Eyeworld Supplements

EWAP SPR 2018 - Sponsored by Carl Zeiss Meditec AG

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The news magazine of the Asia-Pacific Association of Cataract & Refractive Surgeons Offering a treatment for patients with presbyopia APACRS Supplement to EyeWorld Asia-Pacific Spring 2018 Mechanism and outcomes of PRESBYOND M onovision has— arguably until multifocality came into the picture— been the best option for presbyopia, said Glenn Carp, MD, London, U.K. However, there are a number of challenges to the procedure—problems with tolerance, loss of intermediate and distance vision, summation, and stereoacuity. "Modest monovision," which limits the reading add to –1.50 D, is the best improvement on the pro- cedure, addressing most of these problems. Unfortunately, the pro- cedure does not provide enough acuity for reading very small print. Literature suggests this is because a defocus value of –1.3 D delivers the best balance of summation and near acuity—beyond this limit, you stop getting summation between the two eyes and start getting subtraction; at –3.5 D or greater defocus, you get suppression of the reading eye. This means that patients do better with stereoacu- ity and anisometropia with lower reading adds. So while it addresses most of the challenges to monovision, the biggest challenge to modest monovision is the compromise in terms of near visual acuity. This is where PRESBYOND steps in to improve on all of these factors. Spherical aberration and depth of field PRESBYOND increases depth of field by controlling spherical aber- ration along the optical pathway. Spherical aberration is a naturally occurring aberration that increases during accommodation and with age, and therefore something that the human brain is already pro- grammed to process and filter out. Without spherical aberration, light entering the optical pathway comes into focus at a single point, with everything in front of and behind that point out of focus; with spherical aberration, the point of focus expands to a circle of least confusion, resulting in improve- ment in the quality of the image of objects in front of and behind the original point of focus—that is, an increased depth of field (Figure 1). Spherical aberration improves the image quality of a defocus of –1.5 D by increasing edge detection (Figure 2); pupillary constriction—which still occurs in presbyopic patients when looking at near objects—also increases the depth of field, and combining the two results in a clearer image that is further cleaned up by neural processing (Figure 3). Moreover, increased spherical aberration increases depth of field whether it is positive or negative, so long as it is below the "toxic" limit of 1.5 D. More than that, you start to lose quality of vision, and contrast and night vision drop off. To be clear, PRESBYOND is not a multifocal ablation—it simply controls spherical aberration so there is neither too little, when it would be of no benefit, nor too much, when it would become toxic. Applying spherical aberration How can this knowledge be applied scientifically to achieve optimum results? Most people start with a little bit of positive spherical aber- ration naturally. Myopic ablations induce positive spherical aberra- tion, adding to the existing level. Eyes with low to moderate myopia will likely stay below the 1.5 D threshold after treatment, but sur- geons should be wary of treating high levels of myopia. On the other hand, hyperopic ablations induce negative spherical aberration. Reaching the thresh- old even with high hyperopia is therefore unlikely. However, in low hyperopia, the hyperopic ablation might simply eliminate existing In April 2017, Carl Zeiss Meditec AG (Jena, Germany) conducted a user meeting in Singapore. More than just a showcase for their latest technologies, the company's user meeting has grown into a venue for peer-to-peer sharing of information among the world's top ophthalmic surgeons. The third symposium of the meeting focused on the uses of the femtosecond and excimer lasers in the management of a persistent challenge to ophthalmologists, one that has only grown as life expectancies increase and the world's population ages: presbyopia. To establish some baseline information on the prevailing approach to presbyopia among attendees, moderator Sri Ganesh, MD, conducted an audience response survey at the beginning of the session. Based on the survey, the majority of attendees' practices (41%) were less than 5% treatments of presbyopic patients, with 31% of the practices not offering laser vision correction (LVC) for presbyopia. Most attendees (48%) said the largest barrier to increasing treatments of presbyopic patients in their practices was that patient expectations are too difficult to manage, and a similar number (49%) said they did not have enough data to compare monovision LVC with PRESBYOND in terms of visual acuity and patient satisfaction. Sponsored by Carl Zeiss Meditec AG Glenn Carp, MD continued on page 2 Figure 1. Influence of spherical aberration on depth of field Figure 2. Spherical aberration and – 1.5 D of defocus

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