As some background I design contact lenses and IOLs and have not yet designed for keratoconus. I approach my design from the CAD and FEA perspective with bio-machanics and opto-mechanics.

I have always read that keratoconus is caused by the thinning of the cornea. I have always thought that the thinning may be a symptom of material degradation of the cornea.

If you imagine that the eye is an optical bubble with a positive pressure compared to atmospheric pressure. If the stress exceeds the yield stress of the cornea then it will bulge and thin. Since the pressure is regulated elsewhere the volume of aqueous will increase and the pressure will rise to the previous level except now the cornea is thinner.

The mechanical properties of the cornea are very important as you suggest. Finding good material properties for any biological tissue is always problematic. Here we could be concerned with many interesting but challenging mechanical phenomena. The cornea has layers, like an onion, for all you Shrek fans, which makes it non-isotropic. On top of that you can easily add hyperelastic, viscoelastic, plasticity and a whole bunch of other fun ones too.

An interesting problem indeed I look forward to reading other's responses!

Feel free to LinkedIn me as well. Eye biomechanics is a small world.