MAR 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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E W CORNEA 100 March 2014 Considering the matter of scatter E ndothelial keratoplasty passed penetrating kerato- plasty (PK) in popularity in 2012 for procedures used for corneal transplanta- tion, according to Holly B. H indman, MD, Flaum Eye Institute, University of Rochester, Rochester, N.Y. Eye Bank Association of Amer- ica statistics in 2012 showed that 23,049 corneas were used for en- dothelial keratoplasty in the U.S. and 21,422 were used for PK, she reported. With this burgeoning popularity, more attention is being f ocused on attaining the best out- comes. New study results published in the December 13, 2013 issue of Cornea indicate that with Descemet's stripping automated endothelial keratoplasty (DSAEK), it is a decrease in light scatter, not higher order aberrations, that can account for visual improvement in the first year postoperatively. When the endothelial kerato- plasty procedure was first emerging a few years back, Dr. Hindman's in- terest was piqued as to why patients weren't getting back to the same level of acuity with deep lamellar endothelial keratoplasty (DLEK) as they were with penetrating kerato- plasty. "It wasn't major, but early re- ports were showing vision of about 20/40 for DLEK, whereas the pene- trating keratoplasty patients were achieving better visual acuities," Dr. Hindman said. In her view, there were a couple of possible reasons for this. If the retina and optic nerve are intact and the neural pathways are good, Dr. Hindman pointed out, the two main corneal findings that can hin- der visual acuity are scatter and dis- tortion. "When you're driving and there is a lot of salt on the wind- shield, you have the type of effect that is scatter," Dr. Hindman said. "But you can also get distortion, which is aberration." She described such distortion as akin to looking in a fun house mirror. "With endothe- lial keratoplasty, we're leaving the bulk of the host cornea intact and putting the donor tissue onto the back, which changes the posterior corneal profile thereby changing the pathway the light has to travel to get through the eye," she said. "There's also the creation of a donor host stromal interface, which in addition to anterior host stromal changes associated with chronic edema is another source of scatter." Dissecting DSAEK With this in mind, Dr. Hindman and fellow investigators launched the study to determine how these factors changed with time. In partic- ular, investigators wanted to deter- mine how vision was affected by these factors in DSAEK cases. "We studied ocular aberrations rather than corneal aberrations so that we could understand the impact of aberration changes on visual acuity changes," Dr. Hindman said. "We looked postoperatively at the aberrations at one, three, six, and 12 months." Investigators looked at how aberrations in the whole eye affected visual quality. When it came to postop higher order aberrations, they determined that they did not diminish by much. "We found there was a trend that the total average was decreasing, but it wasn't signifi- cant," Dr. Hindman observed. In addition, investigators noticed there was a decrease in corneal light scat- ter occurring with time. "We found that the interface reflectivity de- creased more than the other sources of reflectivity," Dr. Hindman said. It was the scatter that proved significant. "The improvement in vi- sion in our series could be accounted for by the decrease in the scatter we were seeing in the cornea," Dr. Hindman said. The change in scatter was not associated with changes in corneal edema as evidenced by sta- ble corneal thicknesses. Corneal thickness, she pointed out, was another area of interest for a lot of people, who wanted to determine if making the donor button thinner would affect vision. "Ours was a relatively small study, and corneal thickness wasn't our primary end- point but was something we noticed didn't affect the visual outcome," Dr. Hindman said. "It didn't matter if the host donor was thicker, if the total amount was thicker, or if the donor tissue was thicker." However, between the one- and 12-month postoperative marks, a decrease in scatter proved to be an important factor in visual improve- ment. "The variability induced by the scatter could account for the change in the vision we saw," she said. Investigators found that this decrease was most pronounced along the interface. Focusing on scatter Just where is this scatter coming from? Dr. Hindman recently took a look at this in an animal model. Prior studies, she noted, had found one of the primary causes of light scatter was corneal wounding. The bulk of the cornea, she pointed out, is made up of the stroma. When the cornea is injured, there is a release of cytokines and growth factors. Keratocytes, the primary cell type in the stroma, be- come fibroblastic and can transform into wound-healing cells called my- ofibroblasts, she explained. Myofi- broblasts make proteins that can assemble into a contractile apparatus that can close the wound. However, when in the cornea, these wound healing cells may contract the tissue and make the light bend in undesir- able ways, or when these proteins are expressed, they can create scatter. Yet in her animal model of by Maxine Lipner EyeWorld Senior Contributing Writer Eye on optical changes post-DSAEK For eyes that have undergone DSAEK such as this one, study results indicate it is a decrease in light scatter, not in higher order aberrations, that accounts for visual improvements in the first year postoperatively. Source: Holly B. Hindman, MD 88-107 Cornea_EW March 2014-DL2_Layout 1 3/6/14 3:47 PM Page 100

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