Refraction defects

Refraction defects are defects in visual acuity. These are the disorders most often encountered in ophthalmology, and include:

• near-sightedness
• far-sightedness
• astigmatism
• presbyopia (ageing eye)

Near-sightedness is the most commonly occurring sight defect, and involves the image being focussed in front of the retina instead of on it, which leaves farther-off objects looking blurred. It should be remembered that in pregnant women, near-sightedness can worsen.

Far-sightedness is a defect with symptoms opposite to those occurring in the case of near-sightedness. People with minor far-sightedness see objects better if they are farther away, with those closer appearing indistinct. Major far-sightedness causes both close and far objects to appear indistinct.

Astigmatism is a visual disorder which affects a large proportion of the population. Apart from far-sightedness and near-sightedness, it is the most commonly experienced sight defect. Astigmatism is usually the result of a disorder of the surface of the cornea, so that light passing through it is refracted in different ways, causing disturbances to the acuity of vision, or distortion of images – instead of being focussed on one point of the retina, the light is focussed on two. In consequence, people with astigmatism see the outlines of objects as blurred and misshapen. Apart from distortion of vision, astigmatism also causes frequent headaches, exhaustion and burning eyes.

Presbyopia (ageing eye) results from the natural ageing processes taking place in our bodies. The disorder manifests itself in difficulties with reading and seeing from close up, and its first symptom is “arm stretching” – the necessity to hold a book or newspaper farther away. Presbyopia usually appears in the over-40s, with its progression halting around the age of 65.

In order to minimise the negative of sight defects, it is necessary to have regular check-ups by an ophthalmologist, and to keep the eyes appropriately moistened, as well as limiting the amount of time spent in front of computer or TV screens.