Tuesday, February 16, 2010

The Mystery of 3D - Why somepeople see it and others not.

Enlace a entrada en español

Avatar”, as other recent movies, has led the wish to watch movies in a diferent format we are used to or we watch everyday on our televisions.

I suggest to you read this article. Surely you will solve many questions about why some people watch 3D movies without any problem and others feel uncomfortable or can not watch them.

This visual problem can be solve easily with vision therapy in many cases (except in strabismus, amblyopia, monovision or monocular vision).


Don't be startled if 'Avatar' makes you nauseated

Avatar 3-D Images Help to Identify Vision Problems

Thursday, January 21, 2010

Physiological defect: Presbyopia.(3) Solutions

Enlace a entrada en español.


  • In the case of myopic people with fewer than -3.00 diopter, compensate presbiopia for a long time simply by removing their eyeglasses in order to read. I remind you that the myopic people focus the image in front of the retina, and that the presbyopic people focus the image behind it. Here I explain it better:

    A young myopic that looks far away through her well corrected eyeglasses, focuses the image on the retina; when she has to look something at close with her glasses, the image goes behind the retina, but her accommodation helps her to focus it on the retina again.
    Thus, in the case of presbiopic myopic without eyeglasses, when she looks far away, she sees blurry because the image is focused in front of the retina; but when she looks something at close, the image goes back, bringing it closer to the retina, and consequently, seeing it more clear.

  • The most common method to compensate the presbyopia is through some OPHTALMIC LENSES in eyeglasses; but depending on the use of the eyeglasses, that is, for what activities or distances you will use them, there are different options. Therefore, whenever you receive a visual examination, you must give the optician some information about your needs in near vision (reading, computer, work distance, etc.), so that, she can recommend you the best option in your case.

    Basically the compensation of presbyopia requires the use of convergence or positive lenses (magnifying glasses) for near vision tasks. From here, we play with different variations.

    Progressive lenses: These are the lenses that are most used, although their adaptation is not easy.

    These lenses allow to have clear vision at all distances (from far away to up close) simply by changing the inclination of the eyes or the head; this is something everyone wishes, specifically if the focus distance has to be constantly changed. But these lenses have got two main inconvenients:

    1. they have a vertical “corridor” of central vision that is more narrow than any other lens (due to optic aberrations in both side of the lens); therefore, when we look out of the corridor, the vision is blurred;
    2. and we have to learn to use these lenses, since we have to learn by which areas of the lens we must look at, depending on the distance where we want to see. Once achieved, the effort will be worthwhile.

    Bifocals lenses: These are less used lenses (before the progressive lenses appeared in the market, these were the best option), but for those people with certain binocular problems, whose daily activities require clear distance-near vision, and when they do not accept the progressive lenses, the bifocal ones may be their only option.

    The top of the lens has a graduation which is required to see clear distance objects; and the bottom part has a “segment” that has the addition required to see clear close up objects AT A CERTAIN DISTANCE.

    Advantage: The adaptation is much easier than the progressive ones, because the bifocal lenses do not have so many aberrations, nor so many areas with different graduation for different near distances; simply by performing two eye movements, we can focus far away or close.

    Disadventages: Precisely the last advantage is a disadvantage as well: the bifocal lenses allow clear vision in only two specific distances (they lose the intermediate distance) and they are less aesthetic, “they betray the age”.

    Trifocal lenses: They are lenses basically obsolete.

    Reading lenses: These are the best option for those that see very well far away, so they need nothing for distance. They are lenses with only one graduation, so, they are prefect in order to perform prolonged near tasks.

    In this option there is not any specific size of eyeglasses. But if you need to alternate your vision in different distances, mainly far away-close up, it is more recommended to use narrow glasses, known as “half moon reading glasses” which let you look over them when you look far away, without performing strange head positions or movements.
    These small glasses have one inconvenient: as the bifocals lenses, they also “betray the age”, although nowadays there are many models of eyeglasses which do not have the typical shape of “half moon”, and that can be perfectly fine.

    Reading glasses work well with contact lenses.

    Ready-made reading glasses: They are standard reading glasses, that is, they are the same for everyone. THIS IS NOT AN OPTION. These glasses are only good for pulling through at a specific given time, nothing else. But I will write about these glasses in other post.

  • PROGRESSIVE CONTACT LENSES: The adaptation is even more complicated than with progressive lenses in eyeglasses, but the success rate is increasing. The complication resides in that the brain is responsible for learning what RING of the contacts has to look for, depending on whether it wants to focus far o close. It is not easy for everybody, and not everyone achieves a successful behavior.

    With this kind of contacts, a type of adaptation is usually performed called MONOVISION: one eye has better vision for looking far away and the other eye has better vision for looking at near.

  • Besides these solutions, I have mentioned above, during last years the cataract surgeries have promoted the research of the INTRAOCULAR LENSES with accommodative capacity: the ophthalmologist removes the crystalline lens and puts a new lens inside of the eye, with the suitable graduation.
    More information

Friday, December 25, 2009

Tuesday, October 20, 2009

Physiological defect: Presbyopia.(2) Causes and risk factors

Enlace a entrada en español.


As I explain in a previous post, presbyopia is a visual disorder that is product of the time as it goes by.
When we look something at near something in order to focus and to see clear, a phenomenon is caused in our eyes called ACCOMMODATION, and the lens has to change its shape so that the image of what we see, is focused on the retina. But over the years, on one hand, the ciliary muscle, as the rest of body muscles, gets more rigid and shorter; and on the other hand, the lens increases the thickness of its faces, thus losing its elasticity (this therory is the most approved one). So, the muscle loses the ability to contract itself to allow that the lens to be more convex (at the same time, the crystalline lens does not do it because of its stiffness), and the accommodation does not happen.

