Tuesday, June 30, 2009

Refractive disorders: Astigmatism.(1) Vision

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This third refractive disorder is the most common of them all, although the most known is myopia. This can coexist with myopia as well as hyperopia (13 percent of population has only got astigmatism, and 20 percent has astigmatism associated with myopia or hyperopia).

Astigmatic person’s vision

The typical complaints in astigmatism are “`BLURRED VISION´ MAINLY WHEN TRYING TO VIEW DISTANT OBJECTS, AND FREQUENT FRONT HEADACHE”. Only when the astigmatism is high, the complaint is also, “`BLURRED VISION´ AT CLOSE TASKS”.

If you realize I write 'BLURRED VISION' in quotation marks, because this refractive error, usually congenital, causes the outlines of the letters or the objects to be seen distorted; as if there would be some shadows behind every letter or every object, or as if they were seen double or distorted. Actually it is not a BLURRED VISION.

For low and medium quantities of refraction:
  • An uncorrected myopic person has low Visual Acuity at distance but it is good at near.
  • An uncorrected hyperopic person can have a good Visual Acuity at any distance as long as she has enough accommodation.
  • But, in spite of that a little astigmatism of about 0.50 diopter can not appreciably interfere in Visual Acuity in general, a person with uncorrected astigmatism does not have any distance where the image shaped in her retina is perfectly clear. In the case of a hyperopic astigmatism, by using help of the accommodation, it will be easier for itself to achieve better sharpness than a myopic astigmatism.

I am going to show you two simple ways for checking if you or your child has got astigmatism or not:

  1. Put this image in the computer screen and get yourself away about 1 meter or 1 meter and a half, and covering one eye (and without wearing your glasses, if you have it), check if you can see ALL lines with the same contrast, that is, all of them have the same degree of “blackness” or all of them are clear or all of them are blurred.

    If you do not have any astigmatism, the answer will be “yes”; you see it as it is in the drawing, or maybe all drawing is blurred (if you have some myopia or hyperopia).

    But if you have it, the answer will be that you see something like this:

    (Unless myopia or hyperopia, when we give the value of the astigmatism in a prescription, we give the power of the lens and also the axis of said lens).

    This is the most common answer. It would belong to pure astigmatism between 180º and 150º (the astigmatic axis is perpendicular to the lines that you see better). If you have some myopia or hyperopia, as well the rest of axises will be seen out of focus.

  2. Another clear way to check it is looking at the full moon. If you have some astigmatism, it will be impossible to perceive its outlines and it will be seen elongated and out of focus.

Refractive disorders: Astigmatism. (2) Appearance
Refractive disorders: Astigmatism. (3) Different features
Refractive disorders: Astigmtaism. (4) Symptoms
Refractive disorders: Astigmatism. (5) Solutions
Refractive visual disorders. Some clarifications.
Some numbers...

Wednesday, June 17, 2009

Refractive disorders: Hyperopia. (4) Solutions

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Low or even medium hyperopias are difficult to diagnose because, as I wrote in one previous post, they “consume” the refraction. Besides, they are difficult to be detected by parents or teachers because these hyperopic people have a more or less clear vision in any distance. That is why these people need a COMPREHENSIVE EYE EXAM from early age and a chekup once a year.
In that comprehensive visual examination the refraction that the visual system of the hyperopic person is constantly compensating is checked, along with other skills of the visual system, specifically her accommodation which is the one that is working all time, and if it (accommodation) may have disturbed other visual skills.

In the case that the refraction error can be diagnosed or that the error is causing a certain symptomatology, these are the possible solutions:

  • Eyeglasses, either if she needs them to see clear because she has a high hyperopia, or if she has a low one and needs them to avoid that constant effort for close-up tasks, and this way, avoiding certain symptomatology. In the last case, eyeglasses are not used for seeing clear.

    In the case of a high hyperopia, the use of eyeglasses can make sense both for short and long distance seeing, if the visual acuity for long distance is reduced.

    In the case of lower hyperopia, that is causing some symptoms, the option of eyeglasses is good because she does not require wearing them during all day.

    Hyperopia is corrected with plus, positive or convex spherical lenses (thicker at the middle than in the edges of the lens), that optically falls in front the image, on the retina.

  • If hyperopia is higher than +1.50 diopter, another option for compensating it, is by wearing contact lenses for a long period of time. In this case, unlike myopia, each patient may use the best contact lens for her, that is, there is no suitable specific one. There is no one that stops the hyperopia, simply because as I have explained, the hyperopia does not increase.

