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Tear production after vestibular schwannoma surgery and intermediate nerve function. OBJECTIVE: To evaluate the function of the intermediate nerve, the authors objectively quantified tear production before and after vestibular schwannoma (VS) surgery. METHODS: This prospective cohort study comprised 111 patients who underwent resection of unilateral VS. Tear production was objectively assessed in both eyes in millimeters using the Schirmer test. The difference between tear production of the eye on the nontumor side and that of the tumor side was assessed, before and after surgery. Sixty randomly selected patients had a second postoperative Schirmer test to assess change in tear production over time. The postoperative use of eye drops to treat dry eye was evaluated. Tear production was correlated with anterior-posterior tumor size, extent of resection, and facial nerve motor function (House-Brackmann grade) at the time of the Schirmer test with univariate linear regression. RESULTS: The mean ± SD preoperative difference in tear production between the nontumor side and the tumor side eye was 0 ± 9.0 mm. This increased significantly to 8 ± 13.7 mm in the direct postoperative phase (p < 0.001) and remained nearly constant at a mean of 8.0 (SD 4.9) months after surgery, reaching 9 ± 12.2 mm. The postoperative difference in tear production between eyes was significantly correlated to preoperative tumor size (p = 0.039) but not to facial nerve motor function (p = 0.213) nor extent of surgery (p = 0.325). Postoperatively, eye lubricants were used by 74 (67%) patients. The tear production of the eye on the tumor side was significantly lower in patients using eye lubricants (6.6 ± 7.2 mm) compared to patients who did not (10.8 ± 12.2 mm) (p = 0.024). CONCLUSIONS: Tear production after VS resection was affected in the majority of patients. The resulting differences between eyes were not straightforward. The larger the tumor, the greater the postoperative difference in tear production between the eyes. Change in tear production is inherently linked to VS surgery and may require repeated use of eye lubricants, which is cumbersome; this is why patients should be informed about the potential for decreased tear production postoperatively.