Ultrasonographic anatomy of the Asian elephant (Elephas maximus) eye.

Bilateral transpalpebral ultrasonography was performed on 53 captive Asian elephants (Elephas maximus) in order to describe the normal ultrasonographic appearance and measurements of the Asian elephant eye. Transpalpebral ultrasonography was performed using a portable ultrasound unit and a 4-7-MHz broadband curvilinear transducer on animals housed at seven institutions in the United Kingdom and in Sri Lanka. Both males and females were included in the study and ages ranged from 14 mo to 65 yr. Ultrasonic examinations were conducted on unsedated animals, without the use of topical or local anesthesia. The ultrasonographic appearance of the globe and intraocular structures of the Asian elephant eye is similar to that in other species. Biometry measurements recorded for adult (n=41) and juvenile (n=10) Asian elephants were: axial length, 3.44 +/- 0.21 cm and 3.18 +/- 0.19 cm (mean +/- SD); equatorial diameter, 3.88 +/- 0.32 cm and 3.60 +/- 0.24 cm; corneal thickness, 0.17 +/- 0.02 cm and 0.16 +/- 0.02 cm; anterior segment depth, 0.45 +/- 0.08 cm and 0.36 +/- 0.07 cm; lens diameter, 1.90 +/- 0.14 cm and 1.75 +/- 0.19 cm; lens depth, 1.01 +/- 0.12 cm and 0.94 +/- 0.10 cm, and posterior segment depth, 1.82 +/- 0.17 cm and 1.72 +/- 0.15 cm, respectively. Multiple linear regression analysis indicated a significant relationship between the explanatory variables (age, sex, and height) and the dependent variables (axial length, equatorial diameter, corneal thickness, anterior segment depth, lens diameter, and lens depth). The main finding of this statistical test was that the globe increases in size as the animal ages. Transpalpebral ultrasonography was found to be an effective and practical imaging modality in the evaluation of the Asian elephant eye, without the need for chemical restraint.