Corneal biomechanical properties measured with the Ocular Response Analyser in a myopic population Athina Plakitsi 1 , Clare O’Donnell 2 , Marco A Miranda 2 , W Neil Charman 2 and Hema Radhakrishnan 2 1 Department of Optics and Optometry, Technological Educational Institute of Athens, Athens, Greece and 2 Faculty of Life Sciences, University of Manchester, Manchester, UK Citation information: Plakitsi A, O’Donnell C, Miranda MA, Charman WN & Radhakrishnan H. Corneal biomechanical properties measured with the Ocular Response Analyser in a myopic population. Ophthalmic Physiol Opt 2011, 31, 404–412. doi: 10.1111/j.1475-1313.2011.00852.x Keywords: corneal biomechanics, corneal hysteresis, corneal resistance factor, corneal thickness, intraocular pressure, ocular response analyser Correspondence: Hema Radhakrishnan E-mail address: hema.radhakrishnan@manchester.ac.uk Received: 10 November 2010; Accepted: 19 April 2011 Abstract Purpose: To explore the possible association between myopia and corneal bio- mechanical properties in a Caucasian population, and the correlations between the properties of right and left eyes. Methods: Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using the Ocular Response Analyser (ORA) in both eyes of 95 nor- mal adult subjects aged between 19 and 48 years. The spherical equivalent refractive errors of the participants ranged from 0.25 to )14.00 D. The mean CH and CRF values for the right and left eyes were recorded for each subject. CH and CRF data were compared between different refractive groups. Results: CH was found to be slightly lower in high myopes (>)6.00 D, mean CH 10.0 ± 1.2 mmHg) in comparison to moderate myopes (>)3.00 to )6.00 D, 10.1 ± 1.4 mmHg) and emmetropes and low myopes (+0.25 to )2.75 D, 10.9 ± 1.5 mmHg). The decrease in CH with the degree of myopia was about 0.13 mmHg per D or roughly 1% per D (r 2 = 0.084, p < 0.001). Inter-subject variations were much greater than any systematic changes. CRF was not corre- lated with refractive error (r 2 = 0.001, p = 0.66). Although the refractive error was highly correlated between the two eyes (r 2 = 0.89, p < 0.001), CH and CRF showed a lower inter-ocular correlation (r 2 = 0.68, p < 0.001 and r 2 = 0.77, p < 0.001 respectively). Conclusions: These findings may indicate that the viscoelastic properties of the cornea are altered to a minor extent in myopia. However, in this normal popu- lation, any overall systematic changes in CH and CRF with refractive error were small in comparison with the considerable inter-subject scatter at any level of refraction. Introduction Studies in humans and experimental models of myopia have shown that the structure of the eyes of myopes may differ in a variety of ways from that of emmetropes. 1 Some of these changes may be associated with the devel- opment of the myopia, while others may be causative. Eyes with high myopia are known to have larger axial lengths and vitreous depths, 1,2 thinner retinas with degen- erative changes, and altered scleral thickness and visco- elasticity. 3–5 Whether or not changes to the cornea occur with myopia is still under debate. 6–8 It has been claimed that, compared to normal subjects, myopes may have flat- ter corneal curvature, decreased central corneal thickness (CCT) and decreased corneal endothelial cell density. 9 It is, then, possible that the biomechanical properties of the cornea may alter with high myopia. If any such changes were a precursor to myopia development, their measure- ment might be clinically useful as a way of identifying individuals who were at risk of myopization. Corneal biomechanics have traditionally been studied using in vitro techniques that assess factors such as Ophthalmic & Physiological Optics ISSN 0275-5408 404 Ophthalmic & Physiological Optics 31 (2011) 404–412 ª 2011 The College of Optometrists