Corneal hysteresis is a biomechanical behavior measured with infrared light during variable air-jet applanation and has been convincingly associated with glaucoma development and progression in prospective studies.1,2 Deformation amplitude is a newer corneal biomechanical parameter derived from the Corneal Visualization Scheimpflug Technology (Corvis ST, Oculus; Wetzlar, Germany) and describes the amount of combined corneal and eye indentation from an impulse of air. Deformation amplitude differs between glaucoma patients and normal patients and is significantly correlated with IOP in both groups.3
Corneal deflection amplitude (CDA) describes how much the cornea alone indents after an air puff, separate from the rest of the eye's deformation. Put simply: CDA = deformation amplitude minus eye movement. Given that CDA is calculated using deformation amplitude, there is reason to suspect that IOP correlates with CDA as well.
Jung and colleagues present a retrospective study examining the relationship between CDA and visual field progression. The authors found that over the course of five reliable visual fields (or three reliable fields over more than three years), a higher CDA was associated with a linear rate of mean deviation worsening in both univariate and multivariate models. Higher IOP was also associated with progression in the uni- and multivariable models. The authors did not report how deformation amplitude was associated with progression. However, there is literature on this topic and analysis would have been easy to perform.3 While the authors did not find a statistical interaction between CDA and IOP in their multivariable model, they did not report the presence or absence of a correlation between the two.
Like most retrospective studies, in this study CDA was obtained during follow-up or towards the end of the follow-up interval. This is important because CDA is likely a dynamic corneal behavior that changes over time, should be correlated with IOP and medication use, and may be affected by glaucoma progression.
Corneal deflection amplitude is an interesting corneal behavior that may be related to glaucoma progressio
In summary, corneal deflection amplitude is an interesting corneal behavior that may be related to glaucoma progression. Jung and colleagues have revealed useful initial findings. A prospective study accounting for the relationship between CDA and IOP would provide further insight on this potential new risk factor.