At rest, the rays coming parallel to the optical axis of the eye are focused in front of the retina.
Concave concave lenses, contact glass (contact lens) or refractive surgery are used in the treatment of myopia.
1- Axis myopia:
Due to the increased length of the anteroposterior axis of the eye, the focus is in front of the retina. The anteroposterior diameter (axial length) of the eye is 23-24 mm on average. Axial length increases in myopia.
It is the most common type.
a) Simple myopia:
Myopia with a refractive error of up to -6 diopters is usually called simple myopia. It is also referred to by names such as physiological myopia, school-age myopia, and benign myopia.
Axial length is shorter than 26 mm.
It stagnates at the age of 20-25 and remains stable until advanced ages.
Mild type: This type of myopia between 0 and -3 diopters is called mild myopia. With the correction, the vision goes all the way. There is usually no pathological change in the bottom of the eye.
Medium type: Between -3 and -6 diopters. Although the retina of the eye is normal, myopic crescent begins to appear, not exceeding 1/3 of the optic nerve edge. In moderate myopia, various types of peripheral retinal degenerations are seen in the periphery of the retina, up to 40%.
With the correction, the vision goes all the way.
b) Intermediate myopia:
It ranges between -6 and -12 diopters.
It progresses with myopic crescent, flipped disc, and thinned retina.
The incidence of retinal degeneration is high.
Around the age of 30, there is a pause in the increase in myopia.
Visual acuity does not usually improve with correction.
c) Degenerative myopia:
Names such as progressive myopia, malignant myopia, and fort myopia have also been given.
It continues to grow after the age of 30 and myopia constantly increases.
The axial length of the eye is generally above 26 mm.
Corrected visual acuity is usually low. Visual field defects, night vision difficulties, color vision defects can be seen.
In degenerative myopia; The incidence of complications such as glaucoma, strabismus, cataract, retinal tear, choroidal neovascularization and retinal detachment has increased.
2- Curvature myopia:
In cases with increased corneal curvature such as keratoconus and keratoglobus, refraction increases due to increased corneal curvature.
Treatment: Contact glass (hard contact lens) application, refractive surgery or keratoplasty is performed.
3- Refractive (index) myopia:
In nuclear cataract, the refraction of the lens increases.
4- Transient (iatrogenic) myopia:
It occurs in diabetic hyperglycemia.
