The capybara eye: clincial tests, anatomic and biometric features

Abstract

To carry out a descriptive investigation of the capybara (Hydrochaeris hydrochaeris) eye and to perform selected ophthalmic diagnostic tests with the aim of establishing normal physiological reference values for this species. A total of 22 healthy, capybaras were used to test most of the parameters in this investigation. Ages varied from 2 to 4 years of age. Selected diagnostic ocular tests were performed including Schirmer tear test, tonometry using an applanation tonometer (Tonopen), central corneal thickness using an ultrasonic pachymeter (Sonomed, Micropach, Model 200P +), axial globe length and culture of the normal conjunctival bacterial flora. Capybara's normal ocular features include: dorsal and ventral puncta, vestigial third eyelid, true cilia only at the upper eyelid margins. The bulbar conjunctiva is noticeably densely pigmented with a brown to bronze color. The capybara's pupil is oval in shape and vertical in position No tapetum lucidum is present in this species and the retinal blood vessels are almost absent. Results for selected ocular diagnostic tests investigated were: Intraocular pressure: 18.4 +/- 3.8 mmHg; Schirmer tear test: 14.9 +/- 5.1 mm/min; Central corneal thickness: 0.46 +/- 0.03 mm; Axial globe length: 22.20 +/- 1.71 mm. No statistically significant differences between ages or genders were found for any of the results. Corynebacterium sp., Micrococcus sp., Bacillus sp. and Staphylococcus sp. were isolated from healthy conjunctiva, suggesting they are normal constituents of the conjunctival flora of the capybara eye. The corneal epithelium of the capybara possesses a thin and discrete Bowman's layer. Results and parameters obtained in this investigation exposed unique anatomic features of the capybara eye and will help veterinary ophthalmologists to more accurately diagnose discrete or unusual pathological changes of the capybara eye. Furthermore, corneal thickness and axial length of the capybara are similar to that of human beings, revealing that the world's largest living rodent might be an excellent biological model for ophthalmic studies.