Histology

Question 1

Corneoscleral Coat

Answer 1

Modifications
Cornea - anterior 1/6, transparent, convex
Substantial propria - middle, collagen fibres, vascular
Area cribrosa - posterior, perforate passes for optic nerve and retinal vessels.

Question 2

Cornea

Answer 2

Diam: 11mm, Thickness; 0.5 mm centrally to 1mm at edges. No bv’s, transparent

1. Anterior corneal epithelium - 5 layers stratified squamous, microvilli superficially (vermiform ridges), basal cells mitotic, regeneration, free nerve endings
2. Bowman’s membrane - Homogenous collagen fibres, stability and strength, does NOT regenerate.
3. Corneal stroma - 60 lamella of collagen fibrils, right angles. Fibroblasts - keratocytes - flattened between. Keratin and chondroitin sulfates. Transparent
4. Descemet’s Membrane - Homogenous collagen filaments, mesh work, FENESTRATIONS
5. Posterior corneal endothelium - simple squamous, abundant NA/K pumps, maintains hydration of stroma.

Question 3

Sclera

Answer 3

Dense CT, extension of DURA. Collagen type I, elastic fibres.
1. Episcleral layer
Tenon’s space between -
Attachment site for ocular muscles
2. Substantial propria
3. Suprachoroidal lamina
Perforated posteriorly for exit of optic nerve fibres and entry of central retinal vessels.

Question 4

UVEA (Tunica Vasculosa)

Answer 4

Iris, ciliary body, choroid

Features: vascular, loose CT, pigmented cells

Question 5

Choroid

Answer 5

Choroid Proper - closest to sclera (outside), presence of large blood vessels
Chorio-capillary layer - continuos capillaries
Bruch’s membrane - between choroid and RPE - component of blood-retinal barrier

Question 6

Ciliary Processes

Answer 6

1. Provide attachment to the capsule of the lens by zonule fibres - ligaments of Zinn - oxytalan elastic fibres
2. Secrete aqueous humour
3. Fenestrated capillaries

Question 7

Iris

Answer 7

Anterior extension of choroid, ANTERIOR to lens
Anterior surface: irregular, epithelial cells, stellate fibroblasts, stellate melanocytes
Stroma: loose CT, collagen, vascular, fibroblasts, melanocytes
Posterior: two epithelium: - inner (posterior) pigmented epithelium, continuation of RPE
Outer epithelium - pigmented myoepithelial cells *make up dilator pupillae muscle

Question 8

Drainage of Aqueous Humour

Answer 8

Sclerocorneal junction

Spaces of fontana –> canal of schlemm –> aqueous humour drained into ciliary veins

Question 9

Retina

Answer 9

Derived from ectoderm, anterior portion is non-photosensitive lining inner ciliary body and posterior iris.
Junction of anterior and posterior is ORA SERRATA.

Question 10

Retinal pigment epithelium

Answer 10

Single layer of cuboidal cells
Synthesise melanin
Adjacent cells - junctional complex connection
Abundant microvilli, surround and phagocytose shed discs of rods and cones
Establish blood retinal barrier
Estérification of vitamin A

Question 11

Photoreceptors

Answer 11

Light sensitive photoreceptor discs
Flattened membranous disk contains photosensitive pigments
Tips that contain disks are embedded within microvilli of RPE

Inner segments: cell organelles, metabolic processing

Question 12

Rods

Answer 12

120 millions rods,
Disks: Visual Purple/Rhodopsin: contains scotopsin protein + retinal (chromophore, vitamin a derived, covalently attached)

Question 13

Cones

Answer 13

7 million
Thicker and shorter,
Discs: pigment is called iodopsin. Contains photopsin
Sensitive only to light - better visual acuity.

3 types: S cones (short, blue), M cones (medium, green), L cones (long, red) for colour vision. Maximum absorptions at different wavelengths.

Question 14

Bipolar cells of the retina

Answer 14

Extend between inner and outer plexiform layers
Axons synapse with several ganglion cells
Helps in communication with multiple cells
In fovea, however, ONE bipolar cell to ONE ganglion cell increases the visual acuity.

Question 15

Other cells of the retina

Answer 15

Association neurons: horizontal cells, amacrine cells, in the bipolar cell layer
Supporting cells: Muller’s cells on the side, extend from outer limiting membrane (layer 3, next to outer rods and cones) all the way down to inner limiting membrane (layer 10, below optic nerve fibre layer)

Question 16

Outer synaptic plexiform layer

Answer 16

Synapse between bipolar cells and photoreceptors

Question 17

Inner synaptic plexiform layer

Answer 17

Synapse between bipolar cells and ganglion cells

Question 18

Where do you find the cell bodies of muller’s cells?

