Corrective lenses of glass or plastic lenses are worn over, on, or in the eye to help targeted to the eye, so a person can see clearly. There are three main types of corrective lenses, glasses, contacts, and intraocular lenses. An eye care professional such as an ophthalmologist or optometrist can determine whether a person needs corrective lenses with a routine eye exam, and the exam can also be used to achieve a prescription for a specific pair of lenses.
Glasses consist of a frame with glass or plastic lenses that sits on the bridge of the nose and is supported by two legs, called temples that rest on the ears. The glasses come in different varieties, especially:
Glass lenses are often bright, but can be colored for aesthetic reasons or as sunglasses. Some glasses change coverage when exposed to sunlight, the transition to sunglasses when the wearer steps outside in bright light.
Other types of glasses include:
All kinds of spectacles should be regularly cleaned with a microfiber cloth and a mild detergent or a mixture of detergent and lukewarm water. This helps to ensure that the wearer can see well and can also keep the lenses from scratches by debris. Glass should be stored in a case, when it is not in use in order to prevent them from dirt and to protect them from damage.
Most eyeglass lenses require a prescription in the United States, but there are mildly corrective glasses non-prescription available for reading, or less frequently, for myopia. Although these glasses are usually cheaper than glasses, they are not tailored to the person wearing them, and in some cases can worsen eye problems.
Contact lenses are small, round lenses which are placed directly on the surface of the eye. Most modern contact lenses are made of plastic or silicone, but older contact lenses made of glass. Most of the contacts are almost invisible when worn, with the exception of the contacts that are deliberately colored. Some contacts are intentionally tinted or colored, so that the wearer can see them more easily if they fall, or for cosmetic reasons.
Contacts are in:
All types of contacts except for daily contacts need to be cleaned and stored in a sterile environment when it is not worn. Caring for contacts is particularly important, because they come into direct contact with the eyes. Unclean contacts can encourage or cause eye problems, including eye infections, corneal abrasions, and in rare cases, blindness. Some contacts have to be cleaned differently than others, and there are a variety of contact cleaning products, including cleaners, enzymatic cleaners and ultraviolet, so carriers should always follow the instructions of their ophthalmologist.
In the US, all contacts are prescription, even non-focal ones and are colored. Although some vendors sell contacts without a prescription, they are illegal, and should not be purchased.
Intraocular lenses actually implanted in the eyeball, sometimes a lens which has been removed or to be unusable because of cataract or glaucoma, but also easily be replaced to correct vision. Most intraocular lenses are monofocal, which means that the wearer difficulty concentrating on other than the one that the lens is designed to have an distances. They focus on distant, although multifocal intraocular lenses exist. Intraocular lenses can be placed in about 30 minutes by a trained ophthalmologist in an outpatient procedure. Recovery after getting intraocular lenses are usually about 2-3 weeks.
Since intraocular lenses are not removed, they need not worry once they are in the eye, but during the recovery period after the lens is implanted, the carrier can not exercise or things or do to increase her blood pressure.
How corrective lenses work
Corrective lenses work by bending of light to move the focal point of the light into the eyes closer or further away. In a normal eye, the natural lens of the eye bends this light to the correct length for the focus on the retina, the back of the eye, and the eye is able to focus without assistance, but some people's eyes to bend the light, so that it is focused in front of the retina, or at a point behind the retina, which makes unsharp the natural vision.
People with myopia, or nearsightedness, have eye shape that causes light to focus in front of their retinas, lenses so they shift their focus further away to make it possible to see things necessary in the distance. Long-sighted or long-sighted people have eyes to focus light to a point behind their retinas, so that lenses that bring the focus closer, so they can see objects close up required. The figure below shows a concentrate cross section of the light in a normal eye at the top, a hyperopic eye in the middle, and a myopic eye on the bottom.
The depth of the curve of a corrective lens, the thickness of the lens, and the precise shape of the lens can all be used to change the focal point. Even small changes in the degree of the curve of a lens can make a significant impact vision. Lenses for people with myopia convex shape of a thin, long football, while its concave lenses for hyperopia, with the middle portion is thinner than the ends.
There are also special types of corrective lenses for people with astigmatism. While those with myopia or nearsightedness, have have eyeballs that are shorter or longer egg-shaped eyeballs and people with foresight than normal, people with astigmatism have irregularly shaped cornea - not eyeballs - which makes their vision blurry. People with astigmatism have a need for a special type of corrective lens is called a toric lens, which bends at a portion more than the other light.
The strength of the corrective lens is measured in diopters, which is written in a positive or negative form a lens prescription. Thus, a lens with a 2.5-diopter measurement for a myopic person who would be written as "-2.5" on his or her recipe or contact lens box. The following lenses are classified according to their diopters, and are used by ophthalmologists during an eye examination to determine what level of prescribing a person needs.
Most people can only make a distinction between quarter-diopter change, so most corrective lens prescriptions have been written in the quarter-diopter is in the US written diopter measurement in the negative for nearsightedness and farsightedness in the positive, but this the opposite in other countries.
Pros and cons of corrective lenses
Some studies suggest that in people with borderline myopia or hyperopia - mostly children - wearing corrective lenses can lead to dependence on the lenses and may lead to worsening eyesight, but this has not been proven conclusively. For most people, the wearing of corrective lenses by an appropriate recipe will not lead to worsen to their vision.
Wearing corrective lenses with an incorrect prescription can cause eyestrain, headaches and dizziness, and wearing improper contact lenses, especially those who do not fit the eye, can cause serious eye problems, including scarring.
Despite this, corrective lenses are valuable for correcting the vision, and may be a need to drive, do some kinds of work, reading, or for a good quality of life.
Pros and cons of particular Lenses
Alternatives for corrective lenses
The most basic option for corrective lenses is simply not using them and live with the reduced vision. Other alternatives for correcting the vision are:
Video 1 - A tutorial on cleaning glasses.
Video 2 - A tutorial on how to clean contact lenses.
- Laser eye surgery can reduce the need for corrective lenses.
- Corrective lenses can be used for hyperopia, making it easier for people to see close up.
- An eye examination by an optometrist can help in the determination of the need for corrective lenses.
- Some people prefer glasses that transition to sunglasses when in contact with bright light or sunlight.
- An incorrect recipe may cause tension headache and eyes.
- Corrective lenses are used to correct vision problems.
- A normal eye and a with astigmatism.