Corneal collagen cross-linking (CXL) is a technique which uses UV light and a photosensitizer to strengthen chemical bonds in the cornea. The goal of the treatment is to halt the progressive and irregular changes in corneal shape, known as an ectasia such as keratoconus. Also, some studies showed that CXL seems to be effective in improving visual acuity in eyes with progressive keratoconus with reducing corneal keratometry and cylinder. (Link)

What we call the « Cross-Linking Like » Effect (CXL Like Effect), corresponds to the same effect, ie to the reduction of  cylinder and corneal keratometry, spontaneously, and only after immediate cessation of eye rubbing and/or correction of an unhealthy sleep position.

Indeed, we noticed that stopping eye rubbing, in most cases, ensured the stability of the keratoconus but also in some cases it led to a spontaneous regression of the keratoconus with a decrease of corneal cylinder and keratometry, without any other potentially harmful intervention for the eye.

We call this : The « Cross-Linking Like » Effect.

Here is a topography to illustrate this effect on a patient with keratoconus, with a differential map, after immediate cessation of eye rubbing on this eye.

Our experience has shown that this effect (CXL Like) doesn’t occur in all patients, but on a significant and enough number of patients to be able to describe it.

We found that it occurs mainly in the first months after stopping eye rubbing, often on the most affected side.

These are often patients with the habit of rubbing one eye preferentially or sleeping on the same side as the affected eye. Finally, with our practice we can also describe it in patients with unilateral keratoconus. This effect remains stable over time, has been verified with several consecutive measurements.

To better understand this phenomenon, we must focus on Corneal Biomechanics.

The shape of the cornea is the result of a balance between the external forces applied on the eye (eye lid, atmospheric pressure, eye rubbing, heat, or any other compression [sleep position], the internal pressure forces, and the characteristics of biomechanical resistance of the corneal stroma and the sclera. Some devices make it possible to evaluate the corneal biomechanics, like the Ocular Response Analyzer® (ORA, Reichert, Buffalo, NY)

Some individuals have thin corneas or fragile biomechanics (low values of Corneal Hysteresis (CH) for example) but no corneal deformation (keratoconus).

This is explained by the fact that biomechanical equilibrium of their corneas remains respected, and there are no external mechanical forces (eye rubbing, sleep position, compression) disturbing this equilibrium to cause a focal deformation.

The « CXL like » effect, would correspond to the opposite phenomenon, i.e. to a sudden recovery of this balance following the immediate cessation of any external biomechanical factor (eye rubbing and/or sleep position), resulting in the restoration of the corneal equilibrium on a keratoconic (deformed) cornea. A reduction in this corneal deformity would result in a decrease of corneal keratometry (less steep), decrease of corneal cylinder, less spherical aberrations, and sometimes an increase in visual acuity.

Here is the story of a 47-year-old man, with no previous ocular history, and 2 brothers without keratoconus, who has unilateral keratoconus of the left eye.

He describes his daily life, with his habit of eye rubbing and sleeping on the left eye. The deformation of the left frame of his glasses indirectly reveal the force exerted by chronic eye rubbing on the same side.

The differential maps show a CXL-like effect, almost immediately after the correction of these habits. There is a significant and focal reduction of the keratometry and the corneal cylinder after cessation of any ocular compression on this eye. Hence the importance of educating patients about the dangers of these bad habits.

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This case reflects the importance of repeatedly reiterating the harmful effects of a compressive sleep position, to patients in consultation.

This is a 29-year-old woman with keratoconus of the right eye and a forme-fruste keratoconus (FFKC) of the left eye.

Her eyes are « itchy » due to eyelid eczema. This kind of Unilateral Keratoconus is explained by her eye rubbing habits mainly on the right eye, but also by an unhealthy sleep position. After educating the patient on the risks related to these bad habits, we were able to obtain keratoconus stability over 1 year. It’s only 2 years after this cessation, that we can note a « CXL like » effect on the right eye.

This late reduction of keratometry and corneal cylinder can be partly explained by a delayed change and awareness of her unhealthy sleep position and the use of a night protection mask from 2018.

This case reveals to us that it’s never too late to achieve stability and restore the balance of corneal biomechanics.

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Click to slide and enlarge picture

This case tells the story of a 30-year-old man with bilateral keratoconus, more pronounced in the right eye. 

This is explained with his habits of eye rubbing and an unhealthy sleep position. After the cessation of his habits, we note in the first few months a CXL like effect in the right eye. 

This effect continues to evolve and there is a gradual and significant reduction in keratometry over time (1 year later).

This would be explained by a slow and gradual restoration of the corneal dome equilibrium by the removal of any external focal mechanical factor on the cornea.

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This is a 19-year-old patient, who has a strictly unilateral keratoconus of the left eye. 

The right eye has no keratoconus but a congenital regular astigmatism associated with thin pachymetry.

The cornea of ​​the right eye is not deformed without keratoconus, but only thin.

The patient tells us that he used to rub only his left eye and sleep on the same side with his head buried in the pillow.

After educating the patient on the dangers of this practice, we note an early CXL like effect with a significant reduction of keratometry.

This spontaneous reduction after cessation of eye rubbing has a clinical impact, because the patient can wear glasses with less correction and feels an improvement in visual acuity with his new correction.

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