Prior studies have examined the effect of cataract surgery on tear film parameters and reported short-term disruptions in tear function. Ram et al. in 23 postcataract surgery patients (25 eyes) demonstrated decreased Schirmer scores and tear break-up time (TBUT) at various time points up to 2 months postoperation compared to preoperative values [12
]. Li et al, in 37 postcataract surgery patients (50 eyes), similarity found decreased Schirmer and TBUT values at 1-week, 1-month, and 3-month time points compared to preoperative values [4
]. These studies followed patients for a limited time period after surgery, and while there was a trend towards normalization of values, short followup limited the ability to determine whether tear film parameters returned to their baseline values. Our study's purpose, therefore, was to evaluate whether patients who had cataract surgery at least 3 months prior to testing had similar tear film parameters between the surgical and nonsurgical eyes. Indeed, our data suggests that tear film parameters recover after surgery, as all studied parameters were statistically similar between eyes.
Ours is the first study to evaluate not only well established tests such as Schirmer's, TBUT, and corneal staining, but also other less established objective measures of tear function including tear osmolarity, eyelid vascularity, meibomian gland secretion and orifice plugging in the long term after cataract surgery. This is an important study since it can begin to lay the foundation of our knowledge on what long-term changes occur in eyes that had cataract surgery.
One issue to consider when interpreting the results is the small sample size. In a small study, such as this one, a finding of no significant difference cannot be taken to mean that no difference exists. Therefore, we constructed 95% confidence intervals to assess the likely size of any differences between surgical and nonsurgical eyes that our significance tests might have missed. For all variables, the sizes of the confidence intervals were small compared to the ranges of the differences. Further, all continuous variables were without outliers (as classified by 1.5 × IQR), so it is unlikely that distribution of these ranges was overlarge due to skewed distributions.
As with all studies, our conclusions must be interpreted while keeping in mind the study limitations. This study design was different than other cataract surgery studies as we did not measure tear film parameters in the same eye longitudinally. We can therefore only compare the values between eyes without commenting on whether tear film parameters “normalized” in the operated eye. Although it has been shown that fellow eyes have a substantial degree of correlation with respect to tear film parameters [17
], a follow-up study with longitudinal design is needed to confirm our findings. Furthermore, our study could not evaluate the individual effects of race, age, and ethnicity on tear film function. However, by nature of its paired design, these factors were effectively controlled for, as any effect found would be independent of these demographic parameters. Finally, this study could not evaluate the impact between tear film parameters and patients' symptoms. The main source of morbidity in DES is its symptoms and prior studies have shown that correlation between symptoms and clinical tests is poor [18
]. Therefore, a residual gap in knowledge is whether patients who experience increased ocular surface symptoms after surgery have an eventual decrease in their discomfort to preoperative values.
Despite these limitations, our study suggests that patients undergoing cataract surgery can be counseled that their tear film function will mirror that of the fellow eye 3 months after cataract surgery. Increasing patient understanding and giving realistic expectations often improves overall patient satisfaction and the physician-patient relationship. We hope that these findings open the door for future research to confirm our results and further study the mechanisms of tear film disruption and changes after cataract extraction, including the effect of surgery on both symptoms and corneal sensitivity, neither of which were specifically examined in this study.