A descriptive ultrasonographic and histological evaluation of the eyes of humpback whales (Megaptera novaeangliae).

Objective: To describe morphological features of Megaptera novaeangliae eyes using ultrasonography and histology.

Animal studied: A total of 21 globes from 19 M. novaeangliae were used for the study, including two animals with bilateral assessment. Nine stranded animals were found alive, 10 dead.

Procedures: Carcasses were classified according to decomposition state. Globes were assessed ultrasonographically, biometric measurements were taken and then the tissues were sectioned for histological analysis.

Results: Seventeen carcasses were classified as decomposition code 2 and two as code 3. Fifteen animals were calves, three juveniles and one adult, twelve males, and five females. The cornea was thinner in the center of the eye and thicker at the periphery. The lens had an oval shape. Fourteen animals showed a structure in the vitreous body which looked triangular and filamentous by ultrasonography and, histologically, originated in the central part of the optic nerve and extended to the posterior region of the lens, composed of connective tissue. The most common abnormalities found by ultrasonograph were retinal detachment (n = 13) and displacement of the lens into the vitreous (n = 4), along with alterations suggestive of hemorrhage, fibrin deposits, and increased echogenicity in the optic nerve (n = 2).

Conclusions: An intraocular structure not previously described in cetaceans was found in this investigation; its function remains unknown. Circulatory changes that were evident in the histopathological analysis may be due to the stranding process and raise the need to consider ophthalmic examinations before reintroducing stranded mysticetes.