Correcting Higher-order Aberrations
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRé, FAAO
Figure 1. Difference display map of the patient's left eye pre and post corneal reshaping.
Patient MH underwent routine contact lens corneal reshaping using Paragon CRT lenses to correct –1.75D OU of myopia. Within seven days his uncorrected visual acuities were 20/20 OU and were stable from morning to evening. After one month, MH's only complaint was flare and glare at nighttime.
Common Ortho-k Issue
Scotopic viewing symptoms are common in orthokeratology, especially within the first month of the procedure. The reasons for the nighttime symptoms are multifactorial, but a major contributor may be the common 5mm treatment zone. In many patients, scotopic symptoms dramatically lessen with time, probably because of treatment zone stabilization and visual adaptation.
1 shows the difference display map OS with a –1.87D change in apical power.
The map outlines the margins of the pupil and clearly illustrates a slight temporal
displacement of the 5mm treatment zone.
Figure 2. Pupil miosis following the use of Alphagan P.
An Uncommon Solution
Our CL team decided that MH might benefit from a trial of the anti-glaucoma drop, Alphagan P (Allergan). McDonald et al (2001) found that a single drop of Alphagan decreased pupil size approximately 2mm within 30 minutes and that the miosis lasted approximately six hours (Figure 2).
Figure 3 shows the change in MH's post ortho-k higher-order aberrations
before the instillation of Alphagan P (top display) and 30 minutes after (lower
display). It's clear that a dramatic reduction in spherical aberration as well as
most other higher-order aberrations has occurred. Subsequently, MH reported a dramatic
reduction in nighttime symptoms.
Looking Toward the Future
We're currently investigating new corneal reshaping lenses designed to increase the typical treatment zone diameter to 6mm. Preliminary results have shown that these designs do indeed lessen symptoms of nighttime glare and flare.
Additionally, a number of our contact lens patients have successfully
used Alphagan P off label to modulate their pupil size (for improved nighttime viewing)
following RK and LASIK procedures, post HSV and in certain cases of keratoconus.
Patrick Caroline is an associate professor of optometry at Pacific University and is an assistant professor of ophthalmology at the Oregon Health Sciences University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc.
Mark André is director of contact lens services at the Oregon Health Sciences University and serves as an assistant professor of optometry at Pacific University. He is also a consultant for Alcon Labs, CooperVision and SynergEyes, Inc.