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Regular sight tests or eye examinations are important at all ages from the early school years right through to advanced years.
In children examinations are especially important at school entry, age eight, entry to senior school at age eleven and entry into university or the world of work.
Once into adulthood people should have examinations every two years and at every year if they suffer from diabetes. From the age of forty those with a family history of glaucoma should have an examination every year and from the age of 60 it is recommended all people have an examination every year.
These are the normal eye examinations for assessing the state of vision of the eyes (long-sighted, short-sighted) and assessment of the health of the eyes including intraocular pressure and visual fields where appropriate.
This typically lasts half an hour and is covered by the NHS for UK taxpayers, there is however a £20.00 additional charge to cover administration and other costs with the exception of children.
Chronology of Eyesight
At birth, the human infant’s eyes are far from fully developed. The world is a blur of lights and fuzzy shapes, colour vision is crude and there is little coordinated movement of the eyes.
Within the first year, the retina (the light sensitive layer of tissue lining the back of the eye like the film in a camera) starts to mature to give colour vision and detailed vision or acuity. The muscle behind the iris (the visibly coloured part of the eye) which focuses (or accommodates) the eye also begins to mature allowing sharp sight over an increasing range of distances. This fine-tuning of the focus of the eye is accomplished by the muscle behind the iris (termed the ciliary body), contracting to allow the lens within the eye to alter its shape and hence alter its focus.
The maturing of the brain, in tandem with the eyes, results in development of coordinated movements that allow tracking of moving objects in all directions and alignment of the eyes during focussing on near objects; the result is one, dynamic mental image of the world.
These processes continue throughout the pre-school years, so typically by the age of three, a child has a sharp image of the outside world with colour and depth (or stereopsis). Indeed the process continues further all be it more slowly throughout early childhood and may not be complete until about the age of eight.
Not surprisingly this delicate process, which involves coordinated development of eyes and brain, can be disrupted at many points and most of these problems (the commonest being squint which is a misalignment of the two eyes) are screened for and detected in the U.K. by the pre-school health checks. Problems present from birth in infants at risk (e.g. pre-maturity) are evaluated in the maternity unit. More subtle defects may not be detected so an eye examination on entry to primary school is always prudent.
By the age of eight, the visual system is mature but problems such as refractive errors (the need for spectacles or contact lenses to give sharp sight) can begin to manifest anytime onwards especially during adolescence. Sometimes small squints are detectable only for the first time in the early school years.
A general rule (with of course many exceptions) is that hypermetropia (long-sightedness, where the focussing power of the eye is too weak) is manifest from three years plus, and myopia (short-sightedness, where the focussing power of the eye is too strong) is manifest from around the onset of puberty.
An eye examination on entry to secondary school is therefore also prudent.
During life the eyes can be influenced by diseases affecting any of the tissues that make up the eye, or by general disease conditions, most notably diabetes that can affect individuals of all ages. Very often early signs of these and other conditions can be detected by a routine careful eye examination. The modern workplace, be it office or factory floor, places great demands on our eyesight so that even minor defects in vision can become troublesome. For these reasons a routine eye examination every two years is worthwhile.
From the mid-forties we all experience a progressive reduction in accommodation (the range of viewing distance with clear vision). This process (termed presbyopia), which is healthy and not a disease, is a nuisance especially for those who have not had to wear glasses or contact lenses up until now. Modern spectacle lenses and to an extent contact lenses can extend the range of sharp vision, but a check of the prescription along with a full eye examination is advisable every two years.
Glaucoma, which is a major cause of sight loss in the developed world can present at any age but most commonly from the fifth decade onwards. This condition is treatable but is only detected in the early stages by careful eye examination. The tendency to develop glaucoma is inherited so first degree relatives of known glaucoma sufferers should have an annual eye examination from no later than the age of forty.
Cataract, which is eminently treatable, can affect individuals of all ages but becomes more prevalent from the seventh decade onwards. Its development is very gradual. The lens within the eye whose shape is controlled by the ciliary body to focus (or accommodate) the eye continues to grow throughout life. In the early stages of cataract formation, the central portion (or nucleus) becomes denser resulting in a change in the focussing power of the eye, which necessitates a change in spectacle prescription often as frequently as yearly or more. In the early stages, the clarity of vision with appropriate spectacle or contact lens correction is unaffected. When the tissue within the lens starts to become opaque, clarity of vision can start to deteriorate. The rate at which this progresses varies from one individual to another, and even varies between each eye in the same individual. The point at which cataract surgery is considered depends on the individual’s requirements and other technical considerations, but a general benchmark is the D.V.L.A.’s standard for visual acuity.
Macular degeneration is also a significant cause of sight loss and can affect all ages, but is more prevalent in the seventh and eighth decades onwards. There are generally two major subtypes: Wet (or exudative) and dry (or non-exudative). Since the mid 2000′s the wet form has been treatable with anti-VEGF (vascular endothelial growth factor) drugs, so early and accurate diagnosis is important for a good visual outcome. At present there is no effective treatment for the dry form which in any case usually has only a mild effect on vision.