They may lead to blurred vision, inability to read letters, skipping letter lines, diplopia, eye pain and headache after near vision activities. Early diagnosis and correcting refractive errors is very important in order to eliminate those symptoms referred to as asthenopia.
Ability to focus environmental images on retina is achieved by refractive power (approximately 64 Diopters) of the eye. Lens and the layer covering the pupil in the form of a watch glass, namely cornea, are responsible for refraction. Inability to focus the image on retina or the refractive error occurs in three types; hyperopia, myopia and astigmatism. Lack of refractive error is referred as emmetropia.
Of newborns, 75-85 % is hypermetropic and 15% is emmetropic. Hyperopia, myopia and emmetropia occur in 80%, 5% and 15% of all preschool-age children. Although frequency of refractive orders seem such high, these are relatively small values which do not require correction.
Disorders requiring correction glasses develop at rate of 10-20 percent.
In hyperopia, parallel light rays focus at posterior part of the retina. Short anteroposterior axis of the eyeball and low refractive power of cornea or lens may lead to hyperopia. Mild hyperopia cases do not require correction. However, vision is not clear in larger amounts of hyperopia and correction glasses are required. Hypermetropic children require accommodation in order to have well near vision. Excess accommodation may result with eye fatigue, headache and pain in the eyes, esotropia and strabismus. Those children avoid close activities. Reluctance to read, rubbing eyes and blepharitis are commonly observed.
Treatment involves convex lenses. Refractive examination for children aged below 10 years should be made only after pupils are dilated with eye drop.
In myopia, rays lying parallel to the eye at 5-m distance are focused at anterior part of the retina.
Myopic patients have well near vision, though they suffer difficulties in seeing distant objects.
Symptoms of myopia in children may include reluctance to distant objects, watching TV at close distance and inability to see the classroom board.
Astigmatism is characterized with inability to focus rays in the form of spot on the retina since refraction of lens or cornea is not equal on all axes.
Primary school age is the baseline period of the myopia. Genetic predisposition, familial history of high refractive error and environmental factors are responsible for the development of myopia. Myopia progresses rapidly within several years following first onset, and later the progression rate decreases. Therefore, children wearing glasses for the first time should visit the ophthalmologist every 6 months. Later, ophthalmic examination can be made annually. In this period, increase in the refractive error may reach up to 0.5 Dpt per year. This increase is eliminated when the puberty ends and growth of eyeball ceases at or around 18 years of age.
Myopia with visual accuracy of 5/10 or better with both eyes open may not need correction with glasses. This corresponds approximately to -0.50 Dpt.
However, myopia with higher Diopters requires wearing glasses. Wearing myopia glasses particularly when the child reads book will actuate accommodation muscles and it will prevent exotropia at further ages.
If decision is made to prescribe correction glasses, selection of spectacle frame and correction glass is very important.
Gravity center of the frame should be spread along the nose using a silicon part since nasal bones of the children have not completed development yet. The posterior part of the frame should be in the form of “C” in order to completely fit the shape of ear to avoid dislocation of the frame. The frame should not cause pain in and around nose and ear; vertical and horizontal axes of the spectacles should optimally intersect at the point where pupil is located.
Recently, correction glasses are usually made of organic materials. Polycarbonated material can be suitable in order to avoid injury of eye when the glasses are broken. UV filter applied on the correction glasses provides protection against hazardous ultraviolet rays of the atmosphere.
There are two diseases requiring use of contact lens in children. First one is the cataract operation during childhood and the second one is the keratokonus disease, which is characterized with the degeneration of cornea.
Recently, use of contact lens became more common particularly in adolescence period.
However, infections deriving from use of contact lens are among complications which may permanently disorder the vision. Therefore, personal hygiene and selection and use of appropriate lens are very important.
In conclusion, before school starts ophthalmological examination for your children is highly recommended for determining any refractive defects and if required, suitable spectacle and glasses will be prescribed in order to positively influence all aspects of school life.