Short- or far-sighted? What’s the difference?
Struggling to focus on objects in the distance? Or are nearby objects out of focus? An optometrist weighs in.
People are often unsure of the difference between short-sightedness (myopia) and far-sightedness (hypermetropia),’ says Johannesburg optometrist Nicole Levy. Both conditions are due to refractive errors in the eye, which means the eye cannot focus light on the retina properly.
‘Myopia doesn’t affect your close-up vision, but it does affect your ability to see objects in the distance,’ Levy says. ‘On the other hand, hypermetropia causes close-up objects to appear out-of-focus and blurry.’
‘When light enters the eye, it is focused onto the retina (the layer at the back of the eye) so you can see a clear image,’ Levy explains. ‘Light is first bent by the cornea and then the lens in the eye. The retina is made up of cells that transmit the information via nerves to the brain, which then interprets what you are seeing.’
More bending (refraction) of light rays is needed to focus on nearby objects. Less bending of light is needed to focus on objects far away.
What causes short-sightedness?
‘Most cases of myopia are due to a combination of genetic and environmental factors that negatively influence the normal growth of the eye,’ says Levy.
What is it exactly?
‘Myopia a refractive error caused by an imperfection in the eye – the curvature of the cornea is steep or the axial length of the eyeball is long. When light enters the eye, it focuses in front of the retina, instead of directly on the retina.’ This error makes images in the distance appear fuzzy and unclear. Recognising faces at a distance becomes difficult, as does driving. Children with myopia will find it difficult to read the blackboard or watch TV from a distance.
How is it treated?
Refractive errors are corrected with spectacles or contact lenses. Some people are also opting for refractive surgery such as laser on the cornea or insertion of lenses into the eye. ‘Refractive surgery should not be done until the eye has settled,’ Levy adds. ‘Surgery is not good for children whose eyes are still growing.’
What causes far-sightedness?
‘This is caused by the shape of the eye during development,’ Levy says. ‘The eye may be too small or the cornea too flat or the lens in the eye is the wrong shape/power. Some people may get hyperopic shifts due to an eye disease but this needs to be further investigated by an ophthalmologist (eye specialist).’
What is it exactly?
‘This a condition where the curvature of the cornea is flat or the axial length of the eyeball is too short,’ says Levy. When light enters the eye, it focuses beyond the retina instead of directly in the retina, making close-up images look blurry.’ Some people think they are becoming far-sighted as they get older and reading becomes more difficult. This condition is due to the stiffening of the lens in the eye and is called presbyopia.
How is it treated? Far-sightedness is often corrected using glasses or contact lenses. Several laser surgery techniques have also been developed to treat the condition.
How often should you have your eyes examined?
- Children should have an eye examination at least once a year or sooner if they are complaining of blurry vision or headaches.
- Adults should have an eye test every 1 to 2 years.
- Contact lens wearers should have an annual check up.
- Patients with medical conditions such as diabetes should have an annual check up, unless they notice any strange symptoms such as sudden loss of vision.
- If in doubt, contact your eye care practitioner.