The progression of keratoconus is not a certainty

Keratoconus progression can be halted by suppressing the root mechanism of the corneal deformation at play: EYE RUBBING
Documentation of keratoconus progression

Several methods have been described in the literature to both evaluate and document possible changes in keratoconus, but keratoconus progression per se has not been consistently or clearly defined.

When corneal deformation progresses, steepening of the anterior corneal surface with corneal thinning would be expected.

Progression (or stabilization) of the corneal deformation must be assessed by reliable examinations.

The direct inspection of a series of corneal topography maps performed at different time points can be instructive, but it is sometimes difficult to confirm an impression.

Small differences can be observed between even consecutive topographic measurements: some can be caused by measurement noise, and subtle variations in the alignment of the eye with the instrument. Test–retest variability is practically used, for example, in medical monitoring of conditions. In these situations, there is often a predetermined « critical difference » or « threshold ». If the differences in monitored values (ex: maximum keratometry) are smaller than this critical difference, the possibility of pre-test variability as a sole cause of the difference may be considered.

The repeatability (test–retest reliability) of topography instruments is lower in keratoconic eyes than in normal eyes.  For example, we found that the « critical difference » for simulated keratometry (or maximum keratometry) is about 1.50 D for advanced keratoconic eyes i.e. differences in monitored values that are smaller than this critical difference should not be considered as statistically significant (see here for more).

In topography, the difference map allows us to compare two examinations carried out at different times. All the cases reported on this website are monitored with several corneal topography examinations at each visit. We perform a difference map whenever possible, as they provide a direct quantified, and comprehensive representation of the presence (or absence) of significant variations between two examinations.

The difference map provides an objective metric to monitor the evolution of the corneal deformation, which is the hallmark of keratoconus.

In some instances, it is not possible to perform a difference map (when topographic examinations were performed in different institutions). Confronting some of the values obtained at each examination time-point is necessary:

Legend : The direct inspection strongly suggests that there has not been any progression between 2012 and 2016 in an allergic 32 yo patient who had stopped to rub his eyes in 2012. This patient rubbed his right eye more vigorously. He sleeps on the right side.

Several metrics can be used to monitor KC progression. Topographic indices such as maximum keratometry, mean keratometry, simulated keratometry astigmatism, value of the thinnest point (minimal thickness point) can be used.

Legend : In this example, the inspection of the values of some of the analyzed parameters (right eye) show that the indices are stable. This allows us to conclude that the keratoconus did not progress.

The measurement variability is greater in ectatic corneas, and it is important to take the reduced repeatability of corneal topography instruments to appreciate any change between examinations performed at various timepoints.

In the above example, the numbers have changed between 2012 and 2016, in the direction of an improvement (reduction in irregularity, astigmatism). These changes may just reflect the measurement variability which is greater in ectatic corneas. It is important to take into account the reduced repeatability of corneal topography instruments to appreciate any changes between two examinations performed at various time-points. (read more about repeatability of corneal topographers in keratoconic eyes)

In conclusion, the realization of a difference map is the best tool to visualize the changes (or absence of) between two topographic examinations of the same eye made at various time-points:

Legend : In this example, two different examinations are compared: the first examination (second column) was recorded in June 2016, while the second one was recorded in January 2017. The third column plots the direct subtraction between these two examinations.  The values are low, comprising of values between -0.4 D and +0.8D. The inspection of this map is sufficient to check for the stability of the keratoconus. 

If one considers that the primary cause of keratoconus is eye rubbing, it is logical that the cessation of rubbing suffices in stabilizing the disease.

All patients who have been diagnosed with keratoconus and monitored for progression after they had ceased to rub their eyes are reported in this website. Differential maps were performed systematically at each examination to confirm the absence of keratoconus progression.

The cases described here are consecutive cases of keratoconus presenting to us. The newly diagnosed cases were seen from January 2016 onwards. Cases which had been first diagnosed previously were added to the list as soon as they appeared for their follow-up examination.