Peripheral vitreo–retinal pathologies

Abstract

Vitreous occupies about four-fifths of the volume of the eye and weighs approximately 4 g. The vitreous body is somewhat spherical with slight flattening meridionally and has a cup-shaped depression anteriorly, known as the patellar fossa. The vitreous body is attached to all contiguous structures, but the firmness of the attachment varies with topography and age [1–3]. It is most firmly attached at the vitreous base, a 3-dimensional doughnutlike structure that is 3–6 mm wide and straddles the ora serrata. The vitreous base includes the posterior 2 mm of the pars plana and from 1 to 4 mm of the anterior retina posterior to the ora serrata. The posterior border of the vitreous base is located farther posteriorly in older individuals [4] and is more anterior nasally than temporally [5], which may underlie the greater frequency of retinal tears temporally than elsewhere in the peripheral retina [4]. The density of vitreous collagen is greatest within the vitreous base, and the collagen fibers are oriented perpendicular to the retinal plane, whereas elsewhere the orientation is tangential to this plane. The vitreous base contains remnants of the fetal hyaloid vasculature, and it has been suggested that fetal antigens in this region of the vitreous [6] or degenerative products of the vitreous [7] may be immunogenic and play a role in ocular inflammatory diseases, such as pars planitis.