Anatomical Assessment of the Eye of the African Grasscutter (Thryonomys swinderianus)

Purpose: To determine the macroscopic and microscopic ocular morphological characteristics of the African grass-cutter

Materials and Methods: Ten male grasscutters of mean age 4.05 ± 1.44 months and mean weight 1.04 ± 0.56 kg were used for this study. Gross morphologic and light microscopic techniques were employed in the study of the eyes.

Results: Grossly, the eye exhibited typical characteristics of the mammalian eye with a mean eye weight and mean corneal diameter of 0.47 ± 0.14 g and 0.73 ± 0.07 cm, respectively. The horizontal corneal diameter was significantly greater (p < 0.05) than the vertical corneal diameter, and the ratio of mean corneal diameter to mean eye diameter (MCD:MED) was 0.80. The sclera and corneal stroma were dense fibrous connective tissues and had thicknesses of 105.3 ± 25.8 µm and 201.4 ± 91.3µm, respectively, while the corneal epithelium was stratified squamous epithelium and measured 50.1 ± 15.1µm. The choroid, ciliary stroma, and iridal stroma were pigmented connective tissues, while the retina was a multi-layered neuro-epithelial tissue with scanty ganglion cells and a retinal pigment epithelium that was pigmented throughout its length.

Conclusion: The high MCD:MED and scanty retinal ganglion cells observed are associated with nocturnal visual capability. However, the complete pigmentation of the retinal pigment epitheliumsuggest the absence of tapetum lucidum in this species. This could considerably lower its nocturnal visual capability and indicate a low reliance on vision for environmental perception. The biometrical measurements obtained have made data available for use in future ocular studies of the rodent.