The measurement and definition of ptosis.

Measurements of 242 ptotic and normal eyelids were recorded clinically and compared with algebraically derived measurements from projected 35 mm photographs. Accuracy to 1.5 mm or better was obtained in 84% of clinical as compared with photographic measurements. The following definition is suggested: ptosis is present when the upper eyelid is less than 2 mm from midpupil. Reduction of the upper field of vision to 30 degrees or less is present in 97% of eyes with ptosis so defined. Asymmetric ptosis is present in the lower of the two upper eyelids when there is 2 mm or more asymmetry between the levels of the upper eyelids, even if both eyelids are 2 mm or more from midpupil. Although ptosis is best defined in terms of the midpupil to upper lid distance, the diagnosis of ptosis rests with the examining physician based on the clinical evaluation of the patient.