Abstract
Abstract: :
Purpose: The Reichert Ocular Response Analyzer (ORA) utilizes a "normality" relationship between a corneal parameter, the corneal hysteresis (CH) and the conventional IOP (Goldmann equivalent). The "normality" relationship is determined by regression between the CH and IOP, which reveals the dependence of IOP on CH. We determined degrees to which the normality line is a function of race, age or sex with regard to both regression parameters and correlation. We also determined the degree to which the CH distribution and mean values are a function of race, age and sex. Methods: Criteria as follows were used to select "normal" eyes from a base of ORA measurements on 1200 patients in a clinical office. 1) Left and right eye CH differences are within 2 mmHg 2) Left and right eye IOP differences are within 2 mmHg 3) Patients identified as glaucomatous are excluded A total of 840 eyes met the above criteria: 264 Asian, 18 Black, 496 Hispanic and 62 Caucasian eyes. Results: The average CH (in mmHg) for the four racial groups in ascending order are: Blacks 4.19, Asians 4.45, Hispanics 4.67, Caucasians 4.98. The differences between Blacks, Hispanics, Asians and Caucasians are significant. The regression slopes are: Blacks 0.26, Asians 0.50, Hispanics 0.52, Caucasians 0.58. The average CH for male, 4.57, and for female , 4.63. The CH vs. age R2 =0.008. Average age is 53.9 years. Conclusions: Corneal hysteresis seems to represent modulus of elasticity of the cornea, where corneal thickness is a significant component. Blacks have significantly lower CH than Asians, Hispanics and Caucasians, consistent with observations that Blacks tend to have thinner corneas. Distributions of CH for each racial group have significantly different shapes. The regression parameters for Blacks are not reliable because of small sample size. The CH is not correlated significantly with age and sex. CH measured by ORA seems to represent a measure of total corneal resistance including effects of the thickness and rigidity of the "in vivo" corneal tissue which has not been measured clinically by any other methods.
Keywords: clinical (human) or epidemiologic studies: systems/equipment/techniques • intraocular pressure • cornea: basic science