We have read with great interest the article by Yoshioka and associates. The study used a novel measurement system that they developed for measuring eyelid pressure. The results showed that the eyelid pressure on the ocular surface was higher in dry eyes than in normal eyes, and that the eyelid pressure was significantly correlated with the fluorescein ocular surface staining scores of the inferior cornea and inferior conjunctiva. We are confident that the instrument was well designed, but we have the following comments concerning the use of this instrument.
First, the aim of this study was to determine the relationship between eyelid pressure during blinking and fluorescein staining of the cornea and conjunctiva in dry eye patients. Their aim is an important clinical question, and we are also very interested in this subject and have reviewed many related studies. No studies have currently reported the relationship between eyelid pressure during blinking and fluorescein staining of the cornea and conjunctiva in dry eye patients. The word “influence” implies that the eyelid pressure affects fluorescein staining of the ocular surface in dry eye. In their study, the authors reported that their findings did not provide any evidence as to whether a higher eyelid pressure was due to dry eye conditions, or whether dry eye conditions were due to a higher eyelid pressure. We believe it is therefore more appropriate to use “potential relationship study” rather than “influence” in the title.
Second, they analyzed the results from 130 eyes of 65 dry eye patients and 58 eyes of 31 normal controls. In correlations involving the eye, collecting data from 1 or both eyes of a subject in ophthalmic statistics has been used, especially when the correlation between eyes is strong. We recommend that the between-eye correlations in the subjects be estimated and a single subject eye from 65 dry eye patients and 31 normal controls should be used for the final statistical analysis.
Third, the authors mentioned the Japanese Dry Eye Diagnostic Criteria revised in 2006. However, in their study, the description in the Discussion section (page 690) states, “Our dry eye patients were diagnosed based on the 2006 revised Japanese criteria for dry eye, which include BUT scores <5 s and Schirmer I test score >5 mm.” This statement was inconsistent with the description in the Methods section (page 686) stating “(2) presence of either qualitative or quantitative disturbances of the tear film (Schirmer I test ≤5 mm or fluorescein tear break-up time [BUT] ≤5 s).”
Fourth, we suggest that in future studies, the authors should consider the influence of body posture (lying or sitting) when measuring eyelid pressure. Furthermore, it is also important to quantitatively analyze the influence of eyelid pressure on cornea curvature using this novel instrument.