Myopia refractive disorders
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Myopia and Hyperopia, are common eye problems caused by the inability of the eye to focus correctly. Commonly known as nearsightedness farsightedness respectively, these are refractive errors of the eye.

Refractive disorders of the eye

When the eyes fail to refract light properly to focus iton the fovea of the retina, refractive disorders occur. Refraction means the bending of light but in medical terms, it refers to the method of measuring the strength of the lens needed to focus images on the eye retina.

Refraction occurs when light slows down as it travels from one medium (like air) to another of greater density (like water). when light hits a flat surface at right angles all the light particles slow down concurrently. Hence, the light continues to travel in a straight line.

However, if light hits a translucent surface at an angle, the light particles that first enter the new medium slow down first and then the rest follow causing light to bend. When light passes from air into the relatively dense eye cornea, with the help of the lens of the eye, it refracts and then focuses onto the retina. The eye needs to adjust to refract light from various objects, angles and distances. The eye lens power adjusts accordingly for focusing.

The lens of the eye

Lens power is calculated in dioptres (D). There are mainly two groups of lenses:

  • A 'plus' lens is convex and focuses light inwards
  • A 'minus' lens is concave and turns light outwards

The more the dioptre of a lens, the stronger is its power in either plus or minus count.

Myopia or Shortsightedness

In myopia, the eye’s focusing power is stronger than required for a comparatively large eyeball. Hence, the eye power must be weakened with minus power lenses. Severe myopia can lead to serious complications like retinal injury and detachment.

Clinical characteristics of myopia

The physiological condition that marks myopia involves the bulging and swelling of the eyeball. This phenomenon is clinically termed as the origin of the myopic crescent. This is accompanied by significant choroidal and retinal degenerative transformation, retinal detachment, glaucoma and staphyloma development.

Types of myopia

There are mainly three broad categories of Myopia:

  1. =2D (D for diopters) type Myopia or low myopia (also called Physiological or School Myopia).
  2. Moderate myopia or the 2–6D type
  3. >6D type or high myopia (also called pathological myopia)

Physiological or school myopia

Myopia caused by stress related factors is called Physiological or School or =2D type Myopia. It is the low myopic condition and is the most common type. This kind of myopia is often caused by stressful habits like excessive reading from an early age. Statistics have shown that over 60% of the average medical school students suffer from myopia of this kind. However, this kind of myopia also shows a racial and ethnic variation.

Research based on racial and ethnic groups have reported that it is occurs more frequently among Asians and Jews and than among African-Americans. Often it is a combination of a congenital cause and stress related factors that result in myopia.

Treatment for myopia

The treatment of myopia involves refractive correction. Wearing bifocals combined with the continuing use of atropine eye drops is the most common way to control myopia by means of refractive correction. Contact lenses and laser technology can also be used for treatment of myopia.

Pathological myopia

This is the other kind of myopia also termed as the >6D type or high myopia. Certain studies have revealed that 2–3% of the population suffer from this type of myopia.

 
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