Risk factors include the following: Family history of keratoconus An atopic disorder Vigorous eye rubbing Lax eyelids Certain connective tissue disorders (eg, Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfecta) Down syndrome Congenital disorders with poor vision (eg, Leber congenital optic neuropathy, retinopathy of prematurity, aniridia) Obstructive sleep apnea The distorted cone shape of the cornea causes major changes in the refractive characteristics of the cornea (irregular astigmatism) that cannot be fully corrected with glasses.