CR MAN..:P

2. Layers of the eyeball

10. • The most pathetic person in the world is
someone who has sight, but has no vision.
– Helen Keller

15. 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

16. • Refractive media enclosed in 3 coats
1. Fibrous [sclera, cornea]
2. Vascular/uveal coat [choroid, ciliary body, iris]
3. Nervous [retina]

22. Sclera
• Posterior 5/6ths
• Opaque - composed of dense collagen and
elastic fibres
• Thinnest at equator
• Pierced by recti muscles

23. • 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
• Site of muscle insertion

24. • Pierced by ciliary nerves and arteries, venae
vorticosae
• Almost avascular, except ehere connected to
fascial sheath of eye and bulbar conjunctiva

25. Cornea
• Forms anterior 1/6th of fibrous coat
• Transparent fibrous tissue laminae
• Avascular [no transplant rejection]

26. Layers
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

28. 4. Descemet’s membrane /posterior limiting
membrane
5. Corneal endothelium

29. 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 act]

33. • Components choroid, ciliary body, iris
CHOROID
• Thin, pigmented
• Outer layer separated from sclera by
suprachoroid lamina [delicate connective tissue]
• Inner layer firmly attached to pigmented layer of
retina

35. • Rods and cones nourished by choroidal
capillaries
• Venae voricosae [4-5] drain choroid- exit
through sclera

36. 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

38. • Ciliary muscle in scleral surface
• Vitreous surface – bilayered epithelium [outer
pigmented, inner nonpigmented]
• Layers represent pigment and nervous layers of
retina

39. • Scleral surface projected into70-80 ciliary
processes that lie in reciprocal grooves on
anterior surface of vitreous body

40. Iris
• 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
tissue
• Amount of melanin granules increases from
anterior to posterior

41. • Amount of pigment increases with age
• Color is variable in different individuals

42. Sphincter pupillae
• Circular smooth muscle
• Supplied from Edinger – Westphal nucleus of
CN III

43. Dilator pupillae
• Radial smooth muscle
• Supplied by cervical sympathetics
• Preganglionic neurons lie in T1 segment of
spinal cord

47. Trabecular meshwork and scleral
venous sinus

48. Lens
• Transparent, biconvex
• More convex posteriorly
• Transparent ,elastic capsule
• Posteriorly rests on vitreous, anteriorly in
contact with iris
• 10 mm dia., 4 mm thick

49. • Centrally , single layer of cubical cells
• Peripherally , cells elongate to produce fibres
• Increase in length leads to increase in lens
substance

50. 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

54. • 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]

56. • Delicate
• 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
iris

58. Retina - components
1. Retinal pigment epithelium
2. Neural retina

59. Retinal pigment epithelium
• Outer layer
• Simple cuboidal melanin-containing cells
• Firm attachment to choroid via Bruch’s
membrane [thin refractile layer –multilaminar]

60. Neural retina
• Contains light – sensitive receptors [ rods and
cones] + complex neuronal networks
• Potential space exists between neural retina and
RPE
• Layers can be separated mechanically
• Eye disease or trauma also leads to separation
[Retinal detachment]

61. 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

63. Optic disc
• i.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’

64. Fundus
• 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

66. Fovea centralis
• Shallow central pit in macula
• Thinnest area of retina
• Avascular
• No rods
• High concentration of cones=site of most acute
vision

68. Arrangement
• 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

69. 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