Eyeworld

EW RESIDENTS 66 December 2015 Review continued from page 64 statistically significant regression weights, indicating that these were the most predicative factors among all those tested for PRK and LASIK, respectively. The authors further note that the above variables only accounted for 10.7% of prediction in PRK and 11.7% of prediction in LASIK. Thus, despite the extensive testing performed pre- and postop- eratively, there were still unaccount- ed factors that were substantially contributing to chronic dry eye after these procedures. The strengths of this study include the prospective design, the appropriate exclusion of patients with symptoms or examination findings preoperatively consistent with dry eye, and the minimization of variability in surgical technique by having two surgeons performing all procedures. Additionally, the authors used a robust set of tests to monitor dry eye, including both subjective and objective testing. The authors acknowledge that a limitation of this study is the underestimation of dry eye due to the treatment of patients with either artificial tears or punctal plugs. In relation to this, the authors do not report the numbers of patients receiving treatment for dry eye following either LASIK or PRK or their threshold to initiate treatment. These figures are important since they are a reflection of dry eye with- in the study population and could have been reported as endpoints. Furthermore, given that other reports have shown that patients re- main symptomatic for years follow- ing refractive surgery, 4 longer-term follow-up of these patients beyond a 1-year period would have provided useful information on the chronicity of symptoms. Another limitation is the use of a modification of the Japanese dry eye criteria to diagnose chronic dry eye. Given the rigorous requirement for dry eye symptoms, tear film dis- turbance, and epithelial damage to all be present to satisfy the defini- tion of dry eye by these set of crite- ria, it is likely that clinically relevant dry eye was underestimated. Indeed, the incidence of chronic dry eye reported by this study is lower than other reported studies. 4–5 Since the incidence of chronic dry eye is low in this study, the authors' analysis assessing predictive factors for the development of dry eye is perhaps less valuable. Moreover, the reported low incidence of chronic dry eye (6 in the PRK group, 1 in the LASIK group) also unfortunately limits the comparison of the incidence of dry eye between the two groups. Notably, an increased depth of ablation has been implicated as a factor in dry eye. 5 It is thought that a greater depth of ablation necessi- tates a longer distance toward the corneal epithelium for the truncated nerves to regenerate. Therefore, a subgroup analysis in this study eval- uating the effect of ablation depth on chronic dry eye would certainly have been informative. This study is consistent with previously reported findings demon- strating the effect of refractive surgery on the symptoms and signs of dry eye. 2,4 The study also high- lights the importance of undertak- ing a thorough dry eye examination prior to laser refractive surgery, with both quantitative and qualitative assessments of tear function in order to identify patients who may be at higher risk of developing chronic dry eye following surgery. Indeed, preoperative optimization of the ocular surface would not be suffi- cient in mitigating this risk. More studies with longer-term follow-up are required to further elucidate the factors that may predispose patients to developing chronic dry eye post LASIK or PRK. EW References 1. The epidemiology of dry eye disease: report of the Epidemiology Subcommittee of the International Dry Eye WorkShop (2007). Ocul Surf. 2007;5(2):93–107. 2. Ang RT, et al. Dry eye after refractive surgery. Curr Opin Ophthalmol. 2001; 12(4):318–22. 3. Uchino Y, et al. Changes in dry eye diagnos- tic status following implementation of revised Japanese dry eye diagnostic criteria. Jpn J Ophthalmol. 2012; 56(1):8–13. 4. Levitt AE, et al. Chronic dry eye symptoms after LASIK: parallels and lessons to be learned from other persistent post-operative pain disorders. Mol Pain. 2015; 11:21. 5. De Paiva CS, et al. The incidence and risk factors for developing dry eye after myopic LASIK. Am J Ophthalmol. 2006;141(3):438– 445. Contact information Waxman: waxmane@upmc.edu

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