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

Refractive disorders: Astigmatism.(5) Solutions

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Solutions

Just as myopia and hyperopia, astigmatism can be corrected with eyeglasses, contact lenses and/or refractive surgery.
In any treatment, the correction is more complex because of the asymmetry of this refractive error.

• Eyeglasses, with usually the same correction to look far away and to look up close (although there are some cases in which the astigmatism may be different in one distance or another).
  
  The lenses used for compensating astigmatism depend on the kind of astigmatism we have.
  So far, the compensation of a refractive error was simple, because a spherical lens modified equally every ray that crossed it at any point of it; that is, any ray that got to the lens, got to the retina. In the astigmatism, this is MORE COMPLICATED.
  Because all surface (of cornea or crystalline lens) has not got a symmetrical curvature (there will be a meridian with more curvature and other with a lesser one), the light that gets into the eye, gets to different points regarding the retina. Therefore, if we put a spherical lens in front of a astigmatic eye, it will only correct a meridian. This way, all rays, that go through the lens and later through the eye, will keep on getting to different points with respect to the retina, because some of rays will be focused on it, but others will be focused behind or in front of the retina (depending on the kid of astigmatism).
  
  To make it simpler. Think that an astigmatic person sees the image distorted; on the other hand, it is usually accompanied by hyperopia or myopia that causes seeing blurred images. So, for you to understand it better, “this person will see blurred through one meridian, and distorted through the other”. Consequently, we need a lens with two different powers to compensate both effects: one spherical lens to compensate the blur and other cylindrical or toric lens to compensate the distortion. Each one will focus the rays that go through by each meridian, INTO the retina.
  
  The eyeglasses with astigmatism may usually make you feel a little sick when you begin to use them, mainly with refractions over 1.00 or 1.50, that is why it is advisable to start using them gradually. In fact, in high degree, firstly diagnosed astigmatism, the graduation is usually prescribed gradually, increasing it little by little.

• In the past, astigmatism could only be compensated with eyeglasses, because the cylindrical lens demands it to be worn with specific angle degrees. The contact lenses on the eye ares in constant movement because of the blinking, and in the past, this prevented that stability from happening. When said contact lenses were made, these were made with a material that lasted for a long time, because manufacturing was expensive. Latter research lead to the current situation, where there are many systems to stabilize them, and the cylindrical power in disposable contact lenses is higher and higher as time goes by.
  Therefore, nowadays, this refractive disorder may be compensated with soft contact lenses as well as with lenses; and in adults as well as in children.
  
  In the cases of astigmatism caused in keratoconus, they are usually compensated with rigid gas permeable contact lenses, with the purpose of holding the process of growth of the cornea a little bit. But sometimes we choose the soft contact lenses in the cases where the other lenses are impossible to wear due to the blinking; on one hand, because the eyelids may expel the lenses; and on the other, because they are not stabilized in the best position possible, therefore causing blurred image. Anyway, these patients usually achieve better Visual Acuities with contact lenses than with eyeglasses.
  
  Also, the astigmatism caused by a problem such as a deformation of the eyeball by palpebral disorders (as chalazion), treating the underlying cause will resolve the astigmatism. If the patient suffers a severe astigmatism, her best option is the semi-rigid permeable contact lens.

• In the other hand, vision therapy is useful when the visual system has been compensating a little difference of graduation from between some meridians and others, and the focusing (accommodation) and team coordination (fusion) are tired.
  
  We use vision therapy when symptoms exist and we have to teach the visual system to use its accommodation correctly again.
  Many times simply wearing some eyeglasses is just not enough because they do not resolve completely the problem.
  Although initially you see well with them or maybe you have started to use them and everything seems to be going better, shortly you may be uncomfortable again and unable to perform at work or when studying.
  During a time you were using your visual system incorrectly and you have to re-educate it; the eyeglasses by themselves will not do it.

• As the previous refractive disorders, the VISUAL HYGIENE AND ERGONOMIC RULES must always be taken into account.

• And finally, the refractive surgery is another option. It consist of changing the shape of the cornea, and therefore correcting the astigmatism in the cornea or in the crystalline lens.

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Refractive disorders: Astigmatism. (4) Symptoms.

