Eyeglasses are visual aids and are also known as spectacles or glasses. They are medical devices (corrective lenses) used to correct vision disorders including refractive errors and blurring. Glasses are also considered fashion accessories. Photochromatic glasses can block harmful UV rays and may double up as sunglasses.
Eyeglasses have hard plastic or glass lenses supported by plastic or metal frames. The frame holds the lenses in front of the eyes using a bridge over the person’s nose and temples that rest over the ears. They correct vision by increasing or reducing focusing power to the cornea and eye lens.
Glasses are the most popular vision correction method for difficulty in seeing distant objects (nearsightedness or myopia), up close (farsightedness or hyperopia) and blurring because of an irregular cornea (astigmatism).
People are more likely to need glasses as they grow older. Ninety-three per cent of people over the age of 40 need or wear corrective lenses.
The kind of vision problem determines the type of lenses to use in the eyeglasses. Corrective lenses may include:
- Cylindrical lenses - These are often used to correct astigmatism. They curve more in one direction than in the other.
- Convex lenses – This type of lens is like a magnifying glass and is thickest at the center. It is used to correct farsightedness. A plus (+) symbol marks the numerical prescription in diopters.
- Concave lenses - A minus (-) symbol denotes the numerical prescription in diopters. These lenses are thinnest at the center and correct nearsightedness.
Understanding an Eyeglass Prescription
Diopters refer to the measure of the power in the lenses. The measurement indicates the power required to focus images straight onto the retina. The prescription may have abbreviations such as:
- Oculus sinister (OS) - LE may also be used which means the left eye
- Oculus dexterous (OD) - This means the right eye, at times abbreviated as RE
The prescription may also have measurements like:
- Cylinder – It indicates the amount of astigmatism
- Axis – It is a number measurement (in degrees) which shows the direction of the astigmatism
- Sphere - This describes the extent of farsightedness or nearsightedness
Indications & Uses
Over time, the eyes’ ability to accommodate up close and distant focus changes. This occurs because the natural lens of the eye loses its elasticity. This decreases the ability of the lens to bring to focus, objects close to the eye. This condition is known as presbyopia. It is an eye disorder that affects many people over forty years. People including kids, may also experience vision problems due to disease and genetic disorders among other reasons.
Corrective lenses work by bending the incoming light to correct refractive errors. They reduce the effects of disorders like myopia, hyperopia, presbyopia or astigmatism. The lenses conform to the prescription given and bring the object back into focus on the retina.
Glasses may improve a person’s quality of life. They enhance the patient's visual experience and can also minimize the effects of eye strain, such as squinting or headaches. The doctor can also use a lensometer to check the specifications of an older pair of glasses.
Single vision has a uniform refractive index and is the most popular type of corrective lens. Multifocal glasses such as bifocals and trifocals have two or more different refractive index and are useful for presbyopia and hyperopia. Progressive lenses have a continuous gradient and don’t have the visible lines found in multifocal lenses. Reading glasses offer an inexpensive, practical solution to difficulty in seeing up close.
Eyeglasses for Kids
If the children are old enough, the parents should let them play an active role in choosing their glasses. When buying eyeglasses for children, parents should consider:
- Scratch-resistant coating on the lenses
- Straps to help keep the glasses in place
- Silicone nose pads to prevent glasses from slipping
- Frames loaded with springs. They are less likely to be warped or bent
- Impact resistant and shatterproof lenses, especially for kids who play sports
- Earpieces that wrap around the ear, also known as cable temples, suitable for kids under four years