Objective. This study aims to describe and characterize histopathologic changes in the retinal ganglion cell layer and optic nerve of adult albino rates secondary to the administration of the so called safe doses of Ethambutol.
Method. A total of four treatment groups were used with the following dosing regimens: placebo, 15 mg/kg, 25 mg/kg and 50 mg/kg. After four weeks of Ethambutol treatment, the rats were sacrificed and the globe and proximal 4 mm of optic nerve was harvested. Histopathologic examination of the optic nerve-pupil section and cross sections of the proximal 2mm of optic nerve was done.
Results. All groups given variable doses of ethambutol did not show any observable decrease in the retinal ganglion cell density; neither did any treatment group exhibit any observable optic nerve changes. However, changes in the outer nuclear layer (ONL) were noted as either a decrease in cell density, an increase in cell density or a complete absence of the ONL.
Conclusion. No observable changes in the retinal ganglion cell layer nor the proximal 2mm of the optic nerve were observed among the treatment groups. Changes in the ONL were noted among those rats given ethambutol at doses as low as 15mg/kg/day.