Short-sightedness (myopia) is the inability to see distant objects clearly due to a mismatch between the size or shape of the eyeball and the focusing power of the eye.
In shortsightedness, the eyeball is too long and the image forms in front of the retina. Shortsightedness can be corrected with glasses using concave lenses or contact lenses.
Long-sightedness (hypermetropia) is the inability to see close objects clearly because the image cannot be focused precisely on the retina. In Long-sightedness, the eyeball is too short and the image falls behind the retina. Long-sightedness can be corrected with glasses using convex lenses or contact lenses (see box, below). Long-sightedness in children may interfere with reading and early learning and must be corrected when very young.
What Might Be Done?
- Your optician will check your visual acuity and the level of detail you can see and then assess the severity of any visual defect.
- Shortsightedness can be corrected by wearing contact lenses or glasses that have concave lenses. The focusing power of your own lenses decreases gradually with age, and your prescription may need to be updated regularly.
- It’s very important to treat shortsightedness in children, particularly once they are in school. Shortsightedness can prevent a child from following lessons written on the blackboard or from participating fully in sports that involve catching a ball.
- Your optician will check your visual acuity and the level of detail you can see, and then assess the severity of any visual defect.
- Long-sightedness can be corrected by wearing contact lenses or glasses that have convex lenses. The focusing power of your own lenses decreases gradually with age, and your prescription may need to be updated regularly.
- Some people who have Long-sightedness may be helped by laser treatment, which reshapes the surface of the cornea with a laser beam to increase its focusing power.
- Long-sightedness doesn’t cause complications, but people who have it are more prone to acute glaucoma, a serious condition that must be treated promptly. You should, therefore, see an optometrist regularly, so that any problems can be spotted early and dealt with.
It’s crucial to treat Long-sightedness in children. Although it may be detected during routine vision tests at school, children with a family history of Long-sightedness should have a vision test before the age of 3 because early treatment is important for early learning.
Many of us find that the normal reading distance becomes longer and longer as we get older; this is known as presbyopia. As our eyes age they lose the power to focus; deterioration starts around the age of 45 years and by the age of 65 little focusing power remains. Presbyopia can be corrected by simple reading glasses with convex lenses or by contact lenses (see Glasses and contact lenses, below). Lenses may need to be changed four or five times over 20 or 30 years until eventually all focusing is done by lenses.
Treatment – Glasses and Contact Lenses
Most focusing (refractive) errors can be corrected by glasses or, for older children and adults, contact lenses. Glasses can correct most refractive errors and do not cause complications. Contact lenses are most effective for shortsightedness and Long-sightedness . They require careful cleaning to reduce the chance of an infection of the cornea, over which they are placed.
How corrective lenses work
Glasses and contact lenses correct refractive errors by altering the angle of light rays before the rays reach the surface of the cornea, the transparent front layer of the eye, allowing the lens to focus the rays correctly on the retina.
- Shortsightedness is corrected by concave lenses, which make light rays diverge, so that
they are focused on the retina and not in front of it.
- Long-sightedness requires a convex lens to make light rays converge, focusing them on the retina and not behind it.
Three types of contact lenses are available: rigid (hard), gas-permeable and soft. Soft lenses are the most widely used and the least rigid. Disposable soft lenses are worn only once or for a few days, then thrown away. Non-disposable lenses should be disinfected and cleaned daily, unless worn for an extended period of time (not usually recommended). If an eye becomes red or painful, stop wearing your lenses and consult your optometrist immediately