contact lens practice pearls
A Three-Step Approach to Assessing Toric Lens Stability
BY THOMAS G. QUINN, OD, MS, FAAO
Rotational stability is arguably the most important fitting feature of a successful toric soft contact lens. An unstable lens results in variable vision and an unhappy patient. Here is a three-step process to accurately evaluate rotational stability of a toric soft contact lens.
STEP 1. Stability in Straight-Ahead Gaze
With the patient positioned behind the slit lamp, identify the location of the toric lens marking(s). Instruct the patient to look straight ahead and blink. Observe the lens marking as the patient blinks.
This is perhaps the most commonly employed method of assessing rotational stability. While it can help you identify a poor fit, it doesn't necessarily confirm a stable fit because this technique doesn't provide any information on lens behavior during eye movements that take place when patients view objects in day-today activities. A lens whose marking remains relatively constant in straight-ahead gaze, while a good initial observation, may shift when the eye is directed elsewhere.
STEP 2. Stability With Gaze Change
After observing the consistency of orientation in straight-ahead gaze, instruct the patient to look up. As the patient is looking up, instruct him to blink, then look straight ahead. Reassess the location of the toric marking. Repeat this process in down, right and left gaze, remembering to instruct the patient to blink while viewing at the extreme of each of these directions.
At the completion of each gaze change, reassess the position of the lens marking in straightahead gaze. A lens that shows very little variability in the toric marking position throughout this procedure will likely provide the patient with consistent vision.
STEP 3. Digital Displacement Test
The third and final step to assessing rotational stability is a provocative test to see how the lens responds to purposeful displacement.
Once you complete the first two steps, re-establish the orientation of the toric lens marking in straight-ahead gaze. Reach around the slit lamp and, using your clean finger (digit), rotate the lens out of position. If you observe the lens to rotate in a clockwise direction, push it counterclockwise, and vice versa. Once you accomplish this, swing the slit lamp system over to the other eye and repeat.
Now, return to the eye you started with and observe the location of the toric marking. If it has returned to the location it was in prior to displacement, it's likely that this lens will be stable during day-to-day wear. If it hasn't returned to its original location but is nearly so, instruct the patient to look up, blink, then look straight ahead. This allows the downward force of the upper eyelid to have an enhanced effect on the lens. If the lens now appears to have returned to its original location, it's likely the fit will be successful. If the marking is still mal-positioned, change the fit before proceeding.
Efficient and Informative
All three stability assessment steps occur with the patient positioned at the slit lamp. It takes very little time to move seamlessly from one step to the next. This small investment of time will help you identify potential problems early and make changes at the outset to expedite success with your astigmatic lens wearers. CLS
Dr. Quinn is in group practice in Athens, Ohio. He is a diplomate of the Cornea and Contact Lens Section of the American Academy of Optometry and an advisor to the GP Lens Institute.