eye disorders
Contact Lenses
Rigid Corneal Contact Lenses
A rigid lens is able to revise the natural shape of the cornea into a new, better refracting surface than a soft lens and thus tends to provide more consistent improvement in refraction for people who have astigmatism or an irregular corneal surface. Older polymethyl methacrylate rigid contact lenses have been replaced by gas-permeable contact lenses (GPCLs) made of fluorocarbon and polymethyl methacrylate admixtures. GPCLs are 6.5 to 10 mm in diameter and cover part of the cornea, floating on the tear layer overlying it. Rigid contact lenses can improve vision in people with myopia, hyperopia, and astigmatism. Rigid contact lenses can also correct corneal irregularities, such as Keratoconus . In most cases, patients with keratoconus see better with rigid contact lenses than glasses. GPCLs can be designed to fit the eye exactly. For complete wearing comfort, they require an adaptation period, typically about 4 to 7 days. During this time, the wearer gradually increases the number of hours the lenses are worn each day. Importantly, no pain should occur at any time. Pain is a sign of an ill-fitting contact lens or corneal irritation. Wearers may have temporary (<2 hours) blurred vision (spectacle blur) when wearing eyeglasses after removing rigid contact lenses. 