What is the primary mechanism by which a posterior vitreous detachment (PVD) leads to rhegmatogenous retinal detachment?

Explanation

## Pathophysiology of PVD-Induced Retinal Detachment ### Mechanism of Retinal Break Formation **Key Point:** Posterior vitreous detachment causes rhegmatogenous retinal detachment through **vitreous traction** on areas of firm vitreoretinal adhesion, not through simple separation. ### The Traction Process 1. **Normal PVD** — The vitreous gradually separates from the retina as it liquefies with age 2. **Adhesion sites** — Strong vitreoretinal attachments persist at: - Vitreous base (equatorial region) - Optic disc margin - Blood vessel arcades - Areas of previous inflammation or degeneration 3. **Tractional force** — As the vitreous continues to collapse and shrink, it pulls on these adhesion sites 4. **Retinal break formation** — Tangential or radial traction creates a break (horseshoe tear or atrophic hole) 5. **Fluid ingress** — Liquefied vitreous enters through the break into the subretinal space 6. **Progressive detachment** — The retina gradually separates from the RPE ### Risk Factors for Traction-Induced Breaks | Risk Factor | Mechanism | | --- | --- | | Lattice degeneration | Thinned retina more susceptible to traction | | Myopia | Longer eye with greater vitreous traction | | Previous eye surgery | Vitreoretinal adhesions from inflammation | | Diabetic retinopathy | Fibrovascular proliferation increases adhesions | **High-Yield:** The key is **traction**, not simple separation. A PVD alone (without traction on weakened retina) does not cause detachment. **Clinical Pearl:** Horseshoe tears (U-shaped breaks with vitreous traction on the apex) are pathognomonic for tractional PVD-induced RD, whereas atrophic holes (full-thickness breaks in thin retina) may form without obvious traction. **Mnemonic — BREAK formation in PVD:** - **B**ase adhesions (vitreous base) - **R**etinal thinning (lattice, myopia) - **E**xcessive traction (vitreous shrinkage) - **A**dhesion sites (vessels, disc) - **K**inetic pull (tangential forces) [cite:Kanski & Bowling Clinical Ophthalmology 8e Ch 8.2]