Altered Organization of Collagen in the Apex of Keratoconus Corneas

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Abstract
Purpose: In 15 keratoconus corneas, the three-dimensional arrangement of collagen lamellae was investigated by means of scanning electron microscopy. Methods: Keratoconus corneas without visible scars were obtained during perforating keratoplasty. The noncollagenous matrix of the stroma was removed with sodium hydroxide. Descemet’s membrane was removed mechanically and deeper layers of the stroma were exposed by cutting the tissue tangentially to the corneal surface with an ultramicrotome. The apical and the para-apical regions of keratoconus were compared to the central regions of normal corneas. Results: In the apical regions of 11 out of the 15 keratoconus corneas (73%), the arrangement of the collagen lamellae differs from those of the para-apical regions and normal corneas. Their collagen fibrils form uniform layers and no delimited collagen lamellae can be differentiated. Interlacing between adjacent layers is extremely decreased or even absent. In the para-apical region of keratoconus corneas the three-dimensional arrangement of collagen lamellae does not differ from that in normal corneas. Conclusion: Stromal thinning and conical ectasia in the apex of keratoconus corneas alters the organization of collagen. This will certainly affect the biomechanical properties of the cornea and further lead to a progression of keratoconus irrespective of its primary pathogenesis.

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