Seeing the invisible: the challenge of imaging vitreous

Imaging the vitreous is an attempt to view what is by design invisible. The inability to adequately image vitreous hinders a more complete understanding of its normal structure and function and how these change in aging and disease. The combined use of more than one technique could provide better imaging for investigational and clinical purposes. Past and present imaging methodologies are summarized and research and clinical techniques that are currently in development for future applications, are discussed. Dark-field slit microscopy has been used to characterize vitreous anatomy, both within the vitreous body as well as at the vitreo-retinal interface. In addition to this methodology, slit-lamp biomicroscopy; direct, indirect, and scanning laser ophthalmoscopies; ultrasonography; optical coherence tomography; magnetic resonance and Raman spectroscopies; and dynamic light-scattering methodologies for noninvasive evaluation are presented. Dark-field slit microscopy enables in vitro imaging without dehydration or tissue fixatives. Optical coherence tomography enables better in vivo visualization of the vitreo-retinal interface than scanning laser ophthalmoscopy and ultrasonography, but does not image the vitreous body. Dynamic light scattering can determine the average sizes of vitreous macromolecules within the vitreous body as well as possibly image the posterior vitreous cortex once detached, while Raman spectroscopy can detect altered vitreous molecules, such as glycated collagen and other proteins in diabetic vitreopathy.