Vitreous anatomic features characterised

By Lucy Piper, Senior medwireNews Reporter

Researchers have found a direct anteroposterior connection between the retrolental and premacular and preoptic spaces that exits in young adults before the occurrence of vitreous degeneration.

This connection may have important implications with regard to the movement of intrinsic and extrinsic mediators between the anterior and posterior segments, suggest researcher Michael Engelbert (Vitreous Retina Macula Consultants of New York, USA) and colleagues.

Using swept-source optical coherence tomography, the team created comprehensive posterior vitreous maps for 102 eyes of 51 individuals, aged 21 to 54 years, without ocular pathological features.

The maps covered an area of approximately 18 x 18 mm, which included the vascular arcades and approximately 4 mm beyond to halfway between the fovea and the equator, approximately 18 mm from the optic nerve.

Consistently observed in the participants was the premacular bursa, or posterior precortical vitreous pocket, an optically empty space overlying the macular area. This space terminated within the arcades inferiorly, but continued superiorly at a variable angle beyond the posterior pole with the border undetectable in the vast majority of eyes.

There was also a connection between the premacular bursa and the preoptic area of Martegiani or its extension, Cloquet’s canal, in 101 of the 102 eyes studied. This fusion extended to a variable distance from the optic nerve, forming a flat and broad superior channel.

Engelbert et al point out in Ophthalmology that this connection was superior to the optic nerve in almost half the eyes “and has the distinct appearance of 2 independent channels fusing, rather than representing merely a vitreous degeneration fissure plane that is extending with age.”

So the connection may eventually reach the nerve as the vitreous degenerates, but it does not necessarily originate there, the researchers explain.

The skyward extension of the premacular bursa and its fusion with Cloquet’s canal was also gravity dependent, whereas the shape and dimensions of the premacular bursa remained relatively constant.

This vitreous connection could have a detrimental effect in providing a conduit for inflammatory mediators released in the anterior portion of the eye, following cataract surgery, for instance, or facilitating diffusion over the macula, resulting in macular oedema, the researchers point out.

But being able to induce a posterior separation could also mean the more targeted delivery of iatrogenically induced substances , which can be affected by the state of the vitreous spaces, thereby improving efficacy, they add.

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