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Surgeon: Pupil size important to presby-LASIK outcomes
Despite good technical outcomes, the size of the pupil can negate the multifocality created.
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SINGAPORE – A patient’s pupil size cannot be overlooked when preparing to perform presby-LASIK, according to one surgeon.
At the Asia-Pacific Association of Cataract and Refractive Surgeons, Jerry Tan, MD, said that small and large pupils could negate successful topographies.
According to Dr. Tan, the general theory of creating a central myopic correction surrounded by a hyperopic correction appears to work when the refractive numbers are analyzed, but in reality the visual outcomes are not as good as they appear on paper.
“When you focus near, the pupil shrinks, so anything done on the outer surface of the cornea has no effect on vision,” Dr. Tan said.
Accounting for the pupil
To illustrate his point, Dr. Tan presented two cases of patients who had presby-LASIK. Both had excellent technical results, he said, including a prolate cornea and midperipheral correction. After 6 months they complained of poor near vision along with problems such as halos and glare.
A pupil size below 4 mm nullifies wavefront adjustments, according to Dr. Tan. On the other hand, a very large pupil such as one greater than 8 mm can also compromise the desired effects of presby-LASIK.
“I think somewhere along the line somebody has to decide what the pupil size needs to be for presby-LASIK,” he said.
Managing accommodation
To assess whether a patient has improved after surgery, Dr. Tan said preoperative accommodation amplitude should be measured.
“If a person is 50 years old, but has very strong accommodation amplitude, the patient will still maintain very good reading vision. If the patient undergoes presbyopic LASIK treatment or even ‘normal’ LASIK treatment, the patient still would be able to focus strongly using this accommodative amplitude to allow him to see near. This creates a problem with the validity of the results,” Dr. Tan told Ocular Surgery News in an e-mail.
Unfortunately, current tests do not accurately measure accommodation, according to Dr. Tan.
A study Dr. Tan cited showed objective tests garnered more reliable results than subjective tests, but according to Dr. Tan, there was still a wide range of variance between all the tests, illustrating the importance of good measurements and the need to find a more definitive test.
“Presby-LASIK is a hot topic, but I am still up in the air about it. There is still a lot to learn and discover with this procedure.”
For more information:
- Jerry Tan, MD, can be reached at Jerry Tan Eye Surgery, Camden Medical Centre, 1 Orchard Boulevard #10-06, Singapore 248649; +65-6738-8122; fax: +65-6738-3822; e-mail: jtaneyes@singnet.com.sg. Dr. Tan is a Wavelight ambassador for Wavelight AG.
Reference:
- Ostrin LA, Glasser A. Accommodation measurements in a prepresbyopic and presbyopic population. J Cataract Refract Surg. 2004;30(7):1435-1444.
- Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.