Gas permeable contact lens users should discontinue lens wear for six weeks, rather than the traditional three weeks, before LASIK evaluation, a new study suggests.

Refractive stability after stopping lens wear is highly variable, the study says. In some patients, refraction stabilizes in a few weeks; in others, a few months. So, some refractive surgeons require a standard time period (usually three weeks), while others apply a rule of thumb such as a week of lens wear cessation per year of GP lens use.

But often, the patient must return for more than one evaluation, sometimes several, before the refraction stabilizes. To minimize the need for unnecessary evaluations, the researchers investigated how much time is necessary for refractive stability after discontinuing GP lens wear. Their results are published in Novembers Journal of Cataract and Refractive Surgery.

The researchers examined patients at three-week intervals until their refraction stabilized. The study found that only 56% of eyes (31 of 55) achieved a stable refraction after three weeks, but 78% were stable after six weeks. No significant between-group differences were observed in age, gender of patients, or anatomical or optical characteristics of their eyes. However, the study suggests that the number of years that a patient has been wearing GP lenses may influence the time it will take for a stable refraction to be achieved.

We advise counseling patients who are long-term RGP wearers that multiple visits will likely be required before a stable refraction is obtained, the authors conclude.

They add that corneal changes  occur with soft lenses, too, though not as pronounced as with GPs.

This study is good because what it does is re-emphasizes that theres individual variability, and you cant just use a specific time point, says optometrist Milton M. Hom, of Azusa, Calif. Dr. Hom is the author of Manual of Contact Lens Prescribing and Fitting and LASIK: Clinical Co-management.

Even though patients want specific answers about how long theyll have be out of their lenses before LASIK, the real answer is that it all depends on refractive and topographic changes, Dr. Hom says, not a rule-of-thumb benchmark.

This study also underscores the need for monitoring soft lens patientsespecially those wearing soft toric lensesbefore LASIK, he adds.

Tsai PS, Dowidar A, Naseri A, McLeod SD. Predicting time to refractive stability after discontinuation of rigid contact lens wear before refractive surgery. J Cataract Refract Surg 2004 Nov;30(11):2290-4.