Eye defects and what you should know

THE EYE: Window to the soul

One fateful afternoon; bored to death at my 2 week ophthalmology rotation, wondering what I could learn about the eye. It’s such a small organ, with a volume of about 6 mls weighing about 7.5 grams; indeed small. To peak our interest the professor told the story of a middle-aged man, who went about minding his own business. When he drove by he didn’t bother himself with greeting pedestrians or other drivers (because he makes out their faces). One day a man commissioned to do a painting for him but on seeing the finished portrait he was livid, telling the painter that he had done a horrendous job. For some reason a doctor friend got him to do an eye test. They found out he had an error and got glasses for that. On getting home he saw the portrait, a minute later he was calling the painter to apologize for his harsh words. He was seeing the portrait truly for the first time and it was beautiful. This man had a refractive error.

What is a Refractive Error?

Refractive errors are a state of the eye in which light rays do not converge properly on the retina which causes blurry vision. The retina is the light-sensitive part of the eye. The retina is compared to the film in an old camera.

Refractive errors are the most common cause of visual impairment worldwide. An estimated 0.8-2.3 billion suffer from this condition with about 660 million being uncorrected about 9 million of these people are blind according to the WHO.

What are the types of refractive errors?

There are different types of refractive errors (also known as ametropia)
•Far sightedness (hypermetropia)
•Short sightedness (myopia)


Far sightedness is a refractive error; as objects that are close to a person appear blurry. Such individuals fare better with distant objects but do not have eagle eyes or perfect far vision (what a myth).

Far sightedness occurs when the eyeball is too short or the cornea is isn’t curved enough, the light rays fall behind the retina causing the image follow suit. Individuals are usually born with this condition but it doesn’t usually present till adulthood because the young lens has ability to change shape and focus light on retina properly. This ability is lost as one grows older. Hypermetropia is corrected with convex lenses


Short sightedness is a condition where an individual cannot see distant objects but can see near objects. In this case light rays are focused in front of the retina not directly on it causing a blurry image be formed. It is usually caused by an elongated eyeball. Myopia is corrected with concave lenses


Astigmatism is refractive error where the cornea has an uneven curvature the cornea shaped like a volleyball instead of a football. The person may have normal vision in one plane and have a refractive error in another or even have refractive error in both. Astigmatism is corrected with cylindrical lenses.


Presbyopia is not a refractive error; it is actually an error of accommodation. It occurs as the lens starts to lose the ability to change shape. It usually starts in the late 30s to early 40s. It’s corrected with multi focal lenses, this composed of lenses for near and far vision.

How to correct a refractive error?

Correcting refractive errors is easy, they are;

1) See an ophthalmologist

2) Do the necessary tests: automated refractrometry; its possibly done in less than five minutes

3) Know your refractive error and get the appropriate glasses; the refractive error of your lenses in diopters measurement and committed to memory, this can come in handy when you need a replacement.

Visit your eye doctor at least once a year and test your eyes. Correction of ametropia greatly improves quality of life.


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