**4. Disease progression**

Keratoconus progression detection is a critical issue because the treatment nomograms have been proposed based on the grading system and ectasia progression [15, 22]. Moreover, the disease progression is differed considerably among individual. The younger the patients are, the higher their risk for rapid progression [26]. Currently, there is no global consensus of ectasia progression. The Group of Panelists for the Global Delphi Panel of Keratoconus and Ectatic Diseases had defined the definition of "ectasia progression" as a consistent change overtime in at least 2 of the following parameters where the magnitude of the change is above the normal noise of the testing system:


Various clinical studies have used different parameters to define disease progression. The most important parameters include: [27, 28]

1.An increase in maximum corneal refractive power (Kmax) by more than 1 diopter (D) within 1 year


The regular topographic/tomographic check-ups can identify keratoconus progression. Regarding the examination intervals, the individual risk profiles need to be taken into consideration. The risk factors that should be considered include eye rubbing, ocular allergies, young age, steep corneal curvature gradient, high astigmatism, marked visual loss, documented progression in the fellow eye, atopic dermatitis or Down's syndrome [28]. In children, keratoconus tends to be more severe and progress faster requiring closer follow-up intervals [26]. The patient with low risks can be monitored less frequently than the one with high risks. Keratoconus progression is often associated with a decrease in best spectacle-corrected visual acuity (BSCVA), however, a change in both uncorrected visual acuity and BSCVA is not required to document progression [10].
