Refractive disorders: Hyperopia.(2) Different features

Enlace a entrada en español

Appearance of hypermetropic eye


The farsighted eye, unlike the myopic eye, is smaller than usual, or its lenses have less power.
Consequently, the image is focused BEHIND the retina.







Development

Some authors “…concluded that the growth of the eye during infancy is extremely rapid, and its adult size is reached by the age of 3 years…” and that “…the process of emmetropization is evident during the first year of life…”.

“…by the ages of 6 to 8 years old emmetropization has taken place, the great majority of the children being in the emmetropic group, which has its peaks at 1.00 diopter of hyperopia…”

There is a high percentage of children who were born hyperopic, because our eyes, when we were born, are not completely developed, and are small. As time goes by, if this hypermetropia is low, it disappears when the eye grows, so that sometimes, it can even turn it into myopia in school years.

Hyperopia, unlike myopia, do not usually vary until getting into adult years. At that moment, the appearance of presbyopia or “old sight” causes that the hyperopia increases much more, either hyperopia can appear or the myopia can even decrease.


Prevalence

Around 10% of people in Spain suffer from hypermetropia. 22.4% of population in USA and Australia is hyperopic. Specifically, there is a prevalence of 12.8% in American children aged 5-17 years.

In school years, hyperopia is usually lesser worrying than myopia because the clinically significant values of hypermetropia (and astigmatism) are 2-4% of the children who begin the school years, and also, these values do not increase over time.

“Hypermetropia is influenced by ethnicity. Native Americans, African Americans, and Pacific Islanders are among the groups with the highest reported prevalence of hyperopia. A study of 1.880 Chinese schoolchildren in Malaysia showed that the prevalence of hyperopia greater than +1.25 diopter, was only 1.2%”. (pag 8)


Probability


Factors

If you remember, environmental factors are very important in myopia; however, although the majority of children are hypermetropic when they start the school years, the hyperopia does not usually increase, but it decreases if anything.
Therefore, its existence is usually thought to be caused by hereditary factors.

In the other hand, a visual disorder derived from hyperopia is the presbyopia or “old sight”, that is typical of old people. In this case, this disorder is product of the time as it goes by. The ciliary muscle, as the rest of body muscles, loses elasticity and strength, and as well the capacity of being contracted; this way, the lens can not be more convex, and that prevents the accommodation to happen. That is why hyperopic people begin to suffer presbyopia earlier than emmetropic people; and these ones, earlier than myopic people.

RELATED POST
Refractive disorders: Hyperopia , Hypermetropia or Farsightedness. (1) Vision and Accommodation
Refractive disorders: Hyperopia. (3) Symptoms.
Refractive disorders: Hyperopia. (4) Solutions.
Refractive visual disorders. Some clarifications.
Some numbers...

Refractive disorders: Hyperopia, Hypermetropia or Farsightedness. (1) Vision and Accommodation

Enlace a entrada en español

Carrying on with the “refractive disorders series”, and seeing that there have not been a lot of questions or comments regarding myopia, I will keep on writing about hypermetropia or the “refractive defect of children and old people”.

Vision of Hypermetropic people

The typical complaint in hypermetropia is “INSTABILITY OF VISION WITH PROBLEMS AT CLOSE DISTANCE”.

Her distance vision is usually VERY GOOD; as many people say, a hypermetropic person has “EAGLE VISION”; but unlike myopic people, her visual system is an exhausted system, due to it is constantly trying to compensate her refractive error in order not to have any problems, both as from a distance and as close up.

Therefore, as the near effort is higher, the exhaustion will appear earlier at this distance; and therefore, blurred vision will appear first at near, and then, when the visual system is already very exhausted, she will also notice that she has poor distance vision.
But, what does this mean?
In order for you to understand it better, I need to briefly explain to you the concept of “accommodation”, which I have named it many times previously.

Accommodation

In the case of a person without refraction:

• When she looks an object far away, the visual system must be totally relaxed so the image is focused on her retina and she sees in a clear way;
  

• On the other hand, if she wants to see an object (a text, a watch, anything else) which is around 40 cm far from her eyes (for instance), her visual system has to perform the action of ACCOMMODATION, that is, the ciliary muscle has to be contracted and the fibers of the Zonule of Zinn have to be relaxed (to be stretched); this way, it allows that the lens -8- to be more convex, increasing its curvature, and also allowing its power to increase and letting the image of the near object that is being watched, to be focused on the retina, so it is seen in a clear way.
  

In the case of a hyperopic person:

Therefore, the ocular system can perform the effort required to carry on this retarded image to the retina, through a change of the power of its ocular surfaces. This is the reason why an hypermetropic person who sees wrong at distance (because her image is focused behind the retina), if she is a young hypermetropic person and/or her hyperopia is low, she has the capacity in order to focus the image on the retina and to see it clear, through her eye accommodation; this way, her visual system is constantly under “visual stress” situation in order to keep that image clear.
If also, we add the additional effort that hypermetropic person performs when she looks at their close-up tasks (since hers lens has to be more convex than the ones of an emmetropic person), in order to achieve that the image is maintained clear on the retina, in some cases it can be a really daily effort.

All of this causes some problems:

• For themselves: this constant effort in order to keep the image focused on the retina, both as from a distance as for close up objects, creates stress or exhaustion in the long run, causing a certain symptomatology.
  

• For Optometrists: young hypermetropic people are more complicated to diagnose when the refraction is small, because they are able to “consume” it, their accommodation makes up for any lens.

Well, this is only the beginning…

RELATED POST
Refractive disorders: Hyperopia (2) Different features.
Refractive disorders: Hyperopia. (3) Symptoms.
Refractive disorders: Hyperopia. (4) Solutions.
Refractive visual disorders. Some clarifications.
Some numbers...