Atropine induces narrowing of the superior and inferior iridocorneal angle and ciliary cleft in normal horse eyes.

OBJECTIVE

To investigate the effects of atropine on the iridocorneal angle (ICA) and ciliary cleft (CC) of normal equine eyes using ultrasound biomicroscopy (UBM).

METHODS

12 normal adult horses underwent measurement of intraocular pressure (IOP), vertical and horizontal pupil diameter, and UBM of the superior, temporal, inferior, and nasal ICA/CC in both eyes. Measurements were repeated 2 hours following ophthalmic atropine 1% solution application. Measurements of the ICA and CC, including pectinate ligament distance (PLD), CC length (CCL), height of opening distance (HOD), CC area (CCA), and pectinate ligament angle (PLA) were performed.

RESULTS

Mean IOP significantly decreased following atropine administration (14.17 ± 2.34 mm Hg vs 12.67 ± 1.14 mm Hg). No significant differences in pre- or post-atropine ICA/CC measurements occurred nasally or temporally. Superiorly, a significant decrease in mean CCL (2.74 ± 0.52 mm vs 2.62 ± 0.43 mm), CCA (2.67 ± 0.72 mm2 vs 2.42 ± 0.66 mm2), HOD (1.15 ± 0.26 mm vs 1.06 ± 0.20 mm), and PLA (80.33 ± 7.02° vs 73.67 ± 8.50°) occurred. Inferiorly, a significant decrease in PLD (1.46 ± 0.23 mm vs 1.39 ± 0.17 mm), HOD (1.44 ± 0.24 mm vs 1.33 ± 0.15 mm), and PLA (73.18 ± 6.81° vs 69.98 ± 8.92°) occurred.

CONCLUSIONS

Atropine causes narrowing of the superior and inferior ICA and CC in normal horse eyes.

CLINICAL RELEVANCE: Due to its effect in narrowing the ICA and CC, atropine should be used with caution in horses with elevated intraocular pressure or glaucoma.