Objective: To investigate dow-dependent ultratructural changes in rat cornea after oral methylphenidate (Ritalin©) administration. Methods: This study was conducted in the Department of Anatomy, Gazi University Faculty of Medicine, Ankara, Turkey between March and May 2005, with a total of 27 female prepubertal Wistar albino rats, divided into 3 different dose groups (5mg/kg, 10 mg/kg, 20 mg/kg), and their control groups. They were treated orally with methylphenidate, and eye tissue was removed to process for electron microscopic studies. Results: We observed that all cells, and prominently basal cells of the corneal epithelium show dose-dependent degenerative changes such as apoptotic bodies, chromatin condensation, and ondulation in their nuclei and crystolysis of the mitochondrion. In the stroma, the most evideat finding was the increase of the collagen fiber. In addition to dose-dependent changes related to the apoptotic process, which is chromatin condensation in their nuclei, electron dense material accumulation, and pericellular edema in the cytoplasm were also seen. In the endothelial cell lines, disruption of the junctional complexes, vacuolization in the cell cytoplasms, and crystolysis of the mitochondrion's with rough endoplasmic reticulum cisternae activity were observed. Conclusion: Ritalin© is inducing an evident degeneration, especially in epithelium cells with increasing doses. Ultrastructural cell organelle composition degeneration with stromal fibrosis has a negative effect on cornea dehydration. In light of these findings, we believe that the Ritalin© treatment doses and to be kept to a minimum to maintain healthy cornea ultrastructure and related physiology.