Keratonconus

Keratonconus

Keratoconus is a progressive deformation of the cornea (cone-shaped at very advanced stage) due to reduced resistance of the corneal tissue causing progressive myopia and irregular astigmatism.

The pathogenesis is multi-factorial: variable gene expression (can be combined with other genetic abnormalities), hormonal factors, mechanical factors (micro-trauma due to excessive eye rubbing), and a particular frequency of eye allergies.

The cause of the outbreak is unknown.

Diagnosis

In the early stages, a keratoconus is sometimes difficult to locate or not identifiable at all.

Topography:

Asymmetry in the radius of curvature of the cornea.

Low corneal hysteresis

While progressing, the keratoconus is visible during a corneal topography, and on late-stage under the microscope.

Corneal topography



ORA : Ocular Response Analyzer

Ocular Response Analyser (ORA) :

In the early stages, a low hysteresis can be the only element of diagnosis.


Progression

The progression is very variable and is often different between the two eyes. It can start during puberty or later and evolve until 30 or 40 years.

After this age the progression slows down.

The correction depends on the disease’s activity

In the early stages, glasses and contact lensescan correct it.

-If the cornea is too deformed for contact lenses, scleral lenses may be indicated.

-If the disease evolves, the cornea can be strengthened by cross-linking.

In case of difficulties with scleral lenses, intra-corneal rings can be suggested.

When the stage of cornea weakening is reached, a keratoplasty may be necessary (corneal transplantation, anterior lamellar, or transfixing)

Cross-linking :

Intra-corneal rings:

Keratoplasty :

Keratoconus and refractive surgery

In general, the Excimer laser is not indicated in case of keratoconus, this is why we try to detect keratoconus before a refractive procedure, but in the early stages or before, we cannot always make the diagnosis.
A number of keratoconus develop after a laser procedure. Either the cornea has been weakened too much, or that was an invisible keratoconus that evolved after surgery.

Predisposition to keratoconus is not diagnosable. This means that in case of correction by laser, the patient has to be informed that a corneal deformation might occur and in this case a crosslinking treatment may be necessary.

In some cases, a crosslinking can be offered upon the completion of the laser procedure. On diagnosed keratoconus, a crosslinking can stop the progression, but does not improve the useful vision, and it is necessary to propose contact lenses.

When the lenses are not tolerated, a refractive correction by rings can be discussed, if the corneal thickness is sufficient, this can be supplemented by an Excimer laser treatment, as the rings only correct until a certain degree of myopia and astigmatism,

In these correction procedures the cornea is strengthened by cross-linking but is weakened by removing tissues. We must therefore make an assessment of the advantages and disadvantages of this association of treatment.