    There exists a research about Orthokeratology, carried out specifically in Australia, which tries to find a contact lens that model the cornea and reduce the hyperopia; but even, as I say, it is under research.

    Hyperopic people are usually more uncomfortable wearing contact lenses than eyeglasses, because although her visual field is bigger wearing contacts, the size of images is more real; but wearing eyeglasses with plus lenses, they magnify the objects (I will explain this effect later); therefore, as they see everything bigger wearing the glasses, they are more comfortable wearing them than with contact lenses.

  • Vision Therapy is the best allied in this refraction disorder. A hyperopic person does not often respond to lens correction alone, but they are required to “remediate” accommodative dysfunction. With therapy we teach her to control her accommodation and her convergence and to perform her close-up tasks without effort. We will avoid that this to happen again.

    Within vision therapy, besides some simple visual activities, the use of eyeglasses with a low positive refraction will be able to relieve her symptomatology in order to be able to perform the daily close-up tasks. This way, she relieves all accommodative effort that she constantly performs.

  • Besides, as it happens with myopic people, some simple VISUAL HYGIENE AND ERGONOMIC RULES will help prevent her reaching that visual stress. Modification of the patient's habits and visual environment is occasionally useful as an adjunct therapy.


    • Improving lighting or glare reduction
    • Using better quality printed material.
    • Decreasing temporal demands, with frequent rests.
    • Looking far away and focusing on something, frequently, when performing close-up tasks.
    • Etc.

  • Lastly, surgery: hyperopia is a refractive defect that can be operated as well, but except for high hyperopias, it is not considered as the best option.

Refractive disorders: Hyperopia , Hypermetropia or Farsightedness. (1) Vision and Accommodation
Refractive disorders: Hyperopia (2) Different features.
Refractive disorders: Hyperopia. (3) Symptoms.
Refractive visual disorders. Some clarifications.
Some numbers...

Monday, June 01, 2009

Refractive disorders: Hyperopia. (3) Symptoms

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Hyperopia degrees
  • Low: 0 - (+2.00) D
  • Medium: (+2.25)-(+5.00) D
  • High: More than +5.00 D
Behavior of hypermetropic people (symptoms)
Usually, if hyperopia is low, hyperopic people do not have any symptom, and the time can go by until they show any. Besides, the younger the person is, the lesser the symptoms she will have, since her accommdation works perfectly and therefore, she can compensate the problem without any effort.

Either medium hyperopic, or not so young people or in certain cases will show (without wearing the refraction) the following symptoms:

  • Constant or intermittent blurred near vision.
  • If hyperopia is medium/high, it also affects distant vision.
  • Visual inconvenience when she performs close-up tasks.
  • Headache, visual strain, ocular pain, burning, itching, tearing, red eyes… (due to incapacity of keeping the effort of accommodation that is demanded).
  • In the case of low hyperopia that people have always been able to compensate without any problem (both as from a distance and as close up), as time goes by or in a special period with too many close-up tasks (at work or at school), they show inconvenience and discomfort and they do not know the reasons why they are caused. They have always seen well and have not had any previous visual problems; and they do not think, that this can be the cause of their problems. Before seeing blurred at near (while they can still keep the accommodation with effort), they usually show the symptoms above (headache, visual strain, itching, red eyes,...).
  • In the case of children or young people, they usually have problems with the reading: line jumping, jumping letters, letters “seem to dance”, “they don’t stop!”… (presbyopic or old sight people also say these same words). These symptoms cause that they have aversion to reading.
  • They as well perform facial contortions or frequent blinking while reading, that shows the effort that they are doing in their close-up tasks.
  • Poor eye-hand coordination.
  • In children (younger than 3 years old), if hyperopia is high, it can cause accommodative convergent strabismus (crossed-eye). This is because as they are young, they can perform much effort in order to see the image clear; but since accommodation and convergence are related (I will explain this better later), when the eyes perform too much accommodation, they also converge a lot, and one of eyes gets crossed. Consequently, this can also cause lazy eye or amblyopia on that eye.
  • In the case of low hyperopic people who have always been able to compensate without any problem and they have always had a enviable sight in their youth, they inevitably undergo presbyopia. But unfortunately for the hyperopic, they suffer it before that the rest of the people, before they are 40 years old. These people will think that their arms are shorter each time, because they need put their reading text farther (but this refractive disorder deserves its own post later).

Refractive disorders: Hyperopia , Hypermetropia or Farsightedness. (1) Vision and Accommodation
Refractive disorders: Hyperopia (2) Different features.
Refractive disorders: Hyperopia. (4) Solutions.
Refractive visual disorders. Some clarifications.
Some numbers...