Why only the vertical curvature changes in keratoconus

Why only the vertical curvature changes in keratoconus

Why not the horizontal curvature also change ?
It’s becoming cone like in every direction …then why only 1 curvature is affected ?

Where is this written?

sir … You explained this when you said why there is myopic ASTIGMATISM… SO It is Astigmatism as “Vertical curvature is changing but the Horizontal curvature is not” !! .

it is just an example to explain astigmatism.