Rigid lenses are usually replaced every one or two years because they are more durable than soft lenses but they are still available to correct myopia, hyperopia, astigmatism and presbyopia in the same way as soft lenses.
Rigid lenses are not used for overnight wear except in one very particular situation – orthokeratology. A specially designed rigid lens is used while sleeping to force the cornea into an ‘abnormal’ shape that corrects vision during the day. This only works for a very small range of myopic prescriptions and the effect wears off during the day so the lens needs to be used every night.
Specially shaped rigid lenses can correct unusual eye shapes and can give better visual acuity than spectacles in such cases. An example of this would be where a patient suffers from keratoconus.
Haptic lenses are large plastic shells that cover a large portion of the front of the eye and contain a lens. This is usually only used in medical conditions.Back