Upgaze eyelid position allows differentiation between congenital and aponeurotic blepharoptosis according to the neurophysiology of eyelid retraction.

To differentiate between congenital and aponeurotic blepharoptosis, we investigated whether upgaze with stretching of the mechanoreceptor of Mueller muscle increases involuntary reflex contraction of the levator slow-twitch muscle fibers. In 50 cases each of unilateral congenital blepharoptosis and of asymmetric aponeurotic blepharoptosis, the mean increases by upgaze in the upper eyelid margin to the line between the medial and lateral canthi as upper eyelid retraction distance (UERD) of the ptotic eyelid 0.4 mm and 2.9 mm, respectively. These were significantly smaller and significantly larger than those of the corresponding nonptotic eyelid, 2.0 mm and 2.3 mm, respectively.Worsening of ptosis on upgaze is common in congenital ptosis and is an abnormal differentiating sign, lacking the involuntary reflex contraction. Improvement of ptosis on upgaze is common in aponeurotic blepharoptosis and likely represents a normal physiological process, restoring the involuntary reflex contraction.