Refractive disorders: Hyperopia. (4) Solutions

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Solutions

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.
  
  Mainly:
  
  
  • 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.

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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).

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Refractive disorders: Hyperopia.(2) Different features

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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.

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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.

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…

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Enlace a entrada en español

Extracts of the Presentation to the International Society for Geographic and Epidemiologic Ophthalmology by David Dunaway and Ian Berger (InFOCUS Center for Primary Eye Care Development).


[…] Estimates of the number of people worldwide with refractive error range from about 800 million to 2.3 billion. No prevalence data are available from the World Health Organization or from any other source relating to very large populations such as groups of nations, or whole countries. […]

[…] As for the proportion of an entire population with refractive error, Daniel Etyale of the W.H.O. reported at a special session on refractive error at an International Agency for Prevention of Blindness meeting in 2001, that 5 -15 percent of children are considered to have refractive errors, the majority of which are uncorrected, and that there is currently a need for population based studies to ascertain these figures. […]

[…] Although sufficient data have not been collected to accurately predict prevalence per diopter of correction for most populations, general prevalence information on the three types of refractive errors and of presbyopia can provide an orientation of what to expect.
- Hyperopia, for example, is usually present at birth, except in premature infants. Hyperopia decreases in magnitude through age 4 years, and the prevalence of hyperopia less than +1.25 D (an amount usually difficult to compensate accomodatively) is 4-7 percent between ages 5-20 years, remains constant through early middle age, then increases in populations aged 45 or more. […] Hyperopia also occurs in patients with poorly controlled diabetes and in patients who've had cataract surgery.
- Myopia prevalence varies with age, race and sex, increasing at least through adolescence, and is present in 1 per cent of children at age 5 years, increasing to 8 per cent at age 10 years and about 15 per cent at 15 years. Myopia occurs slightly more frequently in females than in males.
- The prevalence of astigmatism may be as high as 70 per cent, if all amounts are included, but is considered to decrease to 3 percent if the extent is limited to 1.25 diopters or more. […] If astigmatism is greater than 1 diopter, it usually develops before age 2 years.
- Not a refractive error, presbyopia is due to a loss of accommodative ability. It usually starts between ages 38-45 years and the prevalence is 100 percent by age 55. Early onset is associated with hyperopia. […]

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Refractive visual disorders. Some clarifications.

Refractive visual Disorders. Some clarifications.

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As I wrote in the previous post, when we assess somebody’s Visual Acuity and the result obtained is not 20/20, it may be, among other reasons, because of the presence of some “ametropia” also called “refractive eye disorder” or “refractive error”.


But before explaining what these words mean, first I will explain what Ocular Refraction is: it is a physical phenomenon where the light rays from the object that we look at and from the whole visual field surrounds it, when crossing certain optical structures of the eye, change their path to focus on the fovea (13) and certain points of the retina. There, these light stimuli are converted into nervous stimuli which are sent to the brain (occipital lobe) in order to convert the information from the both eyes into simple and clear image of the target and all that surrounds it.

This change of the light path is mainly due to two structures which act as lens into the eye: the cornea (1) and the crystalline lens (8) . And to a lesser extent: the aqueous humor (4) (in the anterior and posterior chamber) and the vitreous body (9) (inside of the vitreous chamber), which also influence the “dioptric power” of the eye.

Therefore, when the image of an object, placed at 20 feet (6 meters), is focused on the retina of an eye, it shows that this eye is emmetrope and its Visual Acuity (if it does not have any pathologic disorder that hampers it) will be 20/20 or better. That is, this eye does not suffer any refractive eye disorder.


But if the two following conditions are fulfilled:
- its Visual Acuity is lower than 20/20
- and it improves with the help of eyeglasses, contact lenses or another optical option,
then we can catalog this eye disorder as “Refractive Error” or “Ametropia”. This disorder is due to an upset in the power of either one of or both lenses (surfaces more curved in the case of the myopia and more flat in the case of the hypermetropia), or a change of the eye axial length (the eye is too short in the case of the myopia and too long in the case of the hypermetropia):

Grosso modo, I will now explain the refractive eye disorders, but in later posts I will explain each one of them in detail.

