Thin-flap LASIK in thin corneas compares favorably with conventional method

Thin flaps offered strong visual and refractive outcomes, safety and high predictability, a surgeon says.

Thin-flap LASIK in eyes with corneal thickness of less than 500 µm yielded safety, comfort, and visual and refractive outcomes similar to LASIK in thicker corneas, according to a study.

There was no difference in efficacy, predictability, safety or complication rate for LASIK when corneas of less than 500 µm were compared with corneas of more than 500 µm, Jan Venter, MD, told colleagues during Refractive Subspecialty Day preceding the joint meeting of the American Academy of Ophthalmology and Middle East Africa Council of Ophthalmology in Chicago.

LASIK has been shown to offer safety and efficacy similar to that of PRK, Dr. Venter said.

“If we look at LASIK in the literature, it is less painful, we have quicker visual recovery, we use less medication and, overall, it is a superior experience for the patient,” he said. “Efficacy and safety is equal to what we see with surface ablation.”

However, thin corneas are at greater risk than thicker corneas for development of postoperative ectasia and keratoconus.

Dr. Venter described two theories that may explain the postoperative ectasia. One, the abnormal eye has a thin cornea in which keratoconus may develop. Two, the thin cornea has an unexpected low residual stromal bed and insufficient structural integrity to prevent ectasia. Consequently, thin-flap LASIK is preferable for thin corneas, Dr. Venter said.

Similar preop sphere, cylinder

The retrospective study included 81,715 eyes that underwent LASIK between April 2008 and March 2009. Data were divided into two subgroups: 2,181 eyes with corneas thinner than 500 µm and 79,534 eyes with corneas thicker than 500 µm.

A femtosecond laser was used to create flaps in thin corneas (flap thickness of 100 µm or less), and a mechanical keratome or femtosecond laser was used to cut flaps in corneas thicker than 500 µm. Patients were followed for 18 to 30 months.

Investigators compared predictability, efficacy, safety and complication rates between the two corneal thickness groups. Between-group differences in preoperative sphere and cylinder were statistically insignificant, Dr. Venter said.

“If we look at the preop sphere, there was no significant difference except in the high myopes, where LASIK on thin corneas would be contraindicated,” he said.

No differences between groups

Between-group differences in postoperative uncorrected visual acuity, safety and complication rates were statistically insignificant.

“Uncorrected visual acuity at 3 months: no difference. Safety at 3 months: no difference. Complications: no difference,” Dr. Venter said. “We actually had two ectasias in the thicker-cornea group of patients. Again, no difference. We know from studies from [Jorge] Alió and John Marshall that corneal stability is equal to that of surface ablation when we create the flap with a femtosecond laser.”

At 3 months after surgery, only 1% of eyes lost two lines of best corrected visual acuity in both groups. No eyes lost more than two lines of BCVA.

Results showed 93% of eyes in the thin-cornea group and 92% of eyes in the thick-cornea group attained uncorrected visual acuity of 20/25 or better.

Complication rates were 1.19% for thin corneas and 1.08% for thicker corneas.

“Thin-flap LASIK in thin corneas offers our patients and the surgeon the advantages of both LASIK and PRK. We have great visual recovery, as we see with LASIK. We have comfort associated with LASIK. And, most importantly, we have the biomechanical changes and . . . function that we see with PRK.” – by Matt Hasson

• Jan Venter, MD, can be reached at Optical Express, 22 Harley St, London, United Kingdom, W1G 9AP; 44-0207-580-1200; fax: 44-0207-580-1201; e-mail: drjanventer@googlemail.com.
• Disclosure: No products or companies are mentioned that would require financial disclosure.