EyeWorld India March 2013 Issue

34 EWAP REFRACTIVE March 2013 Presbyond Laser Blended Vision: Another approach to presbyopia by Dan Z. Reinstein, MD T he ideal solution for correcting presbyopia would be to restore accommodation, however, no procedure up to now has been proven to reverse presbyopia and restore the natural focusing mechanism of the eye. While there is ongoing research on techniques to achieve this, clinical applications of these techniques will probably not be available for another 10-20 years. Because of our inability to restore accommodation, current treatments for presbyopia rely on splitting the refractive power for distance and near either within the same eye (multifocality) or between eyes (monovision), but all treatments require some compromise from the patient. The challenge for such treatment options is to achieve good binocular vision at far, intermediate, and near distances while also maintaining optical quality, contrast sensitivity, night vision, stereo acuity, and as a bonus the procedure should be reversible. This was the goal that we set when developing Presbyond Laser Blended Vision with Carl Zeiss Meditec (Jena, Germany), and our approach was to take advantage of the natural mechanisms within our optical system and minimize the need for the patient to adapt. All multifocal approaches require the patient to adjust to the unnatural situation of having to differentiate between two images in the same eye, so it is no surprise that these procedures are associated with loss of CDVA, contrast sensitivity, and night vision disturbances. There have been significant improvements over the years; however, multifocality will always rely on the patient’s ability to adapt to this new and unnatural intraocular rivalry. Multifocal treatments are also usually limited to a small range of refractive error (usually low hyperopic patients). The well-established principles of contact lens monovision have been used in laser refractive surgery; however, many of the limitations of contact lens monovision also affected laser Spherical aberration diagram Source: Dan Z. Reinstein, MD Views from Asia-Pacific PORYongMing, MBBS, FRCS, MMed, MRCOphth Consultant Eye Surgeon, Jerry Tan Eye Surgery & Jerry TAN, MBBS, FRCS, FRCOphth, FAMS Consultant Eye Surgeon, Jerry Tan Eye Surgery Camden Medical Centre, 1 Orchard Boulevard #10-06 Singapore 248649 Tel. no. +65-6738-8122 Fax no. +65-6738-3822 info@jerrytan.com P resbyond as a concept is attractive in potentially enhancing the benefits while moderating the cons of standard monovision. However, a number of aspects of this treatment bear consideration. Theoretically, there is no doubt that spherical aberration (SA) or even coma and astigmatism can improve an eye’s depth of field, but at the expense of some loss of visual quality. Indeed, as Dr. Reinstein mentions, beyond a certain amount of SA the visual cortex no longer compensates and considerable disturbances such as haloes and loss of contrast surface. In real life, we have all seen changes of corneal topography as an eye heals after laser refractive surgery, originating from factors such as epithelial remodeling. As such, attempting to maximize depth of field to 1.50 D by filtering SA while avoiding side effects involves negotiating a fine line which can easily be crossed by individual healing responses. Presbyopic patients are also older than the average LASIK patient, and lenticular changes are not insignificant. The aging lens is associated with increasing SA with time, so even if Presbyond manages to hit the target on the cornea, one cannot be certain how long it will be before the combined corneal and lenticular aberrations cause noticeable visual disturbances. The effects of any optical aberration depend greatly on pupil size, and it is intriguing that pupillometry is not mentioned as a factor considered in the generation of the ablation profile. Unless Presbyond can tailor the SA to suit the range of pupil sizes seen in different patients, the hoped for effects may not materialize. It is also possible that a patient has large scotopic pupils in the dark which magnify the visual disturbance caused by the induced SA. According to the diagram accompanying this article, it appears that positive spherical aberration is induced by the Presbyond ablation profile, causing peripheral rays of light striking the lens periphery to be focused before more central rays. This is reminiscent of night myopia, resulting from scotopic mydriasis in the presence of positive SA. It would be the opposite of what is required for presbyopia, since during close work the pupil becomes miotic. Perhaps a small amount of negative, rather than positive, SA may be helpful in the presence of a bias toward slightly more myopic undercorrection. We look forward to studies comparing standard monovision and Presbyond Laser Blended Vision, to quantify its benefits as well as potential for visual side effects. Editors’ note: Drs. Por and Tan have no financial interests related to their comments. continued on page 36