MYOPIA: It is the refractive error that is better known, worldwide. This prevents the distant objects to be clearly seen. In this case, optically, the light rays from the distant object (placed at 20 feet -6 meters-), are focused in a point in front of the retina, so the image is blurred.

HYPERMETROPIA or HYPEROPIA: This refractive error prevents the nearby objects, and sometimes the distant ones too, to be clearly seen. In this case, optically, the light rays from this object are focused in a point behind of the retina; so, as with the myopic eye, the hypermetropic one also sees the image blurred.
But the difference with the myopic eye is that this defect of vision is more unnoticed, and it is a defect no so well-known by people, because of the modifications that the crystalline lens can perform of its curvature, so this lens can compensate part or all of this hypermetropia ( if this is not very high) so it remains latent.
It is the most common refractive error in the newborn, because when the baby is born, the eye is not completely developed and as the body grows, so does the eyes. So, a baby with a small hypermetropia may turn into an emmetrope when she grows.

ASTIGMATISM: In the previous refractive errors, the cornea is a spherical structure (as if it was an inflated basketball that we have cut in half). However, in this defect of vision the cornea can be seen as an American football also cut in half.
Therefore, each curve in the cornea has a different dioptric power (I will better explain this concept later) and consequently, the light rays that cross each curvature suffer a different change of direction, and causing a focusing of the image on different points regarding to the retina, causing not only a blurred image but also a drop-shadow effect in the surroundings of the distant and/or nearby images. Because of this reason, the astigmatism can co-exist with myopia or hypermetropia in the same eye, but these last errors can not co-exist in the same eye at the same time.


All these refractive eye disorders cause a “faulty vision”, but in these cases this is only due to a wrong Visual Acuity. That’s why, VISION and VISUAL ACUITY are not the same concept, because we can have a value 20/20 of Visual Acuity and not being able to read the registration number of the car in front of us at 2 meters (6 feet) or keep on reading for 1 hour. Visual Acuity is only one of the different features of vision.

These “ametropias” are primary; secondarily, other refractive eye disorders may also arise:

ANISOMETROPIA: It is very strange to find a person with the same quantity of ametropia in both eyes (because we do not have two identical eyes), but anisometropia is the condition in which this difference is so big, that it is difficult that the information from the images from each eye that arrive to the brain, can be fused (I will explain this better) and can create a simple clear image.

AMBLYOPIA: It more well-known as “LAZY EYE”. This may be related to the previous disorder. I am sure some time you had seen a child wearing a patch at school or in the street, since this is one of the many ways to treat this problem (I will explain this one too).
In this case, the difference of eyeglass prescription and the functional features of one eye may be very different from the other, so one of them develops better. In this case the early diagnosis and treatment is VERY IMPORTANT.

PRESBYOPIA: Sooner or later everybody will “suffer” from this ametropia, even the person that think that, while being young, has got the best vision of the world… Sorry
This is just because of the natural aging process of human body. As time goes by we keep on losing our forces and things we could perform some years ago, now we are not capable of doing them; in vision the same fact happens too. Inside the eye, the muscle that controls the change of focus for different distances, by modifying the curvature of crystalline lens, “is more tired” too and keeps on losing flexibility, force and speed of response. As time goes by we have more difficulty for focusing more quickly and we can not see small details of nearby objects. The arms seem to stretch more and more and we would wish we’d have them longer in order to read a medicine directions for use or just a newspaper. In this case, the problem we have I resides in nearby tasks.


In the other hand, there are other disorders that also cause reduced Visual Acuity, but the difference is that this value can not be improved with any optical option, they are not refractive eye disorders but pathological disorders: Cataract, Macular Degeneration, Glaucoma ... In these cases the required treatment can not be offered by the optometrist (medicines and surgeries).


Besides there are defects of vision that are independent of the Visual Acuity value, such as, for instance: a reduced visual field, a disorder of color vision, a problem in order to focus in an efficient way when we read a book, or to work with both eyes as a team, or to discriminate shapes, or to remember what we see, or to copy something we see, or to follow a straight line… Therefore, these are not disorders of the Visual Acuity.

ILYD

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