What is myopia?
Myopia is one of the common visual refractive errors, also known as nearsightedness or shortsightedness. In myopia, the patient can see near objects clearly, while far objects are usually hazy or blurred.
Shortsightedness is one of the common causes of visual impairment globally. In normal people (emmetropes), the light rays are centered on the surface of the retina, so they can see objects clearly. On the other hand, in patients with myopia, the light rays are centered just in front of the retinal surface; this causes the objects to be seen hazy.
What causes myopia?
Recent studies show that during early years of life, the newborn is hyperope, and the eye is changing out to reach normal stable vision at early childhood. The increase of the axial length of the eye during childhood rapid growth is balanced by decreasing in the optical power of the lens.
A study conducted by Mutti et al. showed that myopia is caused by a disturbance to the eye growth physiological balance with excessive lengthening or stretching of the eye, and a change to corneal optimum curvature and crystalline lens.
Myopia can occur at any age. It occurs in cases of:
- The cornea has more curvature than expected
- The lens has excessive curvature than the eye lens in comparable emmetropes
- The longitudinal axis of the eye lens is longer than the usual length
The prevalence of myopia
Myopia is one of the leading causes of visual disability below 50 years old, and it is a cause of concern to the global health systems. A recent research fears that by the year 2050, half of the global population would be complaining of myopia.
Meanwhile, myopia affects more than 25% of the general populations in USA, Europe, and Australia. According to Vitale et al. there is approximately 66% increase in myopia prevalence in USA, and the new cases per year has been documented to be 2.6% of the general population.
The higher prevalence of myopia is in Asian ethnicity, In Asia the prevalence is as high as 90% of the young adults, while in Taiwan 84% of adults aged more than 24 years old have myopia.
In the United Kingdom, myopia prevalence reached 49% in adults aging 44 years old or older. In India, the adults aged 40 year or older have a myopia prevalence of 34.6%. in the Middle east, the myopia prevalence in adult males is 31.5%, and 31.9% in adult females.
Recent studies showed that the prevalence of myopia increases statistically with factors like:
- Family history of refractive errors
- Family level of educations
- Overuse of eye in near work as in reading or using mobile phones excessively