Refractory error or optical error is the inability of the eye to focus image on the retina. It is a leading cause of blurry vision in children.
According to WHO, It is estimated that globally 153 million people over 5 years of age are visually impaired as a result of uncorrected refractive errors, of whom 8 million are blind. Some 12.8 million in the age group 5–15 years are visually impaired from uncorrected or inadequately corrected refractive errors. Uncorrected refractive errors are the second cause of blindness after cataract and the main cause of low vision worldwide.
The most common types of refractory error in children include;
- Myopia (also called nearsightedness/ shortsightdness); the eyeball is longer than normal also the cornea is too steep. The rays of light focus infront of the retina. Near objects are clear while far objects are blurred
- Hyperopia (also called farsightedness/ longsightedness); the eyeball is shorter than normal. Ras of light converge behind the retina. Near objects are blurry especially when reading, or trying to put thread through a needle.
- Astigmatism (distorted vision); both far and near objects are distorted and blurry. This is due to irregularity in the surface of the cornea; it curves more in one direction thean the otherlike a football. A normal cornea should be round and smooth. A child can have astigmatism associated with myopia and hyperopia.
Reports have shown that astigmatism is the most common refractive errors in children and adults followed by hyperopia and myopia.
Signs and symptoms
Parents, teacher and care givers should be observant and should promptly take a child to the ophthalmologist or optometrist when you notice any of the following in a child;
Holding objects close to their eyes to see them
The child moves in a clumsy way
He/she does not notice things happening in the distance
Lack of interest in reading books
Frequent falls or accidents when playing with other children
Squints; It is a condition where the eyes do not look in the same direction. When the child with a refractive error tries to focus to see clearly, an eye may turn in another direction. This type of squint tends to develop in children who are 2 years or older, especially in children with hyperopia. The the most common squint is the inward looking type (an esotropia).
Refractory errors can’t be prevented. Early detection and prompt correction of the error is very important.
The form of treatment depends on the error noticed in the child. The most common form of treatment is the use of glasses to correct the refractory error.
- Lazy eyes; refractory error is the leading cause of lazy eye which is also known as amblyopia. It is a condition in which there is blurry or reduced vision that is not correctable by glasses, contact lenses or eye surgery. The brain, for some reason, does not fully acknowledge the images seen by the lazy (amblyopic) eye.
- Impaired quality of life
- Loss of educational opportunity
- Loss of vision