| (1) Changes in shape and optical properties |
(a) Steepening of keratometry and a shift from with the rule to against the rule astigmatism |
| (b) Transparency is unaffected in central cornea in absence of scar or degeneration |
| (c) Collagen intramolecular and interfibrillar spacing increases—possibly via increased protein glycation |
| (d) Increased thickness of Descemet's membrane |
| (2) Corneal degenerations (influenced by environmental and genetic factors) |
(a) Cornea farinata |
| (b) White limbus girdle |
| (c) Mosaic degeneration |
| (d) Deep crocodile shagreen |
| (e) Hassall‐Henle bodies |
| (f) Arcus senilis |
| (3) Physical properties |
(a) Resistance to infection reduced |
| (b) Failure to upregulate ICAM‐1 and reduced inflammatory cell infiltration |
| (c) Reduced phagocytically active cells after infection |
| (d) Decline in high energy metabolism |
| (e) Increased tear contact time |
| (f) Increased epithelial permeability to fluorescein |