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Behavior of astigmatic people

A low degree of astigmatism USUALLY causes more symptomatology, because the visual system tries to compensate it, and does not show blurred vision symptoms; therefore, at the beginning people do not usually associate the symptoms to a vision problem.

• The main symptom is the distorted and blurred vision in high astigmatism; and headache, visual strain, ocular itching and red eyes in low astigmatism.
  
  As I explained in a previous post, a young hyperopic person with the low degree is able to “disguise” her disorder if her accommodative function works correctly. But in the case of an astigmatic person, although her accommodation is in correct condition, it “gets crazy”, because it has several points or images that fall in different planes regarding the retina; accommodation is constantly trying to focus all of them, without distinction. The closest points of the retina will cause less tension, but those that are farther will be more difficult to compensate. Visual system will be exhausted and the symptoms (red eyes, itching, burning, tearing, headache, visual strain,…) will appear.

• Although a person with astigmatism is usually born with it, if this is low, she could compensate it during the infancy. But as the child grows up and the school request is higher (more number of homework or study hours, more reading, more understanding,…), and her accommodation naturally decreases, the child has got more problems to compensate it; and this moment is when the astigmatism is obvious, showing several symptoms. That is why, many people say their astigmatism appeared between 10 and 20 years old.

• So, an astigmatism will cause more symptoms if it is associated with a hyperopia than with myopia, because hyperopic people have a more exhausted accommodative system due to the excessive effort that she makes to compensate her refractive error.
  

• That is why astigmatism can also cause learning disabilities.

• It can develop wrong postural habits, like tilting her head when looking far away or looking up close, since when the astigmatic person tilts her head, can find the position in which she sees better, or where the image is less distorted. This can cause cervical problems in the long run.

• “Blurred” or double vision greater at near than at distance.

• While she reads, she jumps the line or the letters seem to be moving.

• Visual strain and feeling sleepy.

• Headache mainly in the fronthead and in the eyes.

• Photophobia (light sensitivity).

• Frequent conjunctivitis or blepharitis.

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Ocular injuries after solar exposure

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A digression on the “Astigmatism series”.

Summer is here and many of you had already been on holiday or you are thinking about that, preparing everything to enjoy a well-deserved time for rest :-)

Do not forget to put in the suitcase sunglasses for all your family members (adults and children). Just as you do not forget the sun protection lotions, sunglasses are something indispensable to enjoy some safe holiday.

Think about the time that you are going to be performing outdoor activities, without your eyes being protected. Furthermore, there are more harmful radiations in the beach, because we have to add the ones that are reflected in the sea; but many surfaces reflect those harmful rays (sand, buildings, sidewalks,…). Even in cloudy days, with high clouds, the solar radiation that crosses them is nearly the same one that when there are no clouds at all. Only rain, fog and low clouds reduce UV radiation in a significant way.

Any tissue of the eye, as it happens with the skin, can be burnt. Solar UVA or UVB radiations on the tissues cause a cellular death process and a transformation of cell DNA, which can create irreversible disorders. Therefore, we must take care of our eyes by wearing lenses that comply with health regulations of visual quality. In the case of European sunglasses, the CE mark identifies glasses fulfilling quality regulations.

Atmospheric ozone is a barrier against very detrimental UVC radiation and other UV types; and this moderates the quantity of UVB that arrives to the earth (more harmful than UVA).
The constant slimming of ozone layer causes an increase of the UVB radiation that we receive daily. So, while this keeps being like that (unfortunately), we will have to do everything in our power to protect our eyes.

Some injuries that are caused in the eye due to solar radiation are the following ones:

IN CONJUNCTIVA (5)

• Squamous cell carcinomas
• Pterygium
• Pinguecula

IN CORNEA (1)
Cornea and crystalline lens absorb most of UVA and UVB radiation that get into the eye, damaging these structures; therefore, if a person has got a keratoconus or she has undergone a refractive surgery, her cornea will be thinner and it will be able to absorb less radiation, so, this radiation might get into the eye, causing some injuries.

• Painful superficial keratitis
• Photokeratitis or snow blindness
• Climatic droplet keratopathy or Spheroidal Degeneration

IN AQUEOUS HUMOR (4)
The aqueous humor of the anterior chamber has a lot of Vitamin C (ascorbic acid), which is responsible for filtering UV radiation, and this way, achieving that the least amount possible of radiation gets to the crystalline lens.

