Pulling and Tugging on the Retina: Mechanical Impact of Glaucoma Beyond the Optic Nerve Head

Several retinal conditions have been recently revealed by optical coherence tomography (OCT) to occur more frequently in glaucoma than in healthy eyes: paravascular defects, peripapillary retinoschisis, and pseudo-cysts of the inner nuclear layer (INL). Here the clinical OCT findings described in these reports are reviewed and a framework that could explain why they are related and occur more frequently in glaucoma is proposed. Evidence suggests that these conditions all share in common a strong tendency to develop in association with severe and/or rapidly progressing disease and a likelihood of involving biomechanical forces and differential tissue deformation. Muller glia are mechanosensitive and known to react to shear and axial strain, and to participate in homeostasis of water and ion flux through the retina, and to provide spring-like capability to buffer of mechanical forces. Thus, Muller cell integrity is also likely to be involved in the development and/or response to such events. OCT has also revealed that Muller cell optical properties (scatter and attenuation) appear to be altered in at least two of these retinal conditions: peripapillary retinoschisis and pseudo-cysts of the INL. Future studies applying 3D strain mapping techniques might reveal structural changes over time (either acute or longer-term deformations) that predict the onset and location of these retinal defects and their relationship to progressive optic nerve head deformation, retinal nerve fiber layer, and retinal ganglion cell loss in glaucoma.