Eyeworld

EW REFRACTIVE 62 January 2019 Refractive editor's corner of the world by Michelle Stephenson EyeWorld Contributing Writer cloudy cornea, or keratoconus. I can then proceed with my exam, and if a patient has a vision problem, I know it's not in the optical degradation of the tear film, cornea, or the lens. Also, for a refractive surgery patient, I want to make sure he or she has good optics before elective refractive surgery on the cornea or implanta- tion of a phakic IOL," he explained. Dr. Durrie said that he expects all patients over the age of 45 to have some degradation in their optics, but he wants to make sure it's in the normal range. "The HD Analyzer provides a green, yellow, or red evaluation at the bottom of the screen or printout. If they are in the green, they are good. If they are moving toward yellow, they are starting to have some degradation. People in their late 40s and early 50s typically demonstrate degradation of their lens quality using the HD Analyzer. It is the simplest device to understand because it only does one thing. It looks for optical scatter or degradation of the image," he said. iTrace According to Dr. Kugler, the iTrace is a combination wavefront analyzer/ Placido disc topographer. Its job is to help the ophthalmologist determine which part of the eye is causing the visual distortions that the patient is seeing. "It can help determine the people who have subclinical kerato- conus or other issues. It is also useful for determining the distribution of corneal power in eyes that have had previous refractive surgery," he said. HD Analyzer The iTrace and the HD Analyzer are diagnostic equipment that help oph- thalmologists evaluate the scatter of the image quality as it goes through the lens. "The HD Analyzer is the sim- plest to understand because it takes a low-energy laser ray, bounces it off the retina, and reads it on the way back," Dr. Durrie said. "It knows what should come back through a normal eye that has no degradation in the optics. It measures the point spread function, the modulation transfer function, the cell ratio, and contrast loss scientifically. All of those provide an objective measure- ment of the amount of light that is scattered or lost as it goes through the lens. This device also will pick up abnormalities in the tear film or any corneal opacity or keratoconus." It is used to assess the quality of the optics, according to Dr. Durrie. "It even provides a simulated visual acuity estimate of a patient's best corrected vision. If a patient's optics are great, I know in this part of the exam that I don't have to worry about a cataract, severe dry eyes, a Early cataract diagnosis technology HD Analyzer exam. Right eye has stage 2 dysfunctional lens syndrome with an OSI reading of 2.1, and there is scatter on the point spread function. The left eye has had an IOL and the optics are good with the OSI reading of 0.8 and the tight point spread function. Source: Daniel Durrie, MD T he diagnosis of early cataracts as a source of blur can be challenging based on the slit lamp exam. History is extremely important, especially in low light situations. I call night time image quality with the best possible pair of glasses the "poor man's wavefront analyzer"; with an otherwise healthy eye and an accurate spectacle correction, if night time image quality is reduced early lens changes should be a part of the differential diagnosis. Slit lamp examination can be quite difficult to decipher between an aging change in the lens that is visually significant versus an aging change that is not visually significant. Measuring optical scatter through technolo- gies like the HD Analyzer and iTrace can be helpful. Measuring lenticular density with the Pentacam can also be helpful. In this "Refractive editor's corner of the world," Daniel Durrie, MD, and Lance Kugler, MD, share their thoughts on how these technolo- gies supplement the patient history and slit lamp exam to help them diagnose visually significant changes due to early cataracts. Knowing that the lens is the culprit can be helpful in making sure that we don't perform LASIK on patients with these early lens changes and also can help explain why they're not getting the image they're looking for with glasses or contact lenses. These changes may be too early for the patient to want to proceed with a lens replacement surgery, but it brings them inner peace when they know the source of their reduced image quality in low light situations. Thank you to Dr. Durrie and Dr. Kugler for enhancing our knowledge in this import- ant arena. Vance Thompson, MD, Refractive editor Changes in the lens can now be identified long before a full-blown cataract develops C ataracts can be diagnosed early in their development by tracking changes in pa- tients' lenses. The HD Ana- lyzer (Visiometrics, Costa Mesa, California) and the iTrace (Tracey Technologies, Houston) are employed to quantify optical scatter, while the Pentacam (Oculus, Wet- zlar, Germany) is used to quantify lens density. "I use the HD Analyzer and Pentacam on every patient," said Daniel Durrie, MD, Overland Park, Kansas. "There is a lot of interest in early cataract diagnosis tech- nology because we recognize that changes are going on in the lens before people get a full-on cataract. Ophthalmologists are interested in being able to tell the patient where he or she is in the development of a cataract long before there is loss of best corrected visual acuity. Traditionally, we diagnose a cata- ract when two things happen. First, the patient's best corrected vision drops to 20/40 or worse, which is the legal driving area. Additionally, we look for functional loss, such as using BAT [Brightness Acuity Tester, Marco, Jacksonville, Florida] to look at how patients function under certain lighting situations. Now, we are getting into looking objectively at the scatter in the lens. These three technologies are commonly used to do different things, so it's nice to sort out how they will fit into prac- tice at this point in time." Lance Kugler, MD, Omaha, Nebraska, agreed. "I consider those three devices to be indispensable for modern refractive surgery practice. A Scheimpflug topographer like the Pentacam provides the ability to view the anterior and posterior corneal surface. It uses advanced software analytics to look at the cornea and patterns that might be missed by the ophthalmologist. This provides a more sophisticated analysis, which I think is important. The Pentacam does a good job iden- tifying appropriate candidates for surgical procedures and identifying

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