Purpose of the Study: The purpose of the study was to determine the agreement between smartphone ophthalmoscopy and slit-lamp indirect biomicroscopy when assessing vertical cup-to-disc ratios (VCDRs). Materials and Methods: This was a clinical-based, prospective, comparative instrument study performed in 110 patients with ocular hypertension (OH) or primary open angle glaucoma (POAG). Patients underwent estimation of VCDR by undilated smartphone ophthalmoscopy and slit-lamp biomicroscopy by 2 masked glaucoma specialists. Results: The differences between the mean VCDR estimations obtained by each techniques were not statistically significant. Overall exact agreement between the 2 modalities was found in 21 of 29 eyes (72.4%; simple k=0.63, confidence interval, 0.52-0.73, P