EyeWorld India March 2013 Issue

36 EWAP REFRACTIVE March 2013 Michael LAWLESS, MD Medical Director, Vision Eye Institute 4/270 Victoria Ave., Chatswood, NSW 2067 Australia Tel. no. +61-2-94249999 Michael.lawless@visioneyeinstitute.com.au D r. Reinstein is to be congratulated for exploring the use of spherical aberration to enhance depth of focus in presbyopic patients. The same thoughts have occurred to those using an IOL approach to presbyopia with lenses now being trialled which increase spherical aberration to provide a similar effect. The problem with analyzing the data provided is that the age of the patients would have significant bearing on the results presented, but it is not clear from the article how age would have impacted Dr. Reinstein’s excellent results. All good things come at a cost. Generally, in the normal untouched eye, the cornea has positive spherical aberration which is matched by the negative spherical aberration of the lens, resulting in a more or less neutral state. Of course there is a range through the population in both the degree of corneal and lens spherical aberration. We also know that the natural lens changes from negative to positive spherical aberration with age and this is the very population in which a presbyopia treatment would be required. This is one reason why the quality of vision under mesopic and scotopic conditions declines with age. The impact of spherical aberration on visual function is pupil dependent. So there are many variables to consider when attempting to change the spherical aberration profile of an individual patient. To induce more spherical aberration on the cornea to enhance depth of focus has to unquestionably alter the quality of vision, particularly night vision, which is one of the reasons that LASIK excimer laser profiles moved from conventional to optimized and wavefront guided, based on a knowledge of higher order aberrations and their effect on the visual system. This is an interesting approach and is likely to be helpful in a small way to enhance presbyopic treatments, but I think we need data to support these optimistic first conclusions and perhaps better targeted treatments based on an individual eye’s aberration profile, as Dr. Reinstein rightly points out. Editors’ note: Dr. Lawless is a consultant for Alcon/LenSx (Fort Worth, Texas, USA/Hünenberg, Switzerland) but has no financial interests related to his comments. refractive surgery-induced monovision. These limitations include loss of fusion due to the anisometropia between the two eyes, poor intermediate vision, poor distance vision in the near eye, reduced binocular contrast sensitivity, and reduced (or even broken) stereoacuity. However, monovision is based on the John S. M. CHANG, MD Director, Guy Hugh Chan Refractive Surgery Centre Hong Kong Sanatorium and Hospital 8/F Li Shu Pui Block, Phase II 2 Village Road, Happy Valley, Hong Kong Tel. no. +852-2835-8885 Fax no. +852-2835-8887 johnchang@hksh.com T here have been many approaches in corneal refractive surgery to create a multifocal eye, in order for the eye to see distance, intermediate and near. Some create a central myopic region, so that when we read and the pupil constricts, the induced myopia will compensate for the lack of accommodation. However, if the patient is not satisfied with the result, whether this can be safely and completely reversed is still a matter of discussion and more research. Monovision works very well in patients who live in a city and do not drive. In our experience, the success rate is over 95%. However, in countries where patients have to do a lot of driving, the success rate drops significantly. Recently, Presbyond (Carl Zeiss Meditec), F-Cat (Allegretto, Alcon), Supracor (Baush+Lomb) all involve some form of micro-monovision. In Presbyond and F-Cat, negative spherical aberration is induced, thus increasing the depth of focus. We have had over 5 years of experiences with the Allegretto F-Cat and have found that it works quite well in myopes below –6 to –7 D and, like the Presbyond, when the patient does not like the monovision or micro-monovision, it can be easily removed without any loss of vision. Night vision does not seem to be compromised, however, when the adjustment is pushed too far, or when the patient’s pupil is too small there tends to be an under-correction. The disadvantage is that it is still monovision (although the loss of stereovision should be less) and its effect may not be long lasting because of possible epithelial filling with time. Editors’ note: Dr. Chang has no financial interests related to his comments. natural process of binocular fusion (interocular rivalry as opposed to the unnatural intraocular rivalry experienced in multifocal procedures), and recent studies have demonstrated that many of these limitations could be avoided by limiting the anisometropia to 1.25 D or 1.50 D. But this level of anisometropia does not always give Views from Asia-Pacific Presbyond - from page 34