The relationship between dry eye symptoms and lipid layer thickness.

Purpose: (1) To investigate the relationship between dry eye symptoms and lipid layer thickness (LLT) in patients presenting for routine eye examination and (2) to consider the practicality of interferometry in a clinical practice.

Methods: Patients presenting consecutively for routine eye examinations were recruited (n = 137, age range = 18-60 years, mean = 41.7 +/- 15.5 years, 102 females and 35 males). Patients were required to complete the Standard Patient Evaluation of Eye Dryness (SPEED) questionnaire after which their LLT was evaluated using a new interferometer (Ocular Surface Interferometer). Patients were assigned to 1 of 3 symptom categories: no symptoms (SPEED = 0), mild to moderate symptoms (SPEED = 1-9), and severe symptoms (SPEED > or = 10). Categorical analysis (contingency table) and linear regression were performed on the data.

Results: For patients with severe dry eye symptoms, 74% had an LLT < or =60 nm. Conversely, 72% of patients with no dry eye symptoms had an LLT of > or =75 nm (contingency table, chi = 12.63, df = 2, p = 0.0018). Furthermore, a linear regression of LLT and SPEED score reveal a significant linear relationship (as LLT increases, SPEED score decreases; p = 0.0014).

Conclusions: (1) The data indicate that approximately 3 of 4 patients reporting severe symptoms have relatively thin lipid layers of 60 nm or less, whereas approximately 3 of 4 patients without symptoms have relatively thick lipid layers of 75 nm or more. Thus, the presence of dry eye symptoms significantly increases the likelihood of a relatively thin lipid layer. LLT seems to correlate better to symptoms, especially severe symptoms, than other reported correlations with objective clinical tests for dry eye disease. (2) Interferometry has the potential to be a practical and useful addition to clinical practice.