Abstract
Purpose :
To develop a rheological model of the reaction of ocular structures to air-puff stimulation. To determine the relation between Young's modulus and the viscosity modulus according to different IOP values.
Methods :
A cross-sectional observational study was performed in 20 healthy eyes from different Caucasian subjects (mean age 27.5 ± 3.5 y.o.; mean spherical equivalent refractive error: -1.1 ± 1.5 D). The reaction of the cornea, crystalline lens and the eyeball to an air jet was recorded by a SS-OCT ocular biometer integrated with an air puff chamber at two different IOP levels. First, in physiological normal IOP conditions and 2 hours after administration of IOP-reducing drops (brimonidine tartrate 0.2%). At the same time, the IOP values were measured with a Goldmann Applanation Tonometer. The displacement of each ocular component was used to design a rheological eye model and to calculate elastic (E) and viscosity (η) moduli from each component after applying an optimization process by a Marquardt-Lavenberg algorithm. Finally, moduli from the cornea were correlated with the IOP measurements.
Results :
Fig. 1 demonstrates the rheological model of ocular structures’ dynamics during air-puff stimulation. The cornea, crystalline lens and eyeball movement are described by Maxwell and Kelvin submodels to determine the viscoelastic behavior of each component. Moreover, a mass term was included for the lens and for the eye to simulate the lens wobbling and eye retraction. Fig. 2 represents the predicted theoretical deformations based on experimental data. Regarding the mechanical properties of the cornea with the IOP, higher correlation between E and IOP was found although no statistical significance was detected (corneal E: Pearson's R = 0.7097; corneal η: Pearson's R = 0.5869). Additionally, it was observed that η was strongly linearly dependent on the E (Pearson's R = 0.8552).
Conclusions :
SS-OCT biometers integrated with air puff subsystems enable to image the dynamics of the cornea, crystalline lens and the whole eye. Therefore, OCT can help to develop rheological eye models which might predict the mechanical behavior of different ocular structures. The determination of the elastic and viscosity moduli from cornea and lens can be used to predict correct IOP values in future studies. In particular, both, E and η from the cornea were linearly dependent on the IOP level.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.