Myopia or nearsightedness is clinically described as a refractive defect of the eye in which collimated light produces image focus in front of the retina (a light sensitive tissue situated at the inner surface of the eye).
People with myopia can see near objects clearly but far away vision appears blurred. The problem occurs if the eyeball or the cornea is too long and the clear front cover of the eye has too much curvature. Consequently, the light entering the eye is not focused accurately making distant objects look blurred.
The degree of your nearsightedness determines your ability to see distant objects. People suffering from severe myopia can see clearly only the objects few inches away. These are the main features of myopia. The word myopia has its origin in two Greek words: ‘myein’ (means ‘shut’) and ‘ops’ (means ‘eye’).
Nearsightedness happens when the physical length of the eye exceeds optical length. It often occurs in the rapidly growing school-aged child or teenager, and advances during their growth years. It requires frequent changes in glasses or contact lenses. It generally stops progressing as a person passes the growing period in his or her early twenties.
Causes of Myopia
Nearsightedness is common to both males and females. People having nearsightedness in their family are more likely to develop this ailment. But some having opinion that Myopia, or Nearsightedness is not inherited. It is caused by excessive reading and other close work. Prolonged close work may cause the focusing muscle inside the eye to be locked up into a state of near focus. Gradually, it leads to permanent nearsightedness, an abnormal lengthening of the eye that can turn into an eye disease. Most people with nearsightedness posses entirely healthy eyes, but in some cases a small number of people with myopia develop a form of retinal degeneration.
Environmental factors or other health problems may also give way to myopia:
Some people may posses blurred distance vision only at night. This is called “night myopia”. The situation may occur due to the low level of light which makes it difficult for the eyes to focus properly or the increased pupil size in dark, allowing more peripheral, unfocused light rays to enter the eye.
People performing more near vision work may experience false or “pseudo” myopia. Their blurred distance vision is due to the excessive use of the eyes’ focusing mechanism. Long period of intricate close working makes their eyes unable to refocus to see clearly the distant objects. The symptoms are usually temporary and clear distance vision may return after you give your eyes a little rest. However, constant visual stress may lead to a permanent reduction in distance vision with time.
Symptoms of nearsightedness may signify variations in blood sugar levels in persons with diabetes or an early indication of a developing cataract.
Only an optometrist can evaluate vision and determine the cause of the vision problems.
Symptoms of Myopia:
The person with myopia may have the following symptoms:
- Distant objects appear blurry
- One may need to squint to see clearly
- You may have headaches caused by excessive eyestrain
Nearsightedness is more common among children during their early school years and the later teens. A child with nearsightedness may have the following signs:
- Persistent squint
- Need to sit very close to the television, movie screen or blackboard
- Hold books very close while reading
- Seem to be unaware of distant objects
- Blink excessively
- Rub his or her eyes frequently
How is nearsightedness diagnosed?
Testing for nearsightedness is done following several procedures in order to examine how the eyes focus light and to determine the power of any optical lenses to remedy the reduced vision.
As part of the testing, you may be told to read the letters on a distant chart. This test measures visual acuity, written in fraction such as 20/40. The top number of the fraction is the standard distance at which testing is performed, twenty feet and the bottom number indicates the smallest letter size read. A person with 20/40 visual acuity would have to get within 20 feet to identify a letter that could be seen clearly at forty feet in a “normal” eye. Normal distance visual acuity is 20/20, although many have 20/15 (better) vision.
An instrument called phoropter is used by an optometrist to place a series of lenses in front of your eyes in order to measure how they focus light using a hand held lighted instrument called retinoscope. The doctor may also prefer to use an automated instrument that automatically evaluates the focusing power of the eye. The power is then refined by patient’s responses to determine the lenses that offer the clearest vision.
This testing may be carried on without the using eye drops to determine how the eyes respond under normal visual conditions. In some cases, such as for patients who can’t respond verbally, or when some of the eye’s focusing power may be hidden, eye drops may be applied which helps keeping the eyes from changing focus while testing is performed.
