Reflex lacrimation in patients with glaucoma and healthy control subjects by fluorophotometry

Steady state tear turnover (TTO), defined as TTO under normal physiological conditions, is significantly lower in patients with untreated glaucoma than in healthy control subjects. To obtain more information on the effect of glaucoma on lacrimation, a method for quantification of reflex lacrimation was developed and applied to patients with glaucoma or ocular hypertension and healthy control subjects.

After instillation of 2 microl of fluorescein (2%), the decay of fluorescein concentration in tears was measured by fluorophotometry over 10 minutes to determine steady state TTO. Then, reflex lacrimation was induced by stimulating the trigeminal nerve with ethanol vapor via the nostrils. Thereafter, the decay of fluorescein and corresponding steady state TTO were determined again. An index of reflex lacrimation, defined as the percentage decrease in fluorescein concentration as a result of stimulation, was calculated by forward and backward extrapolation of the steady state decay of the fluorescein concentration in tears, relative to the time of stimulation.

The index of reflex lacrimation was determined in 16 patients with newly discovered but not yet treated glaucoma, 16 patients with untreated ocular hypertension, and 16 healthy control subjects. The values did not differ between groups (mean +/- SD, 67.0%+/-17.7%, 63.5%+/-21.3%, and 70.4%+/-19.6%, respectively; ANOVA, P>0.25). Surprisingly, the steady state TTO after stimulation was lower than that before stimulation in each group (ratio, 0.62+/-0.46; paired t-test, P<0.04).

The method developed is appropriate for the quantification of reflex lacrimation. Reflex lacrimation is not influenced significantly by glaucoma or ocular hypertension. The decreased steady state TTO after reflex stimulation may be caused by exhaustion of the lacrimal glands after excessive reflex lacrimation, indicating that normal lacrimation probably also contains reflex tears.