Classifications of myopia according to different aspects. Essay

There are several classifications of myopia. However, most of the authors classified myopia according to anatomical features, degree of myopia, age of onset as well as simple and pathological myopia.
Anatomical features
Rosenfield, 2006 stated that myopia according to anatomical features could be axial or refractive.
Axial myopia The axial length of the eye is too long as result the image of the distant object (6 m or away) focus in front of the retina.
Refractive myopia The refractive power of the eye is too high with respect to the axial length. The refractive myopia further divided into the following
Curvature myopia This condition result of reduction in radius of curvature of cornea and lens or the curvature of the cornea and lens become steeper.
Index myopia This condition result of the refractive index of ocular media is higher than normal.
Anterior chamber myopia this type of myopia is result of decrease in anterior chamber depth (Rosenfield, 2006 6,7)
Degree of myopia
Myopia classified according to the degree as the following
Low myopia Myopia less than 3.12 D
Moderate myopia Myopia more than 3.12 to 6.00 D
High myopia Myopia greater than 6.00 D
Age of onset
According to age of onset myopia divided in to the following
Congenital myopia Sometime called developmental myopia this kind of myopia present at birth as well as called infantile myopia and the prevalence of it is about 12%.
Youth myopia This type of myopia appears during schoolaged sometime called school myopia, this form of myopia may due to excessive near work it is prevalence about 25%.
Adult onset myopia This eye condition divided in to early adult myopia and late adult myopia.
Early adult myopia Occurs in age between 20 to 40 years.
Late onset myopia this kind of myopia occurs after 40 years old, the prevalence of it about 10%.
Simple and pathological myopia
Simple myopia The most common type of myopia, it is aetiology could be axial or refractive, sometime due to genetic or environmental factors. It is appears in early years of life, not accompanied by degenerative change in the retina, may be more than 6.00 D. The previous studies showed that the rate of it is progressions range from 0.00 to over 1.00 D per year. However, the most progression rate from 0.3 to0.5 D per year (Chaudhry, 2010 47).
Pathological myopia Rosenfield, 2006 reported that the DukeElder and Abram's defined pathological refractive errors as ''those anomalies determined by the presence in the optical system of the eye of an element which lies outside the limits of normal biological variations''. Some authors described pathological myopia as malignant, degeneration or progressive myopia (Rosenfield, 2006 5).
Symptoms of myopia
Myopic patients or nearsightness have problem to see at distant object. Nevertheless, at near they could see clearly, myopic patients have other symptoms such as headaches, asthenopia, difficulty to see at night, and photophobia. The patients with pathological myopia have symptoms like floaters as well as flashes of light (Chaudhry, 2010 48).