Presby-LASIK may be better option than multifocal IOLs, study shows

PARIS — Both multifocal IOLs and presby-LASIK are viable solutions for presbyopia correction, but the latter has a greater range of visual acuity at different distances, according to a study presented here.

"Presbyopic LASIK using the Gaussian ablation type, which means a +1.7 D, 3-mm optical zone, slightly decentered 1 mm inferiorly and nasally, is able to provide an acceptable level of distance vision, on average 20/25 to 20/20 and up to 20/18 in some cases, along with an acceptable or even very good level of near and intermediate vision," Michael Assouline, MD, said at the meeting of the French Society of Ophthalmology.

In comparison, multifocal IOLs have shown less satisfactory visual performance.

"They are, in fact, bifocal, and intermediate vision is generally poor," he said.

Defocus curves show that, on average, visual acuity is 20/25 for a defocus of –1.5 D with presbyopic LASIK and 20/50 to 20/30 with multifocal IOLs.

"Defocusing is the best way of comparing multifocal techniques. It clearly demonstrates for the so-called multifocal IOLs that they have bimodal curves with a peak at 0 D for distance vision and a second peak at around –2.50 D, while the defocus curve for presby-LASIK is a continuous curve that has its highest point at 0 D with a slow decrease toward –3 D. This leaves 80% of vision at –0.5 D and 60% at –3 D, which is good enough for intermediate and near vision respectively," Dr. Assouline said.

In the study, special emphasis was placed on assessing the optical nature of multifocality in presbyopic LASIK patients. A number of tests, based on corneal topography and aberrometry, were performed. "The total power map of the cornea shows an average addition zone, which is taking about 25% of the area of the entrance pupil in the patient and has a +3.8 D average power at the vertex. This shows that the patient sees with part of his entrance pupil for near and with the rest, which is about 75%, at distance," he said.

Presbyopic LASIK is performed only in the nondominant eye, which allows the fellow eye, either non-operated when emmetropic or operated with hyperopic LASIK, to have adequate distance vision.

"This gives us truly satisfied patients," Dr. Assouline said.

Aberrometry was performed with the Bausch & Lomb Zyoptix Zywave system.

"We were able to demonstrate that most of the defocusing effect created with the presbyopic LASIK technique was, in fact, negative spherical aberration and coma," he said. "Having this [higher-order aberration] introduced in the optical system of the patient does not affect emmetropia for most of the entrance pupil but only in the central part of it. This means that the patient has a composite image, made of a near image and a distance image both of them being quite clear."