Traditional Theories of Myopia Development:
According to the old autonomists, intoxication, previous disease or congenital weakness in the ciliary muscles may cause insufficient tension in the choroidal sheath of the eye. This leads to direct reflection of vitreous pressure on the sclera, weakening of the sclera and ultimately elongation of the eyeball.
In 1929 Comberg proposed that the weakness of the sclera was at the root of myopia. According to him, adverse factors such as eye movements during reading and increased intraocular pressure caused stretching of the sclera.
Curtin (1970-1985) stated that there was no single cause of myopia.
In 1986, Avetisov highlighted 3 main factors involved in the development of myopia.
Striving for near vision and poor accommodative relationship,
Hereditary predisposition,
The relationship between weak sclera and intraocular pressure.
I-Relation between near vision effort and weak accommodation: The task of near vision with a weak accommodation is a real muscular effort for the eye. In this case, changes occur in the optical systems of the eye and it is possible to adapt to the near working distance without forcing accommodation. As a result, the anteroposterior diameter of the eye increases during the period of ocular growth and refractive formation. Unsuitable conditions for near vision result in myopia. This type of myopia usually does not exceed -3.00 D. Poor accommodation may be the result of congenital morphologic defects in the ciliary muscles. Accommodation may be due to decreased ciliar muscle activity due to a disturbance in the hemodynamics of the eye or decreased ciliar muscle blood supply.
II-Hereditary predisposition: Myopia is a hereditary disease that can be inherited as autosomal dominant or autosomal recessive. In the autosomal dominant type, myopia occurs in late childhood and does not progress much. The autosomal recessive type is highly familial, but sporadic cases have also been reported. This type has an early onset, is progressive, complications are frequent and may be associated with congenital eye diseases.
III-Relationship between weak sclera and intraocular pressure: Impaired fibrillogenesis due to congenital or systemic disease leads to scleral weakness, resulting in an inappropriate growth response and elongation of the eye even with normal intraocular pressure. Increased intraocular pressure alone does not cause elongation in an eye with a normal strong sclera. Intraocular pressure is not constant, but what is important are the extreme changes in intraocular pressure caused by transient disturbances in ocular fluids with head and body movement. The diaphragm, consisting of the ciliary body and lens in the anterior parts of the eye, acts as a barrier and distortion primarily affects the posterior pole of the eye. In accordance with hemodynamic rules, the radius of curvature increases first in the posterior pole.
In the eye, overextension has the opposite effect on less elastic and physiologically growth-limited tissues such as the retina and choroid. When this limit is exceeded, trophic changes occur in the retina and choroid, especially in high-grade myopes. Disturbance in the hemodynamics of the eye also increases trophic changes.
