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REFRACTIVE lens exchange may be the treatment of choice for high hyperopes, particularly among those who have reached presbyopic age, according to Joseph Colin MD. "Refractive lens exchange is easy to perform and it produces predictable and accurate refractive results in most cases. It also respects the architecture of the centre of the cornea and provides in most cases a superb quality of vision with fast visual rehabilitation," Dr Colin told the XXI Congress of the ESCRS. The aging population of most western countries is likely to contribute to an increased demand for the surgical correction of hyperopia. Hyperopia is much more common than myopia; among adults over 40 years of age, 41% have refractions between +0.75 D to + 4.0 D. Moreover, the severity of hyperopia increases with age, as there is a hyperopic shift that accompanies presbyopia, especially between the ages of 43-59 years, during which refraction changes by an average of +0.45 D. However, it is primarily the approximately 4% of the population with high hyperopia (a refractive error greater than +4.0 D) who are candidates for refractive lens exchange, Dr Colin said. He noted that the eyes of high hyperopes have several anatomical features, such as a shallow anterior chamber and a short axial length, which make them less amenable to treatment with phakic IOLs. They are also beyond the refractive range that may be safely corrected with LASIK or thermokeratoplasty techniques, High hyperopes are also more suited to clear lensectomy than are myopes or presbyopic emmetropes, as they have less vitreoretinal pathology and a lower risk of retinal detachment. Moreover, refractive lens exchange improves the quality of vision in older individuals where there is a pre-cataractous decrease in transparency of the natural lens. The advantages of refractive lens exchange over other techniques for the treatment of high hyperopia appear to be reflected in current surgical practice, Dr Colin added. For example, in David Leaming's 2003 survey of ASCRS members only 5 % had implanted a phakic IOL during 2002 while 25 % performed one or two clear lens extractions per month.Furthermore, when asked what procedure they would recommend for a +5.0 D hyperope, 27% of respondents said they would suggest refractive lens exchange while only 0.5 % would recommend a phakic IOL and only 17% would recommend LASIK. Refractive lens exchange is very easy to perform, he pointed out. In fact, it is in some respects both easier and safer than standard cataract extraction, as no ultrasound energy is necessary to emulsify the crystalline lens. In addition, the advent of newer micro-incision cataract surgery techniques and ultra-thin lenses further enhance the safety of the procedure. "The crystalline lens is easy to remove through micro-incisions and this procedure will benefit very much from all the new technology for cataract surgery and IOLs with a high refractive index." When performing the procedure, Dr Colin recommended using temporal or oblique clear corneal incisions. He also advised using limbal relaxing incisions for preoperative astigmatism greater than 1.0 D. Meticulous cortical cleaning is imperative, as even low grades of PCO can degrade visual acuity, especially with multifocal IOLs. For IOL power calculation he recommended the Holladay 2 formula. Dr Colin noted that very good results are possible with refractive lens exchange. In a study published in the May 2003 issue of the Journal of Cataract and Refractive Surgery (Preetha et al. 2003; 29:895–899) the procedure brought about a mean improvement of three lines in UCVA and one line in BCVA in 20 hyperopic eyes of 12 patients with a mean refractive error of +6.66 D (+/- 2.17 D). In addition, 70% were within 0.5 D of intended refraction. The IOLs used for refractive lens exchange in high hyperopes must be of a higher refractive power than is generally used in cataract surgery. In extreme cases, some surgeons have used the piggybacking of IOLs to achieve the desired refraction. However, Dr Colin strongly advised avoiding that practice as it can frequently lead to interlenticular opacifications. "Now we have more and more high power IOLs and I think that everything must be done to avoid primary piggy-backing but if piggy-backing is necessary we should put one IOL in the bag and the other in the ciliary sulcus." Multifocal IOLs such as the AMO Array are another option for hyperopes. This approach also addresses the problem of loss of accommodation, which is a consequence of clear lens extraction in younger patients. Versions of the lens for high hyperopes are now available and several investigators have reported good results with the lenses. Burkhard Dick MD in Mainz , Germany reported that among 13 high hyperopes who underwent implantation of the lens, all achieved uncorrected binocular visual acuity of 20/30 and J4 or better. Among the drawbacks with multifocal IOLs are photopic effects such as halos around point sources of light at night. The lenses may therefore be less suitable for those with occupations that require nighttime driving. In general, however, neuroadaptation makes the photopic symptoms less noticeable over time. Another drawback of the lenses is that in most series they only provide completely spectacle-free vision in about half of patients. In summary, Dr Colin said that the ideal candidates for hyperopic refractive lens exchange include presbyopic high hyperopes and highly motivated refractive surgery patients. Patients who should not undergo refractive lens exchange include those with extreme hyperopia, as their shallow anterior chambers make them more prone to angle closure glaucoma. "In young eyes with hyperopia ranging from +5.0 D to +10.0 D we do our best to implant phakic IOLs in order to preserve accommodation. Beyond that, we can attempt bioptics or refractive lens exchange. In patients 40-60 years of age we don't use phakic IOLs, we remove the crystalline lens and place a posterior chamber IOL and in those over 60 years of age my personal choice is refractive lens exchange." Dr Joseph Colin MD |
