Keratoconus (KC) is a disorder of the eye which results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, astigmatism, and light sensitivity. Usually both eyes are affected. In more severe cases a scarring or a circle may be seen within the cornea.
On the plus side Hardie Board is primarily made of concrete. It is a fibrous concrete board that termites don't eat. This is good news for warmer climates where termites stay active most of the year. Hardie siding is also impervious to moisture. You can put it in a pail of water and leave it for as long as you like and it will not become saturated.
A product that not long ago was considered the new kid on the block, but now represents an industry gold standard, may be your perfect compromise. It is a wood-look lap siding called HardiePlank. HardiePlank is fiber-cement siding, a combination of cellulose fibers and cementitious materials. In other words, HardiePlank is partly wood (the cellulose) and partly mineral. Break a piece and inside you will see a brittle core interlaced with wood fibers.