Keratoconus is a disease of the eye, specifically of the cornea. Cornea, which is normally in hemispherical form, gradually becomes thinner and bulges like a cone. The disorder of the corneal form disrupts the proper entry of light into the eye and its focus on the retina, so as a consequence visual disorders occur.
The mean age of occurrence of keratoconus is 16 years; however, the onset of symptoms in the age of six is also described. Keratoconus rarely occurs after 30th year.
In 90% of cases the disease affects both eyes. Most often it is developed asymmetrically; the diagnosis of the other eye is set approximately five years after the first eye. The process can be active for five, ten or twenty years and then stabilize, or stop progress over a long period, even a lifetime. During the active phase of disease, progression can be very slow or rapid, individual variations are very large.
The cause of keratoconus is likely multifactorial, a result of various factors. It is assumed that keratoconus is caused by biochemical and physical changes in the corneal tissue; however, no theory fully explains the clinical findings and symptoms.
It is possible that this disease is the end result or the final stage of many physical disorders. There is the relationship between keratoconus and heritage, hypersensitivity diseases, certain systemic disorders and long-wearing hard contact lenses.
Although the disease occurs in a small number of family cases, one of the main causal factors is certainly genetic. The proof is the inheritance of the disease, the difference between the inheritance of monozygotic and fraternal twins and the association with other genetic disorders such as Down’s and Marfan’s syndrome. There is also a difference in developing the disease within various ethnic groups.
Keratoconus can be divided by the shape of a cone, medium keratometric reading or speed of the progress.
According to the curvature it is divided into:
– Slight, less than 45 D (diopters) in both eye meridians
– Moderate, 45-52 D
– Advanced,> 52 D
– Severe,> 62 D
According to the shape of a cone:
– of small diameter of 5 mm, round shape, the easiest way to solve it is with contact lenses
– of large diameter,> 5mm, oval, often with a lag in the lower part and it is very inconvenient to put the lens
– of maximum diameter> 6 mm; affects more than 75% of the cornea and it is most difficult to resolve with contact lenses.
Keratoconus often begins as a short-sightedness and astigmatism, and patients do not even know they have this condition. Cornea slowly or quickly thins differently in individual patients, and along with that process, eyesight becomes weaker. The impairment of the vision can be moderate or very difficult, depending on the amount of affected corneal tissue. Patients often have double vision or multiple images in one eye and complain about the distortion. In some patients there are haloes, circles of light, photophobia and sensitivity to light. Sometimes in the course of the disease may occur sudden visual loss due to rupture of the cornea and aqueous humor entering into it. Thus came the swelling called hydrops. Swelling can last for weeks or months while the rift is healed, and is gradually replaced by scar tissue. When a sudden swelling occurs, the doctor may prescribe eye drops in order to facilitate the symptoms, however, no drug can prevent the progress of the disease.
It is relatively easy to diagnose moderate or advanced keratoconus. His diagnosis at an early stage, on the onset of the disease is heavier and requires more data and search. Often patients with keratoconus have to change visual aids and their dioptre grows in a very short period, but none of the aids provide satisfactory visual correction. Diopters often vary and are different from one examination to the other.
Tests used to diagnose this condition include:
– Direct ophthalmoscopy
– Slit lamp examination, with biomicroscope
Biomicroscope can see many classic signs of keratoconus: Fleischer ring, Vogt lines, scars and thinning of the cornea, the appearance of different colors in the normally transparent cornea, increased visibility of corneal nerves and corneal hydrops.
Fleischer ring is yellow-brown or olive green pigment ring which may, but need not surround the base of the cone. It occurs when the pigment hemosiderin is accumulated in epithelial cells. By disease progression Fleischer ring becomes thinner and more discreet. Attentive examination will reveal this sign in 50% of patients. By using cobalt filter this sign is easily recognized at first.
Vogt lines are small, similar to brush-shape, vertical, but can also be curved. They are located in deep parts of the corneal tissue in the area of maximum curvature. The lines disappear after applying pressure on the eyeball through the eyelid. After pressure reduces, Vogt lines appear again and then it is easier to see them. Hard lenses sometimes emphasize this line.
Thinning of the cornea and the appearance of scars are characteristic of this disease. The scars are usually observed later when cracks occur in Bowman’s membrane. Corneal opacification can occur in patients who have never worn contact lenses. Corneal cells die and are replaced by cells from the peripheral parts. Turbidity can also be caused by rubbing eyes or contact lenses that do not adhere well to the eye.
Corneal hydrops is a buildup of aqueous humor into the cornea in the later stages of the disease when Descemet’s membrane breaks. The sudden appearance of this condition causes a sudden loss of vision and a visible point on the cornea. Hydrops causes swelling and blurring. When the limiting membrane recovers, these symptoms may disappear. Sometimes hydrops improves vision in patients who have corneas too rigid. If a scar appears it is a common consequence of flatter cornea which makes wearing contact lenses easier. Hydrops occurs more frequently in patients with Down syndrome.
Munson’s sign is noticeable without the use of slit lamps. It occurs in advanced stage of keratoconus, when the cornea is so prominent as to cause angular distortion of the lower eyelid when looking down.
Razzuti’s light reflex is the name for the transfer of light reflex to the nasal groove when the light is projected from the temple side. It occurs with other eye diseases, but may help in diagnosis when biomicroscope is not available.