Hyperopia, also termed hypermetropia or farsightedness, is a refractive error in which parallel rays of light entering the eye reach a focal point behind the plane of the retina, while accommodation is maintained in a state of relaxation.
Hyperopia is a common refractive error in children and adults. Its effect varies greatly, depending upon the magnitude of hyperopia, the age of the individual, the status of the accommodative and convergence system, and the demands placed on the visual system.
Signs and symptoms
Young persons with hyperopia generally have sufficient accommodative reserve to maintain clear vision without any asthenopia or eyestrain. However, both younger and older hyperopic patients, even those with mild hyperopia, may be symptomatic as a result of inadequate accommodative reserves for their levels of hyperopia. When the level of hyperopia is too great or the accommodative reserves are insufficient, due to age or fatigue, blurred vision and asthenopia develop. Presbyopia brings an increase in absolute hyperopia, causing blur, especially at near.
The presence and severity of these symptoms varies widely. Some young patients with hyperopia, including those with moderate and high hyperopia, may be relatively free of signs and symptoms.
Individuals with uncorrected hyperopia may experience, especially when the amount varies between the two eyes:
Blurred vision
Asthenopia
Accommodative dysfunction
Binocular dysfunction
Amblyopia
Strabismus
Detection and Prevention
Hyperopia or far-sightedness
A positive family history of hyperopia, amblyopia, or strabismus increases the likelihood that a young patient with suspected eye or vision problems actually has a similar problem.106
The effect of hyperopia on visual acuity depends upon the magnitude of the hyperopia and the patient's age, visual demands, and accommodative amplitude available to overcome the hyperopia. Young patients with low to moderate facultative hyperopia generally have normal visual acuity, but when visual demands are high, they may experience blurred vision and asthenopia. Visual acuity testing of patients with high hyperopia, even when the patients are young, is likely to reveal measurable deficits, especially under significant visual demand.
The patient who has never been optically corrected for a high degree of hyperopia, with or without astigmatism, is at risk for isoametropic amblyopia. Older patients with hyperopia invariably experience reduced vision, especially at near. Pre-presbyopic and early presbyopic patients with hyperopia manifest deficits of near vision before distance visual acuity is adversely affected. In patients with absolute hyperopia, the reduction in visual acuity at both distance and near occurs.
Stats and causes
Most newborn infants have mild hyperopia (approximately +2.00D), with only a small number of cases falling within the moderate to high range (>3.5D). Although emmetropization results in a gradual decrease in the level of hyperopia in most patients, the change occurs more rapidly in patients who have high degrees of hyperopia.
Approximately 4-9% of infants 6-9 months old have hyperopia greater than +3.25 diopters with the prevalence of hyperopia ( > +3.25 D) to 3.6% in the 1-year-old population.
Higher levels of astigmatism are associated with moderate to high hyperopia during infancy, but both tend to decrease by the age of 5 years.
Although at this age the prevalence of refractive error is reduced, its distribution still peaks toward mild hyperopia. Over the next 10-15 years of life, there is a further decrease in the prevalence of hyperopia and an increase in the frequency of myopia.
With the development of presbyopia, latent hyperopia becomes manifest, contributing to an apparent increase in the prevalence of hyperopia. There is however no known gender difference in the prevalence of hyperopia, but there is evidence of the influence of ethnicity on the prevalence of hyperopia. Native Americans, African Americans, and Pacific Islanders are among the groups with the highest reported prevalence of hyperopia.
A study of 1,880 Chinese schoolchildren in Malaysia showed that the prevalence of hyperopia greater than +1.25 D was staggeringly low at only 1.2%.
Treatment
Plus (convex) lenses
Significant hyperopia, if uncorrected, can produce visual discomfort, blurred vision, amblyopia, and binocular dysfunction, including strabismus, and contribute to learning problems. Treatment should be initiated both to remediate symptoms and to reduce the future risk of vision problems resulting from the hyperopia.
The primary modality for treating significant hyperopia is correction with spectacles. Plus-power spherical or spherocylindrical lenses are prescribed to shift the focus of light from behind the eye to a point on the retina.
Accommodation plays an important role in determining the prescription. Some patients with hyperopia do not initially tolerate the full correction indicated by the refraction, and many patients with latent hyperopia do not tolerate the full correction of hyperopia indicated under cycloplegic refraction.
To determine the final spectacle lens prescription, the optometrist carefully considers the patient's vision needs. The lenses prescribed may be either single vision or multifocal.
Newer high-index lens materials and aspheric lens designs have reduced the thickness and weight of high plus-power lenses required with hyperopia, thus increasing their wearability and patient acceptance. Spectacles, especially those with lenses of polycarbonate material, provide protection against trauma to the eye and orbital area.