Eyeworld

EW REFRACTIVE 70 March 2017 by Michelle Dalton EyeWorld Contributing Writer Optical scatter and presbyopia correction Dr. Kugler believes several scenarios are ideal for using the HD Analyz- er: patients in their 40s or 50s who want refractive surgery because the ability to determine the amount of scatter can determine if the patient is better served with a cornea-based procedure or a lens-based one. Pa- tients with forward scatter but clear corneas indicate the scatter is lens- based, for example, and patients will be unhappy post-LASIK—the quality of vision would not have improved, he said. "If the lens is clear and the scatter insignificant, then a corne- al refractive procedure is a good choice," Dr. Cummings said. But "if there is significant scatter coming from the crystalline lens due to dysfunctional lens syndrome stage II or cataract [DLS III], then the pro- cedure of choice is a lens replacing procedure." Patients in their early 50s with a clear crystalline lens "may not develop lens scatter for several more years," Dr. Kugler said, and will likely benefit from a corneal inlay or LASIK procedures. A third category where this tool is useful is in the younger patient—those in their 20s or 30s who are nervous about refrac- tive surgery and are concerned about their potential outcomes. "I can show them that the chance of seeing as well as they currently do with glasses or contacts is very high because their optical system is clear. It just doesn't focus properly," Dr. Kugler said. Evaluating the health of the tear film, "including the optical clarity of the tear film is very important for all refractive procedures, including IOLs and corneal refractive surgery but especially so for premium IOLs," Dr. Cummings said. "Premium IOLs that correct for presbyopia have intentional aberrations in the lens design that provide the different fo- cal points or the extended depth of focus, and these aberrations should ideally be the only aberrations in the visual system. The tear film and cor- neal aberrations should be minimal, and these optical interfaces should be as close to perfect as possible." sclerosis grade II at the slit lamp, but clinicians only see the "light bounc- ing or reflecting off the lens back to the observer, and based on what we see, we grade it. But that's back scatter and not what the patient sees. The patient sees the light that comes through the lens to land on their macula and retina (including the forward scatter)." Measuring vision via a Snellen chart "is not a very accurate repre- sentation of what the patient sees; patients with 20/20 vision but com- plaints of poor vision are affected by optical scatter," Dr. Kugler said. The optical scatter index that's stable is the part due to lens clarity, Dr. Cummings said, but it's not the only scatter. "There's another layer of scatter that fluctuates with each blink, due to the tear film," he said. "The HD Analyzer can separate these two lay- ers, thereby demonstrating the con- tribution of the tear layer and the cornea and/or lens independently." B. Cummings, MB ChB, FCS(SA), MMed(Ophth), FRCS(Edin), Welling- ton Eye Clinic and UPMC Beacon Hospital, Dublin, Ireland. Significant light scatter results in a dull image (poor optical quality), while small light scatter will result in a brighter one (good optical quality)—but until recently clinicians could not easily measure or quantify this anomaly, experts say. The introduction the HD Analyzer (Visiometrics, Barcelona, Spain) radically changed that, as it is "the only device commercially avail- able that measures forward scatter," said Lance Kugler, MD, Omaha, Nebraska. The HD Analyzer "projects an image onto the patient's retina, and it actually looks at that image to see what the patient is seeing. When we look at the HD Analyzer, it's show- ing us what the patient is actually seeing," Dr. Kugler said. Dr. Cummings clarified, noting that a lens may be graded as nuclear Knowing the origin of scatter will benefit patients with unsatisfactory vision K nowing a patient's optical limits is paramount to developing a viable treat- ment plan, and wavefront aberrometry has been an invaluable tool for refractive clinicians. But traditional wavefront aberrometry cannot measure ocular scatter, which can degrade the image quality and pose diagnostic challenges for the clinician. Scatter causes a uniform distribution of light across a wide region of the ret- ina—scattered light that reaches the retina is forward scatter, and scat- tered light that leaves the eye before hitting the retina is backscatter. 1 For the patient, identical wavefront errors will result in varied image quality, depending upon the amount of light scatter the patient has, explained Arthur Devices to measure optical scatter continued on page 72 Device focus A 53-year-old woman presented for refractive surgery. MR +2.00 in each eye, correctable to 20/20. The OSI value of 1.2OD and 1.3OS suggest that there is significant scatter arising from the crystalline lenses and therefore, a refractive lens exchange (RLE) was performed rather than LASIK. Source: Lance Kugler, MD

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