Intraocular pressure reference intervals in eyes of clinically normal miniature donkeys (Equus africanus asinus).

PURPOSE: To determine intraocular pressure (IOP) reference intervals in eyes of healthy miniature donkeys (Equus africanus asinus) via rebound and applanation tonometry. METHODS: Complete ophthalmic and physical examinations were performed by board-certified veterinary ophthalmologists. Inclusion criteria for animals participating in this study were dictated by the American Society for Veterinary Clinical Pathology (ASVCP) reference interval guidelines. Intraocular pressure estimates (TonoVet® and TonoPen XL® ) were obtained in both eyes. Forty animals (San Angelo group) received intramuscular xylazine hydrochloride 10% and auriculopalpebral (AP) nerve blocks prior to obtaining measurements. Twenty-two animals (Austin group) received no sedation or AP block. Statistical analysis followed ASVCP reference interval guidelines. Analysis was performed using the software sas V9 (SAS Institute Inc., Cary, NC, USA). RESULTS: Fifty-seven (114 eyes) healthy miniature donkeys were included in this study. The mean IOP ± standard deviation (SD) was 25.75 ± 5.70 mm Hg for rebound tonometry with reference limits of 14.34 and 37.15. The mean IOP ± SD was 20.69 ± 5.06 mm Hg for applanation tonometry with reference limits of 12.82 and 33.38. No significant difference in IOP was found between the Austin and San Angelo groups (P = .34). A significant difference was noted between rebound and applanation IOP estimates (P < .0001) with rebound tonometric values being higher. CONCLUSIONS: Reference intervals for IOP's were established for this species. Intraocular pressure readings obtained by the rebound tonometer were significantly higher than with applanation. Sedation and AP block did not affect IOP estimates.