Keratoconus

Description:

Keratoconus (from other - Greek   — "horn" and  — "cone") — a degenerative noninflammatory disease of an eye at which the cornea becomes thinner and takes conical shape. The keratoconus can lead to serious deterioration in sight. Most often patients show complaints to a photophobia, doubling, spreading of the image. The disease is the most common form of dystrophy of a cornea. The keratoconus strikes about one person from one thousand, irrespective of a nationality and the place of residence. The diagnosis is usually made in youth, and disease reaches the heaviest stage by twenty or thirty years.

Keratoconus symptoms:

The disease begins to be shown that the person notices small blurring of outlines of objects and asks for the help the oculist. Keratoconus symptoms at early stages often do not allow to distinguish it from others, the defects of a refraction which more often are found. In process of a course of a disease sight worsens, sometimes quickly enough. Regardless of a distance, visual acuity becomes unsatisfactory, the scotopia at the same time is much weaker than day. Sometimes one eye sees much worse than another. At late stages the photophobia, feeling of constant exhaustion of eyes because of need to squint, an itch in eyes can develop. At the same time pain arises seldom.

Images of objects at an onset of the illness appear doubled, then the number of "false" images grows, this classical symptom of a keratoconus is called "a monocular polyopia" and is most noticeable when looking at light objects on a black background. Instead of a white point against the background of the black page, the patient sees several points scattered in the chaotic sequence. This sequence does not change day by day, but in process of progressing of a disease gradually takes the new forms. Also patients often note spreading and roughness of outlines of light sources. Because of thinning of a cornea at the last stages of a disease, these smeared outlines can pulse in a step to blows of heart.

In the analysis of an eye as the optical system which is the most expressed by an aberration of a high order at a keratoconus the so-called coma is.
The ophthalmologist or the oculist usually starts diagnosis without use of special tools. He talks to the patient, paying attention to the main complaints and subjective symptoms of a vision disorder, possible injuries or diseases capable to injure an eye, and family history of eye diseases. Then the table of check of sight is used. Sometimes direct results of the analysis of local curvature of a cornea by means of the manual keratometer at the assumption of a possible keratoconus. In hard cases curvature of a cornea exceeds measuring opportunities of the device. The skiaskopiya at which the doctor directs a ray of light to an iris of the eye of the patient can give one more sign, and monitors reflection, displacing a beam. The keratoconus and some other diseases create at the same time so-called "effect of scissors" when two reflected strips of light move to each other and back as if teeths of scissors.

At suspicion on a keratoconus the doctor performs inspection of a cornea by means of a slit lamp. If the disease developed already enough, such survey allows to make the diagnosis at once, without resorting to specific tests One of signs the so-called "Fleischer's ring" meeting approximately at a half of patients with a keratoconus is. This ring has color in the range from yellowy-brown to olive-green, and consists of iron oxide deposits — hemosiderin — in a cornea epithelium. Fleischer's ring is difficult to be made out without blue filter. In half of cases it is possible to observe also Vogt's strips — stretching striolas on a cornea surface. Strips disappear by easy pressing approximately. When the cone is strongly developed, it is possible to observe "Myunsen's sign" — the V-shaped dredging created by a cornea on the surface of a lower eyelid when the patient looks down. Myunsen's sign is a classical sign, but by the time of its emergence the keratoconus usually already is at the developed stage, and now the sign is seldom used for diagnosis.

By means of a manual keratoskop, or the "Placido's disk" projecting a number of concentric circles on a cornea the visual analysis of its curvature is possible. More exact diagnosis is provided by topography of a cornea at which the drawing projected on a cornea by the special device is analyzed by the computer for calculation of topology of its surface. The topographic map reflects all roughnesses and hems of a cornea, and at a keratoconus the characteristic strengthening of curvature which is usually located below the central line clearly is visible. It is especially important for early diagnosis of a cornea when other signs were not shown yet. Comparing several topographical pictures, it is possible to estimate character and speed of deformation of a cornea.

When existence of a keratoconus is established, its weight is estimated by several criteria:
  1. Degree of the greatest curvature — varies from weak (less than 45 Diopter.) to average (to 52 Diopter.) and heavy (it is more than 52 Diopter.)
  2. Cone morphology: a dot cone (the small size — about 5 mm in the diameter, it is located approximately on the center), an oval cone (the bigger size, it is located below the center and sags), or the globe (more than 75% of a cornea are mentioned).
  3. Thinning of a cornea — from weak (the cornea is thicker than 506 nanometers.) to advanced (the cornea is thinner than 446 nanometers)

Popularity of this system of criteria fell because of development of technologies of receiving topography of a cornea.

Keratoconus reasons:

Still the keratoconus remains the low-studied disease, the reasons of its emergence are not clear, it is also not possible and to predict the disease course after diagnosis.
The keratoconus is genetically determined disease.

Treatment of the Keratoconus:

Timely carrying out this operation at initial stages of a keratoconus and at iatrogenic keratoektaziya allows:

    * to suspend further progressing of a keratoconus (stability of the received results on average 7,5 years at the 10th summer observation);
    * to receive higher visual acuity on average on 1,4 lines; decrease in optical power of a cornea (due to flattening of the central part of a cornea and increase in uniformity of its curvature) on average on 2,1 D;
    * to delay carrying out a through keratoplasty (for indefinite time).

Indications to a method a krosslinking:

    * A keratoconus — initial and developed;
    * An iatrogenic keratoektaziya — the keratoconus which arose after carrying out refraction operations;
    * Pellyutsidny marginal dystrophy;
    * A keratomalacia — thawing of a cornea (cornea melting), as a rule during autoimmune processes;
    * A violent keratopathy — an initial stage.