Short sightedness / nearsighted (myopia)
What is short-sightedness or nearsighted (myopia)
Normal, healthy eyes could focus over a wide range of distances — from far away down to a few centimetres. However, short sightedness / nearsighted (myopia) is a common defect of sight. This is a condition when one or both eyes have difficulty in seeing distant objects clearly.
In America, about 42 percent of people between the ages of 12 and 54 are nearsighted. This is up from 25 percent in the 1970s. The condition is more common in other parts of the world; in Asia, up to 80% of people have myopia.
A 2016 study in the journal of the American Academy of Ophthalmology, predicts that by 2050, half the world's population will have myopia.
The most common type of short-sightedness’ or nearsighted is called simple myopia and tends to be passed down from one generation to another. It usually starts around puberty and increases progressively until the early twenties, when the condition stabilises.
Simple myopia can also sometimes start in the early twenties, although this is more unusual.
Myopia which develops in early childhood often continues to deteriorate and may become quite severe later in life.
Often, there are no symptoms to indicate poor vision.
However, indicators include:
Difficulty recognising people or objects from a distance.
Difficulty reading words on the television screen.
Occasional headaches due to eyestrain.
The most obvious sign of myopia is that objects in the distance appear blurry. However, it is common to notice headaches, eye fatigue, and shoulder pain caused by the eyes straining to focus.
Myopia often develops during childhood, so parents should look for signs such as sitting too close to the television or holding screens close to the face; these are common habits in children with myopia, as are squinting and tilting the head.
Observant teachers may also notice children who have difficulty reading the blackboard.
What causes short sightedness / nearsighted (myopia)
In normal vision the light passes through the cornea (front of the eye) and the pupil. The image is focused onto the retina (at the back of the eye) by the combined focusing power of the cornea and the lens.
The retina then converts the image into nervous impulses which travel down the optic nerve to the brain.
In a myopic eye, the eyeball is too long, so that the focusing power of the cornea and lens are too strong in relation to the length of the eyeball, even when the lens is adjusted to its minimum thinness.
As a result, the image falls in front of the retina and so appears blurred.
How is myopia diagnosed and treated
Short-sightedness’ usually occurs in children. Signs include difficulty in reading the blackboard at school and sitting very close to the television.
If the defect is only present in one eye, the good eye may be strong enough to compensate. The problem can then only be detected by vision testing, especially as simple myopia only rarely causes headaches or eye strain.
Vision tests can be carried out by your GP or ophthalmic optician (optometrist). One simple test involves the use of a retinoscope, an instrument that shines a light beam through the pupil onto the retina at the back of the eye.
Some light bounces back and moves when the retinoscope is moved. This degree of movement indicates whether correction for short sight is needed.
A further test involves reading from a standardised chart of letters of diminishing size, each eye being tested individually.
Normal vision, described as 6/6, means that the letters on the bottom line can be read from 6m away.
Short sight is shown by the inability to read these letters without spectacles and is described, for example, as 6/9 or 6/12, depending on which size of letters can be read.
Standards of vision for driving
You must be able to read (with glasses or contact lenses, if necessary) a car number plate made after 1 September 2001 from 20 metres.
You must also meet the minimum eyesight standard for driving by having a visual acuity of at least decimal 0.5 (6/12) measured on the Snellen scale(with glasses or contact lenses, if necessary) using both eyes together or, if you have sight in one eye only, in that eye.
You must also have an adequate field of vision - your optician can tell you about this and do a test.
Lorry and bus drivers
The requirement is higher for professional drivers and you must have a visual acuity at least 0.8 (6/7.5) measured on the Snellen scale in your best eye and at least 0.1 (6/60) on the Snellen scale in the other eye.
You can reach this standard using glasses with a corrective power not more than (+) 8 dioptres, or with contact lenses. There’s no specific limit for the corrective power of contact lenses.
You must have a horizontal visual field of at least 160 degrees, the extension should be at least 70 degrees left and right and 30 degrees up and down. No defects should be present within a radius of the central 30 degrees.
You must tell DVLA if you’ve got any problem with your eyesight that affects either eye.
Short sightedness is treated by wearing either spectacles or contact lenses. In general, the higher the degree of short-sightedness’, the greater the benefit of contact lenses, but they are also often worn for cosmetic reasons.
While it is not essential to wear spectacles all the time, only when they are required, it is a fallacy that continuous correction of eyesight weakens the eyes.
Spectacles and contact lenses can either be provided by the optometrist who examined your eyes or by a dispensing optician (who should always be registered)
Can surgery help treat myopia
Corrective lenses are the easiest way to treat myopia. They refocus light so it hits the retina rather than the space in front of the retina. An optometrist uses a device called a phoropter to determine the ideal lenses for the patient's needs.
The lens prescription is a number; for myopia, this number will have a minus sign in front of it. For example, -3.00 D is a prescription for mild myopia.
In adults, surgery is an option to correct myopia. The procedures have to wait until after the eyesight has stabilized, so cannot be performed until adulthood.
The two common types of surgery are laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Both reshape the cornea by removing layers of tissue, which helps focus light on the retina.
The surgery is limited in the amount of tissue that can be safely removed, so people with high myopia may not be good candidates. A doctor can instead place a phakic intraocular lenses (IOLs) inside the eye to provide a permanent solution.
When should I have my eyes tested
Children usually have their eyes checked routinely before school entry by their GP or school medical officer, and this is usually repeated before secondary school. Particular attention should be paid to the vision of the brothers or sisters of a short-sighted child.
Adults are advised to have their eyes tested every two years. A check-up is always worthwhile, even if you do not have any of the symptoms such as frequent headaches, tired or strained eyes, blurred vision, or sudden loss of vision.
It is essential for drivers to have their eyes checked regularly.
Driving with vision below the minimum standard of being able to read a number plate at a distance of 20m is illegal and dangerous.
Most adults now have to pay a fee for a full examination by an optometrist. Children under 16 and those in full-time education up to the age of 19 are entitled to free tests.
Sudden loss or blurring of vision are not signs of short-sightedness’ and require urgent medical attention.
Untreated short-sightedness’ in children can lead to learning difficulties.
What can I do myself
If you are short sighted, it is important to have regular eye checks so that any deterioration can be corrected. Never buy ready-made spectacles without a prescription — they are not suitable for short-sightedness’.
They are only sold as reading glasses and have identical lenses in each eye.
It is important to detect short-sightedness in children, especially if it is severe.
If left untreated it can result in amblyopia (lazy eye) which can permanently reduce the eye's accuracy of vision.
What can I do to avoid myopia
Nothing can be done to prevent short-sightedness, but the wearing of appropriate spectacles or contact lenses and regular checks will ensure that visual impairment is minimised.
You can help to avoid straining your eyes by taking care that sufficient light is provided for reading and doing close work, and by ensuring that you do not look at VDU and television screens for long, uninterrupted periods.
Is myopia dangerous
Short sightedness is not dangerous, provided you always wear spectacles or contact lenses when driving.