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Introduction to Eye Glasses
Eyeglasses or spectacles are a common visual aid that used to correct vision. They are the most common means prescribed by eye care professionals to correct eye disorders.
Glasses are usually prescribed for vision problems that are related to the refractive problems that can affect the focus of the eye. This includes such problems as presbyopia, myopia, hypermetropia, astigmatism etc.
Type and strength of spectacle lenses
Eyeglasses are made of either contemporary plastic lenses or the more old-fashioned glass lenses. The type and power of each lense is ground so that it compensates for the degree error of focusing for the eye.
Generally, there are two broad categories of lenses:
The power of a corrective lenses is measured in dioptres (D) and in pluses and minuses that help the doctor gage the severity of your vision loss. The higher the dioptre count the stronger the lens, in either a plus or a minus direction.
Lenses can also be also categorized according to the types of disorders that they correct such as myopia etc. These are called single lenses.
Single lenses are called so because they correct one type of eye malfunction including astigmatism, myopia, hypermetropia and presbyopia. Myopic people need single concave lenses that are thicker around the rims to perceive objects that are far away. A single lens to correct hypermetropia or presbyopia thicker in the centre and thinner at the rims. This makes objects appear larger. The single lens spectacle prescribed for astigmatism has a line through the lens that changes the vision depending on the position of the spectacle.
Combination lenses are also known as bifocals, demi-glasses half-glasses and are used to correct presbyopia. Bifocals contain lenses of two or more powers in the upper half and lower half of the lenses. The upper part of the lens is used for viewing objects at a distance and the lower part is used for close up viewing.
The presbyope type of eyeglass can correct vision on the lower half for near sightedness and the upper half for far away objects. Bifocals are considered convenient as they spare people the fuss of having to own two sets of eyeglasses.
Trifocals are an even greater option for those suffering from a combination of eyesight disorders. Trifocals consist of a third component between the d near viewing sections that can assist with middle vision. This prevents stress on the eye and jumping from near to far vision. It can take some time to get used to trifocals but they are well worth the significant improvement that they provide in vision.
Prisms, also known as Fresnel prisms are fitted in glasses to help correct double vision. Glasses can also often include prisms that bend all light entering through them in a single direction. Prisms can be affixed onto eyeglasses either temporarily or permanently.
How to get the correct eyeglasses?
There are different types of eye car professionals that are qualified to dispense eye glasses. These include optometrist, opticians and opthamalmic medical practitioners. Only these eye care professionals can correctly diagnose your eye needs.
Once the prescription for your eyeglasses have been determined and a prescription issued, you need to get hold of a pair of spectacles, unless you opt for contact lenses. You can opt to get both.
Here are some tips about purchasing spectacles that touch on some laws in the United States.
Do not compromise when it comes to having your eyes assessed. Choose a proper practitioner.
Eyeglass lens types
Glass has historically been used to make spectacles. It is cost effective, good optically and is quite resistant to scratches and heat. However glass is heavier and it can shatter if impacted and embed glass slivers in your eye. The blinder you are the heavier your prescription for spectacles will be. Sometimes glass lenses can be made more durable by being sealed with plastic.
Plastic lenses are the other choice for prescription eyeglass wearers. They are light and durable but the surface of these lenses tend to develop scratches more easily. Nowadays these lenses are coated with resins to prevent damage.
Tinted lenses that lighten and darken in response to light can also be used. They act as sunshades but are also prescribed for conditions like albinism or a dilated pupil.