Development of the Eye

Introduction

• Lecture by Dr. Aizaz from medicovisual.com.
• Overview of eye development.

Germ Layers

• Trilaminar Germ Disc: Only ectoderm and endoderm shown.
• Notable structures mentioned:
  • Oropharyngeal membrane
  • Cloacal membrane
  • Primitive streak

Key Structures

• Notochord:
  • Induces formation of the neural tube.
• Prechordal Plate:
  • Mesodermal tissue between oropharyngeal membrane and cranial end of the notochord.

Formation of Neural Plate

• Notochord induces thickening of overlying ectoderm, forming the neural plate.
• Eye Field formation at the cranial end of the neural plate:
  • Cells express special proteins, notably PAX6.

Eye Field Division

• Initially, single eye field divides into two eye fields due to:
  • Sonic Hedgehog (SHH) released from the prechordal plate.
  • Important for normal eye development; failure leads to cyclopia (single midline eye).

Neurulation Process

1. Neural plate invaginates to form neural tube.
2. Formation of optic grooves (also called optic sulcus) occurs before neural tube closure.

Major Brain Swellings

• Formation of three swellings:
  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain)
• Optic grooves are located in the diencephalon part of the prosencephalon.

Development of Optic Structures

• Optic Vesicle: Formed from optic grooves that grow and swell.
• Optic Stalk: Proximal part becomes narrow, leading to the stalk formation.
• Hyaloid Artery: Grows into optic vesicle for blood supply; forms central retinal artery later.

Choroid Fissure

• Formation occurs as optic vesicle invaginates, creating the choroid (optic) fissure.
• Fissure allows entry of hyaloid artery and ultimately closes.

Lens Development

• Lens Placode: Thickening of ectoderm that forms the lens pit.
• Reciprocal Induction: Interaction between optic vesicle and lens placode induces each other's development.
• Formation of Lens Vesicle: Lens pit invaginates and separates from the ectoderm.

Tunica Vasculosa Lentis

• Temporary capillary layer around the developing lens; not present in fully formed lens.

Lateral to Medial Eye Positioning

• Initial eye positioning is lateral in embryo but later shifts medially for better depth perception in humans.
• Other animals (like prey) retain lateral positioning for wider field of vision.

Conclusion

• Basic overview of eye development discussed.
• Future lectures will focus on detailed development of structures such as cornea, lens, retina, optic nerve, etc.