Answer 18

In the inner nuclear layer with cell bodies of bipolar, horizontal, amacrine as well

Question 19

Layers of the retina

Answer 19

1. Pigment epithelial layer (RPE)
2. Outer segment of rods and cones
3. Outer limiting membrane (outer limit of muller cells)
4. Outer nuclear layer (inner segments of rods and cones)
5. Outer plexiform layer (synapses of photoreceptors and bipolar cells
6. Inner nuclear layer (cell bodies of bipolar, horizontal, amacrine, and muller cells)
7. Inner plexiform layer (Synapses of bipolar cells and ganglion cells)
8. Ganglion cell layer
9. Optic nerve fibre layer (axons of ganglion cells)
10. Inner limiting membrane (inner limit of Muller cells)

Question 20

Blood supply to the retina

Answer 20

First five layers (ie RPE, outer rods, outer limiting, outer nuclear, to outer plexiform (layer 5)) by choriocapillaries

Layers 6-10 (ie inner nuclear layer, inner plexiform, ganglion, optic nerve fibre, inner limiting layer) - by central retinal artery

Question 21

Macular Lutea

Answer 21

Center of the posterior retina at the visual axis of th eye

Fovea central is: small depression in the centre of the macula lutea, area of highest visual acuity, contains ONLY CONES

Question 22

Lens features

Answer 22

Biconvex
AVASCULAR
Held in place by RADIALLY oriented group of zonule fibres - oxytalan, elastic fibres. arise from ciliar processes, play a part in change of shape of lens during process of accomodation. (Ie tight when lens is flat and ciliary muscles are relaxed ie distant )
(Relaxed when ciliary muscles rae contracted and lens is convex, for near sight)

Question 23

Layers of the Lens

Answer 23

1. Lens capsule - thick BL of 10-20microm, produced by ANTERIOR lens cells, attached to zonule fibres
2. Subcapsular epithelium - single layer of simple cuboidal, ONLY on ANTERIOR surface of lens. Source of lens fibres
3. Lens fibres - thin, flattened structures. Lose the organelles and accumulate crystallins (proteins)

Question 24

Vitreous Body

Answer 24

Between lens and retina, 4 mL capacity.
Spindle shaped cells - hyalocytes
Fine collagen fibrils in the matrix
ECM rich in GAGs especially hyaluronic acid

Question 25

Conjunctiva

Answer 25

Lines inside of eyelids and visible part of sclera, secretes MUCIN

Question 26

Glands of the eyelid

Answer 26

Meibomian glands - Sebaceous, within tarsal plate. Lubricates - delays drying of tears Glands of Zeiss - Sebaceous glands within eyelids (where eyelashes come out) Glands of Moll - sweat glands at the lid margins.

Question 27

Lining of the tympanic membrane

Answer 27

External: thin skin Internal: simple squamous epithelium Membrane itself consists of collagen fibres

Question 28

Inner Ear

Answer 28

Bony labyrinthe: 3 semicircular canals, vestibule, cochlea | Membranous labyrinthe: semicircular DUCTS, vestibular LABYRINTH, cochlear labryinth.

Question 29

Membranous labryinths

Answer 29

Communicating sacs and ducts with ENDOLYMPH Vestibular: semicirc ducts, utricle, saccule Cochlear: cochlear duct Endolymph: SImilar to ISF - low in Na high in K

Question 30

Bony labryinths

Answer 30

Contain perilymph - similar to ECF (and CSF) high in Na low in K

Question 31

Cristae

Answer 31

Sensory hair cells - 3 cristae ampullaris (ampullary crests) of semicircular ducts. Detect angular acceleration. Cupula: gelatinous protein - polysaccharide mass, projects into the lumen, surrounded by endolymph and attached to each crista.

Question 32

Macula

Answer 32

Hair cells within utricle and saccule. Sense gravity and linear acceleration of head. Cells of the epithelium face the endolymph. Otolithcic membrane - gelatinous polysaccharide material over the epithelium. Outer limit is crystalline bodies of calcium carbonate and protein otoconia

Question 33

Stria Vascularis

Answer 33

In cochlear duct. Responsible for ionic composition of endolymph

Question 34

Sound conduction

Answer 34

Sound waves within cochlea, vibrate organ of corti, basilar membrane more elastic than tectorial membrane, vibration of basilar membrane causes hair cells to displace, shearing force created against tectorial membrane creates a nerve impulse. High frequency sound - maximum displacement of basilar membrane at base Low frequency sound - apex of cochlea.

Question 35

Sensorineural Deafness

Answer 35

Destruction of nerve (sensory neuroepithelial) cells or central pathway to the brain Level at which sustained exposure may cause hearing loss - 90-95 dB (normal convo is 60-70 dB, rock concert 115, pain begins 125) Death of hearing tissue - 180 Loudest sound possible - 194

Question 36

Corneal Transplant

Answer 36

Indications: keratitis, trauma, keratoconus, corneal degeneration, etc. Types: penetrating kératoplastie, lamellar kératoplastie, endothelial kératoplasty

Question 37

Lens - cataract

Answer 37

Lens = mostly water and protein Crystalline keeps it clear Ageing leads to clumping of protein --> cloudy appearance Visual acuity and contrast sensitivity is lost (contours, shadows, colour vision lost) Some causes; diabetes, homocysteinuria, fabry's Congenital: congenital herpes, congenital syphilis, CMV - cytomegalovirus inclusion disease, rubella Drugs: corticosteroids, haloperidol

Question 38

Glaucoma

Answer 38

Increased intraocular pressure Symptoms: headache, eye pain, loss of vision, vomiting, halo around light Signs: peripheral field of vision is decreased, redness, raised intraocular pressure (tonometry - used to measure IOP) Can cause optic nerve compression, can lead to permanent vision loss

Question 39

Most common site of retinal detachment

Answer 39

Between RPE and rods & cones layer | Some causes: cataract surgery, trauma, extreme dehydration, retinal tears