The chinchilla eye: morphologic observations, echobiometric findings and reference values for selected ophthalmic diagnostic tests

To carry out a descriptive investigation into the most relevant morphological features of the chinchilla eye and bony orbit, as well as to perform selected ophthalmic diagnostic tests with the aim of establishing normal anatomic and physiologic references for this species.

A total of 57 healthy, chinchillas were used to test most of the parameters in this investigation. Besides morphologic observations of the globe and adnexa, selected ocular tests and parameters were investigated, including blink frequency, palpebral fissure length (PFL), Schirmer tear test (STT), esthesiometry, intraocular pressure (IOP), central corneal thickness (CCT), B-mode echobiometric measurements of the globe and culture of the normal conjunctival bacterial microbiota. Morphologic observations were made using six formalin-fixed globes and four macerated skulls.

Normal parameters found for selected ocular diagnostic tests were: blink frequency: 2.6 ± 0.84 blinks per 10 min; STT: 1.07 ± 0.54 mm; esthesiometry: 1.24 ± 0.46 cm; IOP: 17.71 ± 4.17 mmHg; CCT: 0.34 ± 0.03 mm; PFL: 1.44 ± 0.11 cm; anterior chamber depth: 2.01 ± 0.2 mm; axial lens thickness: 5.49 ± 0.43 mm; vitreous chamber depth (internal): 3.69 ± 0.52 mm; axial globe length: 1.14 ± 0.07 cm. The most frequent bacteria isolated from the conjunctiva were Streptococcus sp. (27.45%), Staphylococcus aureus (23.52%) and coagulase-negative Staphylococcus (19.60%). No statistically significant differences between left or right eyes or genders were found for any of the results. Reference data and morphologic observations obtained in this investigation will help veterinary ophthalmologists to recognize unique morphological features and more accurately diagnose ocular diseases in the chinchilla, an animal already being used as a biological model for ophthalmic studies.