Orthokeratology After PRK:
Portend for the Future?

BY JEROME MARTIN GARBER, O.D., F.I.O.S., F.A.A.O.
FEB. 1996

Excimer laser vision correction could herald a resurgence of interest in orthokeratology, not only as an alternative to surgery, but as a means of further correction after PRK.With the recent FDA approval of photorefractive keratectomy, will orthokeratology suffer an early demise? On the contrary! In my opinion, ortho-k will finally be accepted by the myopic masses as an intelligent, safe, non-surgical alternative to laser surgery. And, in many cases, I believe ortho-k will continue to improve patients' unaided vision even after the PRK procedure.

AN ONGOING CASE STUDY

As part of an FDA protocol investigation, E.V., a 32-year-old male, underwent PRK of the right eye in October 1992, and the left eye one year later. He was dissatisfied with his results, and he consulted us regarding orthokeratology. He wanted to improve his poor vision in general, and to qualify for a career as a firefighter, if possible.

E.V.'s entering acuities were 20/400 OD and 20/40 OS. He had not worn spectacles or contact lenses since his first PRK procedure. Topography (Fig. 1) revealed 40.17 @ 170/41.56 @ 80 OD (8.40/8.12), and 42.08 @ 002/43.10 @ 092 OS (8.02/7.83). Intraocular pressure @ 3:55 p.m. was 12mm Hg OD and 11mm Hg OS.

Prior to surgery, E.V.'s spectacle prescription was -4.00 -2.00 x 70, 20/20 OD; -1.00 -1.25 x 85, 20/20 OS. Keratometry was: 42.50 @ 160/45.00 @ 70 OD; and 43.00 @ 015/45.00 @ 105 OS.

His spectacle prescription after PRK was: -1.50 sphere OD and -0.50 -050 x 90 OS. Keratometry was: 40.00 @ 180/41.00 @ 090 OD; and 42.00 @ 005/43.00 @ 095 OS.

We trial fit OK-3 lenses and ordered the first two pairs of lenses as follows:

#1 OD 8.50 B.C., 10.0 dia., -0.50, t.23, 6.0 O.Z.

OS 8.20 B.C., 10.0 dia., +1.00, t.25, 6.0 O.Z.

#2 OD 8.60 B.C., 10.2 dia., plano, t.25, 6.0 O.Z.

OS 8.30 B.C., 10.2 dia., +1.50, t.27, 6.0 O.Z.

COURSE OF TREATMENT

As this was our first experience treating a patient who had undergone PRK, we began with our standard reverse geometry fitting approach, realizing that we would likely have to alter our procedures depending on the patient's response.

Two weeks after the patient began treatment (and now wearing his #2 lenses), he had increased his wearing time to 14 hours. We noted soft minimal apical bearing of 3mm to 4mm, no mid-peripheral tightness and good peripheral clearance. We advised E.V. to continue as is and return in one month.

One month later, we noted 1mm to 2mm superficial abrasions, possibly caused by the lenses moving down to the steeper mid-peripheral area and subsequently rubbing the central cornea. At that visit we designed the third pair of lenses (OK-3: 8.65 B.C., 10.6 dia., +0.25, t.27 6.0 O.Z. OD; 8.35 B.C., 10.6 dia., +1.75, t.29, 6.0 O.Z. OS) which we dispensed the following week.

We saw the patient one month later and found that the right lens was very laterally decentered again. We surmised that a steeper, mid-peripheral tear reservoir might center the lens better. The patient's unaided visual acuity was still 20/200 OD and 20/40 OS.

The turning point came with the fourth pair of lenses. We ordered the OK-65A lens with the same base curve, but a slightly larger optical zone and steeper secondary and aspheric secondary design to align better. The OK-A series lenses are manufactured with an aspheric reverse geometry secondary zone. Unlike the original OK lenses, OK-A lenses have no well-defined junctions and will not tighten as quickly. In addition, the incidence of flare and glare is greatly reduced.

PERSISTENCE PAYS OFF

One month after we dispensed the fourth pair of lenses, we noted significant changes. The patient was still wearing the lenses 14 hours a day or more and he noted that his unaided visual acuity was better after wearing the lenses longer (up to 18 hours). The lenses were still decentered laterally, but unaided visual acuity had improved to 20/80 OD and 20/30 OS. Topography was 40.08 @ 164/41.25 @ 074 OD and 41.41 @ 004/42.29 @ 094. The patient was seeing better, but the topography was not changing significantly.

Before dispensing the fifth pair of lenses, we analyzed the previous fit with fluorescein and found no mid-peripheral tightness but a definite small tight band just before the peripheral clearance.

We prescribed the fifth pair of lenses with a diameter of 11.0 for more coverage. We changed the design to the OK 73-A to compensate for the steepening effect caused by the larger diameter. This design has a larger optical zone (7mm), is looser fitting, and has a three-diopter steeper reverse geometry secondary zone. At the dispensing visit the right lens was high centrally with no lateral decentration; the left lens was also centered and both eyes had good coverage. Our office notes reflected our excitement at this success: "Eureka! Centration at last."

Three weeks later both lenses were high riding. The right lens exhibited no lateral decentration and the left lens was slightly decentered laterally. For the first time, with the lenses in situ, we could overcorrect the patient's right eye with a -1.00 sphere, thus improving his vision to 20/30+.

In addition, topography (Fig. 2) was changing. Apparently, the larger optical zone and flatter secondary curve caused the surgically induced "shelf" to flatten. For the sixth pair of lenses we ordered the same optical zone but with even flatter secondary and base curves to attain further "shelf" flattening.

FIG. 1: POST-PRK (PRE-ORTHO-K)

FIG. 2: AFTER 5 ORTHO-K FITTINGS NOTE THE LESS STEEP "SHELVES" SURROUNDING THE ABLATED ZONE.

CONCLUSION

After six months of orthokeratology, E.V.'s unaided vision has improved from 20/400 to 20/40+2 OD and from 20/40 to 20/30+3 OS. He is now eligible for the firefighter academy, but more important, he finally feels visually balanced without his contact lenses.

One important caveat: When doing post-PRK orthokeratology, the O.D. must concentrate on flattening the bilateral "shelves" and not the surgically ablated zone.

As PRK procedures become more commonplace, some patients with less-than-satisfactory results may seek a non-surgical solution. With patience and persistence, experienced orthokeratologists will be able to help many of these patients to improve their vision. CLS

The author will provide the full text of this case upon request. Dr. Garber is an author, lecturer and clinical investigator in solo practice in Old Westbury, L.I., N.Y. He is founder and past president of the Northeast Orthokeratology Society of the N.E.R.F., and past chairman of the N. Y. State Board for Optometry.