Role of Age and Myopia in Simultaneous Assessment of Corneal and Extraocular Tissue Stiffness by Air-Puff Applanation.

Abstract

To assess the correlation of age and myopia with corneal and extraocular tissue stiffness derived from air-puff applanation using a composite viscoelastic model. This retrospective, cross-sectional study evaluated 155 normal eyes (age range: 5 to 50 years) measured on Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). Manifest refraction spherical equivalent was also analyzed. A linear viscoelastic model that segregated corneal and extraocular tissue stiffness from the applanation deformation waveform was implemented. Corvis ST measured the total deformation (deformation amplitude waveform), which was simply the sum of corneal and extraocular tissue deformation. Age- and myopia-based multivariate analyses of variance between deformation parameters were performed after adjusting for intraocular pressure and central corneal thickness. Corvis ST corneal hysteresis was also calculated from the corneal deformation waveform. All myopia and age groups were matched for intraocular pressure and central corneal thickness. Extraocular tissue stiffness significantly increased with age (P = .03). Some other extraocular tissue deformation parameters also correlated with age, indicating age-related stiffening (P < .05). Corneal and extraocular tissue stiffness decreased with increasing myopia, but the trend was not significant (P = .10). Corvis ST corneal hysteresis increased with increasing age (P = .01) but not with increasing myopia (P = .61). Extraocular deformation parameters indicated stiffening of the extraocular tissues with age. Corneal deformation parameters were unaffected by age and myopia. Further studies with larger sample sizes are needed to clearly understand the effect of myopia on corneal and extraocular tissue stiffness. [J Refract Surg. 2016;32(7):486-493.].