Refractive error | The Fred Hollows Foundation NZ

Refractive error

Globally, refractive error is responsible for 42% of visual impairment. Untreated refractive error can result in a person's vision being so poor that they are classified as being blind.

Fred Hollows Foundation NZ operating theatre technician Belmerio Jeronimo tests a pupil’s vision during a screening at Cotalau Primary School, Timor Leste. Photo: Lucy Lee

The cornea and lens normally focus light to form a clear image on the retina. Refractive error occurs when the light is not being focused properly by the cornea and lens onto the retina, which results in a person seeing blurred images.

Refractive error, at its most serious, can result in blindness.

Spectacles or contact lenses can usually compensate for this loss of focus.

Types of refractive error

The most common forms of refractive error are myopia (short-sightedness) and hyperopia (long-sightedness).

Myopia, also referred to as short- or near- sighted vision. Myopia (short-sightedness) - occurs when light is focused in front of the retina instead of being focused properly on it, making far away objects blurred.

Hypermetropia, also referred to as long- or far- sighted vision. May be referred to as hyperopia in United States medical literature. Hyperopia (long-sightedness) - a person is affected by hyperopia when light is focused behind the retina, allowing longer distance vision to remain clear but close vision is blurred.

Astigmatic vision. Astigmatism - occurs when the cornea is unevenly curved. It causes objects both near and far to blur or become distorted by focusing light both in front of and behind the retina.

Presbyopia - the loss of ability to focus on near objects due to the normal hardening of the lens with age.

With each of the types of refractive error, the greater its degree, the greater the blur and disability experienced.

Who gets refractive error?

Anyone can be affected by refractive error, irrespective of age, sex and ethnic group, and most people live with some degree of the condition.

Presbyopia is experienced by most people over the age of 45 years.

What is the magnitude of the problem?

On a global scale, uncorrected refractive error is the second leading cause of visual impairment, accounting for 42% of global visual impairment and 3% of global blindness.

Can refractive error be treated?

After an eye test, refractive error can be corrected with correctly prescribed glasses or contact lenses. The prescription may need to be changed periodically, especially in children who are myopic and in older adults who are hyperopic.

Laser surgery can be performed on some people so that glasses no longer need to be used. This kind of treatment is only available to those living in developed countries like New Zealand.

Treatment in developing countries

The approach to dealing with refractive error in poorer countries is fairly straightforward.

Detection of refractive error as a cause of poor vision, including the use of school screening, needs to become part of comprehensive eye care delivery.

Training of non-medical staff in the ordering of appropriate glasses is part of the human resource development needed in all eye care programs.

Spectacle supply has been set up in a number of our country programs where we train local nurses and technicians to test eyesight and prescribe spectacles which are sourced from appropriate manufacturers. This creates a small, self sustaining industry and also provides the local people with spectacles they can afford and that correct their eyesight properly.

Note: This information is general in nature and is not a substitute for specialist medical advice. Have your eyes checked regularly every two years, even if you have not noticed any symptoms or changes.

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