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Archive for June, 2012

Myopia (1)

KNOW EVERYTHING ABOUT MYOPIA (NEARSIGHTEDNESS)

Myopia in children and adults is a complex subject, both by its origin and by its evolution. We will try to clear up all the notions which relate to myopia.

Simplistic explanation:

Uncorrected myopia

In a simplistic way, in a nearsighted eye, rays of light are going to focus in front of the retina, which causes blurred vision at distance (far away). Corrected myopia

When we correct myopia with concave or myopic lenses (also called “minus” lenses), rays of light are going to focus in the plane of the retina and the vision is clear. But this is that a simplistic explanation. In fact, a new study finds that myopia develops in children when the crystalline lens stops adapting to the eye’s continued growth, according researchers at The Ohio State University College of Optometry:

The crystalline lens stopped thinning, flattening, and losing power within ±1 year of onset in children who became myopic compared with those who did not become myopes. Myopia onset is characterized by an abrupt loss of compensatory changes in the crystalline lens that continue in emmetropes (non myopes) throughout childhood axial elongation. The mechanism responsible for this decoupling remains speculative but might include restricted equatorial growth from internal mechanical factors.

  • Mutti DO, Mitchell GL, Sinnott LT, et al. Corneal and crystalline lens dimensions before and after myopia onset. Optom Vis Sci. 2012 March;89(3):251-62

Why Myopia? 

There are two theories: the genetic theory and the environmental theory.

Genetic theory

The genetic theory asserts that people become nearsighted because it is registered in their genes and that there is no relationship between nearsightedness and the use of the eyes… The familial incidence, according to this theory, persuades that children who have nearsighted relatives (father and mother) will have no other choice than to become, them too, nearsighted.

Environmental theory

The environmental theory asserts that besides children that are born nearsighted (often they show a very important nearsightedness), nearsightedness is a possible adaptation to “visual stress”: schooling, long hours to read, write and draw, long hours at a computer, at video games, reading and writing, too short reading, writing and computer distance, body posture while reading, etc.

Several scientific studies show that when we compare two populations presenting homogeneous genetic characteristics (Amerindians, Inuit), the proportion of schooled people who become myopic is significantly more. Optometrists qualify this myopia as “school, stress-related or work-related myopia”. We can even assert that today, children become nearsighted younger and show a progression of their myopia that is more rapid than even twenty years ago! So, it is not surprising that the best readers are often myopic.

Today, adults can also become myopic further to a new and important use of the eyes (working in front of a computer is a good example). We qualify this kind of nearsightedness as “late-onset adult myopia”. At the beginning of the century, it was said that the condition would stop progressing with puberty… but this is true but not «really» true. People at the time would stop going to school at a much younger age than today, stop reading and go work hard with their hands. With all the visual requirements our eyes have to face, it often happens that myopia does not stop progressing. It is then necessary to act upon it.

Morgan & Rose, in 2005, discussed the relative importance of genetics versus environmental induced myopia:

A small proportion of myopia is clearly familial, generally early in onset and of high level, with defined chromosomal localisations and in some cases, causal genetic mutations. However, in economically developed societies, most myopia appears during childhood, particularly during the school years. In addition, high heritability sets no limit to the potential for environmentally induced change. There is in fact strong evidence for rapid, environmentally induced change in the prevalence of myopia, associated with increased education and urbanisation. Environmental change appears to be the major factor increasing the prevalence of myopia around the world.

  •  Morgan I, Rose K. How genetic is school myopia? Prog Retin Eye Res. 2005 Jan;24(1):1-38.

This should not convey the idea that the only correction possible are glasses or contact lenses to see at far and that there is nothing we can try to warn or  control the progression of myopia. This is not really true.

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First, what is “really” meant by Vision?

Vision is our most important sensory modality: 80% of what we learn is achieved through our visual system. However, we easily underestimate this important information system (the visual system).

In many  instances, children who manifest visual problems or whose visual abilities are not well integrated will have difficulties to perform properly at school.

