Tear aqueous production rate between symptomatic and asymptomatic soft contact lens wearers

This study demonstrates that asymptomatic habitual soft contact lens (CL) wearers have lower tear aqueous production (TAP) rates compared with non-lens wearers, while symptomatic wearers have higher rates than those of asymptomatic wearers. These findings suggest that the impact of soft CL on TAP rate may differ between symptomatic and asymptomatic soft CL wearers.

To understand the role of TAP rate in symptomatic and asymptomatic soft CL wearers, the TAP rate was measured for four groups: symptomatic CL wearers who remain symptomatic after CL removal (dry eye); symptomatic CL wearers who become asymptomatic after CL removal (contact lens-induced dry eye); asymptomatic CL wearers; asymptomatic non-CL wearers.

Subjects were grouped based on responses to the Berkeley Dry Eye Flow Chart. TAP rate was measured by the modified (sheathed) Schirmer strip test. A recent study showed that TAP rate reached a peak between 12:00 and 14:00 hours; therefore, visit times were designated as "before peak," "peak," and "after peak." The between-group difference in TAP rate was modeled as a fixed effect in a linear mixed model, adjusting for random effects (between-eye correlation, repeated visits) and confounding factors (demographics, visit time, and ocular surface diagnoses).

Data from 115 subjects were analyzed. The grand mean (standard deviation) TAP rate was 1.2 (0.92) µL/min. The mean TAP rate of asymptomatic CL wearers was the lowest among the study groups. Compared with asymptomatic CL wearers, the adjusted mean difference (95% confidence interval) in the TAP rate for asymptomatic non-CL wearers, contact lens-induced dry eye, and dry eye groups were 0.49 (0.09~0.89; p=0.02), 0.44 (0.02~0.86; p=0.04), and 0.56 (0.05~1.07; p=0.03) µL/min higher during the "before peak" period (i.e., in the morning), respectively.

In the morning, asymptomatic CL wearers show lower TAP rates than asymptomatic non-CL wearers, suggesting that habitual CL wear may reduce TAP rate. Symptomatic CL wearers also have higher TAP rates compared to asymptomatic wearers. Further research is warranted to determine how TAP rate differs between the two symptomatic groups to advance our understanding of the interplay between soft CL wear and TAP rate and to shed additional insights into mechanisms for CL discomfort.