Abstract:

Objective To compare the histological staining performance of four various tissue fixatives, including a self-developed fixative, for preparing paraffin sections of rat eyeball tissue. Methods Twenty 5-week-old male Sprague-Dawley (SD) rats were randomly divided into 4 groups (n=5 per group). After anesthesia by intraperitoneal injection of Zoletil? 50 at a dose of 45 mg/kg body weight, the rats were euthanized by exsanguination via the abdominal aorta. Bilateral eyeballs were carefully extracted intact and fixed for 72 h in 10% formaldehyde fixative, glutaraldehyde-formaldehyde mixed fixative, Davidson's fixative, and self-developed fixative, respectively. After fixation, the eyeballs were longitudinally sectioned along the optic nerve, with the portions containing the optic nerve preserved. The tissues were then dehydrated, embedded, and sectioned. Following hematoxylin and eosin (HE) staining, histological staining quality was compared among ocular structures including the cornea, lens, and retina. Results The overall appearance of rat eyeballs showed marked shrinkage in the 10% formaldehyde group and the glutaraldehyde-formaldehyde group, whereas the eye morphology remained round and intact in the modified Davidson's fixative group and self-developed fixative group. The corneal stroma exhibited obvious rupture, and the cells were arranged in folded arrangement in the modified Davidson's fixative group, 10% formaldehyde group, and self-developed fixative group. In contrast, the corneal cells in the glutaraldehyde-formaldehyde group were neatly arranged, showing no rupture or folding, and exhibited clear staining, indicating the highest quality of corneal sectioning among all groups. In the 10% formaldehyde group, cracks were observed in the equatorial and cortical regions of the lens, but the lens fiber structure remained intact. The lenses in the modified Davidson's fixative group showed extensive rupture and detachment. The glutaraldehyde-formaldehyde group displayed only slight cracks at the equator. In the self-developed fixative group, mild red folding was limited to the peripheral lens region, with the remaining structures intact and unbroken. These findings indicated that the glutaraldehyde-formaldehyde and self-developed fixative groups achieved the best lens sectioning quality. The retina was severely detached from the choroid/sclera layer, with extensive rupture of each cellular layer in the 10% formaldehyde fixative group. In the glutaraldehyde-formaldehyde group, partial detachment between the retina and choroid/sclera was observed. The outer plexiform layer and nerve fiber layer showed separation with edema, while the cells in all layers were neatly arranged. In both the Davidson's fixative and the self-developed fixative groups, the retina remained intact without rupture, and no structural separation was observed in any layer. Both demonstrated advantages in preserving the integrity and orderly arrangement of all retinal layers; however, the self-developed fixative group exhibited greater contrast. Conclusion The choice of fixative significantly affects the morphological preservation of various structures in the rat eye. The self-developed fixative demonstrates the best overall performance in maintaining overall eye morphology, the structural integrity of the lens, and retinal adhesion. For studies focusing solely on the corneal structure, the glutaraldehyde-formaldehyde mixed fixative is recommended. The 10% formaldehyde fixative exhibits unsatisfactory fixation effects for all the aforementioned ocular structures and is not recommended for detailed morphological studies of eyeball tissues.

Key words: Eyeball tissue section, Fixative, Cornea, Lens, Retina, Rats