WHAT IS KERATOCONUS?

Keratoconus is a condition where the cornea becomes thin and assumes a « cone-like » shape. It results in visual blurring or distortion from myopia and irregular astigmatism.

Clinical signs of keratoconus on slit lamp biomicroscopy include a thin cornea (upper left), Fleischer ring (lower left) and Vogt’s striae (upper and lower right). Fleischer rings are pigmented rings in the peripheral cornea from iron deposition in the basal epithelial cells, in the form of hemosiderin. Vogt’s striae are thin vertical streaks located in the posterior corneal stroma, at the level of Descemet membrane. In early cases of keratoconus, examination with the slit lamp may be entirely normal.

Corneal topography enables the morphological characterization of the cornea. It is essential for the diagnosis of keratoconus. This non-invasive exploratory technique has the possibility of achieving a great number of measuring points of both anterior and posterior corneal surfaces, All these data can be processed to extract a series of topographic valuation indices which have be conceived to increase the reliability of the clinical diagnosis.

Corneal topography enables the morphological characterization of the cornea. It is essential for the diagnosis of keratoconus. This non-invasive exploratory technique has the possibility of achieving a great number of measuring points of both anterior and posterior corneal surfaces, All these data can be processed to extract a series of topographic valuation indices which have be conceived to increase the reliability of the clinical diagnosis.

The authors of this website have acquired the certitude that the root cause of keratoconus is eye rubbing (1,2). This assertion, which is difficult to prove, but equally difficult to refute, derives from crossed observations and follow-up of hundreds of keratoconus cases. On this website, we present over eighty cases. These were cases of keratoconus that presented consecutively to our clinics, and were not randomly selected for the sole purpose of supporting our eye rubbing hypothesis. We have yet to find cases where eye rubbing, usually correlated with the sleeping position of the patient, was not in existence before the onset or diagnosis of keratoconus.

Recent biomechanical investigations have shown that corneas with keratoconus are focally but not globally weakened (3). In keratoconus, the central portion of the cornea is thinned and weakened, whereas its periphery shows a normal biomechanical behavior. How could a genetic or biomolecular disease involving corneal collagen and/or fibril structures affect focal areas while sparing other parts of the corneal tissue?

Keratoconus is usually described as an unknown collagen dystrophy associated with environmental, cellular and genetic factors causing a degenerative change in the cornea.  This degenerative change results in a reduction in the corneal stiffness. It is thought that impaired corneal biomechanics makes the corneal dome prone to bulge forward under the action of the intraocular pressure and undergo progressive « ectatic » changes. However, there is at least one perfect counter-example to explain the irrelevance of current theories on the pathogenesis of keratoconus. We will therefore pay attention to this disease named « Marfan syndrome« , and describe what could be labeled « The Marfan paradox« .

Marfan syndrome results from the abnormal synthesis of collagen which alters the biomechanics of the soft tissues of the human body such as skin, ligaments and blood vessel walls.  The  main layer of the cornea (the stroma) is made of collagen fibers. If Marfan syndrome should perfectly support the theories of keratoconus that attempt to explain the ectatic process by the occurrence of an alteration of corneal biomechanics via an unknown molecular abnormality, topographic changes similar to keratoconus should be observed. In Marfan syndrome, the corneal biomechanics are indeed impaired, and the cornea thinner. However, as logical as it may appear at first glance….

The weaker cornea in a Marfan patient, unlike in keratoconus, tends NOT TO BE steeper, irregular and ectatic, but rather globally FLATTER and not much irregular(4,5) !

This may not in fact be that surprising: without any additional external trauma, the biomechanical alteration of the corneal tissue in the eyes of Marfan patients causes the cornea to progressively distend. This mechanism may better describe what a « corneal ectasia » truly is : a progressive distension, globally harmonious, which incurs a progressive thinning and flattening of the corneal surfaces (as the radius of curvature of the cornea increases). It is not the same as what is commonly observed in early and mild keratoconus, in which the term « irregular deformation » or « warpage » may better describe the condition affecting the corneal wall. This deformation is caused by repeated local trauma due to the shearing forces vehicled by the hands, fingers and knuckles during eye rubbing episodes. In the absence of excessive eye rubbing, the cornea (even natively thin and soft) has no reason to deform and exhibit the topographic features encountered in keratoconus: this concept is coined as the « No Rub, No Cone » conjecture.