3 Embryology / Pathology
Optic vesicle
anterolateral outpouching of primitive brain stem; evaginates on day 25 and becomes the globe
Optic cup (Figure 3.2)
develops embryologically as an anterolateral evagination of the forebrain
Embryonic fissure
on undersurface of optic cups; closes on day 33 allowing pressurization of globe
Hyaloid artery (Figure 3-3)
enters through embryonic fissure and forms vasa hyaloidea propria (blood supply to primary vitreous)
Primitive epithelial papillae
cells from inner layer of optic cup at superior end of embryonic fissure, which becomes the optic disc

Vitreous
produced by lens, retina, and walls of hyaloid artery; contains mesenchymal cells
Retina
neuroectoderm; vascularization begins at 4 months; temporal periphery is last portion to become vascularized
Cornea
Lens
at 27 days, surface ectoderm adjacent to optic vesicle enlarges to form lens placode (lens plate)
Lens of a newborn is more spherical than that of an adult; therefore, anterior chamber appears shallow
Iris
rim of optic cup grows around lens and forms iris
Ciliary body (CB)
formation begins in 3rd month; fold in optic cup becomes epithelial layers of ciliary processes
Nasolacrimal system
at 6 weeks, surface ectoderm is buried in mesoderm, between maxillary and lateral nasal processes
Eyelids
at 8 weeks, upper lids form by fusion of medial and lateral frontonasal processes; lower lids by fusion of maxillary processes and medial nasal processes
Embryologic tissues and their components
Hematoxylin and eosin (H&E)
hematoxylin is specific for nucleic acids within nuclei and stains blue (basophilic); eosin is specific for most cytoplasmic organelles (such as mitochondria) and stains pink (eosinophilic)
Periodic acid-Schiff (PAS)
stains basement membrane material magenta (Descemet’s, lens capsule, Bruch’s membrane, ILM [internal limiting membrane], gutattae, drusen); also stains glycogen, fungi, conjunctival goblet cells (useful for differentiation of corneal from conjunctival epithelium)
Oil red O
stains neutral lipids red-orange in frozen section; must be used on fresh tissue because formalin leaches out lipid

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