Saccade movements effect on the intravitreal drug delivery in vitreous substitutes: a numerical study.

In this study, the distributions of intravitreal injected drugs in post-vitrectomy human eyes, which are subjected to periodic saccade movements, are investigated. The computational model for the vitreous cavity of human eye is a sphere with one side truncated by the eye lens. A dynamic mesh technique was used to model the eye motion and the unsteady 3-D forms of continuity; Navier-Stokes and concentration transport of drug equations were solved numerically. The numerical model was validated earlier for the vitreous liquid flow field. The predicted drug concentration for idealized geometry was compared with the available analytic solution and excellent agreement was observed. The validated computer model was then used to simulate a real vitreous cavity filled with Balanced Salt Solution or aqueous humor as a vitreous substitute in order to obtain distribution of drugs in the post-vitrectomy eyes or liquefied vitreous. Additionally, effects of locations of drug injection, drug diffusion coefficients and saccade amplitude on the drug distribution and its uniformity were investigated. Although the earlier findings in the literature reported a day or a week as a needed time for drug uniform distribution in the vitreous substitutes, the present work depicts that saccade movements augment the transport of the drug in a way that the uniformity of the drug distribution can be achieved in a matter of minutes. Furthermore, in a vitreous cavity subjected to the saccade movements, the diffusion coefficient of drugs does not significantly affect their distribution after a few minutes. Even the injection location does not matter as uniform distribution is achieved after some time.

Investigation of saccadic eye movement effects on the fluid dynamic in the anterior chamber.

The aqueous humor (AH) flow in the anterior chamber (AC) due to saccadic movements is investigated in this research. The continuity, Navier-Stokes and energy equations in 3D and unsteady forms are solved numerically and the saccadic motion was modeled by the dynamic mesh technique. Firstly, the numerical model was validated for the saccadic movement of a spherical cavity with analytic solutions and experimental data where excellent agreement was observed. Then, two types of periodic and realistic saccadic motions of the AC are simulated, whereby the flow field is computed for various saccade amplitudes and the results are reported for different times. The results show that the acting shear stress on the corneal endothelial cells from AH due to saccadic movements is much higher than that due to normal AH flow by buoyancy induced due to temperature gradient. This shear stress is higher on the central region of the cornea. The results also depict that eye saccade imposes a 3D complicated flow field in the AC consist of various vortex structures. Finally, the enchantment of heat transfer in the AC by AH mixing as a result of saccadic motion is investigated.

Numerical simulation of the fluid dynamics in vitreous cavity due to saccadic eye movement.

In this study, the flow dynamics of vitreous due to saccadic movements following vitreous liquefaction or in post-vitrectomy eyes is investigated. Using a dynamic mesh technique, the eye motion was modeled and unsteady three-dimensional forms of continuity and Navier-Stokes equations were solved numerically. Firstly, the numerical model was validated for a sphere as a model of vitreous chamber and agrees well with the results based on available analytic solutions and experimental data. Then, numerical simulation was performed based on a deformed sphere with an indentation representing the lens. This consists of a vitreous cavity filled with a liquid having the viscosity of liquefied vitreous and balanced salt solution. The wall shear stress on the retina was computed and compared for various saccade amplitudes. Also, the effect of variation in vitreous viscosity and the size of lens indentation are investigated. The results show that the secondary flow in the vertical direction in the vitreous cavity is much higher for the liquefied vitreous and balanced salt solution compared with that for silicone oil. The possible effect of shear stress on the retinal detachment for all studied cases is discussed. A semi-analytic correlation is also developed for maximum wall shear stress of the spherical domain that is subjected to sinusoidal rotations.