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Editors Selection IGR 14-3

Medical Treatment: Dry eye and glaucoma (treatment)

Comment by Fotis Topouzis on:

25462 Characteristics of respondents with glaucoma and dry eye in a national panel survey, Schmier J K; Covert D W, Clinical Ophthalmology, 2009; 3: 645-650

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In a survey conducted by Schmier and Covert (28), a nationally representative sample was used to identify glaucoma subjects with and without dry eye and to evaluate their clinical and treatment characteristics. Glaucoma subjects were compared to a non-glaucoma control group with and without dry eye, selected from the same population. Based on the Medical Expenditure Panel Survey database (MEPS - 2003-2009), 629 glaucoma subjects and 6,934 controls were identified. According to the results, dry eye was more common among glaucoma subjects than among controls (16.5% vs 5.6%, p < 0.0001). Also, there was a trend for higher rates of adjunctive glaucoma treatment among subjects with dry eye, compared to those without dry eye (44.2% vs 35%, p = 0.076). The authors concluded that the rate of dry eye was higher among glaucoma subjects than among controls and that the use of adjunctive glaucoma treatment may increase the rate of dry eye in glaucoma.

The objective of this study was to evaluate the relationship between glaucoma, dry eye and IOP-lowering treatment. The use of a large sample size which is considered to be representative of the general population, is among the strengths of this study. However, there are several methodological issues that need to be addressed, most of which are related to the objective itself. Both glaucoma subjects and controls were identified through the MEPS and were not prospectively examined. More importantly, the sole criterion used to define glaucoma was the use of IOP-lowering treatment. For this reason, a large proportion among those classified as glaucoma possibly had ocular hypertension, while glaucoma subjects who were not using IOP-lowering treatment (e.g., those with low IOP as a result of a prior glaucoma procedure) were classified as controls. Further to that, considering that the prevalence of undiagnosed glaucoma has been reported to be at least 50% in the general population, a significant proportion among those belonging to the control group may have had glaucoma. All of the above point towards serious misclassification bias in the study. Misclassification with regard to the dry eye diagnosis is also possible, because one of the criteria used to define ocular surface disease (OSD) was the self-reported use of over-the-counter medications. In addition, no adjustments were made for possible confounders associated with OSD, such as age, sex and concomitant systemic diseases, which were statistically significantly different between the groups, and the use of systemic medications, which was not assessed. Also, because of the nature of the study, no information was available on the baseline status of glaucoma subjects with regards to OSD. Despite these limitations, because the study provides with large sample size, an association between the use of IOP-lowering treatment and dry eye may be suggested. However, as mentioned above, because of potential misclassification of glaucoma and controls, the conclusion drawn should not involve the glaucoma status.

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