Myopia can also be the result of increased axial length secondary to retinopathy of prematurity, posterior staphyloma, scleral buckle surgery and congenital glaucoma.
Changes to the cornea secondary to keratoconus, congenital glaucoma, and contact lens-induced corneal warpage can also cause myopia. The power of the lens can be increased by osmotic changes (diabetes, galactosemia, uremia, sulfonamides), nuclear sclerotic cataracts, anterior lenticonus, and changes in lens position or shape (miotics, anterior lens dislocation, excessive accommodation). In addition to physiologic, pathologic and syndromic myopia, other processes involving the refractive structures of the eye can also produce myopia. It is reported that there are over 80 million myopic children world wide. showed that myopic prevalence rates for Taiwanese children were reaching 80%. A large epidemiological study in 2000 by Lin et al. Lower prevalence rates were found in African American children with 6.6% followed by Caucasian children with a prevalence rate of 4.4%. The highest rates were found among Asian children with a prevalence of 18.5% and hispanic children with 13.2%. In 2003 a multi-center study the US reported significantly different prevalence rates among children of four different ethnic groups. The majority of the myopic population consists primarily of patients with non-pathologic myopia approximately 66% of patients with myopia have less than 2 diopters (D) of myopia and 95% of myopic patients have less than 6 diopters. The prevalence rates of myopia in the United States have been reported as 20-50% and as high as 80-90% in some parts of Asia. The prevalence of myopia varies greatly between different populations and ethnic groups. This type of myopia is only a small proportion of the overall myopic population and to date, there is no known isolated gene associated with physiologic myopia. The genetic mutations for these syndromes have been identified and the subsequent structural defects of the eye are most commonly related to connective tissue and retina. High myopia is also a symptom of several multi-system complex diseases. Although non-syndromic high myopia is most commonly inherited in an automosomal dominant pattern, multiple chromosomal loci have been identified which suggests genetic heterogeneity.
It is well documented that pathological non-syndromic high myopia and associated syndromic high myopia show evidence of familial inheritance. Myopia is a complex disease with a multi-factorial etiology. Patients with high axial myopia are at a greater risk of developing progressive retinal degeneration and other vision threatening pathology. The degree of non-pathologic myopia is usually minimal to moderate ( 6.00 diopters or axial length >26.5mm.
In non-pathologic myopia the refractive structures of the eye develop within normal limits, however the refractive power of the eye does not correlate with the axial length. Non-pathological myopia is also commonly referred to as physiological, simple or school myopia. Both groups have separate disease processes, clinical features, and prognoses. Myopia is generally classified into two groups: non-pathologic and pathologic myopia. Conversely, visual acuity is greater for objects located between the far point of the eye and the near point of accommodation. Visual acuity of an uncorrected myope will continue to decrease as objects are located further away from the far point and closer to optical infinity. The far point of a myope is located in front of the eye, between the cornea and optical infinity. Light rays from an object at infinity entering a non-accommodating myopic eye are converged too strongly and focus in front of the retina.
Myopia (nearsightedness) is an ocular disorder in which the optical power of the eye is too strong for the corresponding axial length. 7.2 Atropine for the Treatment of Myopia II (ATOM II) 2014įigure 1: Human myopic eye, showing the cornea and lens bending (refracting) incoming light rays so they focus in front of the retina.7.1 Atropine for the Treatment of Myopia I (ATOM I) 2006.4.1 Bifocals, Progressive Lenses, Aspheric Lenslets and Multifocal Contact Lenses.1.7.4 Accommodation and Accommodative lag.1.5 Syndromes with associated myopia are listed below.
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