Corneal biomechanical changes and intraocular pressure in patients with thyroid orbitopathy

AIM: To determine the relevance of the objective parameters addressing the altered biomechanical properties of cornea for glaucoma monitoring in patients with mild or moderate thyroid associated orbitopathy (TAO), and in healthy individuals. METHODS: Twenty-five patients with TAO (group 1) and 25 healthy adults (group 2) were included to the study. Both groups were of a similar age and the ratio women:man. For each patient, the following parameters of both eyes were measured with ocular response analyzer (ORA): corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc). In both groups participating in our study, all measurements were performed within minutes to reduce the diurnal effects. RESULTS: The mean age in group 1 was 56 +/- 11y and 76% were women, 24% were men. The mean age in group 2 was 64 +/- 11y and 68% were women, 32% were men. CH correlated negatively with IOPg in group 1 (r(2)=0.10, P<0.05). IOPg strongly correlated with IOPcc in both groups (group 1: r(2)=0.79, P<0.0001; group 2: r(2)=0.85, P<0.0001). There was positive correlation between CRF and IOPg in group 1 (r(2)=0.12, P<0.05) and in group 2 (r(2)=0.31, P<0.0001). Statistical analysis revealed no significant correlation between CRF and IOPcc in group 1 (r(2)=0.009, P>0.05) and also no significant correlation in group 2 (r(2)=0.04, P>0.05). CRF mean value in group 2 (11.51 +/- 1.72 mm Hg) was higher than in group 1 (10.85 +/- 1.45 mm Hg) (P<0.05). IOPg strongly correlated with IOPcc in both groups (group 1: r(2)=0.79, P<0.0001; group 2: r(2)=0.85, P<0.0001). There was also strong correlation between CRF and CH in both populations: group 1: (r(2)=0.58, P<0.0001), group 2: (r(2)=0.41, P<0.0001). CONCLUSION: Biomechanical parameters of cornea, as quantified by CH and CRF, and measured together with IOPcc, precisely reveal glaucoma staging in TAO and thus are reliable for diagnosing and follow-up in clinical practice.