# Ocular Morphology and Clinical Ophthalmic Parameters of Nile Tilapia Oreochromis niloticus

## TL;DR

This study describes the eye structure and establishes clinical reference standards for Nile tilapia using various imaging techniques.

## Contribution

The study provides the first detailed ocular morphology and clinical ophthalmic reference data for Nile tilapia.

## Key findings

- Nile tilapia have a scleral ring composed of cartilaginous and bony ossicles.
- Clinical evaluations showed no ocular lesions with a mean intraocular pressure of 7.74 mmHg.
- Ultrasonography and computed tomography effectively assessed ocular and retrobulbar structures.

## Abstract

To describe the ocular morphological characteristics and establish clinical and ophthalmic reference standards for Nile tilapia.

Fresh carcasses were used for diaphanization, optical and electron microscopy, and computed tomography analyses. For clinical and ultrasonographic evaluations, 75 adult Nile tilapias of undetermined sex were examined.

Standard diaphanization, optical and electron microscopy, and computed tomography techniques were applied to fresh carcasses of Nile tilapia. Live fish were chemically restrained using propofol. Ophthalmic evaluations included slit‐lamp biomicroscopy, direct ophthalmoscopy, fluorescein staining, and rebound tonometry for intraocular pressure measurement. Ocular ultrasonographic measurements were obtained from both eyes of three individuals.

The diaphanization technique revealed a scleral ring composed of two cartilaginous ossicles (dorsal and ventral) connected by two bony ossicles (rostral and caudal). Microscopic analysis identified the fibrous tunic (comprising the cornea and sclera), the vascular tunic (including the iris and choroid), and the nervous tunic (represented by the retina). Clinical evaluation of Nile tilapia showed no ocular lesions, with a mean intraocular pressure of 7.74 mmHg. Ultrasonography effectively assessed intraocular and retrobulbar structures, while computed tomography enabled visualization and measurement of the eyeballs, lens, and vitreous chamber in sagittal, axial, and coronal planes.

The ocular structures of Nile tilapia, including the cornea, lens, retina, and iris, are similar to those observed in other teleost species. Clinical evaluation methods, such as ultrasonography, slit‐lamp biomicroscopy, and rebound tonometry appear to be reliable diagnostic methods in fish ophthalmology. The data presented in this study are novel for Nile tilapia.