Introducing a new parameter for the assessment of the tear film lipid layer.

PURPOSE The differential diagnosis of dry eye syndrome is still a challenging task. The purpose of this study was to understand the relationship between a novel, objective clinical parameter, the "corrected lipid layer stabilization time," and commonly performed clinical tests for dry eye patients. METHODS Data were obtained from a prospective clinical study with 59 patients of different subjective severity, as determined with the Ocular Surface Disease Index (OSDI). The dynamics of the tear film lipid layer were made visible through a white light source and were stored digitally. Because the distance between the upper and lower eyelid affects the lipid layer dynamics and varies significantly between subjects, the distance of the eyelids was determined and used to correct the lipid layer stabilization time. The resulting parameter was compared with common clinical procedures. RESULTS The corrected lipid layer stabilization time has a highly significant correlation with tear film breakup time (Spearman r = -0.485, P < 0.01), Schirmer test without anesthesia (r = -0.431, P < 0.01) and with the Ocular Surface Disease Index (r = 0.498, P < 0.01). It also correlates with the lissamine green staining score (r = 0.379, P < 0.05), but shows no correlation with the osmolarity of the tear film. Without the correction for the eyelid opening, the correlations decrease considerably. CONCLUSIONS These data suggest that the diagnostic value of the lipid layer stabilization time for the assessment of the severity of dry eye syndrome increases considerably when it is corrected by the distance of the eyelids.