HIGH HYPEROPIA

Phakic IOLs continue to be the best refractive surgery option available for the treatment of high hyperopia, said Beatrice Cochener MD, PhD, CHU Brest, Brest France. “Phakic IOLs are better than photoablation for high hyperopia in terms of predictability and stability. They also provide better quality of vision because of the larger optical zone. Moreover, photoablation procedures can be difficult to centre properly, and highly hyperopic eyes that undergo LASIK are at an increased risk of epithelial in-growth and induced dry eye,” Prof Cochener said at the XXXI Congress of the ESCRS in Amsterdam.

She added that clear lens removal is less risky for the retina in high hyperopes than it is in high myopes, and it is the only option for the surgical correction of high hyperopia in eyes with a very small anterior chamber. However, the loss of accommodation that the treatment causes makes it less suitable for younger patients.

There are two phakic IOL models available for high hyperopia with or without astigmatism. They are the iris claw IOL (Artisan®, Ophtec)/Verisyse®, AMO) and the posterior chamber implantable collamer lens (VisianICL®, Staar). Both have undergone refinements over the years and have toric versions for the twothirds of hyperopic eyes that have astigmatism greater than 1.5 D.

Published studies
The iris-claw anterior chamber lens has been used in high hyperopia since 1997. To be suitable for the iris-fixated implants, eyes must have an anterior chamber depth greater than 3.0mm and normal iris insertion conformation, criteria which high hyperopic eyes do not always meet. Published studies tend to demonstrate good safety and efficacy for the implant in low to moderate hyperopia but an increase of complications in the treatment of moderate to high myopia.

In a study that included 51 hyperopes who underwent implantation of the Artisan/ Verisyse lens to correct a mean hyperopic error of +4.92 D, refraction at two years’ follow-up was +0.02 D. In addition, endothelial cell density was not significantly reduced, remaining at 2560 cells/mm2 at two years' follow-up, compared to 2735/mm2 at preoperatively. (Güell et al Ophthalmology2008;115: 1002-1012.) In another study, where the iris-fixated IOL was combined with LASIK to correct hyperopia in 39 eyes with a mean preoperative spherical equivalent of 7.39 D, there was similar predictability in terms of refractive results. However, one-third of patients lost one line of BCVA, there were frequent complaints of glare and haloes at night and endothelial cell counts fell by 10.9 per cent (Munoz et al J Cataract Refract Surg. 2005; 31:308–317).

In addition, an ultrasound biomicroscopy study of hyperopic eyes with the lens showed indentation of iris tissue by the IOL haptics and optic edge, which could lead to pigment erosion. (Pop et al, J Cataract Refract Surg 2002; 28:1799-1803.) The implantable collamer lens currently reigns supreme among the phakic IOLs. More than 375,000 have been implanted worldwide, with hyperopic eyes accounting for 10 per cent of the implantations. The lens can be inserted through a 2.8mm incision and requires an anterior chamber depth of only 2.8mm, making it more suitable for hyperopic eyes, Prof Cochener said.

The studies published to date show high long-term efficacy and safety for the lenses in moderate to high myopia. For example in a study involving 59 eyes of 34 patients who underwent implantation of the ICL for hyperopia ranging from +2.50 to +11.75 D (mean; +5.78 D), the mean postoperative spherical was +0.07 and remained stable throughout a 10-year follow-up period. Furthermore, the UCVA was 20/20 or better in 49.78 per cent of eyes and 20/40 or better in 87.58 per cent of eyes (Pesando et al, J Cataract Refract Surg. 2007;33(9):1579-84).

Follow-up
In addition, the mean endothelial cell loss was 4.7 per cent, which remained almost unchanged throughout the follow-up period. Complications included cataract in one eye, apparently due to surgical trauma, pupillary block glaucoma in one eye, which resolved when the ICL was explanted, and iris-chafing in two eyes, because of an oversized ICL, which resolved when the ICL was replaced with a smaller one.

Prof Cochener noted that she and her associates have also achieved good results with the ICL lens. She presented a retrospective study of 22 eyes of 12 patients who underwent implantation of the V4 version of the lens at her centre. At five years’ follow-up, decimal corrected visual acuity was better than 1.0 in 68 per cent and better than 0.5 in 87 per cent. Moreover, endothelial cell loss after three months' follow-up occurred at a mean annual rate of only 0.6 per cent. There was one case of pupil block with irreversible mydriasis.