Innovation Spotlight - LASIK

LASIK preferred procedure, but PRK still has a place

Walter Stark, MD

By Alyson G. Yashar, MD
Reviewed by Walter Stark, MD

Baltimore-Although LASIK surgery seems to be the preferred refractive procedure, PRK is a less complex procedure appropriate for situations where LASIK is not advisable, said Walter Stark, MD.

More than 50% of refractive surgeons prefer LASIK for 4 D of myopia, and more than 80% prefer LASIK for higher levels of myopia, said Dr. Stark, professor and director of the Cornea Service at the Wilmer Institute of Johns Hopkins University, Baltimore.

Dr. Stark outlined the results of a survey mailed to faculty and course participants of the refractive surgery symposium at the American Academy of Ophthalmology prior to the meeting. Most of the 180 respondents were from the United States.

Surgeons preferred PRK over LASIK in cases with thin corneas, inability to get good suction, keratome-related complications, low K readings, deep-set eyes, poor patient cooperation, small lid fissures, severe squeezing, asymmetric astigmatism, or eyes with pachymetry measurements less than 500 µm.

Less postop pain with LASIK

According to published studies comparing PRK with LASIK, there were equivalent results at 1 year for myopia of 2 to 5.5 D and myopia up to 14 D, respectively. However, because of less postoperative pain, faster visual recovery, and less corneal haze, LASIK has become the preferred procedure for the majority of refractive surgeons in the United States. Moreover, LASIK can be used to treat higher degrees of myopia. Patients also generally prefer LASIK to PRK.

During the past 12 months, 23% of surgeons polled have performed RK, with an average of 10 procedures per year; 75% are performing PRK, also with the same number performed annually. The top 25% of surgeons perform 90% of the PRK procedures.

Eighty-six percent of respondents perform LASIK, averaging 150 a year. The top 25% of surgeons did 84% of the total LASIK cases.

Only 12% of responding surgeons were using intrastromal corneal ring segments (Intacs, KeraVision). A small subset (25%) had performed 95% of all cases. The average number of cases done was six. Only 14% of respondents were doing phakic IOLs, averaging 30 cases annually. Clear lens extraction was performed by 35% of those polled, with an average of 10 cases a year. The top 25% of surgeons performed 81% of cases.

Two-thirds polled use a VISX excimer laser, 10% use Summit, 8% use Nidek, 1% use Autonomous, 7% use the Bausch & Lomb Technolas 217, and 7% other.

Microkeratome use was broken down by 79% preferring the Bausch & Lomb Hansatome, 10% ACS by Bausch & Lomb, 4% Moria Carriazo Barraquer, 2% Moria LSK-1, and 5% other. Most high-volume surgeons prefer the Hansatome, Dr. Stark reported.

For low to moderate myopia, 65% of the surgeons preferred LASIK, 20% PRK, and 2% RK. In the 4- to 8-D range, 80% of surgeons preferred LASIK. With 8 to 12 D of myopia, 80% of surgeons preferred LASIK. With greater than 12 D of myopia, only 29% of surgeons would opt for LASIK. Forty-eight percent of surgeons would not perform any refractive surgery. Others would consider clear lens extraction or phakic IOLs, he said.

The safest and most effective procedure for low to moderate myopia was considered to be LASIK (67%), followed by PRK (26%). Only 5% considered Intacs to be the safest and most effective and only 2% considered RK.

None performed phakic IOL procedures for low myopia. Most respondents said their preference was determined by personal experience and not peer-reviewed literature or data.

Twenty-five percent of respondents routinely performed bilateral simultaneous PRK. Sixty-seven percent performed bilateral LASIK. Among the most prolific surgeons, around 30% to 40% perform bilateral simultaneous same-day PRK. Eighty-one percent of the busiest surgeons perform bilateral LASIK. However, 17% of the busiest surgeons do not perform bilateral same-day LASIK.

How much residual corneal bed should be left is important in patients with 10 to 12 D of myopia. (FDA guidelines say 250 µm.) Sixty-two percent of respondents said they follow FDA guidelines. Eighteen percent would leave between 225 and 250 µm. Thirteen percent go to less than 225 µm, and 1% do not calculate the residual stromal bed.

When PRK is preferred

Surgeons prefer PRK in patients with low myopia and Cogan's dystrophy, corneal erosions, or even with conjunctival scarring after retinal detachment surgery. Here, the issue arises as to whether adequate suction may be obtained with an anteriorly displaced buckle.

With corneal conditions like corneal scarring of 75 µm, PRK also took the lead with 59% of respondents preferring this technique. Respondents also preferred PRK with tight eyelids.

Most (57%) did not recommend surgery in patients with herpes simplex virus.

"I was glad to see this," Dr. Stark said. "But 29% still said they would perform LASIK under these circumstances."

With K readings <41 where one may get a free cap, 41% preferred LASIK. With K readings >49 where there is a risk of keratoconus and an increased risk of a buttonhole, 42% preferred LASIK. Surgeons preferred LASIK with small corneal diameters, if good suction was obtainable.

Fifty-two percent of respondents preferred LASIK in patients with glaucoma.

"I don't know if LASIK or PRK gives any better pressure reading after surgery," Dr. Stark said. "IOP reading after refractive surgery is not as reliable, so you want to get a good baseline reading before and after so you know what the drop has been from the refractive surgery."

In diabetic patients, despite the added risk of recurrent corneal erosions, 72% preferred LASIK. With collagen vascular disease, most (62%) would defer surgical intervention, with the rest preferring LASIK. Flap melts and corneal melts were more likely with collagen vascular diseases.

With previous PRK, 56% of refractive surgeons preferred LASIK for patients with 1 to 4 D of myopia. With occupational activities like boxing or basketball, where someone might get a fingernail under the flap, 49% of surgeons preferred LASIK, even though many said PRK is a safer procedure under those circumstances. In patients with a complication from PRK in the first eye, 67% would perform LASIK and 5% would perform PRK. In patients with a complication from LASIK in the first eye, a similar number of respondents would perform LASIK in the second eye (47%) and 18% would perform LASIK.

LASIK may not be advisable with thin corneas, inability to get good suction, anterior membrane dystrophies, recurrent corneal erosion, conjunctival scar, corneal scar keratome-related complications, deep-set eyes, poor patient cooperation, small eyelid fissure, asymmetric astigmatism, or eyes with pachymetry measurements less than 500 µm, Dr. Stark said.

LASIK is preferred to PRK in most other situations, including: K readings >49 or <41, small corneal diameter, glaucoma, pterygium, diabetes mellitus, collagen vascular disease, previous PRK, occupational (with possible trauma) PRK complication in the first eye, or even a LASIK complication in the first eye.

Others study contributors were Dan Schneider (from the American Academy of Ophthalmology) and Anthony Kouzis (from the Wilmer Institute).

Ophthalmology Times / APRIL 1, 2000