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Daniela Oehring, Christine Purslow, Phillip Buckhurst, Hetal Buckhurst; Biometric and dynamic predictors of ORA measures of corneal biomechanics. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1390.
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© ARVO (1962-2015); The Authors (2016-present)
The Ocular Response Analyzer (ORA; Reichert) provides in vivo measures of corneal hysteresis (CH) and resistance factor (CRF). Despite the purported clinical utility, there is significant ambiguity as to what extent these metrics represent the intrinsic structural characteristics. The study sought to assess the correspondence between biometric, corneal dynamics on ORA measures to determine predictive models.
Data were collected from 113 healthy adults (226 eyes; 71% females, aged [24.5±6.11]years). The Pentacam (Oculus) measured astigmatism (casti), anterior chamber depth (ACD) and angle (ACA). The Casia AS-OCT (Tomey) was used to determine the corneal (CT), scleral thickness (ST) and limbal length (LL). Refractive error (MSE) and axial length (AL) were assessed using cycloplegic refraction and Haag Streit’s LenStar. The CorvisST (Oculus) was used to assess the dynamic corneal response relating to amplitude (A), length (l) and time (t) of applanation 1 (A1) and 2 (A2), and highest concavity (HC); which were assessed via Matlab referring to the neutral corneal plane. Randomly one eye per subject was chosen model determination, the other for the verification. Multiple regression analyses were used to determine the models. Significant predictors were included, and adjusted R2 from the verification procedure examined. Standardized beta estimated the impact of the model variation.
CH was on average (11.1±1.74)mmHg, CRF was (10.9±1.71)mmHg, CCT was (548±43.8)µm and IOP was (14.1±2.38)mmHg. Biometry explained 48.5% of the variability of CH and 49.9% to CRF, the dynamic corneal response to 30.9% for CH and 36.4% for CRF. Combing both, CH was predicted to 98.7% (verified 51.7%) and CRF to 99.6% (verified 72.7%). Predicting models (standardized beta):CH =-11.499+0.056ACA(°;0.035)+0.004STSP(µm;0.119)+ 2.106LL(mm;0.075)–0.007ST1mm(µm;-0.146)–0.296AL(mm;-0.250)+2.001A1t(ms;0.278)+ 19.230A1v(m/s;-0.150)+3.933A2v(m/s;0.094)+4.495A2DA(mm;0.260)+1.339HCl(mm;0.038)CRF=-18.331+0.005CCT(µm;0.256)-0.113casti(D;0.069)+3.194A1t(ms;0.532)+8.220A2DA(mm;0.245)
The new models are the first considering a wide range of ocular biometrics and the dynamic corneal response; providing a highly valuable inside of the information contained within the ORA metrics. The models show that biometry contributes the most to the individual value variability. The models will help researchers and clinician to interpret ORA metrics.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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