Impact of unilateral trigeminal neuralgia on bilateral ocular surface alterations

To evaluate ocular surface alterations in both eyes of patients with unilateral trigeminal neuralgia (TN) compared with controls.

Corneal nerves mainly originate from the trigeminal nerve, and neurosensory abnormalities are important factors in ocular surface alterations and dry eye etiopathogenesis.

Twenty-four patients with idiopathic unilateral TN and 24 healthy controls with similar sex and age distributions were included in this cross-sectional study conducted from February 15 to September 15, 2021. The eyes on the affected sides of the patients with TN were treated as Group 1, their contralateral eyes as Group 2, and the right eyes of the controls as Group 3. All participants were evaluated for tear film and ocular surface using the Schirmer 1 test, tear breakup time (TBUT), Ocular Surface Disease Index (OSDI) score, and conjunctival impression cytology grading.

The mean (SD) ages of the patients with TN (17 of 24 females, 70.8%) and controls (15 of 24 females, 62.5%) were 49.7 (11.7) and 48.5 (9. 6) years, respectively. The median [25th, 75th percentile] Schirmer 1 test results in Groups 1, 2, and 3 were 5.0 [4.0, 14.0], 7.0 [3.2, 11.7], and 10.0 [6.0, 15.7] mm, respectively, with no statistically significant differences between Groups 1 and 2 (p = 0.697), Groups 1 and 3 (p = 0.133), or Groups 2 and 3 (p = 0.129). The median TBUT scores in Groups 1, 2, and 3 were 7.0 [5.0, 10.0], 8.0 [5.2, 10.0], and 12.5 [8.0, 13.0] s, respectively, showing reduced times for both Groups 1 and 2 versus Group 3 (median difference = -3.0 [95% CI: -5.0, -1.0], p = 0.001, and median difference = -3.0 [95% CI: -5.0, -2.0], p = 0.001, respectively). Conjunctival impression cytology grades were significantly higher in Groups 1 and 2 versus Group 3 (median difference = 2.0 [95% CI: 1.0, 2.0], p < 0.001, and median difference = 1.0 [95% CI: 1.0, 2.0], p < 0.001, respectively). The median OSDI score in TN patients (30.2 [25.0, 34.9]) was significantly higher than in the controls (8.3 [0.0, 18.7]), with a median difference of 20.8 (95% CI: 14.7, 27.1), p < 0.001.

Even if pain is unilateral in patients with TN, there are significant abnormalities in conjunctival cytology and tear functions in both eyes. There seem to be various pathophysiological mechanisms of TN that affect the bilateral ocular surface and lead to significant alterations.