Aims To explore the relationship between the amount of resected Müller's muscle–conjunctiva (MMCR) and clinical outcome in patients undergoing upper eyelid ptosis surgery.

Methods 49 patients underwent 87 MMCR surgeries. The total areas of the specimen and of MM were measured in pixels.

Results The average percentage of muscle tissue in relation to total excised tissue was 21%. Intraoperative MMC tissue measurements and postoperative improvement in eyelid position (delta marginal reflex distance 1 (MRD₁)) were positively correlated (R=0.427, p=0.09). There was a weak correlation between total areas measured on the histological slides and the intraoperative MMCR values (R=0.3, p=0.057). Total histological areas did not correlate with the delta change in eyelid position or with the amount and percentage of resected muscle tissue and the extent of improvement in eyelid position (delta MRD₁) or final eyelid position (postoperative MRD₁).

Conclusions Post-MMCR improvement in eyelid positions did not correlate with the percentage of MM in the excised tissue. We believe that the mechanism responsible for surgical outcome is plication or scarring of the posterior lamella and not the amount of resected MM. More lift in eyelid position can be anticipated when more tissue is excised by MMCR, and not when more muscle is excised.