Foveal Development and Posterior Precortical Vitreous Pocket Formation

While the shape of the premacular bursa, or posterior precortical vitreous pocket (PPVP), and its connections to other vitreous spaces during life have been well characterized, its origin and possible physiological role are enigmatic.¹ Here, we report two subjects with ocular albinism, foveal hypoplasia, and absent PPVP but presence of the prepapillary gap and prevascular vitreous fissures.

The cortical vitreous consists of a collagen mesh and hyaluronic acid. It is formed by cells of the inner retina during ocular development.² The collagen fibers surround the liquid spaces³ overlying the optic nerve (the prepapillary gap of Eisner⁴ or area of Martegiani), the larger retinal vessels (the prevascular vitreous fissures of Eisner,⁴ which are likely precursors to the perimacular cisterns of Worst⁵), and the PPVP. Eisner hypothesized that the prepapillary gap and prevascular fissures are essential sites of absent vitreous production over the optic nerve head and retinal vessels, where there are no retinal cells (personal communication). The two cases reported here suggest that PPVP formation is tied to foveal development. During foveal development, the inner retina is displaced centrifugally and with it any cortical vitreous that was produced by those cells. In the case of foveal hypoplasia, there is significantly less centrifugal displacement of the inner retina and, consequently, less displacement of cortical vitreous, with cortical vitreous production similar to more peripheral retina. We observed cortical vitreous fibers and small hyperreflective dots probably representing hyalocytes⁶ in lieu of a PPVP in a 10-year-old boy (Figure 1A) and a 33-year-old (Figure 1B) female patient with foveal hypoplasia in the context of ocular albinism, but no other ocular or systemic comorbidities were observed. From optical coherence tomography imaging, it has been shown that the PPVP in normal childhood is present but enlarges in adulthood.⁷ Since foveal development occurs between weeks 28 and 32 of gestation and vitreous preparations of fetuses are hard to come by, this represents the strongest evidence for a link between foveal formation and PPVP development yet.

Fig. 1.: A. Horizontal ultra-high-definition line scan through the fovea and optic nerve of a 10-year-old boy with oculocutaneous albinism and foveal hypoplasia demonstrates the absence of a PPVP despite excellent scan quality as evidenced by the visualization of such details as cortical fibers (arrow) (note the presence of the prepapillary gap [circle]). B. Horizontal ultra-high-definition line scan through the fovea and optic nerve of a 31-year-old woman with oculocutaneous albinism and foveal hypoplasia. Similar findings exist including the absence of a PPVP, cortical fibers (arrow), and the presence of the prepapillary gap (circle).