Keratoconus classification
There are different types of keratoconus classification. According to the classification of Titarenko (1982), the disease has 5 stages: I and II stages are characterized by small subclinical changes in the cornea (the presence of areas of "thinning", thickening of nerve fibers); for stage III is characterized by a decrease in vision (to 0.1), the formation of opacities at the top of the keratoconus, the formation of Vogt lines; at stage IV there is a sharp deterioration of vision (to 0.02), the cornea is thinning and turbid, in the descemet shell there are cracks; Stage V is characterized by severe changes in the cornea and its almost complete turbidity.
The classification of Slonimsky (1993) is usually used to diagnose symptoms, which determine the possibility and timing of surgical intervention. According to it, stage I is a pre-surgical-vision reduction, which is difficult to correct with glasses, but is successfully corrected with the help of contact lenses. Stage II is surgical-the presence of epitheliopathy and poor tolerance of contact lenses. Stage III is terminal, it is characterized by rough scar processes, accompanied by a rapid deterioration of visual acuity.
There is a classification by J. Buxton (1973) based on the degree of increase of the cornea curvature. I degree corresponds to the radius of the cornea about 7.5 mm and irregular astigmatism, II degree-radius 7.5-6.5 mm and changes in ophthalmometric parameters. The radius of less than 6.5 mm corresponds to the III degree, and the final stage of the disease, IV degree, is characterized by a radius of the cornea less than 5.6 mm.
The greatest popularity has gained classification by Amsler (1961). The basis for it are ophthalmometric changes and biomicroscopic view of the cornea.
At stage I there is a "rarefaction" of the stroma, there are changes in endothelial cells and ophthalmometric parameters. The value of the minimum radius of curvature of the cornea is more than 7.2 mm. visual Acuity is in the range of 0.1-0.5 and can be corrected by means of cylindrical glasses. Eccentric steepening on a corneal topography.
At stage II, the value of the minimum radius of curvature of the cornea is reduced to 7.19–7.1 mm.visual Acuity is 0.1–0.4 and can also be corrected with the help of astigmatic glasses, it is possible to show mild ectasia and thinning of the cornea.
For stage III is characterized by a significant protrusion of the cornea, as well as its thinning. Visual acuity (0.02-0.12) can be corrected only with hard contact lenses, and on the part of patients their intolerance is often noted. The value of the minimum radius of curvature of the cornea is in the range of 7.09-7.0 mm, manifested turbidity Bowman membrane.
Stage IV is terminal. There are stromal opacities, changes in descemet shell. Ophthalmometry is often impossible. Visual acuity does not exceed 0.01–0.02 and can not be corrected. The minimum radius of curvature of the cornea is less than 6.9 mm. it Should be noted that the appearance of the Fleischner ring can occur at any stage.
According to the modern classification of keratoconus by Rabinowitz-McDonell, the stages of the disease are subdivided by Amsler:
- I and II stages are considered to be subclinical or refractive stage.
- Stages III and IV are called the clinical stage.
It is especially necessary to distinguish the following types of classification:
Anterior or true keratoconus, in which pathological processes develop in the Bowman membrane, and almost transparent ectasia is formed. It is characterized by a chronic course.
Keratoconus degrees
Degree of Keratoconus depends on the distance of the apex from the center of the cornea, which have pathological process:
Degree I – Central
Degree II – Paracentral
Degree III – Peripheral
Degree IV – Perennial degeneration pellucida
Hydrops of the cornea or acute keratoconus. There is damage to the descemet membrane and violation of the barrier function, there is a perspiration of watery moisture from the anterior chamber of the eye into the layers of the cornea. As a result, turbidity and swelling of the stroma develop Learn more about acute keratoconus >>>
Posterior keratoconus is an anomaly that occurs due to improper development of the mesoderm. For this pathology, the formation of thinning in the center or its saucer-like form is characteristic, as a result of which the cornea acquires a flat shape and optical weakness. This condition is stable.
