Tear lipocalin and lysozyme concentrations in postmenopausal women

Abstract

To investigate the potential relationship between subjective symptomatology, tear volume, and tear break up time with tear film lipocalin and lysozyme concentrations in a group of symptomatic dry-eyed postmenopausal (PM) women compared to age-matched controls. Eighty-five healthy PM females (>50 years of age) were categorized as mild or moderate dry eye (DE), or asymptomatic [non-dry eye (NDE)] based on their responses to the Ocular Surface Disease Index (OSDI) questionnaire. Non invasive tear breakup time (NITBUT) and tear secretion were measured. Tears were collected via capillary tube and an eye wash method. Tear lysozyme and lipocalin concentrations were determined via Western blotting. Ocular Surface Disease Index responses revealed 16 mild DE, 30 moderate DE, and 39 NDE. The OSDI total score and sub scores for the DE groups were significantly greater than for the NDE group (p < 0.001). The mild and moderate DE groups exhibited significantly shorter NITBUTs compared to NDE (p < 0.004). Tear secretion using the Phenol Red Thread (PRT) test was found to be significantly lower in the moderate DE group compared to NDE (p < 0.001). No difference in tear lysozyme or lipocalin concentration was found between DE and NDE groups, irrespective of tear collection method, although method of collection significantly influenced absolute concentrations (p < 0.008). Significant correlations were not found between symptoms or signs of DE compared to either lipocalin or lysozyme concentration. Within a PM population, lipocalin and lysozyme are invariant, irrespective of the presence and severity of DE symptoms. This is the first comprehensive study of lipocalin and lysozyme in dry-eyed PM women and our results suggest that neither protein would offer utility as a biomarker of DE.