Hyperopia

Hyperopia is a refractive abnormality in which the child can not clearly see objects that are close to him. It is often referred to as the opposite of myopia, but it is not always correct, because children with hyperopia may not be able to see well even in a far distance.
In hyperopia, the image of the distant object we are trying to see, is not focused on the retina, so that we can have a clear picture, but behind it.

This may happen either because the system of the refractive media of the eye does not have enough power, or because the anteroposterior diameter of the eyeball is smaller.

 

The development of hyperopia

Since the sagittal axis of the eye is naturally small in the neonatal and childhood age, up to a point hyperopia is considered normal or even expected.

The procedure of hyperopia is prescribed, meaning that, as the child grows, so does its eye and the anomaly will gradually decrease. This does not mean that the final outcome will be an emmetropic (normal) eye. Some degree of hyperopia may remain or even (after some stage emmetropia) the eye might become myopic.

Generally hyperopia may slightly increase until the 6th or 7th year of life, but thereafter it decreases continuously until the end of puberty where the development of the child is completed.

 
Adaptation and convergence

For a better understanding of hyperopia and the relationship it may have to strabismus, we should clarify two main functions of vision, adaptation and convergence.

Adaptation is the ability of the eye to focus at different distances from infinity to very close. The range of adjustment is very large in children and a child with normal vision or a child with properly corrected vision by wearing glasses, can practically see at all distances.

 
In adults the ability to adapt is increasingly reduced. When loss becomes so great that it causes problems in our daily life (when e.g. it is hard to read a book), then we are talking about presbyopia.

 
The adjustment is achieved thanks to the ciliary muscle, an annular muscle surrounding the lens of the eye. The contraction of the ciliary muscle depresses the lens and changes schematically, making it thicker. A thicker lens has a greater refractive power and can focus better on objects that are closer. When the ciliary muscle
relaxes, the lens becomes thinner with less refractive power and it ideally focuses at infinity.

[The adjustment is not enough by itself, when we want to see an object that is close to us.The lens of the eye (blue) under the action of the ciliary muscle is thickened and increased strength allows it to focus on objects that are close to it.]

When we focus far away, our two eyes have substantially parallel axes. But when we need to focus on a nearby object that lies ahead, the optical
axes cannot remain parallel, but must converge towards the object. This is accomplished by turning the eyes inward (towards the nose), a
phenomenon called convergence.

 
The module of the convergence is the prism diopter (D).

 

The amount of convergence (the inward turning of the eyes) caused solely by adaptation, is called adaptive convergence.

 

 
The quotient of adaptive convergence and adaptation

 
The quotient AC/A, ie the amount of adaptive convergence per diopter adjustment, ranges from 3: 1 to 5: 1 and is for most people stable.
The quotient of AC/A is responsible for any changes in the angle of strabismus depending on the distance that the patient focuses in.

A high ratio of AC/A may explain why a child does not squint when looking away, but shows a convergent strabismus (squints inwards)
when focusing close.

 
The hyperopic glasses

 In contrast to myopia, the correction of hyperopia requires lenses, which are thicker at the center and thinner at the periphery (convex). As in the case of myopia, hyperopia glasses are not a permanent cure or treatment, but the necessity of a daily use is different.

 A child with low or moderate hyperopia may be able to focus on an object without wearing glasses, thanks to its large reserve of adaptive potential. As mentioned above, the radial muscles are responsible for the adaptation and after some time, fatigue occurs to these muscles and the child displays fatigue symptoms such as dizziness, blurred vision or headache. So hyperopic glasses do not only help the child see clearer, but also contributes to it feeling better.

 One issue that arises with hyperopic glasses, especially if strong, is that they act as magnifiers and the child's eyes appear larger, causing sometimes teasing by his classmates at school, which can affect the child’s psychology.
A parent’s frequent question is if the child could replace glasses with contact lenses and the answer is different for every individual and has to do with the degree of responsibility of every child.