Keratoconus and normal-tension glaucoma: a study of the possible association with abnormal biomechanical properties as measured by corneal hysteresis.

PURPOSE

To test the hypothesis that patients with keratoconus and pellucid who have glaucoma or are glaucoma suspects have lower corneal hysteresis (CH) and/or corneal resistance factor (CRF) measurements compared with controls.

METHODS

A prospective study at a tertiary eye center of patients with keratoconus and pellucid, with glaucoma or suspect glaucoma and age-matched keratoconus and pellucid controls, was performed. After informed consent was obtained, corneal topography, ocular response analyzer (ORA; Reicher, Buffalo, NY), pachymetry, intraocular pressure, A scan measurements, Humphrey visual fields (VFs), and disk photographs were done. Analyses compared cases with controls on primary (CH and CRF) and secondary variables. Disk photographs and VFs were rated in a masked fashion.

RESULTS

The mean CH [8.2 (SD = 1.6) and 8.3 (SD = 1.5)] and CRF [7.3 (SD = 2.0) and 6.9 (SD = 2.1)] were low and did not differ significantly between 20 study (29 eyes) and 40 control patients (61 eyes), respectively. CH had a negative significant correlation with maximum corneal curvature by topography (P < 0.002) and positive significant correlation with central corneal thickness (P < 0.003). The mean cup to disk ratio was larger (0.54, SD = 0.20) among cases than in controls (0.38, SD = 0.20), P = 0.003. VFs were suspicious for glaucoma more often among the study eyes (11 of 29, 33.9%) than controls (8 of 60, 13.3%), P = 0.019.

CONCLUSIONS

CH was low in study and control patients and was correlated with severity of keratoconus/pellucid but not with glaucoma/glaucoma suspect or control status. Evidence of glaucoma was more common in study eyes than in controls but was present in both.