Patient Education - Refractive errors
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Refractive errors

In normal vision, light rays from an object focus on the retina (emmetropia). Alternatively, in the presence of a refractive error, the light rays get focused in front or behind the retina causing blurred vision. Under normal conditions, as the eye ball grows in size from infancy to adulthood, there will be a corresponding change in curvature of cornea and the lens enabling the eye to remain emmetropic, at all ages.
When one of these fails to happen, refractive error occurs: patient4
• The eye ball being larger or smaller than the normal size
• The corneal curvature being flatter or steeper than usual
• Increase or decrease in the power of the lens
These refractive errors can be classified as myopia (near sightedness) and hyperopia (far sightedness), astigmatism and presbyopia

What is hyperopia ?

In hyperopia or far sightedness, the light rays from an object form an image behind the retina.
Children with hyperopia
• Find difficulty in reading, writing and looking at both near and distant objects.
• Eye strain while trying to read for long hours
• May have squint (crossed eyes)


What is myopia?

In myopia or near sightedness, the light rays from an object form an image in front of the retina.
Children with myopia
• Have defective vision for distance and clear vision for near
• Squeeze their eyes while trying to see distant objects
• Hold books close to their face while reading

What is astigmatism?

• Astigmatism is a condition in which objects, both near and distant, appear blurred. The cornea and lens of the eye should be spherical. When one or both are curved more steeply in one meridian than another, the optics take on a toric shape.
• This uneven curvature prevents light rays entering the eye from focusing to a single point on the retina.
• Astigmatism often occurs in combination with myopia and hyperopia.
• Astigmatism is corrected with glasses or contact lenses.

What is presbyopia?

• After 40 years of age, most people find it increasingly difficult to read or see clearly at close range.
• This condition is a normal part of aging and is called presbyopia often referred to as farsightedness.
• Presbyopia develops as the lens of the eye becomes less flexible and loses its ability to focus on near objects.
• Presbyopia is treated with reading glasses which can be single vision, bifocals or progressive lenses.

Treatment of refractive errors

• Corrective spectacle is the best option available.
• The power of the glasses may change depending on the growth of the eye ball. An eye check-up and change of glasses if necessary, has to be done once in 6 months for children under 5 years of age and once a year thereafter. Failure to wear glasses in childhood when needed will retard the development of vision in that eye.
• Children older than 15 years can use contact lenses if they don’t want spectacles.
• Those over 20 years of age with stable refraction also have the option of LASIK, a laser refractive surgery.