Many people throughout the world wear glasses or contacts in order to improve their vision. Vision problems can occur due to a variety of issues with the lens of the eye or shape of the eyeball. Corrective lenses serve to fix these issues and provide optimal sight.
The Most Common Sight Problems
There are three common issues that cause someone to have poor vision that is correctible with a lens.
Myopia
Myopia, also called nearsightedness, occurs when an image comes into focus before it reaches the retina at the back of the eye. This can be caused by a problem with the lens or the slight lengthening of the eyeball, causing the retina to be farther from the lens than was intended. Those with myopia have trouble seeing objects at a distance.
Hyperopia
Hyperopia, also called farsightedness, is the exact opposite of myopia. It occurs when an image comes into focus after it reaches the retina. This can happen due to a change in the lens or the widening of the eyeball, causing the retina to be closer to the lens than was intended. Those with hyperopia have trouble seeing objects up close.
Astigmatism
Astigmatism occurs when the lens is distorted in some way. This results in a second point of focus and can cause problems at all distances.
The Different Types of Lenses
According to The Eyewear Place, most corrective lenses are shaped to specially handle one or more of these three common types of vision problems. All of the lenses work by bending the light passing through them similar to how a prism works. This changes the focal point, or point where the image is most focused, to match the location of the retina.
A lens prescription indicates the type of strength of the lens. There are five basic types of lenses.
Plus Lens
A plus lens is thicker in the center. The light is bent toward the center, moving the focal point back. A plus lens corrects hyperopia. Reading glasses are plus lenses. These glasses are among the easiest to make and can be found at many stores.
Minus Lens
A minus lens is thinner in the center. The light is bent away from the center, moving the focal point forward. A minus lens is used to correct myopia. These glasses usually require a specialized prescription and are more expensive.
Cylindrical Lenses
These lenses are used to correct astigmatism. The lens looks like a length of pipe cut lengthwise. The lens bends light only along the spine of the curve and can be oriented in whatever direction is needed to correct the astigmatism.
Bifocals
This is a hybrid lens that combines a minus lens with a small piece of plus lens. It often appears to have a small rectangular thick patch that is quite noticeable. The advantage is that it allows a person who struggles with both myopia and hyperopia to be able to correct for all distances. Until recently, bifocals were the only way to correct such a condition.
Progressive Lenses
More advanced lens making techniques now allow the creation of a progressive lens. This lens has changes in thickness that are continuous and for the most part not noticeable upon first glance, unlike a bifocal. A wearer can use different parts of the lens to correct for different viewing distances. The top of the lens corrects for long-distance vision, the center corrects for intermediate vision and the bottom corrects for close-up vision.
When a person notices problems with their vision, the first step is always to contact an eye doctor. The doctor will be able to determine what kind and what strength of corrective lenses are needed. Most types of lenses are now available in either eyeglass or soft contact form, but some specialty lenses may only be available as eyeglasses. Your doctor can help you make a lens choice that is right for your needs and lifestyle.