Glasses, also known as eyeglasses or spectacles, are devices consisting of glass or hard plastic lenses mounted in a frame that holds them in front of a person’s eyes, typically using a bridge over the nose and arms which rest over the ears.

Glasses are typically used for vision correction, such as with reading glasses and glasses used for nearsightedness. Safety glasses provide eye protection against flying debris for construction workers or lab technicians; these glasses may have protection for the sides of the eyes as well as in the lenses. Some types of safety glasses are used to protect against visible and near-visible light or radiation.

Corrective lenses are used to correct refractive errors by bending the light entering the eye in order to alleviate the effects of conditions such as nearsightedness, farsightedness or astigmatism.

The ability of one’s eyes to accommodate their focus to near and distant focus alters over time.

Also, few people have eyes that show exactly equal refractive characteristics; one may need a “stronger”, lens than the other. A common condition in people over forty years old is presbyopia, which is caused by the eye’s crystalline lens losing elasticity, progressively reducing the ability of the lens to accommodate (i.e. to focus on objects close to the eye). Corrective lenses, to bring the image back into focus on the retina, are made to conform to the prescription of an ophthalmologist or optometrist.

A lensmeter can be used to verify the specifications of an existing pair of glasses. Corrective eyeglasses can significantly improve the life quality of the wearer. Not only do they enhance the wearer’s visual experience, but can also reduce problems that result from eye strain, such as headaches or squinting.