Purpose: To study the hypothesis that in normal patients, changes in eyelid elasticity may occur asymmetrically and in relation to the side on which the individual sleeps. Design: Prospective, consecutive, single-center study within a large, tertiary-referral ophthalmology department within a university hospital. Methods: This prospective study was carried out consecutively on 262 normal patients. The 3 inclusion criteria were 1) age ?55 years, 2) absence of facial nerve palsy, and 3) absence of eyelid trauma or surgery. Immediately before the ocular plastic surgeon assessed the patient, each patient was questioned in a separate consulting room by the attending orthoptist as to his or her customary side of sleeping. After detailed explanation, the "historymasked" ocular plastic surgeon then assessed the patient's upper eyelid laxity, the main outcome measurement. This was performed by asking the seated patient to look down and then gently grasping the upper eyelids close to the eyelid margin, just medial to the lateral commissure. The ocular plastic surgeon, with thumbs pronated, simultaneously distracted both upper eyelids superiorly, laterally, and anteriorly. The measured separation of the upper eyelid from the globe conjunctiva was obtained using calipers. Eyelid laxity grading was designated as grade 1: 0 to 1.9 mm; grade 2: 2.0 to 3.9 mm; grade 3: 4 to 9 mm; and grade 4: floppy. Results: Two hundred sixty-two patients (58% females) who consecutively satisfied the selection criteria were evaluated, of which 70.22% (183/262) patients had significantly greater laxity of the upper eyelid that corresponded to the side on which they customarily slept. An unpaired t test used to compare the eyelid laxity between the sleeping side and nonsleeping side was statistically significant (p < 0.001). Conclusion: Normal patients demonstrate a correlation between the side on which they historically or customarily sleep and the laxity of their ipsilateral upper eyelid.