SSN Histology: The Eye
Structural Overview of the Eye
- The eye has 3 main layers:
I. Outer Layer - Corneosclera
1. Cornea
2. Sclera
II. Middle Layer – Uvea
1. Choroid
2. Iris
3. Ciliary Body
III. Inner Layer – Retina
1. Pigmented epithelium
2. Neuroretina
- The lens divides the eye into an anterior and a
posterior compartment.
- The iris divides the anterior compartment into
anterior and posterior chambers.
- The posterior chamber is filled with vitreous
fluid, a LCT made of thin, randomly oriented
collagen II.
I.
Corneosclera
Cornea
- Layers
 Corneal epithelium – stratified, non-keratinized
 Bowman’s membrane – acellular
 Stroma (substantia propria) – transparent, avascular, regularly arranged collagen fibrils and keratocytes
 Decemet’s membrane – thick basal lamina of corneal endothelium
 Corneal endothelium – single layer of flattened hexagonal cells involved in metabolic exchange with
aqueous humor
- Transparent because of:
 regular arrangement of collagen fibrils in corneal stroma
 avascularity
2. Sclera – white outer coat of the eye; DFICT
3. Limbus
- junction of cornea and sclera
- endothelium-lined channels merge to form the Canal of Schlemm, which absorbs aqueous humor
1.
II. Uvea
 Choroid

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
 Iris



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absorbs light that passes through the retina, preventing reflective interference
highly vascular & pigmented connective tissue adjacent to retina
separated from retinal pigment epithelium (RPE) by Bruch’s membrane (a thick basement membrane)
contractile diaphragm which controls the amount of light that reaches the lens
anterior – pigment cells (melanocytes) determine eye color
posterior – double layer of epithelium (because iris forms from double-layered optic cup), papillary sphincter
and dilator muscles
Ciliary Body
 Covered by double layer of epithelium between the root of the iris and ora serrata (anterior end of the
retina)
zonular fibers from the outer non-pigmented layer (facing the posterior chamber) attach to the lens
 contains the ciliary muscle, which controls the shape of the lens for accommodation (near and far sight)
Ciliary m.
relaxed
Ciliary m.
contracted
Flat lens
Taut zonules
Far-sight accommodation

Round lens
Ro
Near-sight accommodation
u
Lax zonules
ciliary processes – finger-like projections from the ciliary body into the posterior chamber
- contain large blood vessels and long fenestrated capillaries
- produces aqueous humor, which maintains intraocular pressure and provides nutrients to the avascular
cornea and lens
Pathway of aqueous humor
1. humor is secreted into the posterior chamber by the ciliary processes
2. passes between the iris and lens into the and the anterior chamber
3. enters through the trabecular membrane into the Canal of Schlemm
4. aqueous veins convey the fluid to the veins in the sclera
The Lens

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functions: accommodation, absorption of UV to protect retina, transmission of visible light
transparent with minimal light scattering
- lens fibers have few organelles and a very uniform cytoplasm packed with evenly distributed crystallins
- avascular, non-innervated
 monolayer of cuboidal epithelial cells on the anterior surface (only) serves as lens fiber progenitors
 the lens capsule (a thickened basal lamina) is suspended by zonular fibers anchored on the ciliary processes
III. Retina
 pigmented epithelium – pigmented cells with microvillae which:
- absorb the light which passes the photoreceptors and prevents interference
- phagocytose packets of outer segment membrane from the photoreceptor cells
 macula – oval depression in the retina that contains the fovea, a single layer of cone cells specialized for high acuity
vision
 Layers of the neural retina:
10. Inner limiting membrane - basal
lamina of Muller’s cells (glial cells)
9. Optic nerve fibers – processes of
ganglion cells that lead from the
retina to the brain, exiting the eye
via the optic disc where there are
no photoreceptors (blind spot)
8. Ganglion cell layer – cell bodies
7. Inner plexiform layer – processes
from 8 and 6
6. Inner nuclear layer – cell bodies
of of horizontal, amacrine, bipolar,
and Muller cells
5. Outer plexiform layer – processes
from 6 and 4
4. Outer nuclear layer – cell bodies
of rods and cones
3. Outer limiting membrane – apical
boundary of Muller’s cells
2. Rod and cone processes
1. Pigmented epithelium