Unfortunately, many still believe that a child who has “good vision” (a visual acuity of 20/20 or 100% at far) should be performing well in school and that learning or reading difficulties are then not related to their vision…

To really understand what we, optometrists specialized in visual training, mean by the word “vision”, we will discuss the four components of vision:

1- THE STRUCTURAL COMPONENT (OCULAR HEALTH)

This first component consists of eye health.

Fortunately, the frequency of eye diseases in school age children is very low. Approximately, 1% of children have eye diseases at birth. Needless to say, eye diseases are not related to learning or reading difficulties.

2- THE OPTICAL COMPONENT

This component determines if the child can see clearly at far: he may be nearsighted (myopia), farsighted (hyperopia) or have astigmatism. But “seeing clear” at far is not the whole aspect of vision. By experience, we know that 95% of children who have learning or reading disabilities, for example, can see clearly at far. Near vision is thus more important than far vision and has to be assessed.

Among the problems we find in this component are: child reads or writes very close, vision can be blurred in books, child cannot sustain proper concentration or attention, he does not understand easily what he reads.

Reading glasses (for the brain) can help children decode or perform better and sustain focus longer while reading.

3- THE FUNCTIONAL COMPONENT

Another aspect of vision is how the eyes function together. Here, we must assess how well the focusing mechanism of the eyes can perform (if not performing well, near vision will be blurred), how the eyes are aligned (visual-motor coordination), and if eye tracking (eye movements) is easy, smooth, precise. Needless to say adequate eye movements are essential to good reading! Unfortunately, this functional component is not always tested in a conventional eye examination.

Among the problems we find here are: the child cannot focus on what he reads or writes more than a few minutes (homework takes forever), the child tires easily when reading because of the muscular effort required, and eye movements are jerky, imprecise and head movements are most often used (instead of eyes).

“Saccades are the ability to switch fixation from one target to another. This skills permits easy shifting of the eyes along the line of print in a book, a rapid and accurate return to the next line, and quick and accurate shifts between desk and chalkboard, or from one distance to another. By the time child starts reading his eyes are capable to read at least 11 character letters at a time before his eyes start shifting. Inadequate eye movement control may cause a child to lose his place while reading, have difficulty copying from the  blackboard, and skip or omit words when reading.”

(Jean Ayres, Sensory Integration and the child)

4- THE PERCEPTUAL COMPONENT

The perceptual abilities of the child are the refinement and the end-product  of all visual abilities: perceptual-motor abilities are related more directly to the ability to decode  visual information.

Among the perceptual abilities we must assess are: form perception (can child recognize basic forms?), eye-hand reproduction (can child reproduce with hands what eyes see?), eye-hand coordination (are eyes and hand matched to perform adequately?), visual memory, auditive memory, etc.

Among the perceptual problems we can find are: form perception is weak, eye-hand coordination is difficult, visual and/or auditive memory is low, fine motor control of the hand is inefficient.

All these visual and perceptual abilities are of great importance: they help make the child succeed in school. We must remember that for children, the most difficult task in life is to learn to read and write. A complete visual-perceptual examination is thus required to be able to analyse how the child performs visually and perceptually.

“Visual perceptual skills relate to the ability to understand and interpret symbols, shapes, numbers, and letters. For such skills as reading readiness, puzzle completion, and figure ground perception. In other words, it is the capacity to interpret or give meaning to what is seen. This includes recognition, insight, and interpretation. Visual perception is made
up of several categories.”

(Jean Ayres, Sensory Integration and the child)

Welcome!

Welcome!

I thought it would be useful to create this blog to inform as many people  as possible on children’s vision. Two main themes will be covered: vision problems related to learning problems in school and myopia (nearsightedness) and it’s control amongst young people. 

Feel free to ask me questions or contact me at: jplagaceopto@gmail.com.

I hope that you will find this information useful and hopefully help children to have better performance in school or to help better control your child’s myopia . Myopia progression is becoming commonplace and there are all kinds of treatments  (special glasses or special contact lenses) to try to prevent it from progressing.

Thank you.

Clinique d’optométrie Centre-Sud
851, de Maisonneuve Blvd, east
Montreal, Quebec, H2L 1Y8
Phone: 514-527-8039