INTRODUCTION-AIM: To examine the ocular effects of methylphenidate used in children and adolescents diagnosed with attention-deficit hyperactivity disorder (ADHD). METHOD: Children diagnosed with ADHD and healthy control children were included in the study. The cases were divided into three groups-those with attention-deficit and hyperactivity and receiving methylphenidate therapy (Group 1), newly diagnosed cases not using medication (Group 2), and healthy, control group children (Group 3), and the results obtained were compared between them. The morphology and numbers of corneal endothelial cells, corneal thickness, choroidal thickness (CT), retinal thickness (RT), the ganglion cell layer (GCL), and retina nerve fiber layer were evaluated. RESULTS: Thirty children diagnosed with ADHD and receiving methylphenidate therapy for at least one year (Group 1), 32 children newly diagnosed with ADHD and not started on medication (Group 2), and a control group of 35 healthy children (Group 3) were included in the study. Mean ages were 10.53 ± 2.78 years in Group 1, 9.21 ± 1.85 in Group 2, and 11.03 ± 3.01 in Group 3. No statistically significant differences were observed among the three groups in terms of age, visual acuity, or refraction values (p >
0.05). However, significant differences were determined in endothelial cell counts and hexagonality values between groups 1 and 2 (p = 0.041 and p = 0.031, respectively). No significant difference was observed among the three groups in terms of central CT, central RT, or mean RNFL values (p >
0.05). However, GCL values differed between groups 1 and 2 and between groups 2 and 3 (p = 0.0001 and p = 0.02, respectively), but no significant difference was observed between groups 1 and 3 (p = 0.551). CONCLUSION: Corneal endothelial counts were lower in the children diagnosed with ADHD and receiving methylphenidate therapy than in those not receiving treatment and the control group. In addition, GCL measurements were lower in the children diagnosed with ADHD and not using medication compared to those using methylphenidate and the control group.