"progressive bulged cornea"
KERATOCONUS: A WEAK CORNEA THAT PROGRESSIVELY PROTRUDES, WHAT BLURRS THE VISION OF THE EYE
SELDOM YOU CAN SEE IT
A TOPOGRAPHER SHOWS A KERATOCONUS CLEARLY: A RED ZONE (elevation zone) IN THE UNDERSECTOR OF THE CORNEA
THE FIRST TREATMENT FOR KERATOCONUS IS HARD LENSES (prevent from further protrusion)
IF THERE IS AN EVOLUTION OF THE KERATOCONUS DESPITE HARD LENSES A CROSSLINKING OF THE CONEA FIBERS (reinforces the cornea) CAN BE THE NEXT STEP
PMMA SEGMENT CAN REINFORCE THE CORNEA
LAST POSSIBLE SOLUTION: CORNEAL TRANSPLANTATION
KERATOCONE
- Definition
Keratocone is a disorder caused by a dilution of the cornea, which leads to deformation and bulge. The dilution concerns the central part of the cornea while the lateral parts are relatively spared. The top of the bulging cone, so formed, is usually below the pupil. Due to the bulge created nearsightedness (myopia) and irregular astigmatism, so that the patient consults an ophthalmologist because of loss of vision. At first this can still be corrected with ordinary glasses. After some time, vision may not be corrected with glasses and a different way of correction must be selected!
- Occurrence and course
The incidence reported in the literature varies from 50 to 230 per 100,000 patients. Keratoconus can occur in all races and is equally in men and women. Keratocone usually appears during puberty. Over a period of 10 to 20 years the disease evolves and then to stabilize in the third or fourth decade of life. Keratocone can also start later in life and evolve or stop at any age. The severity of the disorder at the time that the evolution stops, can be very vary. From a slightly irregular astigmatism with myopia, which is correctable with glasses, to extreme dilution with scarring, which corneal necessary. The younger the disease begins the more chance on evolution.
The disease usually occurs in both eyes. Sometimes one eye starts much later. A close examination of a patient with keratoconus in 1 eye, can reveal early signs in the second eye. Especially topography devices can show early signs of keratoconus!
Keratoconus patients should be aware of the possibility of 'hydrops' (cfr infra). This condition, which results from a break in the Descemet membrane, requires an urgent consultation. If the patient experiences the following signs: a sudden dramatic loss or vision / possibly redness, discomfort and photophobia.
- Diagnosis
A) slit-lamp examination:
The typical patient is a teenager or twenties who comes for consultation because of progressive loss of vision. The diagnosis may become clear by the slit lamp examination (= eyemicroscopy): slightly lower bulge of the cornea and dilution of the cornea (this is most notable at the top of the cone).
Clinically, we distinguish two types of cone:
- the small nipple-shaped cone
- the larger oval cone that is more lateral of the cornea
This distinction is important for the treatment, both in terms of the contact lens adjustment or surgery. A small hard contact lens can be beautiful centering on a small central cone, but is harder on a bigger cone, because the lens slides downwards. Also for the surgery, is a smaller central cone better: a small cone can be completely removed, leaving a normal cornea-rim, which is ideal for the new cornea to attach. They can also stay away from the edge of the cornea, which benefits the survival of the transplanted cornea. In slit lamp examination may also folds (Vogt striae) are present, which are at the level of the back of the cornea, just before the membrane of Descemet. Usually the folds look like a number of sharp, white, vertical lines that run parallel to each other. When you increase the pressure by gently pushing on the sclera, one can eliminate these wrinkles. These fine pleats should be distinguished from the superficial linear scars we can see thv the top of the cone. This white opacities are due to cracks in the membrane of Bowman, which are filled by stromal tissue. Thus, a significant scar appear at the top of taper. These scars are responsible for a loss of vision, that can't be corrected with glasses or contact lenses, also responsible for complaints of photophobia and ray characters around lights (glare).
Characteristic to the slitlamp findings is a Fleisher ring: It is a partial or a whole, yellow-brown ring at the base of the cone. It is formed by an iron-containing pigment ("haemosiderin"), which is located in the superficial layers of the cornea (namely in the basal epithelial cells). When the ring is present, then this is a good marker of the borders of the cone. In the beginning you see a very fine ring, which is better seen in a wide exposure to the blue light from the slit lamp. In some patients, there are deep scars at level at the top of the cone. These is the result of tears in the Descemet membrane.
This can sometimes lead to an "Acute keratocone" or "corneal hydrops". This is an accumulation in the central cornea, from liquid of the anterior chambre (corneal oedema), which flowed through the cracks in the membrane of Descemet. These patients are present with a sudden, painful loss of vision. The corneal oedema remains for several weeks or months, but usually decreases gradually.
Ultimately, the oedema is replaced by scar tissue, which in some cases may lead to a flattening of the cone. In advanced cases, bulging of the cornea can cause a distortion of the lower eyelid when looking down. This is called the sign of Munson.
