Importance of the lipid layer in providing tear stability

Abstract

Previous tear film investigations on patients with rheumatoid arthritis (Craig et al., 1995) suggested that a poor meibomian lipid layer on the surface of the tears resulted in tear film instability and could allow increased evaporation of the tears. This, in turn, could raise the osmolality of the tears, causing ocular surface, damage which is visible with rose bengal staining. The study was conducted to determine the importance of this lipid layer in providing stability for the tears. Tear film appearance and stability were assessed in a masked fashion on 20 control subjects and compared to 40 test subjects in whom forced meibomian gland expression was carried out unilaterally, 10 min prior to tear film assessment. The appearance of the tear film was assessed by thin film interferometry (Keeler Tearscope®) and the time of the break-up of this image (non-invasive break-up time) measured to ±0.1 s. The modal tear film lipid layer pattern changed from a marble-like appearance to a coloured fringe pattern with meibomian gland expression (P < 0.001). Concurrently, tear film stability improved from a mean of 21.6 ± 11.5 s to 42.2 ± 21.2 (P < 0.001). Surprisingly, there were subtle changes in the contralateral eye of the test subjects. No change in modal lipid layer appearance was observed (P > 0.05) but stability had improved slightly to a mean of 30.8 ± 14.5 s (P = 0.011). Improvement of tear stability in normal eyes by addition of lipid to the tear film suggests that incorporation of lipomimetics in artificial tear supplements should help improve tear stability. This could perhaps prevent development of ocular surface damage, and consequently symptoms, in patients with rheumatoid arthritis and in other dry-eye patients.