A mechanical model of posterior vitreous detachment and generation of vitreoretinal tractions.

ABSTRACT

We propose a mechanical model of generation of vitreoretinal tractions in the presence of posterior vitreous detachment (PVD). PVD is a common occurrence with aging, and it consists in the separation of the vitreous body from the retina at the back pole of the eye, due to progressive shrinking of the vitreous gel. During this separation process, vitreoretinal tractions are generated at regions of high adhesion between the vitreous and the retina. Such tractions are mainly responsible for the creation of retinal tears, which can lead to retinal detachment. We describe the PVD evolution developing a continuum model of a shrinking soft body, representing the vitreous humor gel phase. In the model, the vitreous is surrounded by a membrane, stiffer than the bulk, the vitreous cortex, and it is contained within a rigid spherical domain, the vitreous chamber. The membrane is attached to the spherical wall and the adhesion strength is spatially non-uniform, increasing from the back to the front of the chamber, according to clinical observations. During the shrinking process, the vitreous undergoes elastic distortions, owing to the spatially variable adhesion on the wall, and this produces boundary tractions. We also consider the clinically relevant case of anomalous PVD, in which regions of focal adhesion between the vitreous and the retina exist, leading to the generation of strong, localized tractions. The model reproduces a PVD evolution in good qualitative agreement with clinical observations and makes it possible to correlate the shape of the detached vitreous with the intensity of vitreoretinal tractions.