Eyes – Short Sightedness (Myopia)

Myopia (Greek: μυωπία, muōpia, "nearsightedness"), also called nearsightedness or shortsightedness, is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed.

Those with myopia see near objects clearly but far away objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"—this is where the cornea is too horizontal or the eye is too small.

Mainstream eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, but this does have many risks and side effects. The corrective lenses have a negative optical power (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.

Diagnosis

A diagnosis of myopia is typically confirmed during an eye examination by an ophthalmologist, optometrist or orthoptist. Frequently an autorefractor or retinoscope is used to give an initial objective assessment of the refractive status of each eye, then a phoropter is used to subjectively refine the patient's eyeglass prescription.

Treatment, management, and prevention

Eyeglasses, contact lenses, and refractive surgery are the primary options to treat the visual symptoms of those with myopia. Orthokeratology is the practice of using special rigid contact lenses to flatten the cornea to reduce myopia. Occasionally, pinhole glasses are used by patients with low-level myopia. These work by reducing the blur circle formed on the retina, but their adverse effects on peripheral vision, contrast and brightness make them unsuitable in most situations.

Chromatic aberration of strong eyeglasses

For people with a high degree of myopia, very strong eyeglass prescriptions are needed to correct the focus error. However, strong eyeglass prescriptions have a negative side effect in that off-axis viewing of objects away from the center of the lens results in prismatic movement and separation of colors, known as chromatic aberration. This prismatic distortion is visible to the wearer as color fringes around strongly contrasting colors. The fringes move around as the wearer's gaze through the lenses changes, and the prismatic shifting reverses on either side, above, and below the exact center of the lenses. Color fringing can make accurate drawing and painting difficult for users of strong eyeglass prescriptions.

Strongly nearsighted wearers of contact lenses do not experience chromatic aberration because the lens moves with the cornea and always stays centered in the middle of the wearer's gaze.

Eye-exercises and biofeedback

Practitioners and advocates of alternative therapies often recommend eye exercises and relaxation techniques such as the Bates method. However, the efficacy of these practices is disputed by scientists and eye care practitioners. A 2005 review of scientific papers on the subject concluded that there was "no clear scientific evidence" that eye exercises were effective in treating myopia.

In the 1980s and 1990s, there was a flurry of interest in biofeedback as a possible treatment for myopia. A 1997 review of this biofeedback research concluded that "controlled studies to validate such methods … have been rare and contradictory." It was found in one study that myopes could improve their visual acuity with biofeedback training, but that this improvement was "instrument-specific" and did not generalise to other measures or situations. In another study an "improvement" in visual acuity was found but the authors concluded that this could be a result of subjects learning the task. Finally, in an evaluation of a training system designed to improve acuity, "no significant difference was found between the control and experimental subjects".

Prevention

There is no universally accepted method of preventing myopia. Commonly attempted preventative methods include wearing reading glasses, eye drops and participating in more outdoor activities are described below. Some clinicians and researchers recommend plus power (convex) lenses in the form of reading glasses when engaged in close work or reading instead of using single focal concave lens glasses commonly prescribed. The reasoning behind convex lense's possible effectiveness in preventing myopia is simple to understand: Convex lenses's refractive property of converging light are used in reading glasses to help reduce the accommodation needed when reading and doing close work. For people with Presbyopia whose eye's lens can not accommodate enough for very near focus; reading glasses help converge the light before it enters the eye to complement the refractive power of the eye lens so near objects focus clearly on the retina.  By reducing the focusing effort needed (accommodation), reading glasses or convex lenses essentially relax the focusing ciliary muscles and may consequently reduce chances of developing myopia. source: Inexpensive non prescription reading glasses are commonly sold in drug stores and dollar stores. Alternatively, reading glasses fitted by optometrists have a wider range of styles and lens choices. source: A recent Malaysian study reported in New Scientist suggested that undercorrection of myopia caused more rapid progression of myopia. However, the reliability of these data has been called into question. Many myopia treatment studies suffer from any of a number of design drawbacks: small numbers, lack of adequate control group, failure to mask examiners from knowledge of treatments used, etc.

Pirenzepine eyedrops had a limited effect on retarding myopic progression in a recent, placebo-control, double-blinded prospective controlled study.

Daylight

Daylight may prevent myopia. Australian researchers had concluded that exposure to daylight appeared to play a critical role in restricting the growth of the eyeball, which is responsible for myopia or short-sightedness. They compared children from other developed countries such as Singapore and Australian children spent about 2–3 hours a day outdoors which could increased dopamine in the eyes that restrict distorted shaping of the eyes.

Myopia control

Various methods have been employed in an attempt to decrease the progression of myopia. Dr Chua Weihan and his team at National Eye Centre Singapore have conducted large scale studies on the effect of Atropine of varying strength in stabilizing, and in some case, reducing myopia. The use of reading glasses when doing close work may provide success by reducing or eliminating the need to accommodate. Altering the use of eyeglasses between full-time, part-time, and not at all does not appear to alter myopia progression. The American Optometric Association's Clinical Practice Guidelines for Myopia refers to numerous studies which indicated the effectiveness of bifocal lenses and recommends it as the method for "Myopia Control". In some study, bifocal and progressive lenses have not shown significant differences in altering the progression of myopia.