The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Myopia

Myopia is commonly referred to as nearsightedness. In this condition, light that comes into the eye does not come directly into focus on the retina, but instead it focuses in front of the retina. This causes an object far away to be seen out of focus and an object closer to the eye to be seen in focus.

Classification

Myopia is classified in two different groups: axial and refractive. Axial myopia is due to an increase in the eye’s axial length, whereas refractive myopia refers to the condition of the refractive elements of the eye. Further classifications include curvature myopia, which is excessive curvature in one or more of the refractive surfaces of the eye, mostly the cornea. Index myopia is a variation in the index of refraction of one or more ocular media. All of these classifications still result in the same basic issue, the inability of the eye to focus on objects that are far away from the lens.

Degree of Myopia

Myopia comes in different degrees depending on the person. Myopia is measured in diopters, the strength or optical power of a corrective lens that focuses distant images on the retina. Low myopia is usually —3.00 diopters or less, closer to 0.00. Medium myopia is usually between —3.00 diopters and —6.00 diopters. These individuals typically have pigment dispersion syndrome, which leads to glaucoma. High myopia is usually —6.00 diopters or more. These individuals are more likely to have retinal detachments and open angle glaucoma. Approximately 30 percent of people with myopia have high myopia. The higher the number of diopters, the worse the patient’s ability to focus on objects far from the lens.

Signs and Symptoms

Myopia presents mostly with blurred vision when looking at distant objects. When examined by an ophthalmologist, the optic nerve tends to be tilted, and an area where white sclera can be seen next to a disc with a line of hyperpigmentation is separating this area from the normal retina.

Risk Factors

Genetics have been shown to be a risk factor associated with juvenile myopia, while work, higher school achievement, and less time spent doing sports activity contributed relatively little to the development of myopia in individuals. Performing close work (e.g., using a computer or microscope), however, has been implicated as a factor in the pathogenesis of myopia, as seen in the United States where the prevalence of myopia rose with family income and education level (Sperduto et al., 1983). It has been shown that persons with higher education tend to perform close work.

Prevention, Control, and Management

There is really no universally approved method of preventing myopia, although many attempts have been made. Myopia can be controlled using various methods. The most common form of control is reading glasses, contact lenses, or surgery. Pharmaceuticals such as antimuscarinic topical medications and eye drops have been shown to be effective in slowing myopia. A final form of control and management of myopia is surgery. Laser in-situ keratomileusis or laser-assisted in-situ keratomileusis (LASIK) surgery is the most common form of eye surgery, which is a procedure that includes cutting the cornea to make a corneal flap to allow a laser beam access to the exposed corneal tissue. The laser reshapes the cornea by clearing tissue to correct the misshapen lens. This results in the vision being corrected. After reshaping the cornea, the corneal flap is then flipped back over to cover the corneal tissue that was reshaped. LASIK is not painful and has a very short recovery time but has the potential for flap complications and potential loss of corneal stability. Additionally, there is sometimes a need to fine-tune the surgery to ensure 20/20 vision. Another option for correcting myopia is photo-refractive keratectomy (PRK). While very similar to LASIK in that it uses a laser to reshape the surface of the cornea, it does not remove as much tissue and no flap is formed. The reshaping happens on the surface of the cornea. This means there is a much longer healing period, but this might be a more viable option for individuals with a higher degree of myopia as there is less risk of the cornea being reduced to too small a size, as might happen with LASIK.

Renee Johnson

See also: Amblyopia; Diplopia; Hyperopia; Presbyopia; Retina; Visual Perception

Further Reading

National Eye Institute (NEI). (2010). Facts about myopia. National Eye Institute. Retrieved from https://nei.nih.gov/health/errors/myopia

Sivak, Jacob. (2012). The cause(s) of myopia and the efforts that have been made to prevent it. Clinical and Experimental Optometry, 95(6), 572—582. http://dx.doi.org/10.1111/j.1444-0938.2012.00781.x

Sperduto, Robert D., Daniel Seigel, Jean Roberts, & Michael Rowland. (1983). Prevalence of myopia in the United States. Archives in Ophthalmology, 101(3), 405—407. http://dx.doi.org/10.1001/archopht.1983.01040010405011