Vitreous Anatomy and Pathology

Although vitreous is the largest structure within the eye, constituting 80% of the ocular volume, investigators of vitreous anatomy are hampered by two fundamental diffi culties: ● Any attempts to defi ne vitreous morphology are efforts to “visualize” a tissue that is invisible by design ( Fig. 6-46-1 ). ● The various techniques that were employed previously to defi ne vitreous structure were fl awed by artifacts induced by tissue fi xatives, which caused precipitation of hyaluronan (formerly called hyaluronic acid), a glycosaminoglycan. The development of slit-lamp biomicroscopy by Gullstrand in 1912 was expected to enable clinical investigation of vitreous structure without the introduction of the aforementioned artifacts. Yet, a widely disparate set of descriptions resulted because of the fi rst of the inherent diffi culties just described; that is, the vitreous is largely invisible. This problem even persists in so-called modern investigations. Consider, for example, that in the 1970s Eisner 1 described “membranelles” and Worst 2 “cisterns,” in the 1980s Sebag and Balazs 3, 4 identifi ed “fi bers,” and in the 1990s Kishi and Shimizu 5 found “pockets” in the vitreous. The discrepant observations of the last-mentioned group have now been explained largely as an age-related phenomenon with no relevance to the inherent macromolecular structure or anatomy. 6, 7