Overview
This lecture covers the embryology of the vitreous body of the eye, focusing on its development, types, origins, and related disorders due to abnormal regression of embryonic structures.
Anatomy and Development of the Vitreous
- The vitreous cavity forms 2/3 of the eye's volume, located behind the lens and ciliary body, and in front of the retina.
- The optic cup forms as an outpouching from the anterior neural tube during embryogenesis.
- The hyaloid artery enters the optic cup via the choroidal (optic) fissure to supply the developing lens.
- Three types of vitreous develop: primary (initial, vascular), secondary (replaces primary, avascular), and tertiary (forms later, peripheral).
Types and Origins of Vitreous
- Primary vitreous forms at 5 weeks gestation, mainly from the hyaloid artery (mixed mesenchymal and ectodermal origin).
- The Tunica vasculosa lentis, a vascular plexus for the lens, is supplied by the hyaloid artery (posteriorly) and long posterior ciliary arteries (anteriorly).
- Secondary vitreous (definitive vitreous) forms between 5.5-12 weeks gestation, created by hyalocytes (mesenchymal origin) which deposit collagen.
- Most hyaluronic acid and type II collagen in the adult vitreous forms after birth.
- Tertiary vitreous develops around the third month, originating from non-pigmented ciliary epithelial cells in the pars plana, forming the vitreous base and zonular fibers.
Regression and Vestiges of Embryonic Structures
- The primary vitreous regresses, leaving the Cloquet’s canal (central channel), extending from the posterior lens (patellar fossa) to the optic nerve head.
- The Cloquet’s canal has a funnel-shaped dilation near the optic disc called the space of Martegiani.
- Macrophage-like hyalocytes digest the hyaloid system, aiding vitreous maturation.
Disorders of Vitreous Development
- Failure of regression leads to persistent embryonic structures:
- Persistent pupillary membrane: remnants of the anterior Tunica vasculosa lentis, often asymptomatic but may rarely obscure the pupil.
- Persistent hyperplastic primary vitreous (PHPV): persistence of hyaloid artery or its branches, classified as anterior (fibrovascular tissue behind lens) or posterior (hyaloid artery persists to retina, distortions and retinal folds).
- Other remnants include:
- Bergmeister papilla: glial tissue at the optic disc (space of Martegiani).
- Mittendorf dot: small remnant on posterior lens capsule, associated with posterior polar cataract.
Key Terms & Definitions
- Vitreal cavity — Largest eye cavity, filled with vitreous humor.
- Hyaloid artery — Embryonic artery supplying the developing lens.
- Choroidal (optic) fissure — Embryonic fissure allowing vessel entry.
- Primary vitreous — Initial vascular vitreous, replaced during development.
- Secondary vitreous — Definitive avascular vitreous filling adult eye.
- Tertiary vitreous — Peripheral vitreous condensing near pars plana, forms vitreous base.
- Cloquet’s canal — Remnant central channel of the hyaloid artery.
- Tunica vasculosa lentis — Embryonic vascular network supplying lens.
- PHPV — Persistent hyperplastic primary vitreous, disorder with residual embryonic vasculature.
- Bergmeister papilla — Glial remnant at optic disc.
- Mittendorf dot — Small remnant on posterior lens capsule.
Action Items / Next Steps
- Review diagrams of optic cup formation, Cloquet’s canal, and PHPV variants.
- Memorize the origins and timelines of primary, secondary, and tertiary vitreous formation.
- Understand clinical implications of persistent fetal vasculature for exams.