|Classification and external resources|
Hyperopia, commonly known as being farsighted (American English), being longsighted (British English), or hypermetropia, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or the lens cannot become round enough), causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred.
People with hyperopia can experience blurred vision, asthenopia, accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus, another condition that frequently causes blurry near vision. Presbyopes who report good far vision typically experience blurry near vision because of a reduced accommodative amplitude brought about by natural aging changes with the crystalline lens. It is also sometimes referred to as farsightedness, since in otherwise normally-sighted persons it makes it more difficult to focus on near objects than on far objects.
The causes of hyperopia are typically genetic and involve an eye that is too short or a cornea that is too flat, so that images focus at a point behind the retina.
The opposite of hyperopia is myopia.
Classification of hyperopia
Classification by clinical appearance
- Simple hyperopia
- Pathological hyperopia
- Functional hyperopia
- Blurred vision of close objects
- Crossed eyes (strabismus) in some children
- Eye strain
- Headache while reading
Mild farsightedness may not cause any problems except for a need for reading glasses.
Signs and tests
A general eye examination, or standard ophthalmic exam may include:
- Eye pressure measurement (Tonometry)
- Refraction test, to determine the correct prescription for glasses
- Retinal examination
- Slit-lamp exam of the structures at the front of the eyes
- Test of color vision, to look for possible color blindness
- Tests of the muscles that move the eyes
- Visual acuity, both at a distance (Snellen), and close up (Jaeger)
Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It is mainly cause by two reasons-
- Low converging power of eye lens because of weak action of ciliary muscles.
- Eyeball being too short because of which the distance between eye lens and retina decreases.
Farsightedness is often present from birth, but children have a very flexible eye lens, which helps make up for the problem. As aging occurs, glasses or contact lenses may be required to correct the vision. Farsightedness is hereditary.
In severe cases of hyperopia from birth, the brain has difficulty merging the images that each individual eye sees. This is because the images the brain receives from each eye are always blurred. A child with severe hyperopia has never seen objects in detail and might present with amblyopia or strabismus. If the brain never learns to see objects in detail, then there is a high chance that one eye will become dominant. The result is that the brain will block the impulses of the nondominant eye with resulting amblyopia or strabismus. In contrast, the child with myopia can see objects close to the eye in detail and does learn at an early age to see detail in objects.
The child with hyperopia will typically stand close in front of a television. One would have expected that the child would stand far away because the child is hyperopic, but because the brain has never learned to see detailed lines and object contours the child sees objects blurred. While children with myopia learn to see sharp lines because they can see perfectly well very close to their eyes, the brain of a child with hyperopia cannot see sharp lines, so they stand right in front of the television to at least see blurred images. This blurred vision may also cause a child to develop a squint because the two eyes do not detect sharp lines which the brain can use to map the separate images of the two eyes together to form a single image. Each eye functions independently. So a child with hyperopia from birth presents with decreased visual perception.
The parents of a child with hyperopia do not always realize that the child has a problem at an early age. A hyperopic child might have problems with catching a ball because of blurred vision and because of a decreased ability to see three-dimensional objects. The child will typically perform below average at school. As soon as a child starts identifying images, a parent might find that the child cannot see small objects or pictures.
In many circumstances mild to moderate hyperopia can be mistaken for ADHD; or other learning and personality disorders. One coping mechanism many children subconsciously use is constant head and body movement to attempt to maintain focus.
Various eye care professionals, including ophthalmologists, optometrists, orthoptists, and opticians, are involved in the treatment and management of hyperopia. At the conclusion of an eye examination, an eye doctor (ophthalmologist or optometrist) may provide the patient with an eyeglass prescription for corrective lenses. Minor amounts of hyperopia are sometimes left uncorrected. However, larger amounts may be corrected with convex lenses in eyeglasses or contact lenses. Convex lenses have a positive dioptric value, which causes the light to focus closer than its normal range.
- American Optometric Association. Optometric Clinic ef_error_pres.htm "Refractive Error and Presbyopia." Refractive Source.com Accessed September 20, 2006.
- American Optometric Association. Optometric Clinical Practice Guideline: Care of the patient with presbyopia. 1998.
- Kazuo Tsubota, Brian S. Boxer Wacher, Dimitri T. Azar, and Douglas D. Koch, editors, Hyperopia and Presbyopia, New York: Marcel Decker, 2003
- Vision - Learn how Hyperopia happens by pupilEyes
- Scottish Sensory Centre - Medical Info on Hypermetropia
- LASIK - Medical Info on refractive disorders by eMedicine
- Farsightedness by EyeTopics