BACKGROUND:Both external levator resection (ELR) and Müller's muscle-conjunctival resection (MMCR) are procedures well known to improve marginal reflex distance (MRD1) in patients with ptosis. This study aims to understand differential post-operative changes in eyelid contour for MMCR and ELR surgery. METHODS:In this cross-sectional cohort study, patients affected by involutional ptosis were randomized into two groups: those who underwent ELR or MMCR surgery. Pre-operative and late post-operative photographs were obtained. Digital analysis of the lid contour was performed by measuring the vertical distance from a line intersecting the center of the pupil to the eyelid margin at 10 positions at 2 mm intervals. Mean distance at each position was compared pre- and post-operatively between the groups. RESULTS:The final sample included 60 eyes from 39 patients, 30 eyes per group. At each time point there was significant variation in height across the eyelid (p < 0.05). A significant (p < 0.05) group difference in vertical height was noted only at the 2 and 4 mm temporal positions in the post-operative analysis, with the ELR group being slightly higher. There were no significant differences in MRD1, pre- or post-operatively, between the ELR and MMCR groups. CONCLUSIONS:Both ELR and MMCR are effective at elevating the eyelid in multiple positions across the length of the eyelid. Although they do not produce significantly different MRD1 results, ELR was associated with a greater eyelid height at the 2 and 4 mm temporal positions.