Ocular morphology and morphometry of the great egret (Ardea alba): A comprehensive anatomical description.

Abstract

Ardea alba (Linnaeus, 1758) is widely distributed, yet knowledge of its ocular morphology remains limited. This study described the morphometry and morphology of the eyeball and its accessory glands in six specimens using radiography, morphometry, light and scanning electron microscopy, and 3D scanning. The eyeballs showed similar descriptive morphometric values in the right and left eyes, accounting for approximately 11.2% of head mass and 12.12% of total skull length. The eye was classified as the flat type, a morphology previously associated in the literature with diurnal birds, featuring a yellow iris and a circular pupil. The scleral ring consists of 14 bilateral type A ossicles associated with hyaline scleral cartilage. Histologically, the cornea showed a well-defined Bowman's membrane, and the retina had 10 distinct layers. The pleated type pecten emerged from the optic nerve and extended toward the vitreous body. The accessory glands were characterized as follows: the Harderian gland (type II) was the most developed; the lacrimal gland was "hockey-stick" shaped; and the nasal gland (salt gland) was supraorbital in location and pyramidal in appearance. These results provide a robust anatomical basis for comparative avian ophthalmology.