LAUSR

2011). The reference population is assumed to be the total underlying population from which the blepharoptosis cases derive (Survey by the CBS, 2010). This population is assumed to be so large, that the distribution of lens wearing in this population is a fixed distribution, not (or hardly) subjected to sampling variability. The odds ratio for soft contact lens wear is 11.7 (6.4–21.4; CI = 95) and for hard contact lenses 33.6 (18.9–59.8; CI = 95). The mechanism for the development of contact lens-induced blepharoptosis is likely recurrent manipulation and subsequent stretching of upper eyelid structures during contact lens insertion and removal, and increased rubbing of the upper eyelid over the ocular surface. The difference between hard and soft contact lenses in material, size, shape and thickness of the lens margin, could lead to variances in mechanical trauma of the levator aponeurosis. This could explain the difference in frequency of blepharoptosis in patients with hard versus soft contact lenses. According to our results, soft contact lens wear is a risk factor for the development of blepharoptosis. We founds a 12 times increased risk with soft contact lens wear. Hard contact lens wear already is a widely accepted risk factor for the development of blepharoptosis. Indeed, in our study hard contact lens wearers had a 34 times increased risk of developing blepharoptosis. References