The physiological assessment of the human tear film using confocal microscopy and its correlation with ocular pathology

Purpose: To observe the tear film with confocal microscopy and define parameters which correlate its appearance with tear physiology and disease process. Methods: We assigned a clinical classification to 45 patients based on their physiology: normal, dry eye, obstructive MGD and seborrheic MGD. Confocal microscopy was performed and the tear film was assessed using a non parametric scale we devised; lipid thickness (1 thin, 10 thick), linear pattern (1 linear, 10 nonlinear), debris (1 rare, 10 heavy), pattern stability (1 stable, 10 nonstable) and dry spots (1 few, 10 many). The data was analyzed for the correlation between the physiologic diagnosis and the assessment of the tear film appearance. We also correlated the tear film assessment with each physiologic parameter. Results: Significant correlations were obtained between the tear film appearance and physiologic variables. Linearity correlated well with osmolarity (p=0.48), Schirmer's (p=-0.40), tear volume (p=-0.30), tear flow(p=-0.30) and evaporation (p=0.26). Significant correlations were also observed between debris, stability and dryspot and the tear film appearance. Significant differences in the appearance of the tear film between the four clinical classification groups was observed and was consistent within the individual groups. Conclusion: Assessment of the tear film image using confocal microscopy reveals meaningful correlations between the appearance of the tear film, the clinical diagnosis and tear function parameters.