measuring Rotation
Measuring Rotation
Toric Markings
Toric Markings • Tyler’s Quarterly
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LARS
Adjust for Consistent Rotation
• Try to align rotated contact lens axis with refractive astigmatism • Look at…
• CL: ‐2.50 ‐2.25 X 090 • Rotation: 10° right (counterclockwise) • Order: ‐2.50 ‐2.25 X 080
• Bottom of lens • As you look at lens Lens Rotation Left (clockwise) Right (counterclockwise)
Axis Compensation Add Subtract
Adjust for Consistent Rotation
Adjust for Consistent Rotation
• CL: ‐2.50 ‐2.25 X 180 • Rotation: 10° ? • Order: ? 10° Left Rotation
10° Left Rotation
Axis adjusted: lens marking still in same place
Assessment of Soft Toric • Visual acuity • SOR
• Slit lamp • Contact lens fit • Movement • Centration (coverage) • Rotation
• Ocular health
Poor Visual Acuity • Confirm rotational stability • Tighter base curve or different lens
• Compensate for stable rotation • Spherical over‐refraction • Spherocylindrical over‐refraction? • SCOR, CL power, and cross cylinder effect
• Recheck baseline data • New lens
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Example
Example
• MR: ‐4.00 ‐3.50 X 180 • Proclear Toric
-7.50
-7.00 -4.00
vertex
-4.00
• What is your first contact lens order? • ‐4.00 ‐3.00 X 180 • Only comes up to ‐2.25 DC • Spherical equivalent • ‐4.25 – 2.25 X 180
Example
Example: Final Rx • Base curve = 8.4 • Diameter = 14.4 • Power = ‐4.25 ‐2.25 X 165
15 degree rotation
How GP Corrects Astigmatism
Fitting Philosophies – All Back Torics
• Lacrimal lens
• Full alignment (saddle fit) • Typically 2.00 to 2.50 D K toricity • On K for each meridian • Tighter fit, more centered • Smaller diameter, interpalpebral fit
• Toric front and / or back surface
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Fitting Philosophies – All Back Torics
All Back Surface Torics ‐ Base Curve
• Low toric simulation
• Ks: 42.50 / 45.50 @ 090
• Typically when K toricity >2.50 D • Base curve undercorrects corneal toricity • BC aligns (± 0.25 D) with flat meridian and undercorrects steep meridian • Typically 75% of corneal toricity
• Small amount of “rock” over flat meridian • Diameters can be bigger
• ≥ 1 D residual astigmatism and • ≤ 2.00 corneal toricity • Typically soft toric, but patient may not like vision
• Ks: 41.00 / 41.50 @ 090 • MR: ‐1.00 ‐2.00 X 180 • CL: BC = 40.75; Power = ‐3.00 Toricity
Initial BC
Spherical
0.50 D flatter than flat K
0.12 D - 0.75 D 0.25 D flatter than flat K 0.87 D - 1.37 D flat K ≥ 1.50 D
Front Surface Toric Example 8.28
9.28
-0.75 -1.50 X180
0.4
11.28
0.2
(0.33 X diff b/t K’s) steeper than flat K
Summary 9.2
8.0
• Toric contact lenses are often necessary for clear vision • Soft toric are most common • GP bitoric provide excellent vision • Front and back surface GP torics rarely used