The effect of unilateral corneal anesthesia on the Schirmer test

Unilateral corneal anesthesia (or hyperesthesia) caused by trigeminal nerve disease has an unknown effect on the Schirmer test. Using topical anesthesia, we found that unilateral corneal anesthesia reduces tearing bilaterally, with a greater decrease on the anesthetized side. Clinicians should be aware that trigeminal nerve deficit may alter Schirmer test results, and use bilateral topical corneal anesthesia or alternative methods to stimulate tearing in these cases.