From THE DEPARTMENT OF ANTERIOR SEGMENT SURGERY AT ST. ERIK EYE HOSPITAL AND THE DEPARTMENT OF CLINICAL NEUROSCIENCE AT KAROLINSKA INSTITUTET, STOCKHOLM, SWEDEN LONG-TERM RESULTS OF PHAKIC REFRACTIVE LENSES FOR CORRECTION OF MYOPIA AND HYPEROPIA

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 study, the first 20 consecutive cases with PRL implantation were followed for 1 year after surgery. The visual acuity results were comparable to other refractive methods and demonstrated high safety and efficacy indexes. The mean distance between the posterior surface of the PRL and the anterior lens surface decreased significantly in all eyes during the 1-year follow-up. The retroillumination photographs revealed slight rotation of the PRL in most eyes. The endothelial cell count decreased significantly 1 week after surgery without changes thereafter indicating that the difference in cell density was caused by surgical trauma and not the PRL. Few complications were observed. Increased intraocular pressure (IOP) related to pupillary block developed in two eyes (1 myopic and 1 hyperopic) during the first postoperative days. A myopic eye developed corticosteroid-induced high IOP 1 week postoperatively, which resolved after discontinuation of the steroid drops. One hyperopic eye unexpectedly developed myopia after PRL implantation. The PRL was exchanged with success. Iris transillumination defects were noticed in a hyperopic eye 1 year postoperatively. No ongoing inflammation, lens opacification or glaucoma was found. The second study was a prospective 2-year follow-up study of the same myopic and hyperopic population as in the first study. A parallel substudy was designed to evaluate the precision of the analytical methods used in the main study. Ninety-five percent of eyes had an uncorrected visual acuity (UCVA) of 0.5 or better even though the PRL with its floating design did not correct astigmatism. In 65 % of cases the best-corrected visual acuity (BCVA) improved over the preoperative level. Fifteen eyes (75%) were within ±0.5 diopter (D) of the desired refraction and all eyes (100%) were within ±1.0 D. During the first year, the distance between the PRL and the anterior lens surface decreased 59% but stabilized without changes during the second year. Fifteen PRLs (75%) rotated 10 degrees or more during the first follow-up year and three PRLs (15%) between 1 and 2 years. These study parameters, the rotation of the PRL and distance measurements, indicated stabilization of the PRL position in the posterior chamber 1 year after implantation. Endothelial cell count measurements 1 week after surgery showed 8.4% endothelial cell loss with slight recovery at 1 year without significant changes at 2 years. No PRL-induced lens opacification or inflammation was seen. The study showed excellent visual outcomes in myopic and hyperopic eyes with PRL implantation without serious intraor postoperative complications. Evaluation of the precision of the laser flare meter and Scheimpflug method showed relatively high random errors, 17% and 10%, respectively. The endothelial cell count, however, showed low random error (2.8%) and indicated that this method is a reliable indicator for evaluation of the corneal endothelium. In the third study, 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). To evaluate the precision of Visante OCT, we conducted a double-independent measurement study, which showed a random error of 5% in the measurements between the PRL and the anterior lens surface. This result indicated that Visante OCT is sufficiently accurate and reliable to allow an analysis of distances in the anterior segment. Fifty-two patients were examined at least 1 year after PRL implantation using the Visante 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. Both eyes had PRL 101 model. During accommodation, an additional implant in the PRL 101 and in the PRL 100 groups came in contact with the crystalline lens. In hyperopic eyes, there was no contact with the crystalline lens at baseline. During accommodation, the PRL 200 was in contact in three cases. 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 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 mean IOP remained unchanged during the entire follow-up period. 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. There was no gain in corrected visual acuity. Despite two iridotomies performed 2 weeks preoperatively, the main complication was early pupillary block. LIST OF PUBLICATIONS I. Koivula A, Petrelius A, Zetterström C. Clinical outcomes of PRL in myopic and hyperopic eyes: one-year results. Journal of Cataract & Refractive Surgery, 2005, 31:1145-1152. II. Koivula A, Taube M, Zetterström C. Phakic Refractive Lens: Two-year Results. Journal of Refractive Surgery (In press) III. Koivula A, Kugelberg M. Optical Coherence Tomography of the Anterior Segment in Eyes with Phakic Refractive Lenses. Ophthalmology [Epub ahead of print]. IV. Koivula A, Zetterström C. Phakic Refractive Lens for Correction of Hyperopia. (Submitted) CONTENTS