Managing Overcorrection Following PRK

BY JAMES V. AQUAVELLA, M.D.
FEB. 1997

One of the major disadvantages of radial keratotomy is the incidence of overcorrection in the pre-presbyopic age group. The prospect for significant hyperopia following enhancement procedures and the difficulty in correcting these hyperopic shifts is intimidating to refractive surgeons and discouraging to patients. While this problem is greatly reduced by PRK, overcorrection can still occur.

DEPENDABLE DATA REQUIRED

Refractive data that's acquired in a subjective, qualitative manner can incorrectly imply elevated levels of myopia. A surgical procedure based on this faulty data could result in an overcorrection.

Using careful quantitative endpoint refractive techniques and cycloplegic refractions should result in dependable baseline data that can be used to formulate a surgical plan to be programmed into the laser. Although technical programming errors are possible, they are rare in the hands of an experienced surgical team.

STEROID TITRATION

In the presence of a mild physiological healing response, aggressive postoperative steroids can prolong the early routine postoperative hyperopia. The relationship between the aggressive use of steroids during the early postoperative period and the development of stable, long-term hyperopia or overcorrection is still unclear. However, careful postoperative refractions will enable more precise titration of steroids with healing response.

MONOVISION

In attempting monovision with PRK, a relative overcorrection can result if the planned degree of undercorrection is not achieved. While both patient and physician may be disappointed, appropriate near vision spectacle correction will usually suffice. Since treatment modalities for this problem are limited, it's best to avoid it.

TREAT EACH PATIENT AS AN INDIVIDUAL

The decision to treat overcorrection can be compared to Mount Everest -- just because it's there doesn't mean you have to climb it. The primary consideration should be how unhappy the patient is with the result.

In the absence of reliable and predictable laser or other surgical techniques to reduce overcorrection, an acceptable remedy for some patients may be as simple as placing a contact lens on one eye, or using reading spectacles if they are younger and the hyperopia is moderate. In young individuals, modest amounts of postoperative hyperopia (less than a diopter) can be well tolerated and can afford good distance acuity. However, in older, pre-presbyopic individuals, even a small overcorrection may precipitate the necessity for a reading correction and produce a very unhappy patient. While still a problem, this is often manageable with an appropriate near vision spectacle correction. The key is to treat each patient as an individual, not as an eyeball.

The patient should be informed about the overcorrection only after the referring optometrist and the refractive surgeon have established a uniform treatment plan. It doesn't matter who tells the patient, as long as it's the same message.

OTHER MANAGEMENT TECHNIQUES

Microkeratome lamellar keratotomy techniques such as LASIK may present an inordinate risk-to-benefit ratio in dealing with low levels of hyperopia. When the laser surgical treatment of hyperopia becomes available in the United States, the approved treatment protocols may offer additional modalities for dealing with overcorrections. Currently, off-label techniques that reduce hyperopia by treating a peripheral annulus while sparing the central cornea are available. Centering a small diameter rigid contact lens over the visual acuity axis may also achieve a similar result. All these techniques, however, are highly individualized and their efficacy will vary depending upon the experience and innovative skill of the surgeon.

In view of the above, many refractive surgeons plan a modest undercorrection for their older patients to avoid complications, although patients who have opted for PRK to correct myopia will be unhappy if they still require spectacles for distance vision. Refractive surgeons will be more aggressive if they are confident in their ability to correct the small levels of overcorrection that may occur following PRK. CLS

Dr. Aquavella is chairman of the Genesee Valley Eye Institute and director of the corneal research lab at the University of Rochester.