Long-term results of phakic refractive lenses (PRL) for correction of myopia and hyperopia

Abstract

The phakic refractive lens (PRL) is a silicone lens implanted into the posterior chamber to correct myopia and hyperopia. At the beginning of 2002, when the PRL was introduced at St. Erik Eye Hospital, there had been no reports published on this lens model and therefore the pilot studies of myopic and hyperopic eyes were conducted to investigate the surgical outcome.

In the first and second study, the first 20 consecutive cases with PRL implantation were followed for 1 year (study I) and 2 years (study II) after surgery. The visual acuity results demonstrated high safety and efficacy indexes. All eyes were within ±1.0 diopter (D) of the desired refraction. The mean distance between the posterior surface of the PRL and the anterior lens surface decreased 59% during the 1-year follow-up but stabilized without changes during the second year. The PRL rotated in most eyes. The endothelial cell count decreased -8.4% one week after surgery without changes thereafter. Few complications were observed. Increased intraocular pressure (IOP) related to pupillary block developed in two eyes during the first postoperative days. A myopic eye developed corticosteroid-induced high IOP 1 week postoperatively. One hyperopic eye unexpectedly developed myopia after PRL implantation. Iris transillumination defects were noticed in a hyperopic eye 1 year postoperatively. No ongoing inflammation, cataract or glaucoma was found. The studies showed excellent visual outcomes in myopic and hyperopic eyes with PRL implantation without serious intra- or postoperative complications.

In the third study of 52 eyes, the movement of the PRL was evaluated in relation to the behavior of the crystalline lens and the pupil during accommodation in three groups: eyes with PRL 101, PRL 100, and PRL 200. The effect of accommodation was studied with optical coherence tomography (OCT). During accommodation, significant forward movement of the anterior lens surface and the PRL was observed in each group. Although the PRL moved anteriorly with accommodation with all three lens models, the space between the PRL and the crystalline lens was preserved only with PRL 100, and the space decreased significantly with the other two models. With the PRL 101, the baseline distance between the PRL and the anterior lens surface was significantly smaller in older eyes, indicating a decreased posterior chamber depth with aging of the lens. In three myopic cases, the PRL touched the anterior lens surface at baseline and two of them developed lens opacification. In eight eyes, the PRL touched the anterior lens surface during accommodation. This study showed that the PRL and the anterior lens surface moved forward during accommodation, and in most cases there was no mechanical contact with the anterior lens surface during accommodation.

The fourth study was conducted to evaluate the surgical outcome and adverse events associated with PRL implantation in 40 hyperopic eyes. The results showed excellent predictability with all eyes within ±1.0 D of the attempted refraction. There was no gain in BCVA and three eyes (7.5%) lost two lines of corrected visual acuity. The initial endothelial cell loss postoperatively was -4.6% and remained stable thereafter. The most frequent complication was development of postoperative pupillary block in seven eyes (17.5%). Two eyes with severe glare and one eye with unexpected myopia and discomfort underwent PRL explantation. Unexpected postoperative myopia was treated with PRL exchange in two eyes and with laser epithelial keratomileusis (LASEK) in one eye. No PRL-induced glaucoma or cataract developed. The study showed high refractive stability and predictability at the 1-year follow-up.