B) keratometry (corneal measurements)
In the early stages of the disease process, the cornea may appear completely normal at the slit lamp examination. In these cases it is the keratometer who can give us the diagnosis. Irregular corneal distortion (astigmatism) is a typical characteristic of keratoconus. Also a progressive increase in corneal curvature over time is an indication of keratoconus. Today, there are also computer-assisted Opthalmometers (corneal topography), which is much earlier than with hand-Opthalmometers, astigmatism and bulging in the light can make. This device is the ultimate way to diagnose keratoconus and to follow.
Three characteristics appear to be characteristic for keratoconus and are not seen in normals:
- a localized area where the cornea is steeper
- asymmetry between the lower and upper half of the cornea
- the axes of astigmatism are rotated relative to each other
If progression is determined, one is sure of the diagnosis of keratoconus. Otherwise it is going to irregular astigmatism. The most common cause is wearing of contact lenses (soft lenses, especially with hard lenses). The difference with keratoconus is not always easy in such patterns will disappear over time if the patient lets out his/her lenses, while keratoconus earlier increases.
NOTE: The early detection of keratoconus is very important because it often prevents a keratoconus patient who asks for surgery to eliminate his glasses ("refractive surgery"). Such surgery means that a portion of the cornea is dragged away, what constitutes a weakness. This is no problem with normal corneas, but already weakened corneas from keratoconus patients can more quickly evolve after refractive surgery. Keratoconus patients (also early) are excluded for such surgery.
C) Pachymetry (= measurement of corneal thickness)
Thickness measurements in different places over time, the presence of dilution, especially in the lower part of the cornea, help prove the diagnosis of keratoconus. A documented increase in the curvature of the cornea with a progressively increasing dilution over time are a proof of keratoconus.
- Associated disease
In the great majority of cases, keratoconus an isolated condition, which occurs not hereditary. One often sees it, other diseases
a) systemic disease, such as eczema, mongolism and connective tissue diseases (Ehlers-Danlos syndrome and osteogenesis imperfecta)
b) eye disease: allergy and wearing hard contact lenses
- Cause
The cause is still unclear. It seems likely that keratoconus is caused by abnormalities in the middle part of the cornea (= 'corneal stroma). This theory would explain the association with connective tissue diseases. More specifically, there is an accelerated degradation done by an increased action of the afbraakenzymes and premature death of the cells present. Heredity probably plays an important role. The disease is inherited in families especially, but not absolute: in keratoconus patients is found in the family, people with abnormal topography. If you have keratoconus, you could pass it to your children, but only 6 to 8%: "dominantly inherited with variable expression.
Several reports also show that rubbing the eyes an important factor in the development of keratoconus. Rubbing the eyes means a microtrauma and if this happens repeatedly, this leads ultimately to a weakening of the cornea. It is known that people with eczema also thv itchy eyes experienced and therefore more rub. This probably explained the finding that patients with eczema and other forms of oogallergie further develop keratoconus. Wearing contact lenses would thus also be explained as a damaging factor: rubbing lenses also slightly over the eyes, especially hard lenses!
Summary: environmental factors such as rubbing and wearing contact lenses can potentially accelerate the evolution of the disease in genetically suitable for individuals. Moral of the story: RUBBING IN THE EYE IS ALSO STRICTLY PROHIBITED!
- Treatment
A) keratoconus:
The treatment of keratoconus begins with glasses correction. Once that no longer can achieve good visual acuity with glasses (because of clear corneal distortion), we will switch to hard contact lenses, which captures the distortion by filling with tears. Furthermore, the contact pressure against a protrusion of the cornea, which inhibits progression somewhat. Successful adaptation to hard lenses requires a lot more time in keratoconus patients, because it is not easy to find a lens that fits on the bulging cornea and to know what correction is needed. Regular lenses must be exchanged. Fortunately, we can now, based on the topography "lenses custom" make faster success indicate that conventional lenses! For most patients can be a good vision reach an acceptable comfort (the lenses move is more than in normal subjects! Contact lenses are the mainstay of treatment of keratoconus based and represent the treatment preferred by nearly 90% of the patients. why they are reimbursed by health insurance. Most of these lenses for years tolerated (if any adjustment after several years for the progression of keratoconus to compensate). Only when there is no stable adaptation can achieve more or if the vision is limited continues to scar formation, surgery is recommended. In practice, only a minority of keratoconus (10 to 20%) have to be operated
Which surgery is possible:
A. stabilize the keratoconus:
This can happen with UV cross-linking of the fibers of the cornea. The stabilization is useful when the visibility is quite good with correction. After that visual rehabilitation process (cfr infra). When visibility is not so good, crosslinking has little effect. There can be tried to improve the visibility of corneal rings, which are inserted into the depth of the cornea. This strengthens the cornea and reduces the distortion of the cornea. If corneal rings can not, can only benefit expected from a corneal transplant.
B. Visual Rehabilitation (at the earliest 3 months after UV cross-linking - in young patients is best to wait two years to ensure stability):
Should have good vision can be obtained by cross-linking may be an effort to improve the visibility of surface laser (if the deviation is small) or lens-lens implants above their own.
C. Hydrops
The treatment of hydrops can exist in a context or an associated lens, cycloplegie, hypertonic saline and reassurance. Local cortisone drops are sometimes necessary but they have sometimes to poor healing of draining the anterior chamber (corneal perforation).).