The information obtained from these tests, along with the results of other tests of eye focusing and eye teaming, helps your optometrist to determine if you have myopia. The optometrist will also determine the power of any lens correction needed to provide his patient clear vision. After the tests are done properly, your optometrist can discuss options for treatment.
Myopia Treatment:
Nearsightedness may be corrected with glasses, contact lenses or performing an eye surgery. Whether you need to wear your glasses or contact lenses all the time or only when you need distance vision, like driving, seeing a chalkboard or watching a movie depend on your vision problem. If you\’re myopic, you’ll be prescribed a negative number. The lens power is directly proportional to the numerical value.
Refractive surgery is useful to reduce or even eliminate your need for glasses or contact lenses. Normally it is performed with an excimer laser.
In the process called PRK the laser is used to remove a layer of corneal tissue, which flattens the cornea and allows light rays to focus closer to or even on the retina.
In LASIK, the most common refractive procedure, a flap is cut through the top of the cornea so that a laser can remove some corneal tissue. After that, the flap is put into place.
Orthokeratology: It is a non-surgical procedure where you are given special contact lenses to put on. It slowly reshapes the cornea over time to correct your myopia. Once the lenses are removed, the cornea temporarily retains the new shape. Now you can see clearly without the lenses.
Orthokeratology or corneal refractive therapy (CRT) is an orthokeratology-like procedure approved by the FDA in 2002; in this process you have to wear cornea-shaped lenses only at night ensuring daytime vision without contacts or glasses.
Implantable lenses or phakic IOLs are a newer surgical option for correcting nearsightedness. It is applied particularly to more extreme cases which are the tests like LASIK or other vision correction surgery is unsuitable.
Phakic IOLs work like contact lenses, if they are not surgically placed within the eye and made permanent, which needs no maintenance. In phakic IOLs, the eye\’s natural lens is left intact and is not replaced.
Pathologic Myopia:
Nearsightedness usually is a mildly incapacitating condition and can easily be corrected applying glasses, contacts or performing vision surgery. Occasionally the myopia becomes so severe. It is called pathologic. Pathologic, or degenerative, myopia typically develops by age 12 in those with an extraordinarily drawn out eyeball.
However, in 2001, the FDA permitted the injectable photosensitive drug called Visudyne (verteporfin) along with non-thermal laser application as a treatment for the neovascularization in pathologic myopia. In clinical trials, this treatment known as photodynamic therapy or PDT found effective in stabilizing or enhancing the vision of 72% of patients after one year, versus 44% on placebo.
Recent studies also reveal the effectiveness of this therapy. Japanese research reported in the March 2008 edition of American Journal of Ophthalmology expressed that PDT helped stabilize damage from neovascularization, or it would have come out in the form of pathologic myopia.
Prevention:
Some doctors and researchers recommend plus power (convex) lenses in the form of reading glasses at the time of close work or reading instead of single focal concave lens glasses. Myopia can be prevented by the use of reading glasses. The distance glasses should not be used for intricate close work but only for distance.
Daylight:
Daylight may prevent myopia. Australian researchers had confirmed that exposure to daylight play a crucial role in preventing the growth of the eyeball, responsible for myopia or short-sightedness. Comparing children from other developed countries including Singapore and Australian children who spend about 2–3 hours a day outdoors, they came to a conclusion that exposure to sunlight could increase Dopamine in the eyes that restricts distorted shaping of the eye.
Various methods have been adapted to decrease the development of myopia. Dr Chua Weihan and his team at National Eye Centre Singapore have conducted extensive studies on the impact of Atropine of varying strength in stabilizing, sometimes in reducing myopia. The use of reading glasses when doing near work may prove helpful to reduce or eliminate the necessity to accommodate. It is to be noted that alteration of the eyeglasses between full-time, part-time, and not at all does not help alter myopia development.
The American Optometric Association\’s Clinical Practice Guidelines for Myopia refers to various studies indicating the effectiveness of bifocal lenses and recommends it as the method for “Myopia Control”. However, in some cases, bifocal and progressive lenses have not shown significant differences in restricting the development of myopia. Extensive studies on children have revealed that Orthokeratology and Centre Distance bifocal contact lenses may control myopic development.
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