contact lens Q&A

When Presbyopia Strikes Post-RK

BY DAVID I. GEFFEN, OD
APRIL 1998

One of my 40-year-old patients had radial keratotomy (RK) approximately 10 years ago and had been very happy with the results, but now he notices decreasing near and far acuity. The manifest refraction is OD +2.00 -1.25 x 95, 20/25; OS +1.50 -1.00 x 74, 20/25. Uncorrected visual acuities are: OD 20/40 and OS 20/30. Keratometry readings are OD 40.25@10/39.00@100 with trace distortion; OS 39.50@160/ 38.50@070 with trace distortion. The patient is 20/20 at near with the manifest in place.

This type of patient is becoming commonplace in many of our practices. Many of the people who had RK five to 10 years ago are now approaching presbyopia. They had been very happy with their vision and do not wish to return to their dependence on visual correction devices. These patients have three options: surgery, eyeglasses and contact lenses.

What are the surgical options?

More RK and/or astigmatic keratectomy (AK) will not provide the increased acuity the patient requires. AK may reduce the astigmatism, but will induce even more hyperopia. PRK, while an option in other countries, is not yet available in the United States and is not as successful on previous RK eyes as some other procedures. LASIK has a relatively high success rate in correcting previous RK eyes and is probably the best surgical alternative, but the software for this particular patient is also not yet available in the United States.

What about spectacles?

Eyeglasses should provide excellent acuity at both near and far and as presbyopia proceeds, you can easily switch to multifocals. While eyeglasses are a viable option, patients may not want them because they underwent surgery to eliminate the need for them.

What do I need to know about post-RK lens fitting?

Contact lenses should provide the best visual acuity of all the options. Rigid gas permeable lenses are the best choice due to the irregular topography of the post-RK eye. Soft lenses often provide poor, fluctuating acuity due partially to the molding effect of the soft lens. Corneal neovascularization is also a concern, which is common along the incisions with soft lens wear.

Corneal topography is often valuable when fitting gas permeable lenses. Midperipheral topography is a good place to evaluate for your starting point with trial lenses. Trial lens fitting is imperative with post-RK corneas because it is extremely difficult to predict how a lens will perform by topography or keratometry alone.

In prescribing contact lenses for post-RK corneas, there are many RGP lens choices available. Generally, I fit this type of patient with very large diameters, typically starting with an 11.0mm lens. I use spherical, aspheric, aspheric periphery, reverse geometry and plateau designs. I also prescribe SoftPerm and occasionally hydrogel contact lenses. Fluorescein evaluation with RGPs will show moderate apical pooling due to the central flattening caused by the RK. There should be light touch in the intermediate area with slight peripheral pooling. Watch for excessive edge lift, which will cause discomfort.

It's important to inform patients that their vision will be more distorted after lens removal. RGP lens wear tends to cause changes in the corneal topography, which may last from 30 minutes to over several hours and may affect vision with spectacle wear. Therefore, patients will need to wear their lenses over 14 hours per day, and this reinforces the importance of helping them achieve optimal comfort with their lenses. CLS

Dr. Geffen is in a joint refractive surgery practice in San Diego. He is also a consultant for Infinity Optical.