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Stephanie Cox, Jason J Nichols; Association between conjunctival sensitivity and tear film characteristics. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):356.
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The purpose of this work is to assess if altered sensitivity of the inferior palpebral conjunctiva is associated with other tear film characteristics.
Clinical examination of recruited subjects included assessment of the sensitivity of the inferior palpebral conjunctiva using a Cochet-Bonnet aesthesiometer and average lipid layer thickness (LLT) using the LipiView. In addition, two measures of the non-invasive keratograph tear break up time (NIK-BUT) using the Keratograph 5M and three measures of fluorescein tear break up time (Fl-BUT) were attained. The two first NIK-BUT measures, two average NIK-BUT measures, and three Fl-BUT measures were each averaged. Symptoms were assessed using the Ocular Surface Disease Index (OSDI). Subjects were grouped into a high sensitivity group (HS) and a low sensitivity group (LS) based on the median value of the distribution of sensitivity measures. SPSS version 22 was used for all statistics. A Pearson Chi-Square test was used for binomial data comparisons and Mann-Whitney U tests were used for all other data comparisons.
The median sensitivity measure was 1.4 g/mm2 yielding 28 HS subjects and 31 LS subjects. In HS, 64.3% of the subjects were female compared to 61.3% of the LS group (p = 0.81). The median ages of the HS and LS subjects were 27.5 years (range: 21-84) and 26.0 years (range: 20-64), respectively (p = 0.20). The median LLT for HS was 64.5 ICU (range: 32-100) and 53.5 ICU (range: 41-100) for LS (p = 0.38). The median first NIK-BUT for HS and LS was 6.1 sec (range: 2.7-15.7) and 8.0 sec (range: 3.1-19.3), respectively (p = 0.15). The average NIK-BUT was 8.1 sec (range: 2.8-19.3) in HS and 12.2 sec (range: 5.3-21.4) in LS (p = 0.03). The Fl-BUT medians were 6.6 sec (range: 2.7-35.7) for HS and 6.4 sec (range: 2.8-35.4) for LS (p = 0.87). HS median OSDI score was 10.8 (range: 0-47.9) while the LS median was 6.3 (range: 0-50.0) (p = 0.26).
The average NIK-BUT was the only tear film characteristic that showed a statistically significant difference based on conjunctival sensitivity. Further testing is necessary to explain the reason for this association. It is possible that increased sensitivity of the ocular surface could adversely affect the tear film via overstimulation of reflex mechanisms initiated there. It can also be argued that tear film changes lead to exposure of nerves of the ocular surface, which increases sensitivity.
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