Vision can be restored fast after PRK using epithelial scrub, cooled saline

According to a prospective study comparing differences in patient comfort levels, PRK is not dead.

SANDTON, South Africa - A regimen combining cooled saline rinse and rotary epithelial removal with photorefractive keratectomy (PRK) using a scanning excimer laser allows accurate correction of myopia and astigmatism and a quick return of vision, according to a refractive surgeon here.

The technique described by S. Percy Amoils, MD, uses a Nidek (Fremont, U.S.A.) EC-5000 scanning laser after removal of the epithelium with the Rotary Epithelial Scrubber (Innovative Excimer Solutions, Toronto), along with pre-scrub and post-laser saline cooling

Dr. Amoils presented a preliminary prospective study of his PRK technique at this year's meeting of the American Society of Cataract and Refractive Surgery, and recently updated his results in an interview. He examined patient comfort levels, complications and incidence of glare and night driving problems in his PRK patients.

"I certainly feel that PRK is not dead, but I think there are a lot of problems with LASIK that are beginning to emerge," said Dr. Amoils, who does not perform LASIK. According to Dr. Amoils, many surgeons perform LASIK in South Africa, and he has seen problems in some of these other surgeons patients postoperatively.

PRK vs. LASIK

In Dr. Amoils' experience using the Nidek EC-5000 for bilateral PRK, he has detected little discomfort in patients. Complication rates are minimal and there are few glare and night driving difficulties. Dr. Amoils said visual acuity in his PRK patients at 1 week following surgery was better than most LASIK cases he has seen.

Since his presentation in San Diego, Dr. Amoils said, he no has performed more than 450 cases with a follow-up of up to 18 months and no retreatments.

Care of the epithelium

photograph ---To prepare the eye for excimer laser ablation, the Rotary Epithelial Scrubber is used to remove an accurate amount of epithelium without trauma to Bowman's layer.

In PRK, the epithelium must be treated with as much care and attention as a corneal flap in LASIK, Dr. Amoils said. Minimal epithelial removal with preservation of a healthy and undisturbed regenerative epithelial margin and a polished Bowman's membrane is vital in obtaining good outcomes. This is more crucial in re-lasering, where the epithelium is emulsified off the stroma, he said.

Precise epithelial removal, just enough to clear the margins of the ablated area, permits rapid healing in 36 hours with little inflammation, he said. When using the scrubber, healing appeared complete in 90% of eyes by day 3.

Bilateral PRK

The prospective study to date included the use of the Nidek EC-5000 excimer laser on 389 eyes with myopia from 1 D to 12.75 D and astigmatism up to 4.5 D. Bilateral PRK was performed in 85.35% of eyes. Follow-up was from 1 week to 24 months, with an average 5.25 months. About 78% of patients had myopia of 6 D or less, with an average value of 3.89 D.

The treatment protocol consisted of cooling the cornea before PRK with 20 drops of balanced salt solution chilled to 4°C to 6°C. "You don't want the balanced salt solution any cooler," Dr. Amoils said. "You can burn the cornea if the balanced salt solution is too cold." Dr. Amoils used a scrubber saturated with cool balanced salt solution. Post-laser, the ablated cornea is wiped with a damp Merocel sponge.

Astigmatism first

"I treat the astigmatism first and then the sphere with the Nidek EC-5000," Dr. Amoils said. "I pause for 5 seconds every 25 seconds if the myopia is greater than 9 D. Then immediately I flood the cornea with 5 mL chilled balanced salt solution for 10 seconds after the laser ablation is complete." Dr. Amoils said he uses the Nidek laser at a speed of 30 cycles a second, not 40 cycles a second like most Nideks.

The cornea was covered with an Acuvue (Vistakon, Jacksonville, U.S.A.) 8.4-mm base curve or a Focus (Ciba Vision Ophthalmics, Atlanta) 8.6-mm bandage lens after medication was instilled. Patients were examined after 15 to 30 minutes to ensure the lens was not moving excessively and was not inside out.

In patients with 1 D to 3.25 D of myopia, an optical zone of 6 mm and a transitional zone of 7 mm were used. For 3.5 D to 6 D, an optical zone of 5.5 mm and a transitional zone of 6 mm to 6.5 mm were used, depending on the patients' age and pupil size. For 6 D to 12 D, an optical zone of 5 mm and a transitional zone of 6 mm to 6.5 mm were utilized.

Follow-up visual acuity

GRAPH ---Unaided visual acuity (no re-operations) shown over a 24-month period using the Nidek EC-5000, rotary epithelial scrubber and chilled balanced salt solution in PRK.

No eyes in Dr. Amoils' study required retreatment and no eyes lost best corrected visual acuity (BCVA), he said. Three eyes gained one line of BCVA. No visually significant haze has been seen. Minimal halos or night driving problems occurred, but had decreased considerably after 3 months and disappeared by 6 months.

The scanning laser produces less heat in the cornea than a broad beam laser, especially if used at no more than 30 Hz, Dr. Amoils said. The heat difference, together with the smooth ablation of the scanning slit, are the most important reasons for the consistent good results and absence of myopic regression to date, he said.

According to the results that were presented in San Diego, the day following surgery, bilateral vision with a bandage lens was 20/30 in 25%, 20/40 in 60% and 20/60 in 100% of patients. In the expanded study of 389 patients, bilateral vision on the following day with a bandage lens was 20/20 in 0.6%, 20/25 in 10%, 20/30 in 31%, 20/40 in 77%, 20/60 in 97%, 20/80 in 99% and 20/100 in 100% of patients. Uniocular vision for the preliminary results was 20/20 in 2%, 20/25 in 4%, 20/30 in 7%, 20/40 in 36%, 20/60 in 71%, 20/80 in 93% and 20/100 in 100% of patients.

The bandage lens was not removed before the third day. For all patients with high myopia or incomplete epithelialization, the bandage lens was kept in for an additional day.

The most recent results illustrated that uniocular vision with the bandage lens on the first post-laser day was 20/20 in 0.5%, 20/25 in 4%, 20/30 in 15%, 20/40 in 48%, 20/60 in 86%, 20/80 in 95%, 20/100 in 99% and 20/200 or better in 100% of eyes.

One week following surgery, uncorrected visual acuity (UCVA) was 20/20 in 10%, 20/25 in 40%, 20/30 in 72%, 20/40 in 91%, 20/60 in 98% and 20/80 in 100% of patients.

At 6 months, UCVA in 165 eyes was 20/15 in 13%, 20/20 in 74%, 20/25 in 95%, 20/30 in 96% and 20/40 in 99% of patients.

At 12 months, UCVA in 58 eyes was 20/15 in 7%, 20/20 in 76%, 20/25 in 93% and 20/40 in 100% of patients.

Quick healing of the epithelium alleviates discomfort and permits rapid restoration of vision, Dr. Amoils said. This, along with the low heat generation characteristic of the scanning slit laser, as well as the pre-laser and immediate post-laser cooling, results in accurate and consistent visual results, he said.

For Your Information:

S. Percy Amoils, MD, can be reached at 90 Protea Ave., Athol, Sandton, 2196 South Africa; ++(11) 884-5624; fax: ++(11) 884-5624; e-mail: percy@icon.co.za. Dr. Amoils has a direct financial interest in the Rotary Epithelial Scrubber. He is a paid consultant for Innovative Excimer Solutions Inc.