Reduction in corneal volume with severity of keratoconus.

PURPOSE: To compare the corneal volume in keratoconic and normal eyes to improve our understanding of the tissue distribution associated with the disease. MATERIALS AND METHOD: The Oculus Pentacam tomographer (Oculus Inc., Wetzlar, Germany) was used to analyze the corneal volume contained within discs with diameters of 3, 5, 7, and 10 mm in 21 patients with keratoconus and 21 matched healthy control subjects. RESULTS: Corneal volume was significantly decreased in the keratoconus group (keratoconus vs. control group: 3.44 ± 0.39 vs. 4.05 ± 0.29 mm(3), 10.34 ± 0.95 vs. 11.79 ± 0.84 mm(3), 22.80 ± 1.73 vs. 25.26 ± 1.74 mm(3), and 57.17 ± 3.94 vs. 61.90 ± 4.12 mm(3) for the 3-, 5-, 7-, and 10-mm diameter discs, respectively; p < 0.001). As the corneal disc diameter analyzed increased, fewer differences were found between the control corneas and keratoconic corneas at different stages of the disease. Within the 3-mm and 5-mm diameter discs, significant differences were detected between the control group, moderate keratoconus, and the severe keratoconus groups (p < 0.05). However, within the 10-mm discs, differences were only detected between the control group and the severe keratoconus group (p = 0.005). CONCLUSIONS: Corneal volume was significantly decreased in keratoconus, particularly in the central and paracentral area. The decrease in corneal volume in moderate and severe keratoconus as detected by the Pentacam tomographer, may be explained by loss of corneal tissue. In the early stages of the disease, the altered metabolic activity may cause tissue stretching and, as the disease progresses, this stretching is then accompanied by tissue loss.

Corneal nerve structure and function in keratoconus: a case report.

PURPOSE: To investigate corneal nerve structure and function in a 24-year-old patient with keratoconus and prominent corneal nerves. METHODS: Corneal nerve appearance was assessed by using a corneal confocal microscope, and corneal nerve function was assessed by using a Cochet-Bonnet aesthesiometer. Findings were compared to those of an age-matched control subject without keratoconus. RESULTS: The patient with keratoconus was found to have thicker nerve fiber bundles in the stroma (keratoconus vs. control, 9.8 +/- 5.0 microm vs. 5.4 +/- 2.7 microm) and reduced nerve fiber density in the subepithelial plexus (keratoconus vs. control, 269.7 +/- 145.6 microm vs. 1,258 +/- 254.8 mum) compared to the control subject. The patient with keratoconus was found to have reduced corneal sensitivity compared to the control subject (keratoconus vs. control 0.39 gr/mm2 vs. 1.59 gr/mm2). CONCLUSIONS: Corneal confocal microscopy proved to be a useful in vivo technique for assessing corneal nerve structure in this patient with keratoconus. Although the total number of stromal nerve fiber bundles was reduced in the patient with keratoconus versus the control subject, the increased tortuosity and increased nerve fiber diameter may explain why the corneal nerves appear more visible in this patient with keratoconus.