PVD, peripheral degenerations and retinal breaks

The Vitreoretinal Interface & Posterior Vitreous Detachment (PVD)

The human vitreous body is an optically transparent, viscoelastic gel occupying approximately $4\,\text{mL}$ (roughly $80\%$) of the globe's volume. Composed of $99\%$ water, its structural framework is maintained by an interlacing scaffolding of type II collagen fibrils (interspersed with types IX and V/XI) cross-linked by hydrophilic hyaluronic acid (hyaluronan) glycosaminoglycan chains.

Biochemical Mechanisms of PVD: Synchysis and Syneresis

Posterior vitreous detachment is the natural, age-dependent separation of the posterior vitreous cortex (posterior hyaloid membrane) from the internal limiting membrane (ILM) of the retina. It involves two distinct biochemical and biophysical phenomena:

1. Synchysis Senilis (Vitreous Liquefaction): Progressive conformational destabilization of the collagen-hyaluronan matrix leads to depolymerization of hyaluronic acid, causing unbundling and lateral aggregation of collagen fibrils into coarse microscopic threads. Water molecules dissociate from the glycosaminoglycan network, pooling into fluid-filled cavities known as lacunae. By age 70, over $50\%$ of the vitreous core is completely liquefied.
2. Syneresis (Vitreous Collapse): Concurrently, the aggregated collagen fibrils contract, causing the central vitreous gel to shrink and collapse inward. As fluid lacunae coalesce, the posterior cortical vitreous thins. Eventually, a microscopic breach develops in the retro-hyaloid membrane over the perifovea. Liquid vitreous rushes through this defect into the potential retro-hyaloid space, rapidly peeling the detached cortical vitreous forward away from the retinal ILM.

The Weiss Ring and Clinical Symptoms

• The Weiss Ring: The vitreous cortex is most tenaciously adherent to the retina at four anatomical sites, ranked in order of decreasing adhesion strength: $\text{Vitreous Base (Ora Serrata)} > \text{Optic Nerve Margin} > \text{Macula} > \text{Retinal Blood Vessels}$ When the posterior hyaloid separates completely from the circular margin of the optic nerve head, it avulses the peripapillary condensed glial attachment, forming a mobile, circular, or annular dark floater: the Weiss ring (evidence of separation at the disc, without proving complete macular separation).
• Photopsias (Flashes): Mechanical, dynamic traction exerted by the collapsing vitreous gel on peripheral photoreceptors triggers action potentials, entoptically perceived as brief, lightning-like, arcuate flashes of light, typically localized to the temporal visual field in dark environments.
• Floaters (Myodesopsias): Entoptic shadows cast onto the neurosensory retina by mobile collagen aggregates, blood, or the Weiss ring suspended within the visual axis.

Peripheral Retinal Degenerations: Risk Stratification

Peripheral retinal degenerations are common, but only a distinct subset predisposes to retinal breaks and rhegmatogenous detachment:

Retinal Breaks: Flap Tears, Operculated Holes & Atrophic Holes

A full-thickness retinal break allows liquefied vitreous to gain access to the subretinal space. Retinal breaks fall into three morphologic categories:

1. Flap (Horseshoe) Tear:
   • A U-shaped, full-thickness retinal break with its apex pointed posteriorly toward the optic disc and its broad base directed anteriorly toward the ora serrata.
   • Caused by dynamic, ongoing anteroposterior and tangential vitreoretinal traction: the detached cortical vitreous remains tenaciously anchored to the apex of the flap.
   • Prognostic Impact: Symptomatic horseshoe tears carry the highest risk of progressing to clinical RRD (approx. $50\%$) if left untreated. They mandate urgent prophylactic barrier retinopexy (laser photocoagulation or transscleral cryotherapy).
2. Operculated Hole:
   • A round or oval full-thickness hole resulting from dynamic vitreous traction that has completely avulsed the retinal plug away from the retina.
   • The avulsed tissue plug—the operculum—floats freely in the overlying vitreous cavity directly above the hole.
   • Prognostic Impact: Because the vitreous traction on the retinal margin has been completely relieved, the risk of progressing to RRD is substantially lower ($<15\%$) than with a flap tear, unless persistent vitreous traction exists on adjacent tissue.
3. Atrophic Round Hole:
   • A circular full-thickness break resulting from progressive, localized cellular atrophy and metabolic thinning of the neurosensory retina, rather than active vitreoretinal traction.
   • Frequently encountered within islands of lattice degeneration or in highly myopic eyes.
   • Very low progression risk in asymptomatic individuals; usually managed with observation.

Giant retinal tears

A giant retinal tear is a full-thickness circumferential tear extending at least 90 degrees, often with a mobile posterior flap. Trauma, high myopia and inherited vitreoretinal disorders can be associated. Examine the fellow eye and the whole periphery, document macular status and assess proliferative vitreoretinopathy. The large flap can fold or slip, so a small-break pneumatic strategy cannot simply be extrapolated.

Repair commonly uses vitrectomy to release traction, intraoperative perfluorocarbon liquid to unfold/stabilise the retina, retinopexy and selected gas or silicone-oil tamponade. Control fluid exchange to avoid posterior-flap slippage and retained subretinal droplets. Perfluorocarbon is a surgical tool rather than routine permanent tamponade: retained material can harm the retina, and any planned short-term retention needs a defined specialist removal strategy. The multicentre primary series used intraoperative perfluoro-n-octane and explicitly defined the 90-degree extent. Prognosis depends on presentation, macular involvement, PVR and repair complexity; the tear label alone does not prescribe one buckle or one oil-removal date.