Oxidative stress measures in human tears and associations with conjunctival ultraviolet autofluorescence

Abstract

Purpose : Oxidative stress is known to accompany ultraviolet (UV) radiation exposure. Conjunctival ultraviolet autofluorescence (UVAF) is reported as a possible objective biomarker for ocular UV exposure. The purpose of this study was to test the hypothesis that oxidative stress measures for in vivo human tear samples will be increased in those with larger areas of conjunctival UVAF.

Methods : Thirty four volunteers were seen for 2 visits 14 ± 2 days apart. Tears were collected by glass microcapillary tube from the inferior meniscus. Ocular sun exposure was estimated by questionnaires. Conjunctival UVAF images were obtained using a Nikon D7000 camera with appropriate flash and filter system; image analysis was completed with ImageJ software. Hexanoyl-lysine (HEL) and 8-hydroxy-2’-deoxyguanosine (8OHdG) ELISAs were used to quantify lipid and DNA damage products, respectively. Non-normally distributed data (Shapiro-Wilk) was transformed by either log₁₀ or square root methods. Repeatability estimates were obtained using Bland Altman plots. Univariate and multivariate linear regression evaluated relationships among study variables.

Results : Means (±SD) were obtained for both raw and transformed data. Acceptable repeatability was demonstrated for each variable using Bland Altman plots. Univariate linear regression demonstrated a significant inverse relationship between conjunctival UVAF and tear 8OHdG expression (p=0.015); direct relationships were found between conjunctival UVAF and outdoor occupation (p=0.031) and winter season of collection (p=0.028). Linear regression models showed tear 8OHdG expression was positively related to tear HEL expression (p=0.003) and inversely related to age (p=0.024). Furthermore, linear regression modeling supported the inverse relationship between conjunctival UVAF and tear 8OHdG expression (p=0.037).

Conclusions : Our findings report for the first time association of an oxidative stress marker in tears with conjunctival UVAF. Contrary to our hypothesis, an inverse relationship between conjunctival UVAF and DNA damage in tears was identified; relevance of the inverse relationship as it relates to ocular disease and other variables remains to be further delineated. Evidence here also supports our previous findings of concurrent lipid and DNA damage on the ocular surface.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.