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Speaking at the 7th ESCRS Winter Refractive Surgery meeting, Bo Philipson MD, PhD reported that among 130 myopic patients undergoing implantation of the lens for myopia ranging from –3.0 D to -27 D, mean postoperative UCVA after one year was 20/30 — as good or better than the mean preoperative best corrected acuity. Mean BCVA improved from a preoperative value of 20/30 to 20/20 and 80% gained at least one line, while 50% gained two or more lines. In addition, 68% of eyes were within 0.5 D of intended refraction and almost 90% were within 1.0 D. The PRL is a non-fixated one-piece ‘floating’ posterior chamber IOL. It is made of a hydrophobic silicone material, with a high refractive index and is very thin as a result. The curvature of its posterior surface corresponds to the anterior surface of the crystalline lens. Its haptics rest on the zonules. The aim of the IOL’s design is to prevent it touching the crystalline lens. The refractive IOL has an optic diameter of 4.5 to 5.0mm and an overall length of 10.8mm, or 11.3mm in the myopic model and 10.6mm on the hyperopic model. The refractive range of the myopic implant is -3.0 D to –20 D and that of the hyperopic design is +3.0 D to +15 D. Both are available in increments of 0.5 D. Dr Philipson noted that there were no instances of cataract in the study. In addition, endothelial cell loss was low, averaging at around 5% after one year. However, PRL rotation occurred in 3% of eyes. More serious complications included one case of luxation of the PRL into the vitreous body. PRL explantation was necessary in 2% of eyes due to calculation errors. Some 3% of eyes showed increases in IOP during the early postoperative period, which probably resulted from incomplete removal of the viscoelastic. Dr Philipson noted that, when completed, the study would include one-year follow-up data on 220 myopic and hyperopic eyes. “We think the PRL is a very promising posterior chamber IOL for the correction of high myopia, although we need a longer follow-up to confirm the safety and efficacy of the lens,” he said.
In addition, the distance between the IOL and the natural lens appeared to continue to decrease slightly over time. In the retrospective clinical study, which involved 14 myopic and six hyperopic PRL-implanted eyes, retroillumination photography showed that the PRL rotated by 10 to 60 degrees in seven eyes at one postoperative week and by 50 to 100 degrees in three eyes between one week and three months. Dr Zetterström pointed out that the patient in whom the PRL had rotated the most at three months actually had only a fairly negligible rotation of around 10 degrees at one week. The Swedish team used Scheimpflug images to measure the distance between the IOL and the crystalline lens. They found that the mean distance decreased slightly between the first postoperative day and the first postoperative week, and decreased slightly further at three month’s follow-up.
Study participants ranged in age from 23 to 43 years, with a mean of 31, and had myopia from -3.0 D to -27.0 D, or hyperopia from +3.0 D to +11.5 D. All had a pre-operative BCVA better than 20/40, anterior chamber depth greater than 3.0 mm, endothelial cell count greater than 2,500 cell/mm2, and were free of ocular morbidities such as cataract, corneal disease, glaucoma or retinopathy. The Swedish team performed YAG iridotomies two weeks prior to PRL implantation. They inserted the lens through a 3.0mm to 3.2mm clear corneal incision with a forceps or injector. Complications included pupillary block in two eyes, which resolved after repeat YAG iridotomy, and corticosteroid induced ocular hypertension in one eye, which persisted for a week. All except one patient experienced an improvement in UCVA. The patient whose UCVA did not improve was slightly hyperopic before the procedure and slightly myopic afterwards, she noted. Dimitrii Dementiev MD told the conference that the new injector which has recently become available for the lens may improve the efficacy and safety of PRL implantation. “There are difficulties implanting the PRL lens with the forceps, especially with low power lenses. Occasionally the lens comes out during withdrawal of the implantation forceps and this increases the risk of endothelial cell loss,” he said. He reported on a study in which 18 surgeons implanted 124 eyes with the PRL with the new injector. The surgeons were able to successfully load and inject the PRL in more than 96% of the cases and there were no instances of lens expulsion during implantation, Dr Dementiev said.
Dr Dementiev noted that some surgeons did encounter problems with the injector and some design modifications are now underway to resolve the difficulties. The researchers observed rotation of the lens inside the cartridge in some 4% of cases. Those lenses were injected upside down and had to be removed and re-injected. The lens broke during loading in another two cases. And in two more, the incision had to be enlarged and sutures were necessary to close the wound. Nonetheless the visual outcome was good in all patients, he said. At two month’s follow-up the mean UCVA improved from counting fingers to 20/30 and the mean BCVA improved from 20/30 to 20/20. Furthermore, none of the eyes lost any lines of BCVA while 60% gained one line and 40% gained two lines. “The PRL injector has shown to be efficient and safe when used for the implantation for the PRL. It can be an alternative to the forceps implantation technique. Both can be used and the final decision depends on the preference of the surgeon,” Dr Dementiev said. Bo Philipson MD, PhD |
