Night vision complaints after LASIK: Author reply

Abstract

I welcome this opportunity to respond to Drs Brown and Khanani. Although results may be contrary to certain beliefs within the medical practice concerning the role of pupil size in night vision complaints (NVCs) after refractive surgery, I believe that good scientific interpretation of data should lead to better objective conclusions. First, a retrospective cohort study is a robust protocol for exploratory data mining, which is different than a confirmative cohort study through long-term investigation. The use of a retrospective cohort study also differs from that of a case–control study; such a study could not investigate risk factors within matched criteria between controls and disease. For example, if controls and NVC patients had been matched by pupil size, because the ratio of control to NVC would have been 1, it would have been impossible to detect the role of pupil size in NVCs. Therefore, a retrospective cohort study was chosen to consider a broad analysis of the phenomenon, because clinical data on NVCs were sparse, and the phenomenon is not clearly understood. Before this study, assessment of pupil size measurement protocol was published1Pop M Payette Y Santoriello E Comparison of the pupil card and pupillometer in measuring pupil size.J Cataract Refract Surg. 2002; 28: 283-288Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar and cited in our “Discussion.” This study reflected general practice of pupil size measurement in a clinical setting using a good and proper standard-of-care protocol. As stated in our “Discussion,” “even if measured more precisely, pupil size may not be the most important clinical predictor of postoperative NVCs, because other variables demonstrated a high degree of statistical significance.” In this study, the odds ratio (OR) for pupil size greater than 7 mm was 0.92 (P = 0.82). If pupil size was to surpass spherical correction of >5 diopters as a risk factor, it would have to exceed a 2.8 OR (P = 0.002). Although Schallhorn et al's results2Schallhorn S.C Kaupp S.E Tanzer D.J et al.Pupil size and quality of vision after LASIK.Ophthalmology. 2003; 110: 1606-1614Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar differed slightly from those of the present study, their conclusion was that “most of the variability in visual quality could not be explained by preoperative or clinical outcome measures, including pupil size.” The present study differs in its conclusions, as preoperative spherical correction, age, optical zone, and postoperative spherical equivalent were predictive of NVCs. However, as in the study by Schallhorn et al, the direct implication of pupil size was a negligible factor in the prediction of the long-term quality of vision after LASIK. In our study, criticism suggesting greater emphasis on statistics is not reasonable. I believe that statistical analysis is merely an objective tool to gain knowledge of a phenomenon. Too often, studies contain too little or inappropriate statistical analysis.3Cummings P Rivara F.P Reporting statistical information in the medical journal articles.Arch Pediatr Adolesc Med. 2003; 157: 321-324Crossref PubMed Scopus (37) Google Scholar, 4Schachat A.P Chambers W.A Liesegang T.J Albert D.A Safe and effective.Ophthalmology. 2003; 110: 2073-2074Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar The present study used the best statistical tools available to assess ORs of NVCs after LASIK while exploring bilaterality among patients.5Murdoch I.E Morris S.S Cousens S.N People and eyes statistical approaches in ophthalmology.Br J Ophthalmol. 1998; 82: 971-973Crossref PubMed Scopus (221) Google Scholar As medical knowledge grows, so do statistical tools used to scrutinize its results. The present study discussing 12-month findings in over 750 eyes took 2 years to complete. There was an additional 2-year period for the review and revision process, during which time valuable comments from 5 reviewers were received and considered. I do not believe the credibility of the Journal or the peer review process has been undermined. In this study, the rating of NVCs was subjective; to measure NVCs objectively may even prove to be harder. I sincerely hope the present article will help point to new directions for future studies.