Objective The aim of the study is to compare performance and ease-of-use (EOU) of optic disk assessment using a smartphone direct ophthalmoscope attachment (D-EYE) to the gold standard direct ophthalmoscope (DO). Design The type of study involved is prospective, randomized, crossover, and educational trial. Participants The participants involved were first year medical students inexperienced in ophthalmoscopy. Methods Optic disks of standardized and volunteer patients were examined using the D-EYE and a conventional DO. Optic disk identification, EOU ratings of the devices, self-reported confidence level in their examination with the devices, and estimation of vertical cup-to-disk ratio (VCDR) were compared. Analyses included Chi-square tests, independent samples t -tests, correlations, and multivariable linear regression. Results Forty-four medical students voluntarily participated in the study. Students using the DO required more attempts (3.57 vs. 2.69, p = 0.010) and time (197.00 vs. 168.02 seconds, p = 0.043) to match the patient's fundus to the correct photograph. Overall EOU between the devices (6.40 vs. 4.79, p < 0.001) and overall confidence in examination (5.65 vs. 4.49, p = 0.003) were greater when using the D-EYE. There were no statistically significant differences in accuracy of VCDR estimations between the two ophthalmoscopes. Conclusion Smartphone ophthalmoscopy could offer additional learning opportunities in medical education and may be considered in clinical practice by non-specialist physicians given its greater EOU and increased success in visualizing the optic disk., Competing Interests: Conflict of Interest R.C. reports grants from Physicians' Services Incorporated Grant, during the conduct of the study; D.L. reports grants from Physician's Services Incorporated Grant, during the conduct of the study; I.I. reports grants from Physicians' Services Incorporated Grant, during the conduct of the study; .J.K. reports grants from Physician's Services Incorporated Grant, during the conduct of the study; S.B. reports grants from Physician Services Incorporated, during the conduct of the study; W.H. reports grants from Physician's Services Incorporated Grant, during the conduct of the study; M.X. reports grants from Physicians' Services Incorporated Grant, during the conduct of the study., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. ( https://creativecommons.org/licenses/by-nc-nd/4.0/ ).)