1. What types of contact lenses exist?
Contact lenses can be classified by the nature of the material from which they are made, by their wearing schedule, by their purpose, or by their design.
Nature of the Material
1. Hard
2. Rigid gas permeable
2. Hydrogel
3. Hybrid
Wear and Replacement Schedule
1. Daily wear (removed daily and not utilized during sleep).
2. Continuous or extended wear (utilized both during waking and sleep hours for a specified number of days continuously). These lenses are generally made from high water content or high DK material.
3. Flexible wear (utilized during the day and occasionally overnight).
4. Traditional/conventional: replaced annually.
5. Disposable or planned replacement (discarded after a specifiedwearing period defined by manufacturer’s guidelines). Can be dis- posed of daily, weekly, biweekly, monthly, bimonthly, or quarterly.
6. Occasional (indicated for occasional use, e.g., athletic or social activ-ities).
Purpose
1. Therapeutic (for protection or healing of the cornea).
2. Cosmetic (for modification of the color of the eye or to improve the appearance of a disfigured eye).
3. Optical (for correction of refractive errors and/or regularization of the corneal surface).
Design
1. Spherical (having anterior and posterior spherical surfaces).
2. Aspheric (different radii of curvature in the center and periphery,simulating the structure of the cornea).
3. Toric (two principal meridians have different radii of curvature; this may be the anterior or posterior surfaces of the lens or both). Used
to correct astigmatism.
● Front surface toric lenses
● Back surface toric lenses
● Bitoric lenses (when both the anterior and posterior surfaces are toric)
4. Bifocal
5. Progressive
6. Multicurve (two or more posterior curves).
7. Reverse curve (a central posterior curve, which is flatter, utilized primarily for fitting after refractive surgery for myopia or orthok-eratology)
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Contact lens