Myopia (nearsightedness) is a refractive error. Refractive error is when the eye does not bend (refract) light properly. Light does not focus correctly so images are not clear. In myopia, close objects look clear but distant objects appear blurred (fig 1). Other symptoms may include headaches and eye strain. Severe near-sightedness is associated with an increased risk of retinal detachment, cataracts, and glaucoma.
Near-sightedness is the most common eye problem and is estimated to affect 1.5 billion people (22% of the population). Rates vary significantly in different areas of the world. Rates among adults are between 15% to 49%.
Environmental factors which increase the risk of nearsightedness include insufficient light exposure, low physical activity, near work, and increased year of education.
Modern lifestyle that involves spending most of their time indoors, in dimly or fluorescently lit buildings may be at risk of development of myopia.
People, and children especially, who spend more time doing physical exercise and outdoor play have lower rates of myopia, suggesting the increased magnitude and complexity of the visual stimuli encountered during these types of activities decrease myopic progression. There is preliminary evidence that the protective effect of outdoor activities on the development of myopia is due, at least in part, to the effect of long hours of exposure to daylight on the production and the release of retinal dopamine.
The near work hypothesis, also referred to as the “use-abuse theory” states that spending time involved in near work strains the intraocular and extraocular muscles. Some studies support the hypothesis, while other studies do not. While an association is present, it is not clearly causal.
Various forms of myopia have been described by their clinical appearance:
Simple myopia: Myopia in an otherwise normal eye, typically less than 4.00 to 6.00 diopters. This is the most common form of myopia.
Degenerative myopia, also known as malignant, pathological, or progressive myopia, is characterized by marked funduschanges, such as posterior staphyloma, and associated with a high refractive error and subnormal visual acuity after correction. This form of myopia gets progressively worse over time. Degenerative myopia has been reported as one of the main causes of visual impairment.
Index myopia is attributed to variation in the index of refraction of one or more of the ocular media. Cataracts may lead to index myopia.
Age at onset
Myopia is sometimes classified by the age at onset
Congenital myopia, also known as infantile myopia, is present at birth and persists through infancy.
Youth onset myopia occurs in early childhood or teenage, and the ocular power can keep varying until the age of 21, before which any form of corrective surgery is usually not recommended by ophthalmic specialists around the world.
School myopia appears during childhood, particularly the school-age years. This form of myopia is attributed to the use of the eyes for close work during the school years.
Adult onset myopia
Early adult onset myopia occurs between ages 20 and 40.
Late adult onset myopia occurs after age 40.
1.more time spent outdoors during childhood is effective for prevention
2.Medication: eye drop atropine (0.01%) has been effective to control the progress of myopia.
Corrective lenses or contact lenses bend the light entering the eye in a way that places a focused image accurately onto the retina. The power of any lens system can be expressed in diopters, the reciprocal of its focal length in meters. Corrective lenses for myopia have negative powers because a divergent lens is required to move the far point of focus out to the distance. More severe myopia needs lens powers further from zero (more negative). However, strong eyeglass prescriptions create distortions such as prismatic movement and chromatic aberration.
2. Surgery: Refractive surgery includes procedures which alter the corneal curvature of some structure of the eye or which add additional refractive means inside the eye. Eg : Photorefractive keratectomy (PRK), LASIK, Phakic intra-ocular lens etc.
Orthokeratology or simply Ortho-K is a temporary corneal reshaping process using rigid gas permeable (RGP) contact lenses.