Poorer visual acuity—as opposed to worse contrast sensitivity—is the driver behind vision symptoms and complaints in dry eye, a study in Optometry and Vision Science reports. The researchers also found contrast sensitivity measurements were more sensitive to worse tear film stability measures—such as tear break-up time (TBUT) and obstructed meibomian glands—than standard visual acuity assessments.

These results substantiate the finding that even among patients with relatively good visual acuity (20/50 or better), worse visual acuity corresponded to worse scores on the Ocular Surface Disease Index (OSDI) in dry eye patients, investigators said. However, none of the dry eye signs measured in the study deleteriously impacted visual acuity, they added.

Although subtle visual acuity changes could be documented based on differences in the tear film debris and TBUT, the mean changes were small (approximately two letters) and not in the direction one would expect, the study noted.

The investigation used baseline data from participants in the Dry Eye Assessment and Management (DREAM) study. Researchers reviewed the results of the patients’ OSDI score, high-contrast logMAR visual acuity, contrast sensitivity, tear film debris, TBUT, corneal fluorescein staining, meibomian gland evaluation, conjunctival lissamine green staining and Schirmer test scores. The study also used generalized linear models including age, refractive error and cataract status to assess the association between visual acuity and contrast sensitivity with the OSDI score and each dry eye sign.

Other study highlights included:

• Worse visual acuity was associated with worse mean score on the OSDI vision subscale (39.4 for visual acuity 20/32 or worse vs. 32.4 for visual acuity 20/16 or better). The scores were not associated with contrast sensitivity.
• Severe meibomian gland obstruction and abnormal secretions were associated with worse mean log contrast sensitivity (1.48 for severe vs. 1.54 for not plugged, and 1.49 for obstructed vs. 1.57 for clear, respectively).
• Longer TBUT was associated with better mean log contrast sensitivity (1.57 for TBUT >5 seconds and 1.51 for TBUT ≤2 seconds).

Future studies that examine how specific ocular signs affect various measures of visual function would be helpful in elucidating these relationships and could in turn guide therapies, researchers said.