This loss of accommodation process is gradual. It begins affecting the vision in the closest distance, and the changes of focus in different near distances are slower and with worse quality (those changes of focus are what we call “accommodative flexibility”). Little by little the ability to focus on near distances and increasingly farther from oneself its more difficult; this happens when our arms begin to stretch and in a certain moment they seem short. When it happens, this indicates that our focus is failing and we need a lens that compensates the accommodative effort that we can not perform anymore.

When a child is 10 years old, has an accommodation of around 14 diopters (that means, the closest distance where she can focus something very small is at around 7 cm); this quantity decreases linearly with the age, until that, at 50 years old, the accommodation is around 2.50 diopters (the closest distance where she can focus something very small is at around 40 cm, as you see the focusing ability has decreased almost 6 times the one of the child).
This process begins between the 40’s and 50’s (depending on the refractive error that we already have at a young age; at the beginning the presbyopia starts adding a little positive lens for near distance -1.00 diopter approximately - over the graduation that we need to see far away); it usually stops around 58 years old (with a addition of around 2.25 or 2.50 diopters).

Presbyopia equally affects everyone, but hyperopic people start to suffer it at an earlier age than the emmetropic one; and these ones earlier than myopic people. Some of these myopic people (low and medium), when the presbyopia appears in their lifes, they are capable to read without using their eyeglasses, because of the compensation that is caused between both phenomenons.
From the moment presbyopia appears, this increases during a period of 10 or 12 years and then it is strabilized. Some of you, seeing how fast presbyopia increases when it begins, might think that it will never stop, but I assure you that it does.

In the case of some emmetropic or low hyperopic people, they suffer an increase of hyperopia after using reading eyeglasses of +1.00 dipoter during some time, when presbyopia is evident; so that after a couple of years, that graduation is not enough for the close up tasks, but they are only useful for distance vision. This is called HYPEROPIA OF PRESBYOPIA.

Risk Factors

According to American Optometric Association

Physiological defect: Presbyopia.(1) Vision, Appearance and Symptoms
Refractive visual disorders. Some clarifications.
Some numbers...

Physiological defect: Presbyopia.(1) Vision, Appearance and Symptoms

Enlace a entrada en español

Presbyopia is what everybody knows as “old sight”. It is not considered as refractive disorder or an ocular illness.

Vision of presbyopic

The typical complaint in presbyopia is “BLURRED VISION AT CLOSE DISTANCE”. A presbyopic person stretches her arms in order to see better, but in a certain moment “THEY ARE TOO SHORT”.

Distance vision may have not any changes, at least in the first stages.

Appearance of presbyopic eye

The shape of the eye is like a myopic or hyperopic or even emmetropic one at young age; but the difference is given by the crystalline lens. When a person looks at objects up close, she is not capable of focusing them on the retina, but behind (as hyperopic people), therefore seeing them blurred.


Everybody will have suffered presbyopia sooner or later, after 45 years old.

As presbyopia is age-related, its prevalence is higher in societies in which larger proportions of the population survive into old age.

For instance, from all Spanish population, 43% suffers “old sight”. And from this 43%, 7% of presbyopic people have never checked their vision in any previous occasion. Because of the increased life expectancy, within 10 years, more than half of the Spanish population will suffer from this condition.

It does not exist any way tested to be true in order to prevent it.


Incipient presbyopia (the first symptoms)
  • It is difficult to maintain the performance of near task in a continuous way.
  • Headache because of the continuing effort.
  • The letters seem to move on the paper.
  • More light is necessary in order to see better.Near vision is worse at the end of the day.
  • Sometimes it seems that we “do not control” our eyes (as the accommodation and convergence are related, the gradual loss of accommodation involves the progressive worsening of our fusion, resulting in Convergence insufficiency, and even in a double vision when we are more tired).

Evident presbyopia
  • We stretch our arms in order to find the distance where we can read whatever we want, until a certain moment where we do not get to read although we stretch them completely.
  • At the beginning presbyopia only affects near distance (documents, handicrafts,…), and little by little it starts affecting intermediate distance too (computer,…)
  • We tend to avoid the small texts and precision tasks in near vision whenever we can (we do not sew anymore, we do not read so much, we do not perform certain leisure activities that we liked… :-( )
  • We always look for natural light or a good light lamp.
  • It is usually accompanied by “Dry eye”.

Refractive visual disorders. Some clarifications.
Some numbers...
Refractive disorders: Hyperopia , Hypermetropia or Farsightedness. (1) Vision and Accommodation

Thursday, September 17, 2009

World Sight Day 2009 (WSD)

Información en español

8 OCTOBER 2009

World Sight Day (WSD) is an international day of awareness, held annually on the second Thursday of October to focus attention on the global issue of avoidable blindness and visual impairment. This year, it focuses on gender and eye health–equal access to care.

VISION 2020 is the global initiative for the elimination of avoidable blindness, a joint programme of the World Health Organization (WHO) and the International Agency for the Prevention of Blindness (IAPB) with an international membership of NGOs, professional associations, eye care institutions and corporations.

Over the next two decades, Vision 2020 will take steps to prevent an estimated 100 million people from becoming blind.
Vision 2020 focuses on creating adequate eyecare facilities, a foundation of well-trained eyecare
workers, implementing programmes to control the major causes of blindness, and integrating
eye-care into general health care services... (more)

More information:
VISION 2020: The Right to Sight
What is VISION 2020: The Right to Sight?
International Key Messages