Ever wonder how glasses work to correct your vision? In a person with uncorrected vision, their cornea and lens refract (bend) light that enters the eye, to focus a sharp, clear image on the retina. Now if your eyes are not shaped properly (spherically) and are either too short or too long, your point of focus will not be on the correct spot within the eye, causing certain images, objects and/or distances to become blurry. These types of visual imperfections can be corrected with a custom built lens that compensates for any errors in the shape of your eyes. There are three different shapes for these lenses; cylindrical, convex and concave.
The amount of corrective power that your lenses need to correct your vision is dependent upon your specific vision problem and the prescription of correction your optometrist prescribes. When your optometrist tests your eyes, they are able to determine what prescription you require. This prescription then tells your optician what type of lenses and correction you need. The higher the numbers the stronger the prescription. The thickness of your lens can also vary depending on whether you have slightly or extremely myopic (nearsighted).
The different shapes correct different issues. Concave lenses correct nearsightedness, convex corrects farsightedness and cylindrical usually corrects for astigmatism. Glasses can also be made out of different materials. Glass lenses can be more scratch resistant; however they can sit rather heavy on your face. High-index plastics are about 20% thinner, which can make them most ideal for higher prescription. Polycarbonate plastic are the strongest available, which makes them preferred for active children. Your optician can help you chose the best type and frames based on your lifestyle and visual needs.