Monday, May 04, 2009

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

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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.


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…

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


Anonymous said...

Very Interesting!
Thank You!

Anonymous said...

It took me a while to search on the net, only your site explain the fully details, bookmarked and thanks again.

- Laura

Anonymous said...

Very good entry. Anticipating the next.