Vision correction for refractory errors of the eye is done using lenses that are worn in front of the eye – either as spectacles or as contact lenses. Intraocular lenses are surgically implanted lenses to correct vision, usually done after cataract removal.
Refractory errors occur when the light that enters the eye is not focused on the retina at the back of the eye. The vision is therefore blurred or hazy. The refractory errors are caused by the differences in the shape or curvature of the lens and the cornea that cause the image of the objects to focus beyond or in front of the retina.
Refractory errors that are caused by too much or too little curving of the cornea or the lens and also the irregular curvature of cornea can be corrected with glasses or lenses that compensate the curvature.
Glasses or spectacles:
There are two main types of lenses that come with eye glasses – Single vision and multifocal glasses.
Single vision lenses:
Single vision glasses are used by people who have either myopia or hyperopia. Vision correction is done only for one distance.
Usually multifocal lenses come into use when there is a requirement of correction of already existing vision loss along with the vision loss occurring due to age.
Materials used for making lenses:
Ideally eyeglass lenses are made of glass, but currently, most of the lenses are made of plastic. Some other materials used for making lenses are:
Choice of protective coatings on lenses:
Opticians give you some choices of using protective coatings on your lenses.