EyeWorld Asia-Pacific September 2013 Issue

35 EWAP CAtArACt/IOL September 2013 Implanting an EDF lens in one eye, he said, does indeed extend the depth of focus, improving the vision to about 1–1.5 lines of additional acuity. “If the eye is targeted for modest monovision, there’s a greater overlap between the two eyes and an opportunity for blended vision. “This is even more apparent if you use an EDF lens in both eyes, where the overlap is substantial,” he added. “This then provides an extended depth of focus, less spectacle dependence, and better opportunity for binocular vision.” The binocular defocus curve for two eyes implanted with EDF lenses, he said, is very much like the normal accommodative response. “It’s quite distinct from the defocus curve that you have with a diffractive multifocal, and the biggest difference is in the intermediate vision.” Compared with multifocal IOLs, he said, patients receiving monovision with the EDF lens can expect perfect clarity at all levels—near, intermediate, and distance— “perhaps with a bit of blur at 40 cm, but that can be improved with glasses if required.” In addition, the extended depth of focus makes the lens less sensitive to small errors in prediction, especially compared with multifocals. Dr. Barrett and his colleagues also tested reading acuity and stereoacuity, with results that were not significantly different and in some cases—e.g., reading for the EDF lenses versus corneal inlays—even better than those with other lenses and devices currently being used to treat presbyopia. Overall, the results of Dr. Barrett’s study suggest that “the Hoya EDF monofocal lens should be considered an alternative in our universe of multifocal, monofocal, and accommodative lenses because it is indeed possible to extend the depth of focus, provide greater spectacle independence, and maintain optical quality.” Of course, good outcomes also require optimal correction of refractive error—including astigmatism. “About 30% of patients have more than 1.0 D of keratometric astigmatism,” said Geoff M. Whitehouse, MD, senior consultant ophthalmologist, Manning Base Hospital and Gloucester Soldiers’ Memorial Hospital, New South Wales, Australia. “You need 0.5 D or less of refractive astigmatism to be truly spectacle independent.” Dr. Whitehouse cited a 2013 study by Mencucci et al. 1 in which the visual refractive and aberrometric results of emmetropic patients receiving monofocal lenses were compared with those of patients with astigmatism who received toric IOLs. “Not only did [Mencucci et al.] show that the aberrometric side of things was very good, but the patients also reported that their quality of life was signifi- cantly improved if they had less astigmatism,” said Dr. Whitehouse. Today’s toric lenses, he added, are “safe, they’re predictable, completely reversible, very easy, and very quick. At most they add 2–3 minutes to a case.” In his clinic, Dr. Whitehouse routinely uses a toric IOL in patients with more than 0.75 D of astigmatism. “Our target is less than or equal to 0.5 D of residual refractive astigmatism,” he said. When Hoya’s toric IOLs first came out, Dr. Whitehouse said they reached target in 86% of cases with more than 1.0 D of astigmatism; 93% had less than 0.75 D of residual refractive astigmatism. There are, however, contraindications—irregular or unpredictable corneal astigmatism and capsular bag instability among them. Once you’ve decided on using a toric, there remains the matter of selecting what toric IOL to use. Dr. Whitehouse suggested there may be an advantage to hydrophobic acrylic materials, being the stickiest and therefore theoretically allowing less rotation, providing more stability than other materials. Current haptic designs, whether plate or loop, do not seem to present any problems. “You need to look at other lens issues when you’re deciding on the lens: the wound size you use, loading reliability, and material reliability,” said Dr. Whitehouse. Implantation at present, he added, is in a practical sense a two-stage procedure. “You need to mark the horizontal axis with the patient sitting up prior to surgery, and then lie them down and use something like a Mendez gauge intraoperatively.” There are also automated systems available to help with marking, but these are expensive and not in common use, said Dr. Whitehouse. Surgeons should be wary of calculation errors. “You can have problems with your corneal measurement,” said Dr. Whitehouse. “You need to be consistent whether you use manual, IOLMaster [Carl Zeiss Meditec, Jena, Germany], or topographic keratometry for your preoperative measurements, and you need to look at the calculator you’re using and how it calculates.” Other factors to consider include anterior chamberdepth and posterior corneal curvature. Accuracy is critical: Every degree that a toric lens is rotated off the correct axis equates to a 3.3% loss in the final effect. “The closer you get to where you’re aiming, the better,” said Dr. Whitehouse. All the advances described thus far illustrate the change taking place in the field of cataract surgery—it is becoming the most common refractive surgery on the market, according to Rohit Shetty, MD , vice chairman and senior consultant, neuro-ophthalmology, refractive surgery, and electrophysiology services, Narayana Nethralaya, Bangalore, India. According to Dr. Shetty, standards and expectations for cataract surgery these days are no different from those for LASIK. But while the statistical parame- ters of efficacy, predictability, safety, and stability might match between the two procedures, patient expectations can be completely different from realistic expec- tations. “That sometimes is very difficult to match,” he said. “That’s where the challenge is.” Being primarily interested in optics, Dr. Shetty has tried to “decode” the unhappy patient. Dr. Shetty believes that the perfect cataract and refractive surgery—the kind that makes patients happy—begins with diagnostics. “Over time, everybody becomes good with the surgery, but what ultimately helps you to get the optimal results is the diagnostics,” he said. When analyzing the error that needs correction—essentially, seeking the origin of the visual complaint—Dr. Shetty said that aberration can be divided into corneal, lenticular, and total (involving the entire visual system). “It’s always important to know the culprit,” he said. “Once you know that then the rest becomes easy.” For example, focusing on the corneal level, spherical aberration can change the axis, cylinder, and sphere of the patient; in this case, the surgeon’s measure- ments are affected by the axis of the pupil and the axis of the refractive error. “As the pupil size changes, the whole refraction changes,” he said. “This is what in- duces more of a night myopia … this happens when the patient has more of a spherical aberration on the corneal surface.” The problem is compounded when a patient who has had previous LASIK surgery comes in a decade or so later with cataract. In these cases, Dr. Shetty is exploring the possibility of customizing the cornea—performing topography- guided surface ablation not to correct the refractive error but to make the cornea more regular—before implanting an IOL. “Why we need to do that is because [in] these patients, the ablation and the amount of aberration is so high, so they will end up with a problem,” said Dr. Shetty. “Ultimately, all this brings us to one thing: The patient should see the benefit,” he concluded. “That should be the ultimate goal.” Reference 1. Mencucci R, Giordano C, Favuzza E, Gicquel JJ, Spadea L, Menchini U. Astigmatism correction with toric intraocular lenses: Wavefront aberrometry and quality of life. Br J Ophthalmol . 2013 May; 97(5):578-82. Contact information Barrett : barrett@cyllene.uwa.edu.au Ganesh : chairman@nethradhama.org Mamalis: nick.mamalis@hsc.utah.edu Oshika : +81-(0)29-853-3148 Shetty : drrohitshetty@yahoo.com Whitehouse: geoff@forstereyesurgery.com.au refractive procedure The supplement was produced by EyeWorld and sponsored by Hoya Surgical Optics. Copyright 2013 ASCRS Ophthalmic Corporation. All rights reserved. The views expressed here do not necessarily reflect those of the editor, editorial board, or the publisher, and in no way imply endorsement by EyeWorld, ASCRS, or APACRS. Sponsored by Hoya Surgical Optics