Refractive errors are eye disorders that occur when the curvature of the eye inhibits light from focusing directly at the back. This usually results in blurred visions.
Normally, light refracts as it passes through the lens and the cornea and then focuses directly on the retina. However, with varying eye shapes in individuals, light may not be focused correctly. When this happens, one is said to have a refractive error.
In myopia, the light is focused in front of the retina instead of on it. Therefore, only close objects can be seen clearly while distant images appear blurred.
In hyperopic persons, the light is directed behind the retina. This causes distant objects to appear clearer than close-up objects.
Astigmatism arises from an asymmetrical curvature of the lens or cornea. As a result of the irregular shape, light is unevenly focused on the retina. Individuals with astigmatism experience blurry vision at a certain distance.
After years of proper vision, presbyopia may also develop. This condition causes loss of near vision with age. It occurs after around 40 years when the natural lens of the eye hardens up and cannot easily flex to direct focus on nearby images.
- Myopia (nearsightedness)
- Hyperopia (farsightedness)
Causes and Risk Factors
Different factors can cause errors in the refraction of light. These include:
- The curvature of the lens
- Normal aging
- The length of the eyeball
Longer-than-usual eyeballs cause nearsightedness whereas short eyeballs cause farsightedness.
- The shape of the cornea
Conditions such as keratoconus can also cause changes in the curvature of the cornea leading to vision blurs.
- Majority of the refractive errors are hereditary
Those with a family history of any of the refractive errors are at a higher risk of developing the same.
Signs & Symptoms
- Blurred vision
- Straining of the eyes
- Squinting of the eyes
- Halos around bright lights
As they are quite common, refractive errors are easily diagnosable. A dilated eye exam, visual acuity test, a refraction exam or a keratometry test may be done to diagnose the exact error.
Treatment of refractive errors is aimed at focusing the light rays directly on the retina.
Corrective lenses are the most common treatment for refractive errors. Eye care professionals may prescribe eyeglasses or contact lenses. Contact lenses need to be fitted correctly and should only be used by individuals without certain limiting eye conditions. Reading glasses are effective for presbyopia as there are no other refractive errors.
The most popular refractive surgery is the Laser eye surgery or laser vision correction (LASIK). It is performed to correct myopia, hyperopia, and astigmatism by changing the shape of the cornea and restoring the focusing power on the retina.
Orthokeratology is used for astigmatism. It involves wearing specially designed contact lenses to restore the corneal curvature.
Most refractive errors are irreversible. However, with normal visual development, some can resolve on their own. On the flip-side, vision can also get worse without proper management.
Regular eye exams can help prevent refractive errors that arise from other eye conditions.