Investigation of corneal biomechanics at moderate to high refractive errors.

PURPOSE: Corneal hysteresis (CH) and corneal resistance factor (CRF) are corneal biomechanical parameters which were measured by ocular response analyzer (ORA). Aim of this study was to define the CH and CRF in high myopic and hyperopic patients and compare the results with emmetropic control group. METHODS: A total of 193 eyes of 100 healthy volunteers were included. Study groups were high myopic patients (n = 27) with spherical refractive errors (SRE) of greater than -5.00D, high hyperopic patients (n = 20) with SRE of greater than +3.00D and controls (n = 53) with SRE between ± 1.00D. All subjects underwent IOP and corneal biomechanical evaluation with the ORA. Also Goldmann applanation tonometry (GAT), central corneal thickness (CCT), corneal curvature and axial length measurements were taken. RESULTS: Mean age of groups was 30.7 ± 6.9, 29.1 ± 7.7, 28.9 ± 5.6 years (p > 0.05). Among study groups except CRF and CCT, all parameters were significantly different between study groups. CH was lowest in the high myopic group and highest in the high hyperopia. In all groups, there were significant correlations between CH and CRF, CCT, SRE, SE (spherical equivalent), AL (axial length) and between CRF and CCT. GAT and IOPg (Goldmann-correlated intraocular pressure) measurements were significantly correlated with CCT (p < 0.05). One of the major findings was as the CH approaches 11.2 mmHg, IOPcc (corneal-compensated intraocular pressure) and IOPg get close to each other. CONCLUSIONS: The results revealed that CRF is not affected by refractive errors and IOPcc is not affected by any other ocular parameter. The difference between IOPcc and IOPg was greatest in myopic group, and IOP (intraocular pressure) measurement in these patients deserves high suspicion.

Corneal hysteresis, corneal resistance factor, and intraocular pressure measurement in patients with scleroderma using the reichert ocular response analyzer.

PURPOSE: The Reichert ocular response analyzer (ORA) measures corneal biomechanical properties in vivo by monitoring and analyzing the corneal behavior when its structure is submitted to a force induced by an air jet. This study was designed to examine corneal biomechanical properties and intraocular pressure in patients with systemic sclerosis (SSc) and to compare with control eyes. PATIENTS AND METHODS: ORA measurements were performed on the right eyes of 29 patients with SSc (group 1) and 29 healthy people who served as the control group (group 2). Corneal hysteresis, corneal resistance factor (CRF), and intraocular pressure [Goldmann correlated (IOPg) and corneal compensated] were recorded with ORA. RESULTS: Mean age of patients with SSc and control groups were 51.7 +/- 11.1 and 50.3 +/- 10.8 years, respectively. Mean (+/-SD) of the corneal hysteresis and CRF readings were 9.8 +/- 1.7 versus 9.5 +/- 1.2 mm Hg (P > 0.05) and 10.0 +/- 1.5 versus 9.2 +/- 1.4 mm Hg (P < 0.05), in groups 1 and 2, respectively. Mean (+/-SD) of the IOPg and intraocular pressure corneal-compensated recordings were 15.9 +/- 2.5 versus 14.1 +/- 2.4 mm Hg (P < 0.05) and 16.9 +/- 3.2 versus 15.6 +/- 2.9 mm Hg (P > 0.05), in groups 1 and 2, respectively. Statistical analysis revealed significant differences for CRF and IOPg between the study groups. CONCLUSIONS: The mean CRF and IOPg values of patients with SSc were higher when compared with normal controls. According to the results of our study, one can conclude that corneal biomechanical properties would be changed in patients with SSc and this can be determined by CRF.