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EW RESIDENTS 64 December 2015 by Anton M. Kolomeyer, MD, PhD, Shilpa M. Kodati, MD, John S. Swogger, DO, Colin J. Prensky, MD, Benjamin R. Strauss, MD, Alex Mammen, MD, and Evan "Jake" Waxman, MD, PhD, UPMC Eye Center, University of Pittsburgh School of Medicine L aser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) are both widely performed refractive surgery techniques with a known risk of postoperative dry eye syndrome. The prevalence of dry eye after laser refractive surgery has been shown to be highly variable based on several publications, ranging from 0.25% to 48%, 1 but the preva- lence of "chronic" dry eye is difficult to ascertain because of differences in how symptoms and exam findings are reported in the literature. In the December issue of the Journal of Cataract & Refractive Surgery, Bower et al reported their findings of a prospective non- randomized study comparing 143 patients who underwent LASIK to those who underwent PRK at Walter Reed Army Medical Center. Because of the different locations at which PRK and LASIK affect the corneal afferent nerves, 2 the authors wished to compare the incidence of dry eye syndrome, both subjectively and objectively, in a population that was otherwise not felt to have dry eye preoperatively. A further goal of this work was to identify preoperative risk factors for development of post- operative dry eye. All study participants were active U.S. military active duty personnel with an average age of 29.9±5.2 years of age at the time of As far as subjective testing, the McMonnies questionnaire scores were consistently higher, indicative of an increase in symptoms, for all postoperative visits for both LASIK and PRK. The authors discuss that aberrant firing of healing nerves may be responsible for dry eye symptoms. Videokeratoscopy/topog- raphy showed a statistically signifi- cant decrease in Surface Regularity Index (SRI) only in PRK at 3 and 12 months. A modification of the Japanese dry eye criteria 3 was used to evaluate for dry eye that the authors deemed "chronic," which was defined as having at least "probable" dry eye at either the 6- or 12-month exam in addition to probable dry eye at any other exam. Patients who had probable dry eye at either the 6- or 12-month visit without dry eye at any other exam were deemed to have "transient" dry eye. Using these definitions, chronic dry eye was uncommon in both PRK and LASIK patients, affecting only 5.0% (6 cases) in PRK and 0.8% (1 case) in LASIK patients. The authors note that their relatively young popu- lation may be responsible for the lower incidence of dry eye than in other studies. Finally, the authors used the battery of preoperative testing (Schirmer, TBUT, esthesiometry, rose bengal staining, and SRI) to propose a predictive model for patients at risk for development of chronic dry eye. Interestingly, the correla- tion analysis revealed differences between LASIK and PRK patients. For PRK, Schirmer testing and TBUT were negatively correlated, while SRI was positively correlated. In LASIK patients, Schirmer testing was again negatively correlated, while rose bengal staining was positively cor- related. Per the authors, regression modeling showed that the above variables "significantly accounted for the occurrence of chronic dry eye" in both LASIK and PRK pa- tients. Within the selected variables, however, only Schirmer testing in PRK patients and rose bengal staining in LASIK patients had their participation. Patients were excluded from the study if they had a Schirmer test of zero, subjective complaints of dry eye symptoms, or findings during slit lamp examina- tion consistent with dry eye. Finally, all surgery was performed by two surgeons. All patients were treated either for myopia or myopia with astig- matism, with a manifest spherical equivalent of –3.83±1.96. A battery of dry eye tests were performed: Schirmer testing with anesthesia, computerized videokeratoscopy, tear film break-up time (TBUT), and rose bengal staining. Corneal sensitivity with a Cochet-Bonnet esthesiometer was also part of the baseline exam. Finally, patients completed the McMonnies dry eye questionnaire. Dry eye testing, esthesiometry, and the McMonnie questionnaire were repeated at 1, 3, 6, and 12 months postoperatively. The authors looked at Schirmer testing with anesthesia and TBUT as indicators of the health of the tear film. Corneal nerve sensi- tivity and rose bengal staining were used as surrogates for ocular surface health. LASIK patients showed no difference in Schirmer testing, but TBUT was significantly faster at 1, 3, and 12 months. This was inter- preted as a qualitative rather than a quantitative change in the tear film after LASIK. Corneal sensitivity was reduced at the 1-, 3-, and 6-month exams, and rose bengal staining was significantly higher at all postopera- tive exams. For patients undergoing PRK, Schirmer testing was significantly different at the 1- and 3-month exam, but there was no difference in the TBUT. Rose bengal staining was significantly different only at the 3-month exam. Corneal sensitivity was decreased at 1 month, but not statistically significantly different from baseline at the 3-, 6-, and 9-month exams. Sensitivity was very slightly but significantly increased at 12 months postoperatively. The au- thors postulate that quicker recovery of corneal nerve sensation may limit epithelial pathology. Review of "Chronic dry eye in PRK and LASIK: manifestations, incidence and predictive factors" Chronic dry eye in PRK and LASIK: manifestations, incidence and predictive factors Kraig S. Bower, MD, Rose K. Sia, MD, Denise S. Ryan, MS, Michael J. Mines, MD, Darlene A. Dartt, PhD J Cataract Refract Surg (Dec) 2015;41. Article in press Purpose: To evaluate dry eye manifestations following photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) and determine the incidence and predictive factors of chronic dry eye using a set of dry eye criteria. Setting: Walter Reed Army Medical Center, Washington, D.C. Design: Comparative case series. Methods: This is a prospective non-randomized clinical study of 143 active duty U.S. Army personnel aged 29.9±5.2 years with myopia or myopic astigmatism (manifest spherical equivalent –3.83±1.96 diopters) undergoing either PRK or LASIK. Dry eye evaluation was performed pre- and postoperatively. Main outcome measures included dry eye manifestations, incidence, and predictive factors of chronic dry eye. Results: Schirmer scores, corneal sensitivity, ocular surface staining, surface regularity index (SRI), and responses to dry eye questionnaire significantly changed over time after PRK. After LASIK, significant changes were observed in tear break-up time, corneal sensitivity, ocular surface staining, and responses to questionnaire. At 12 months postoperatively, 5.0% of PRK and 0.8% of LASIK participants developed chronic dry eye. Regression analysis showed preoperatively lower Schirmer score will significantly influence development of chronic dry eye after PRK whereas preoperatively lower Schirmer score or higher ocular surface staining score will significantly influence the occurrence of chronic dry eye after LASIK. Conclusions: Chronic dry eye is uncommon after PRK and LASIK. Ocular surface and tear film characteristics during preoperative examination may help predict chronic dry eye development in PRK and LASIK. continued on page 66 EyeWorld journal club

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