(1) Changes in shape and optical properties | (i) Steepening of keratometry and a shift from with the rule to against the rule astigmatism38 39 |
(ii) Transparency is unaffected in central cornea in absence of scar or degeneration40 |
(iii) Collagen intramolecular and interfibrillar spacing increases—possibly via increased protein glycation41 42 |
(iv) Increased thickness of Descemet’s membrane |
| |
(2) Corneal degenerations (influenced by environmental and genetic factors) | (i) Cornea farinata |
(ii) White limbus girdle |
(iii) Mosaic degeneration |
(iv) Deep crocodile shagreen |
(v) Hassall–Henle bodies |
(vi) Arcus senilis |
| |
(3) Physical properties | (i) Resistance to infection reduced |
(ii) Failure to upregulate ICAM-1 and reduced inflammatory cell infiltration43 |
(iii) Reduced phagocytically active cells after infection44 |
(iv) Decline in high energy metabolism45 |
(v) Increased tear contact time46 |
(vi) Increased epithelial permeability to flourescein47
|