Reliable measurement of distance between PRL and crystalline lens vital

Stockholm, Sweden-Induced cataract is the primary complication associated with implantation of any phakic posterior IOL, and direct mechanical contact with the crystalline lens is one of the main risk factors, said Annemari Koivula, MD, St. Eriks Eye Hospital, Stockholm, Sweden. Therefore, the distance measurement between the phakic IOL and the crystalline lens seems to be extremely important for the evaluation of different phakic IOL models.

Dr. Koivula reported results of a study in which the distance between a phakic refractive lens (PRL) and the crystalline lens was measured with and without accommodation.

“The PRL and the anterior lens surface moved forward during accommodation in all eyes, and in most cases (85%), there was no mechanical contact between the PRL and the anterior lens surface,” Dr. Koivula said. “But if you find contact, watch for lens opacification.”

Optical coherence tomography ([OCT] Visante OCT, Carl Zeiss Meditec) was used to evaluate PRL movement in relation to the lens and the cornea. Baseline measurements were taken in a nonaccommodative state; thereafter, the eye was stimulated with negative lenses in the OCT to induce accommodation. Additional measurements were taken with the OCT software after scanning.

In a previous PRL study, Dr. Koivula and colleagues found the distance between the PRL and the crystalline lens decreased significantly during the first follow-up year with no subsequent changes. This standard was used in the inclusion criteria for the present study, as was the inclusion of only one eye of each patient to avoid bias. Eyes that had undergone any other refractive surgery combined with the PRL procedure were excluded.

Mean patient age was 34 years at the time of scanning. The series included 41 myopic eyes, with large (PRL 101) and small (PRL 100) myopic models implanted, and 11 hyperopic eyes that all received the same hyperopic PRL model.

Dr. Koivula said the crystalline lens takes a more rounded shape during accommodation to increase its accommodative power. “We measured the distance between the lens and the cornea and could show a significant forward movement of the anterior lens surface during accommodation, as expected, in all the groups. We did the same kind of measurements between the cornea and the PRL, and here as well could see significant forward movement of the PRL during accommodation in all eyes,” she said.

“So now we know that both the PRL and the anterior lens surface moved forward during accommodation, but was this enough to preserve space between the PRL and the crystalline lens? The answer is definitely ‘Yes’ in the PRL 100 group, in which the distance remained the same during accommodation. In the PRL 101 group and the hyperopic eyes, however, the distance decreased significantly during accommodation,” Dr. Koivula said.

The PRL made contact with the lens in three myopic eyes and none of the hyperopic eyes at baseline. During accommodation, two additional eyes in the myopic groups experienced contact with the lens, as did three hyperopic eyes.

Two cases of lens opacification were seen in the total study group. In both cases, the PRL had contact at baseline with the crystalline lens.OT