eye-layers 1

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Transcript eye-layers 1

Layers of the eyeball
• The most pathetic person in the world is
someone who has sight, but has no vision.
– Helen Keller
Eye and camera
• Both deal with similar sets of issues
• Maintaining a stable relationship between a
focusing apparatus and a focusing apparatus
• Focusing on near and far objects
• Regulating the amount of light reaching the
photosensitive surface
• Recording the pattern of incoming light
General features
• Image focusing system, composed of
1. Cornea
2. Lens
3. Refractive media
• Internally black- prevents ‘scatter effect’
• In front of iris – anterior chamber
• Behind the iris – posterior chamber
• Refractive media enclosed in 3 coats
1. Fibrous [sclera, cornea]
2. Vascular/uveal coat [choroid, ciliary body, iris]
3. Nervous [retina]
Sclera[‘white of the eye’]
• Posterior 5/6ths
• Opaque - composed of dense collagen and
elastic fibres
• Thinnest at equator
• Pierced by recti muscles
• Thickest at back, except where pierced by fibres
of CN II [lamina cribrosa]
• ‘cupping’ of optic disc= posterior bulging of disc
in sustained ↑in intraocular pressure
• Blends with dura mater
• Continues posteriorly as the sheath of CN II
• Site of muscle insertion
• Pierced by ciliary nerves and arteries, venae
• Almost avascular, except where connected to
fascial sheath of eye and bulbar conjunctiva
• Limbus is a transition zone between sclera and
• Beginning from limbus, cornea forms anterior
1/6th of fibrous coat
• Transparent fibrous tissue laminae
• Avascular [no transplant rejection]
1. Corneal epithelium
2. Bowman’s membrane /anterior limiting
membrane; scattered collagen fibrils and
ground substance
3. Corneal stroma/substantia propria
• 200 collagen fibril lamellae
• Scattered fibroblasts
• Transparency because of lattice arrangement
4. Descemet’s membrane /posterior limiting
5. Corneal endothelium
Nerve supply
• Short and long ciliary nerves
• Mainly short ciliary
• Corneal reflex pathway; short ciliary nerves→
trigeminal ganglion→ main CN V sensory
nucleus→ reticular formation→ both CN VII
motor nuclei [both orbicularis oculi muscles
Uvea/uveal tract
• Heavily vascularised
• Similar to arachnoid and pia
• Principal route through which blood vessels and
nerves [other than CN II]
• Components \ choroid, ciliary body, iris
• Thin, pigmented
• Outer layer separated from sclera by
suprachoroid lamina [delicate connective tissue]
• Inner layer firmly attached to pigmented layer of
• Rods and cones nourished by choroidal
• Venae voricosae [4-5] drain choroid- exit
through sclera
Ciliary body
Continuous with choroid behind and iris in front
Like a flat ring applied to inner scleral surface
Thick in front, thin behind
Triangular ;2 lond sides in contact with sclera
and vitroeus
• Attachment of iris halfway along flat anterior
short base
• Ciliary muscle in scleral surface
• Vitreous surface – bilayered epithelium [outer
pigmented, inner nonpigmented]
• Layers represent pigment and nervous layers of
• Scleral surface projected into70-80 ciliary
processes that lie in reciprocal grooves on
anterior surface of vitreous body
• Attached at periphery to anterior surface of
ciliary body and a narrow rim of sclera to form
iridocorneal angle of anterior chamber
• Perforated centrally by pupil
• Main bulk- vascular connective tissue connective
• Amount of melanin granules increases from
anterior to posterior
• Amount of pigment increases with age
• Color is variable in different individuals
Sphincter pupillae
• Circular smooth muscle
• Supplied from Edinger – Westphal nucleus of
Dilator pupillae
• Radial smooth muscle
• Supplied by cervical sympathetics
• Preganglionic neurons lie in T1 segment of
spinal cord
Trabecular meshwork and scleral
venous sinus
Transparent, biconvex
More convex posteriorly
Transparent ,elastic capsule
Posteriorly rests on vitreous, anteriorly in
contact with iris
• 10 mm dia., 4 mm thick
• Centrally , single layer of cubical cells
• Peripherally , cells elongate to produce fibres
• Increase in length leads to increase in lens
Suspensory ligament/zonule
• Series of delicate fibrils attached to ciliary
processes and through the furrows between
them, further back on ciliary body
• Most fibres attach themselves to the lens- mostly
in front and a few behind the circumference
• Holds lens flattened under tension
• Contraction of ciliary muscle→ forward
displacement of choroid and ciliary body
• This relieves some tension exerted by zonule on
the lens; makes it more globular→ increased
refractive power [Accomodation]
Outer surface in contact with choroid
Inner surface in contact with vitreous
Ora serrata- anterior limit of light ssensitive area
Beyond ora serrata- thin light insensitive layer
continues as epithelial layers of ciliary body and
Retina - components
1. Retinal pigment epithelium
2. Neural retina
Retinal pigment epithelium
• Outer layer
• Simple cuboidal melanin-containing cells
• Firm attachment to choroid via Bruch’s
membrane [thin refractile layer –multilaminar]
Neural retina
• Contains light – sensitive receptors [ rods and
cones] + complex neuronal networks
• Potential space exists between neural retina and
• Layers can be separated mechanically
• Eye disease or trauma also leads to separation
[Retinal detachment]
Components of neural retina
• Nonvisual part; anterior to ora serrata- lines
inner aspect of ciliary body and posterior surface
of iris
• Photosensitive /visual part; lines inner
surface of eye posterior to ora serrata, except
where it is pierced by CN II
Optic disc
1.5 mm dia.
Site of entry of CN II
Overlies lamina cribrosa of sclera
Deepened to a variable degree to form a
‘physiological’ cup
• Insensitive to light – ‘blind spot’
• Disc and whole of surrounding area at the back
of the eye seen with ophthalmoscope
Macula lutea –
• yellowish shallow depression, avascular
• 3mm lateral to optic disc
Fovea centralis
Shallow central pit in macula
Thinnest area of retina
No rods
High concentration of cones=site of most acute
• Outer layer- pigmented cells attached to choroid
• Not a firm attachment
• In retinal detachment- pigmented cells remain
in position; rods and cones and other layers
displaced onwards
Physiological arrangement
• Similar to any sensory pathway
• 1st order neuron – bipolar cell – peripheral
process connected to rods and cones
• Synapses with 2nd order neurons – ganglion cell
• Passes to thalamus [lateral geniculate body]
which has 3rd order neurons
• Axons pass through retrolentiform part of
internal capsule to visual cortex