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The purpose of this study was to validate the accuracy of marginal reflex distance 1 (MRD1) measurements obtained by the Volk Eye Check system, a modified smartphone that measures MRD1 automatically, relative to clinical and digital measurements.In this prospective observational study of adults with normal eyelids and ptosis, MRD1 was measured clinically, digitally, and automatically with the Volk device. Eyes were divided into successful versus unsuccessful Volk trial groups; successful eyes were then subdivided into control and ptosis subgroups. The primary outcome measures were mean MRD1 obtained by the 3 modalities. Secondary outcome measures included the success rate of the device and the prevalence of ptosis within the successful and unsuccessful groups.In the overall sample of 88 eyes, clinical and digital MRD1 were not significantly different. Among eyes with successful Volk trials, significant differences in MRD1 measured by the 3 modalities were as follows: in the successful group, Volk MRD1 (3.05 mm) was significantly (p < 0.01) higher than digital MRD1 (2.68 mm); in the ptosis subgroup, Volk MRD1 (2.47 mm) was significantly higher than clinical (2.05 mm; p < 0.05) and digital MRD1 (1.91 mm; p < 0.01). Eyes in the successful group (66% of attempted collections) demonstrated significantly higher MRD1 (mean difference, 1.21 mm; p < 0.01) and were significantly less likely to demonstrate ptosis (2.7×; p < 0.05) than those in the unsuccessful group.The Volk device measures MRD1 well in normal patients but overestimates MRD1 in patients with ptosis. It may be most appropriate in assessing patients with normal or elevated eyelid position. Clinical and digital MRD1 measurements were not different than each other.