Soft Toric Advances and Fitting Trends
Thomas Quinn, O.D., M.S., F.A.A.O.
I. Perspective on the low astigmat
A. Defined: 0.75 to 1.00D of astigmatism
B. Spherical masking: does not adequately correct astigmatism >0.75DC
C. Other studies: significant improvement in vision when low astigmats are
moved from spherical lens correction to toric lenses.
D. Success rate?
1. Bayer and Young :
a. achieved a 97% fitting success rate
b. 91% achieved success with only one diagnostic fitting.
II. The Phoropter Three Step
A. Demonstrate astigmatic correction
1. prepares them for alternate treatment plan
2. prepares them for higher fees
B. Assess sensitivity to axis mislocation (Becherer Twist Test)
1. minimal rotation illicits blur response: guarded prognosis
2. generous rotation required to illicit blur: good prognosis
C. Assess sensitivity to cylinder power
1. reduce cylinder power until patient reports reduced acuity
2. adjust spherical component as needed
III. Cylinder power considerations
A. Higher the cylinder power, greater residual astigmatism induced with rotation
rotational misalignment of the lens
B. Higher the toric power in a contact lens, greater the likelihood the patient will
complain of visual disturbance with rotational variability.
C. Strategy to minimize symptoms
1. Select the lowest toric lens cylinder power that will provide the patient
with good vision.
D. Vertex issues
1. A myopic patient’s cylinder error will decrease when the spectacle
power is vertexed to the corneal plane
2. A hyperopic patient’s cylinder error will increase when the spectacle
power is vertexed to the corneal plane
IV. Benefits of Silicone Hydrogel Torics
A. Increased oxygen to cornea through thick toric designs
B. Improved corneal health
1. reduced limbal hyperemia
2. reduced corneal edema
3. reduced corneal neovascularization.
C. Dehydrate at a slower rate and to a lesser extent
1. less tightening of the lens following application
2. faster settling/ rotational stabilization
Soft Toric Advances and Fitting Trends
Thomas Quinn, O.D., M.S., F.A.A.O.
Page 2
V. Toric lens rotation
A. Acceptable as long as it does so consistently in the same direction and to the
same degree.
B. Axis modification: LARS rule
1. if the lens rotates Left, Add to the axis
2. if the lens rotates Right, Subtract from the axis
C. Corneal topographic effects
1. greater amounts of rotation if astigmatism extends limbus-to-limbus
2. minimal rotation if astigmatism is confined to the central cornea
VI. Assessing Rotation: Location
A. Two common methods
1. aligning slitlamp beam with lens marking
2. estimation
a. accurate within 8 degrees in 95 percent of cases
b. accuracy drops when observing higher degrees of lens rotation
c. errors have more severe consequences with higher astigmatism
B. Estimation method acceptable if low cylinder powers and little rotation
C. Slitlamp beam alignment technique best if high cylinder or high rotation
VII. Assessing Rotation: Stability
A. Importance of stability to clear vision
B. Methods of assessment
1. straight ahead gaze with blink
2. effects of gaze change
a. look in 4 major quadrants
b. instruct patient to blink in each gaze
c. assess lens marking location
3. The Digital Displacement Test
a. assess lens marking in straight ahead gaze
b. manually rotate lens out of position using finger (digit)
c. move slitlamp to other eye and repeat
d. return to original eye and assess position
i. if returned to original location, good stability
ii. if not returned to original location, consider change
VIII. Troubleshooting
A. Patient description of visual complaint
1. blur is fluctuating
a. rotational instability; confirm with slitlamp
b. irregular lens flexure; confirm viewing red reflex or
keratometry mires
c. dirty lens
2. blur is constant
a. lens power is wrong
B. Rule of thumb:
1. When blur is constant, change the lens power and/or axis
2. When blur is variable, change the design or fit.
Soft Toric Advances and Fitting Trends
Thomas Quinn, O.D., M.S., F.A.A.O.
Page 3
IX. Over-refraction (OR) analysis
A. Only perform over a rotationally stable lens
B. Method 1: observed rotation combined with OR and lens power
http://virtualconsultant.cibavision.com/toric_lens.jsp or www.eyedock.com.
C. Method 2: spectacle prescription combined with OR and lens power
(www.coopervision.com or Contact Lens Calculator Plus at www.palmgear.com
X. Use telephone follow-up
A. If lens fit has already been determined to be stable
B. If physiological response has already been assessed and found acceptable
C. To assess visual response to lens power adjustments
D. To save both the office and the patient time
XI. New Toric Lenses in the Marketplace
XII. Expectations are key
A. Fitting toric contact lenses is a process.
1. not unusual to need to make some adjustments
2. alert to possible physical adaptation required to thicker toric lenses
3. the no surprise approach to eyecare