Eyeworld

EW INTERNATIONAL 102 October 2015 by Matt Young and Gloria D. Gamat EyeWorld Contributing Writers prospective interventional study at an apex tertiary care ophthalmology center in India. Their findings, pub- lished in a recent issue of Optometry & Vision Science, demonstrated that near and distance stereoacuity show significant improvement after LASIK. While previous studies have not evaluated distance stereoacuity, the research group from India evaluated near and distance stereoacuity and found that both have shown signifi- cant improvement after LASIK. Additionally, distance stereoacu- ity was found to be more affected in the preoperative period with more cases having subnormal stereoacuity for distance than for near. Further, the researchers empha- sized another important observation in this study: "stereoacuity is associ- ated with the degree of anisometro- pia, but the change in stereoacuity did not depend on the amount of refractive error corrected." Vision is a comprehensive function with many aspects, Dr. Saxena said, and stereoacuity is one of them. For example, even with the best optical correction, induced A s refractive surgeons have fine-tuned the art of per- forming LASIK through- out the years, the usual markers of a successful LASIK surgery (20/15, 20/20 vision) are now becoming easily achieved, and therefore may no longer be the only measure of the procedure's success. Although LASIK has provided unaided visual acuity and better quality of life to patients, the proce- dure has shown to have an impact on other visual functions as well, including contrast sensitivity and induced astigmatism, among others. In a new study, researchers from India analyzed LASIK results in a much different way: by looking at stereoacuity. While the scientific lit- erature reports that LASIK improves near stereopsis, most of the evidence previously available has been either anecdotal or incomplete. The importance of stereoacuity in LASIK results The research team postulated that since the 20/20 vision goal is now achieved with current LASIK tech- nology, the finer functions need evaluation, and if required, future development of this technology may be directed to provide greater quality of vision. "Traditionally, LASIK has always been about achieving 20/20 visu- al acuity, but the effects on other visual functions have been gaining prominence," said Rohit Saxena, MD, additional professor, Dr. Rajendra Prasad Centre for Ophthal- mic Sciences, All India Institute of Medical Sciences, New Delhi. The world is increasingly be- coming 3D, Dr. Saxena said. "In our daily lives [especially in India], there is a huge requirement for binocu- larity with the advent of 3D movies and games, TVs and holographic projection technology; consequently [stereoacuity] is an important visual function that people may need, and they realize its utility," he explained. Stereoacuity is a fine but essen- tial visual function. Although it is not the primary parameter for LASIK correction, according to Dr. Saxena, the next level for a refractive surgery outcome should be 20 seconds of arc stereoacuity (20/20/20). The quality of the visual expe- rience after LASIK is greatly affected by the level of stereoacuity achieved, he said. "Therefore, I think that we need to aim for wavefront-guided and optimized LASIK protocols, keeping in mind a goal of good visu- al acuity, correction of anisometro- pia and introduction of minimal aberrations that will ensure the best chance for improved stereoacuity." Affected by various physiologic and pathologic conditions (age, opti- cal blur, intereye differences, strabis- mus, and amblyopia), stereoacuity is the highest grade of binocular vision and a cortical function that has a significant role in everyday life. "Once we have consistently achieved 20/20 monocular vision, stereoacuity, which depends on many factors—particularly good monocular vision—should be the next goal to consistently achieve," Dr. Saxena said. "Therefore, I [think] stereoacuity should now be considered a better parameter to evaluate outcomes of any refractive surgery." Clinical evidence In evaluating changes in near and distance stereoacuity after LASIK, Dr. Saxena and colleagues conducted a Stereoacuity: A new measure of LASIK success? A 3D Delta sign image as seen binocularly on the Distance Randot Stereotest (Stereo Optical, Chicago) Source: Rohit Saxena, MD Q uality of vision is a subjective assessment, and for this reason it is difficult to quantify. We know quality of vision is important, and after safety, it may be the most important factor influencing patient satisfaction. All refractive surgeons know that Snellen acuity does not always predict if a patient will be happy with his or her vision. Stereoacuity has largely been overlooked as a quantitative measure of visual quality following refrac- tive surgery. Could this be another factor to consider? John A. Vukich, MD, international editor International outlook

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