Myopia is a visual dysfunction from which more and more people start suffering due to the development of computer technologies. Myopia usually occurs “when an eye is too long when the cornea is too steeply curved when the eye’s lens is unable to relax enough to provide accurate distance vision, or from some combination of these and other factors” (Anshel 2008, p. 8). Two main types of myopia, axial and refractive, can be classified according to what causes this visual disability biologically; myopia may be caused by a range of genetic and environmental factors (or a combination of these), but, since it is a dysfunction, rather than a disease, it cannot be treated and can only be fixed using refractive surgery or managed with the help of eyeglasses or contact lenses.
First of all, according to its causes, myopia can be divided into two types. Thus, by cause, myopia can be either axial or refractive with the latter being further subdivided into curvature and index myopia. Axial myopia takes place when “the distance between the lens system and the retina is too large” (Schmid 2004, p. 7). In the case of axial myopia, the length of the eye gets increased abnormally together with the visual axis.
The main reason for this is, as a rule, the increased pressure on the vitreous body of the eye, which results in its deformation and subsequent blurring of vision. Axial myopia is irreversible and quite often it results in progressive myopia leading to the stretching of the sclera (Schmid 2004). Refractive myopia occurs when “the refractive power of the lens system is too high” (Schmid 2004, p. 6). Refractive myopia occurs due to damaging of one of the lens system parameters which include “the curvature of the cornea, the curvature of the lens at the front as well as at the back, and the refractive indices of the anterior chamber, the lens, and the vitreous body” (Schmid 2004, p. 6).
Thus, for instance, curvature myopia is the reduction of the radius of curvature, which results in increasing the power of the eye to more than +60.00 D (Keirl & Christie 2007). In the case of index myopia, this power is also more than +60.00 D, but the main deviation is not the radius of curvature, but the refractive index of the eye which is too high. This leads to forming the second focus in front of the macula (Keirl & Christie 2007). Such deformations mostly happen with older people and are a symptom of nuclear sclerotic lens opacities.
Furthermore, causes of myopia are numerous with genetic and environmental factors impact being the most widespread ones. Myopia, just like a range of other diseases, can be hereditary. Inheritance of myopia can be observed quite often; this has been proved by numerous familial aggregation and twin studies that have pointed at the autosomal dominant mode of inheritance (Harley, Nelson & Olitsky 2005). It has been found that parental myopia leads to this disability in their children as well: “Children with a family history of myopia had on average less hyperopia, deeper anterior chambers, and longer vitreous chambers even before becoming myopic” (Harley, Nelson & Olitsky 2005).
In addition to genetic factors, the environmental ones also contribute greatly to the development of myopia. Some researchers suggest that environmental factors can be even more powerful than genetic ones, especially taking into account that some forms of myopia (school myopia, for instance) develop under the influence of namely these factors (Rosenfield & Logan 2009). Myopia is closely associated with near work in both children and adults. Though it still has not been proven that near work may cause myopia, certain relation between them does exist (Rosenfield & Logan 2009). A further connection has also been discovered between the intelligence levels and myopia rates with myopic children having “higher intelligence test scores, higher achievement test scores, and better grades in school than non-myopes” (Rosenfield & Logan 2009, p. 167).
The combined effect of genetic and environmental factors on myopia development consists in that educational attainments can be inherited either together with myopia or without it, which often serves as a limitation to myopia studies. However, most of the researchers still agree with the idea that both heredity and near work are “significantly associated with myopia, with heredity being the more important factor” (Rosenfield & Logan 2009, p. 167). This means that children having myopic parents are more likely to develop myopia than those who are continuously affected by near work but do not have a disposition to myopia.
Finally, myopia is not a disease as such this is why curing it is not possible, though nearsightedness can be fixed if refractive surgery is carried out and managed if a myopic wears eyeglasses or contact lenses. Eyeglasses are one of the first methods invented to deal with myopia. They consist of a frame with lenses for vision correction made usually from plastic. Modern eyeglasses manufacturers made them especially convenient and reliable with some of the plastic lenses having even scratch-resistant coating which makes them of similar resistance to glass. The power of lenses in the glasses is measured in diopters with the eyeglasses for myopia having negative diopter strengths.
The main disadvantage of eyeglasses is they get misted in cold weather (especially in winter) or they’re getting wet in case of rain. This is where contact lenses are more advantageous. Modern contact lenses are made of gel, which makes them soft and convenient to wear. They are used for corrective purposes and their greatest advantage is that they are almost invisible and, unlike eyeglasses, the width of the lens does not depend on how bad the eyesight is.
The most drastic method of dealing with myopia is a refractive surgery which consists of remodeling of the cornea using the excimer laser. Such a procedure is relatively painless and takes several minutes to complete. However, it is often associated with risks due to certain medical conditions, such as serious eye diseases (glaucoma, for instance), as well as autoimmune diseases or diabetes.
In conclusion, myopia may have numerous causes and, since it can be predetermined both genetically and environmentally, it does not depend on age and gender. Two main types of myopia are axial and refractive; they both take place when the lens system parameters (such as eye length, vitreous body, or curvature of the lens) are defective. Myopia can be dealt with using eyeglasses, contact lenses, and refractory surgery from which the former is the safest, while the latter is more effective for it allows restoring the eyesight completely or at least for a long time.
Bibliography
Anschel, J 1998, Visual economic in workplace, Taylor & Francis, London.
Harley, RD, Nelson, LB & Olitsky, SE 2005, Harley’s pediatric ophthalmology, Lippincott Williams & Wilkins, London.
Keirl, A & Christie, A 2007, Clinical optics and refraction: a guide for optometrists, contact lens opticians and dispensing opticians, Elsevier Health Sciences, London.
Rosenfield, M & Logahn, N 2009, Optometry: science, techniques and clinical management, Elsevier Health Sciences, London.
Schmid, K 2004, Myopia manual, Pagefree Publishing, London.