EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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June 2012 EW NEWS & OPINION Using OCT to diagnose retinal disorders Device focus by Michelle Dalton EyeWorld Contributing Editor Before the imaging device was popularized, it was next to impossible to diagnose some disorders with any confidence I n an era when every premium lens patient not only expects perfect vision but also expects no complications from the sur- gery, any and every diagnostic tool in a surgeon's armamentarium becomes even more important to weed out the most minute of potential issues. "In this era of multifocal/pre- mium IOLs, patient expectations post-cataract surgery are extremely high," said Nalin J. Mehta, M.D., Colorado Retina Center, Lakewood, Colo. "A good number of cataract surgeons are not using optical coher- ence tomography (OCT) to evaluate the macula for subclinical, pre-oper- ative macular disorders that may af- fect final visual outcomes." For example, a recent study found deeper and wider lamellar defects are associated with poor visual out- comes—and only 28% of lamellar holes diagnosed by OCT had been detected clinically on fundus exam.1 A major advantage in using OCT to assess retinal diseases is its ability to provide cross-sectional im- ages of the retina and to perform quantitative analysis of retinal mor- phology. "Every ophthalmologist should become familiar with OCT images, as we can no longer trust our eyes in the evaluation of retinal status," said Roberto Bellucci, M.D., Hospital and University of Verona, Italy. During the 2012 ASCRS•ASOA Symposium & Congress, David S. Boyer, M.D., clinical professor of ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, told sympo- sium attendees vitreomacular trac- tion and epiretinal membranes were underdiagnosed before the use of OCT became so widespread. A key pearl, he said, is to remember cataracts don't cause distortions— retinal disorders do. Steven G. Safran, M.D., in pri- vate practice, Lawrenceville, N.J., agreed, saying some retinal patholo- gies such as vitreomacular traction, Figure 1. An epiretinal membrane denoted by the arrow distorts the retinal anatomy and may decrease vision lamellar macular holes, and age-re- lated choroidal atrophy were impos- sible to visualize and in some cases were only identified once the retinal surgeon began doing a dissection. "With OCT, you can see the posterior hyaloid, and you can de- termine its relationship with the macula," Dr. Safran said. "The vitre- omacular interface is now under- stood to play a role in macular edema and macular degeneration." OCT is also the "only way" to view choroidal abnormalities, Dr. Safran said. "We're just beginning to understand how many disease states are affected by the choroid." People with very thin choroids (age-related choroidal atrophy) may be at a higher risk for glaucoma, especially if those patients present with peri- papillary atrophy, according to a study.2 These patients may not see well even if the macula is clear, Dr. Safran said, and myopes are at a greater risk of vision loss due to my- opic degeneration with a thin choroid as well. "Cataract surgery can infre- quently accelerate/induce vitreous degeneration, with subsequent pos- Phaco continued from page 25 ability to dissociate the irrigating and aspirating tips can help to pre- vent misdirection of irrigating fluid through the zonular defect (Figure 5). If capsule retractors are used, placing a capsular tension ring can usually be delayed until the cortex has been removed. One must be careful not to snag or tear posterior capsular folds with the leading tip of a CTR during its insertion. Fully ex- panding the capsular bag with OVD prior to injecting the ring is critical for this reason. Brian Little, F.R.C.S., described the fish tail method of re- ducing zonular stress when inserting a ring without an injector.1 Using an injector has the advantage of intro- ducing the CTR into the capsular bag without excessively stretching the capsulorhexis. One can either load the ring manually with a reusable metal injector or use a pre- loaded, disposable plastic injector from Morcher (Stuttgart, Germany) or FCI Ophthalmics (Marshfield Hills, Mass.). The injector tip should be positioned as far peripherally within the bag as possible in order to minimize lateral displacement of the capsular bag as the ring emerges. If used, capsular retractors should be left in place to counter the lateral decentering forces of the CTR as it is injected. In fact, an additional ad- vantage of capsular retractors is to reduce the potential for zonular damage caused during insertion of a CTR. The retractors can then be re- moved prior to IOL implantation. EW Reference 1. Angunawela RI, Little B. Fish-tail technique for capsular tension ring insertion. J Cataract Refract Surg. 2007;33:767-769. Editors' note: Dr. Chang is clinical professor, University of California, San Francisco, and is in private practice, Los Altos, Calif. He has no financial interests related to this article. Figure 2. The macular hole seen here through OCT will necessitate immediate surgery to avoid vision loss Source (all): Roberto Bellucci, M.D., and Miriam Cargnoni, O.D. terior vitreous detachment; this could in turn result in antero-poste- rior vitreomacular traction or the evolution of an epimacular mem- brane; increased symptomatology from pre-existing epimacular mem- branes/macular pucker may also occur; and posterior vitreous detach- ment (PVD) conceivably leads to macular hole formation or progres- sion. In one study,3 20% of eyes de- veloped PVD at 1 week after surgery," Dr. Mehta said. When to image, what to look for Dr. Safran advises "anyone who is implanting premium lenses" to get an OCT of the retina before surgery. "It is an avoidable error to rec- ommend to patients with undiag- nosed macula pathology a premium lens that can't live up to expecta- tions. In some cases a multifocal that the patient pays extra for may do more harm than good," Dr. Safran said. "The important thing is that surgeons must be aware of the macula pathology beforehand if they are recommending (and charg- ing extra) for the lens, and not hav- ing an OCT is just not a good excuse anymore." In his opinion, epiretinal membranes should be a contraindi- cation for multifocal lenses, and patients should be advised if they have thin retinas that visual out- comes may not be exemplary. Dr. Bellucci advises performing OCT "when the measured visual acuity does not match with the as- pect of the retina and with the den- sity of the cataract." Epiretinal membranes, for instance, are more frequent after other pathologies such as retinal photocoagulation, retinal detachment, or uveitis; for surgeons unfamiliar with OCT, these membranes "look like a black line at the retinal surface, cancelling the foveal depression," Dr. Bellucci said (see Figure 1). Post-op, Dr. Mehta said studies showing macular thickening and PVD occur as early as 1 week post- cataract, and he'd advise obtaining a post-surgical OCT image at that time. "If the case is complex, and there is a significant chance for corneal decompensation in the im- mediate post-op period, then intra- continued on page 28 27