keratoconus: Stages and clinical forms
Stages and clinical forms
There are several stages of keratoconus, and different classifications exist to group them. The so-called clinical forms and the so-called infra-clinical forms are classically distinguished.
– Clinical Forms correspond to an advanced stage of the disease: Corneal deformation is sometimes visible at the biomicroscopic examination (Slit lamp), the visual acuity corrected in the bezel barely reaches the 10/10 due to a large irregular astigmatism (induction of high-degree aberrations). Patients have a long history of eye rubbing Repeated. The corneal topography is characteristic: marked thinning of the corneal wall, asymmetric and irregular deformation of the anterior face of the cornea, marked elevation of the posterior face, etc.
It is rare to diagnose keratoconus only at a very advanced clinical stage, because the visual disorders characterized by a astigmatism Fast evolution poorly corrected in glasses, rapid accentuation in adolescence, often lead to raise the diagnosis of keratoconus at an earlier stage (in all case , this diagnosis must be confirmed by the corneal topography).
When the disease-related deformation reaches a very advanced stage, it is visible for direct examination; Munson's sign corresponds to a deformation characteristic of the palpebral ledge in the downward look:
– Thesubclinical forms characterized by an often chance discovery, on the occasion of an ophthalmological checkup (sometimes in the context of a pre-refractive surgery balance, i.e. before a eye laser surgery To correct myopia and astigmatism).
This discovery is made through the realization of a corneal topography, which must be systematic in this context.
The corneal topography reveals signs that arouse suspicion vis-à-vis a beginning form of keratoconus. Depending on these topographic anomalies, the cornea may be classified as " suspect of Keratoconus", or a '" crude form of Keratoconus "(or more simply:" Keratoconus fruste »). These designations combine the forms that present certain characteristics that may evoke the presence of a beginner keratoconus.
Patients with "suspicious" topography are often those who rub their eyes regularly, sometimes (often) without their knowledge, and/or sleep on the side or on the belly. However, friction has not yet been sufficiently intense and or prolonged to cause greater deformation, and there is a slight topographic irregularity below the detection thresholds established for keratoconus.
The variability of eye rubbing In intensity, laterality, duration, etc. Explains the existence of topographic forms so different, in terms of evolutionary stage, when discovering a keratoconus.
Certain however: regardless of its stage and its evolutionary character. Keratoconus, even beginner represents an absolute contraindication to surgery through LASIK, because the realization of this technique can only be done if the cornea has sufficient thickness and regularity.
The cutting of a flap stromal and the photoablation are able to weaken brutally corneal resistance already weakened by repeated rubbing, and then, deformation can be accentuated by the crossing of the threshold of biomechanics decompensation.
As a result, it is crucial to detect the presence of an early form of keratoconus in patients seeking refractive surgery. In the spirit of the author of this site, a starting form of keratoconus corresponds more exactly to a moderate corneal deformation, induced by the repetition of eye rubbing whose intensity and duration are not sufficiently pronounced To trigger the appearance of a proven form, characterized by a more severe corneal deformation and a source of non-correctable visual disturbances in spectacles.
For the same duration and the same intensity of friction, a thicker and more resistant cornea may present a deformation less pronounced than a fine and less resistant cornea (role favouring the "Kératotype").
The completion of a LASIK in a patient with keratoconus says "fruste" usually causes an increase in corneal deformation. A proven form of keratoconus is then observed, which is then referred to as "Keratoconus iatrogenic", or more generally of LASIK-induced ectasia.
An aspect of beginner keratoconus reflects the presence of a certain degree of biomechanical fragility (mechanical origin: friction); LASIK produces an additional weakening that can increase this fragility and accelerate the biomechanical decompensation of the cornea.
Functional treatment of proven Keratoconus is the optical patient rehabilitation and includes glasses, contact lenses, inserting intra corneal ring segments, the corneal transplant (lamellar keratoplasty, deep). The realization of one «» cross-linking » Corneal Collagen has been proposed to curb (or even halt) the evolution of keratoconus; This approach presupposes that keratoconus is the result of a primitive tissue anomaly ("soft" cornea). However, as explained on this site, the keratoconus is the consequence of the repeated eye rubbing: The shutdown of these is the safest method to stop the evolution.