Eyeworld

23 July 2015 by Lauren Lipuma EyeWorld Staff Writer Retinal surgeons are exploring novel ways to prevent post-vitrectomy cataracts C ataract formation is such a common complication of vitrectomy that in many cases, it makes sense to combine macular surgery with phacoemulsification rather than performing the surgeries se- quentially. "If you do a vitrectomy, 95% of people are going to get accelerated post-vitrectomy nuclear sclerot- ic cataracts and require cataract surgery within 2 years," said Nancy Holekamp, MD, associate professor of clinical ophthalmology and visual sciences, Washington University School of Medicine, St. Louis. Many physicians agree that combining the 2 procedures provides better outcomes and decreased risk for the patient, but Dr. Holekamp believes that there is an even better option—modifying vitrectomy surgery to prevent cataract formation in the first place. Over the past several years, retinal surgeons have uncovered the mechanism behind post-vitrec- tomy cataract formation, and Dr. Holekamp believes they can now use that knowledge to develop novel surgical techniques to protect the lens from opacification. The oxygen hypothesis "The only way to prevent cataract formation is to understand what causes cataract formation," Dr. Holekamp said. "And what causes cataracts is oxygen." Oxygen coming from the highly vascularized retina enters the pos- terior segment and encounters the vitreous. The vitreous absorbs that oxygen and protects the anterior ocular structures—including the lens—from oxidation. "The price you pay for taking a breath every day of your life is that a little bit of that oxygen works its way to the crystalline clear lens and causes it to oxidize," Dr. Holekamp said. "It rusts, like iron rusts or a cut up apple turns brown sitting on the kitchen counter." The vitreous consumes ox- ygen and protects the lens from oxidation—so long as it's a gel, Dr. Holekamp said. As the vitreous slow- ly liquefies with age, more oxygen circulates in the posterior chamber, causing a slowly progressive nuclear sclerotic cataract to form. When the vitreous is surgically removed, oxy- gen reaches the lens more quickly, resulting in a rapid acceleration of nuclear sclerotic cataract formation. The idea that oxidation causes cataract formation has come to be known as the oxygen hypothesis, an idea that has emerged only with- in the last several years. Now that retinal surgeons understand this process, Dr. Holekamp said, they can begin to develop strategies to prevent it. "Now that we know it's oxygen, we have to develop some mecha- nism for preventing oxygen from reaching the lens," she said. Potential solutions The vitreous consumes oxygen be- cause it has high levels of ascorbate, Dr. Holekamp said, so implanting a drug delivery device that deliv- ers ascorbate to the vitreous cavity could restore its ability to consume oxygen and protect the lens. Ophthalmologists at the Uni- versity of Louisville are exploring another option—placing a clear barrier behind the lens at the time of surgery. Working with bioengineers, they have designed a biocompatible hydrogel that can be injected behind the lens during vitrectomy. So far, the bioengineered gel has served as a successful oxygen barrier in animal models, but it has not yet been test- ed in human eyes. The researchers hope to test the gel in clinical trials within the next year, according to a press release from the University of Louisville. The ultimate solution would be to provide a vitreous substitute with gel-like properties, Dr. Holekamp said, or to inject small molecules into the vitreous that would reform the natural gel. Researchers at Purdue University are currently studying the protective effect of biomimetic proteoglycans in cartilage degradation, a meth- od that could be adapted to treat the vitreous, Dr. Holekamp said. Although they differ in function, cartilage and vitreous share many structural similarities—they are extremely hypocellular tissues that begin as firm, gel-like substances that slowly liquefy over time. "These strategies at this point are hypothetical, but they're rational strategies because we now under- stand what causes post-vitrectomy cataracts," Dr. Holekamp said. "And once we understand what causes post-vitrectomy cataracts, we can actually understand what causes age-related cataracts. So we should be able to devise strategies or methods for preventing age-related cataracts—that's the end game." Conducting more research on the vitreous will be key to develop- ing these techniques, Dr. Holekamp said. "No one is doing research on this area," she said. "If more people knew about this, maybe we could get more young people interested in studying the vitreous gel or explor- ing these possibilities. I think this is the next frontier in ophthalmology research." EW Editors' note: Dr. Holekamp has no financial interests related to this article. Contact information Holekamp: nholekamp@gmail.com Vitrectomy that prevents cataract formation Advancing CATARACT SURGERY LenSx ® LASER ® ACRYSOF ® IQ RESTOR ® FAMILY OF IOLS IMPORTANT PRODUCT INFORMATION CAUTION: Federal (USA) law restricts this device to the sale by or on the order of a physician. INDICATIONS: The AcrySof ® IQ ReSTOR ® Posterior Chamber Intraocular Lens (IOL) is intended for primary implantation for the visual correction of aphakia secondary to removal of a cataractous lens in adult patients with and without presbyopia, who desire near, intermediate and distance vision with increased spectacle independence. The lens is intended to be placed in the capsular bag. WARNINGS/PRECAUTIONS: Careful preoperative evaluation and sound clinical judgment should be used by the surgeon to decide the risk/benefi t ratio before implanting a lens in a patient with any of the conditions described in the Directions for Use labeling. Physicians should target emmetropia, and ensure that IOL centration is achieved. Care should be taken to remove viscoelastic from the eye at the close of surgery. Some patients may experience visual disturbances and/ or discomfort due to multifocality, especially under dim light conditions. As with other multifocal IOLs, visual symptoms may be signifi cant enough that the patient will request explant of the multifocal IOL. Spectacle independence rates vary with all multifocal IOLs; as such, some patients may need glasses when reading small print or looking at small objects. Clinical studies with the AcrySof ® ReSTOR ® lens indicated that posterior capsule opacifi cation (PCO), when present, developed earlier into clinically signifi cant PCO. Prior to surgery, physicians should provide prospective patients with a copy of the Patient Information Brochure available from Alcon for this product informing them of possible risks and benefi ts associated with the AcrySof ® IQ ReSTOR ® IOLs. Studies have shown that color vision discrimination is not adversely aff ected in individuals with the AcrySof ® Natural IOL and normal color vision. The eff ect on vision of the AcrySof ® Natural IOL in subjects with hereditary color vision defects and acquired color vision defects secondary to ocular disease (e.g., glaucoma, diabetic retinopathy, chronic uveitis, and other retinal or optic nerve diseases) has not been studied. Do not resterilize; do not store over 45° C; use only sterile irrigating solutions such as BSS ® or BSS PLUS ® Sterile Intraocular Irrigating Solutions. ATTENTION: Reference the Directions for Use labeling for a complete listing of indications, warnings and precautions. © 2015 Novartis 4/15 RES15029JAD-PI " Now that we know it's oxygen, we have to develop some mechanism for preventing oxygen from reaching the lens. " –Nancy Holekamp, MD

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