Contact lenses can be classified in many different manners. Contact lenses can be separated by their primary function, material, wear schedule and replacement schedule.
Corrective contact lenses are designed to improve vision, most commonly by correcting refractive error. This is done by directly focusing the light so that it enters the eye with the proper power for clear vision. There has been renewed interest in orthokeratology, the correction of myopia by deliberate overnight flattening of the corneal epithelium, leaving the eye without a refractive error during the day.
A spherical contact lens bends light evenly in every direction. They are typically used to correct myopia and hyperopia. A toric contact lens has a different focusing power horizontally than it does vertically and as a result can correct for astigmatism. Some spherical rigid lenses can also correct for astigmatism.