Keratoconus suspect

Suspicious forms of Keratoconus

Suspicious forms of Keratoconus ("Keratoconus suspect") belong to the group of corneal anomalies that are grouped under the name of  » subclinical keratoconus « : Their diagnosis is based on the specular topography of Placidowhich reveals anomalies, which, without being sufficiently pronounced to make the diagnosis of Keratoconus, evoke the possibility of a intermediate form, little or no progressive disease. One speaks for example of form fruste in front of a topographical picture very little modified on one eye, while the other one has a frank Keratoconus. We know today that this type of asymmetry between the right and left eyes of the same patient is explained by a difference between intensity and/or frequency and/or duration of the eye rubbing.

There are no clinical signs of affection outside of a possible refractive anomaly (the examination to the slit lamp is normal, the cornea is transparent, the best corrected visual acuity retained).

Myopia and a Astigmatism of corneal origin (typically oblique or inverse direction) are often associated with the infra-clinical forms of keratoconus.

Generally, the presence of an allergic terrain (atopy) is often noted in the patient concerned and/or the notion of overwork, chronic fatigue, intense studies, prolonged work on screen, stress, etc. These elements have in common to promote the occurrence of itching (pruritus) marked ocular,... which caused the realization of eye rubbing repeated.

These frictions, beyond a certain frequency, intensity duration, can cause in the long term a permanent deformation of the cornea which, when it is weakly pronounced, is akin to what is designated as a suspicious form of keratoconus.

The keratoconus itself is no other than the marked and permanent corneal deformation, which is itself the translation of repeated mechanical stress (rubbing).

form suspect of Keratoconus

Form classified as suspect of Keratoconus by the specular topographer OPD SCAN (analysis by computing the indices of Klyce and Maeda and a neural network)

Suggestive signs of a suspicious form of keratoconus 

In the absence of an automated detection index, the suspicion of the presence of an infra-clinical keratoconus may be evoked before:

-one asymmetry of the cornea: A more accentuated camber in lower or inféro temporal than in superior, a deviation of the most arched hemi-meridians (SRAX)

-reduced corneal thickness (ex: 500 microns and less for the minimum thickness)

-A lower deflection of the most fine point of the cornea (maps of thickness/tomography)

-a topographical discordance between the earlier rise and the subsequent elevation of the cornea (see article dedicated to the corneal elevation of suspicious forms of Keratoconus)

-a discordance between topographic aspect of the right eye and the left eye (low enantiomorphism)

-a (boost) evolution of the topographical anomalies in time.

 

Refractive surgery and suspects forms of Keratoconus

The finding of a verdict of "suspicion of keratoconus" during the course of a topographic examination must formally re-consider the indication of LASIK, under penalty of provoking a ectasia, which is a biomechanical decompensation of the wall of a cornea Initially "fragile", due to the presence of a beginning or little evolutionary form of keratoconus.

However, like all medical tests, there is a risk of the diagnosis of Keratoconus suspect form by excess. For example, the existence of a keratometry is a classic topographic sign of Keratoconus, this disease often associated with a camber accentuated of the cornea.  However, corneas that camber is naturally high, but who are otherwise healthy. So it is sometimes permissible to disregard the diagnosis of Keratoconus suspect, when there are enough reassuring elements also: absence of corneal amincisssement, good enantiomorphisme, corneal biomechanical measures normal, etc.

false positives for automated diagnosis of Keratoconus

Automated analysis of maps of specular topography of a candidate for refractive surgery astigmatism Bilateral myopia concludes with a non-zero probability of keratoconus right (9%) and left (25.3%) (OPD SCAN). However, the study in elevation topography (Orbscan) stresses the presence of normal thick corneas, albeit arched, but without major asymmetry, and above all an excellent enantiomorphism. Biomechanical measurements (ORA) were satisfactory. This patient has finally benefited from surgery by LASIK And did not introduce Ectasia post LASIK with a 5-year setback.

In many situations where there is a suspicion of subclinical Keratoconus, there is a possibility to achieve a surface laser technique (PKR). Cases of corneal ectasia after PKR are exceptional. Some authors have even reported use of PKR for shapes turned of Keratoconus, designed to regularize the profile of the cornea.

The absence of cutting the flap (unlike LASIK) is certainly one of the explanations for this preservation of the Biomechanics of the cornea after PKR. We have recently published a series of case of PKR for low and medium myopia issued on corneas with a topographic infra clinical Keratoconus suspicion. No case of ectasia has been reported with a decline of 5 years.

One response to "keratoconus Suspect – suspicious forms"

  1. Macailing Max says:

    Dear Master Excuse My audacity I am neophyte but in your definition you say and I quote: Keratoconus Infra-clinical ": their diagnosis is based on the specular topography of Placido, which reveals anomalies ... ..." I understand that the topgraphie specular never allowed Diagnostiauer a FFKC since the latter concerned mainly the rear face of the cornea said Saurface which can only be studied by the Topog a elevation type scheimpflug .... not to mention the maps pachymetriques absent In the Placido devices ... would I misunderstand?

    PS I have loved your book ... a Bible

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