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Hyperopia or farsightedness, is an ophthalmological condition, which presents as blurry near vision, but clear far vision. Most babies born at term, are hyperopic and this tends to self-correct during the first 5 years of life.
However, as many as 10% of the adult population is hyperopic, and while some people may not experience any problems, others do. While there is no discrepancy in the distribution of the condition between the sexes, it is more prevalent in Native and African American ethnic groups and in Pacific Islanders as well.
When there is an accommodative system that is strong enough to allow clear images to fall on the retina, a hyperopic individual will not experience asthenopia (i.e. eye strain). This is usually the case in youth. However, at the lower and upper ends of the age spectrum (outside of this age group, i.e. the very young and older persons), accommodative reserve is weaker. Symptoms are more prone to manifest with higher degrees of hyperopia.
Asthenopia presents with headache, blurred vision, eye fatigue and, occasionally, double vision. With age-related decrease in one’s ability to see near vision objects clearly, also known as presbyopia, latent hyperopia becomes manifested.
Additional signs and symptoms that are present in hyperopic individuals are red eyes and increased tearing. These individuals may have problems focusing and difficulties with reading. They may squint or make grimaces that signify the presence of reading difficulty at near distances. With regard to the binocularity of their vision, it is decreased, as well as the eye-to-hand coordination. All in all, there is a wide variation in the clinical presentation of hyperopia. Some patients may experience all the symptoms mentioned, while others may experience some or none, even with a high degree of hyperopia.
Hyperopia is due to an error in refraction. Refraction is the process whereby light is bent as it passes through the cornea and the lens. Most of the light is bent by the cornea, while the remainder is bent by the lens. The tear film, aqueous humor and vitreous also have some refractive properties. This light is subsequently focused on the retina and from there the image is sent to the brain via the optic nerve for image processing. An individual is said to be hyperopic when the light that enters the eyes is not focused on to the retina, but at a point behind it. This error in refraction may be due to having an eyeball that is too short in length or could be due to pathologies in the lens or the shape of the corneal surface.
In terms of classification, hyperopia may be divided into simple, pathological or functional hyperopia. Normal variations in biology gives rise to simple hyperopia that may have refractive or axial etiology. Pathological hyperopia, on the other hand, may be caused by trauma, eye diseases, or congenital malformations of the eye.
A loss of lens function or paralysis of accommodation gives rise to functional hyperopia. Hyperopia is classified into low, moderate and high hyperopia as a way to denote the degree of hyperopia. An error of +2.00 diopters (D) or less is considered to be low hyperopia. Between +2.25 – 5.00 D is considered moderate hyperopia and above this range it is regarded as high hyperopia.