• A prolonged exposure to sunlight decreases the quantity of vitamin C in the aqueous humor.

IN CRYSTALLINE LENS (8)
The same as solar exposure can cause that your skin aged sooner, the same happens with the lens; it might suffer from a premature aging, because of the damages in DNA.

• Cataratas

IN RETINA (10)
Looking directly at sun (in a eclipse or not), without adequate eye protection, causes a photochemical damage of the photoreceptors, inducing a burn at macular level (area of maximum vision of the retina) and being the reason of an irreversible blindness.

• Early development of Macular degeneration
• Melanomas

Refractive disorders: Astigmatism. (3) Different features

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Development

Astigmatism relatively changes a little throughout all life.

Astigmatism is not very frequent during school age and it has got few changes of frequency and degree. One study made in Orinda, California, showed that the frequency of increase in an astigmatism of 1 diopter or more, at 6 years old, rises gradually from 2% by 3%, at 14 years old.

Higher levels of astigmatism are associated with moderate to high hyperopia during infancy, but both tend to decrease by the age of 5 years.

If a child is going to have a high astigmatism, it should already exist before beginning school stage.

In adult age, astigmatism does not usually change; if it do it, it usually indicates tension-related one, as myopia (in both cases vision therapy is very useful in order to structure a correct vision).

The little astigmatism that appears during infancy can be due to the strength that the upper eyelid exerts on the cornea causing that the vertical meridian to be more curve than the horizontal one.
In a more mature age, this astigmatism may change its shape, turning the vertical axis flatter, because of the laxity of palpebral muscle that rests on the eyeball. That is the reason why the axis or degrees of our astigmatism change through the years.


Prevalence

According to an American study published in Archives of Ophthalmology, nearly 30% of children between the ages of 5 and 17 have astigmatism.
On the other hand, a recent Brazilian study found that 34% of the students in one city of the country were astigmatic.
The National Autonomous University of Mexico revealed that astigmatism is the visual problem with most prevalence among people younger than 23 years old, and even 23% of population younger than 14 years old, put up with it.
Regarding the prevalence in adults, a study in Bangladesh found that nearly 32.4% of those over the age of 30 had astigmatism.
Also, several studies have found that the prevalence of astigmatism increases with age.


Factors and Causes

FACTORS:
If a child is going to have a high astigmatism or hyperopia, these will appear from birth or in early age. This means the factors are hereditary.

CAUSES:

• High weight of the upper eyelid.
• Slightly fallen upper eyelid (Ptosis).
• Ocular contusions.
• Corneal scars or lacerations, due to hits, injuries and infections in the eye.
• Changes in corneal shape following eye surgery (refractive one, of catarata,…)
• KERATOCONUS (this disorder will have its own post later, but let me briefly explain that the cornea acquires a conical shape as time goes by, and each time it gets thinner).
• Metabolic changes, as for instance high sugar levels in the blood that changes the shape of the lens of the eye, and this causes astigmatism. When this sugar level is normalized, the lens usually gets back to its shape and said astigmatism disappears.

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Refractive disorders: Astigmatism.(2) Appearance

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Appearance of astigmatic eye

As I wrote in a previous post, one characteristic of the astigmatic eye is that the external face of its cornea -1- is not spherical (as a pure myopic or hyperopic eye), but elliptical. It is similar an American football cut in half (CORNEAL ASTIGMATISM).

But astigmatism may be more complicated than all that, since because the cornea has a thickness, the curvature of the internal face of the cornea may also cause an astigmatism that is more complicated to diagnose and treat; the same happens with the one that is caused also because of an unusual slope of the crystalline lens -8 (INTERNAL ASTIGMATISMS). Those last cases are less frequent.

But both of them (corneal and internal ones), may exist at the same time; and the addition of both, is the result of the total astigmatism that one person has got.

This typical shape of the ocular surfaces causes that their different "meridians" (horizontal and vertical ones) do not have the same power; therefore, some of them are more curve than others, and this causes the light is focused on two or more planes regarding the retina, instead of only on the retina itself. The light is clearly focused along one plane but is blurred along the other. The result is blurred vision at all distances.


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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.

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