Module 2

Question 1

Gastrulation and neurulation

Answer 1

Gastrulation (day 10); epiblasts migrate towards primitive streak and invaginate –> mesoderm. Ectoderm, mesoderm, endoderm.
Neurulation; the columnar surface ectoderm proliferates, forms elevations, neural folds–> elevate and approach each other and will form neural tube. Mesenchymal cells forming neural crest migrate out, spread throughout the embryo giving rise to connective tissue for the eye.
In other parts of the body mesenchyme is predominantly mesoderm in origin, not from neural crest.
The exterior is covered with surface ectoderm, then neural segmentation occurs forming forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon. Forebrain–>optic vesicle from neuroectoderm, midbrain–> connective tissues from neural crest

Question 2

Optic vesicle and optic cup

Answer 2

By day 13 - optic sulci; paired evaginations of forebrain, then transformed to optic vesicle simultaneously with neural tube closure (day 15, also when aqueous humour starts to be produced).
Optic vesicle enlarges, approaches surface ectoderm. Optic vesicle significant in determining palpebral fissure and other orbital structures. Bulge seen by day 17. Optic vesicle and stalk invaginate. Surface ectoderm thickens–> lens placode –> invaginates within neural ectoderm –> double layer of neuroectoderm in the optic cup –> inferior to superior progression; note optic fissure, day 25 hyaloid artery develops in optic fissure and supplies lens. Fissure meets and closes (failure here results in colobomas as 6 o’clock position) –> IOP can be established

Question 3

Lens formation

Answer 3

Adhesion of lens placode and optic vesicle assure alignment with retina. Lens placode invaginates - hollow sphere; lens vesicle, which then detaches (day 25). (Failures = anterior lenticonus, anterior capsular cataracts, anterior segment dysgenesis).
Vesicle then lined with a monolayer of cuboidal cells with basal lamina - lens capsule.
Primary lens fibres - stim by retina, form embryonic lens nucleus.
Cortex; minimal at birth, continues to develop, anterior cuboidal epithelial cells, differentiate into secondary fibres at equator and meet at Y sutures.
Zonule fibres (tertiary vitreous) - ?origin, ?ciliary epithelium or endothelium of posterior tunica vasculosis lentis.
Lens abnormalities: spherophakia, coloboma, flattened equator

Question 4

Vascular development

Answer 4

Mesoderm–> hyaloid vasculature. Hyaloid artery = termination of ophthalmic artery. Hyaloid vessels enclosed in ON as fissure closed.
Anterior and posterior tunica vasculosis lentis; hyaloid artery branches around posterior lens and continues anteriorly, anastomoses with the vessels in the pupillary membrane (mesenchyme and vessels overlying anterior lens capsule) (at max day 45).
Hyaloid regresses posterior to anterior as lens now nourished by aqueous although may still support lens up to 3 days postnatally.
Mittendorf’s dot fibrosis on posterior lens capsule, incomplete regression.
Choroid develops on outer surface of optic cup –> ciliary arteries –> retinal vessels. Glial cells sheathing hyaloid may persist at ONH; Bergmeister’s papilla.

Question 5

Cornea and anterior chamber

Answer 5

Surface ectoderm–> thick matrix; primary stroma
Mesenchymal neural crest –> endothelium and stroma, anterior iris stroma, ciliary muscle, iridocorneal angle structures. Also sheet of mesenchymal tissue, some of which forms pupillary membrane, rest eventually becomes anterior chamber
Endothelium day 30-35 –> secretes Descemet’s membrane
Cornea - transparent by end of gestation
Lids open day 14, corneal thickness increases initially for 4 weeks, then decreases over 6 months.

Question 6

Development of iris, ciliary body and iridocorneal angle

Answer 6

Neuroectoderm layers cover ciliary muscle and posterior surface of pupillary membrane, then fuse with open centre to become iris and pupil.
Pupillary membrane starts to degenerate day 45 and continues to degenerate until day 14 postnatally.
Two layers of neuroectoderm- non-pigmented (inner) pigmented (outer)
Iris and ciliary body epithelium - anterior rim of cup, retina - posterior cup

Question 7

Retina and ON development

Answer 7

From forebrain. Ectoderm from outer optic cup –> RPE.
Ectoderm of inner optic cup –> neurosensory retina.
Two layers of epithelia are separated by a space, the cavity of the optic cup, which has decreased during invagination, disease occurs in this space, separating RPE from sensory retina.
Neuroblastic layer –> inner and outer neuroblastic layer separated by a fibre layer. Outer neuroblastic layer –> cones and rods externally and horizontal cells (thus next to choroid and own blood supply). Inner neuroblastic layer –> ganglion cells, amacrine cells, bipolar cells and muller’s cells.
ERG signals reach adult amplitude at 5-8weeks.
Axons from ganglion cells –>towards optic stalk–>nerve fibre layer; innermost layer of the retina. Converge forming bundles–> ON. Synapse at lateral geniculate nucleus.

Question 8

Sclera, choroid, tapetum

Answer 8

Neural crest–> inner vascular layer (–> choroid) & outer fibrous layer (–> sclera, which is continuous with dura mata of ON).
Tapetum continues to develop 4 months after birth, initially mottled blue appearance is replaced by blue/green to yellow/orange sheet.
Subalbinotic animals have a higher incidence of posterior segment colobomas with reduced RPE pigmentation being the marker e.g. CEA

Question 9

Vitreous

Answer 9

Primary: mesodermal tissue - hyaloid vasculature–> tunica vasculosis lentis, nourishes lens until day 45. Compressed by secondary vitreous, atrophied by 2-4 weeks postnatally.
Secondary: adult vitreous. Ectoderm and neuroectoderm, forms fibrils continuous with muller cells. Attached at pars plana, ora ciliaris retina, hyaloidiocapsular ligament. Remnants: mittendorf’s dot on posterior capsule or a clear central canal cloquet’s canal.
Tertiary: len zonules - secreted by ciliary epithelium?

Question 10

Eyelids and TEL

Answer 10

Lower and TEL from maxillary processes
Upper from paraxial mesoderm
Upper and lower fused until 10-14 days postnatally
Surface ectoderm: conjunctiva, cilia, glands, lid epidermis
Neural crest: tarsus, lid dermis
Mesoderm: lid muscles

Question 11

Nasolacrimal system

Answer 11

Nasolacrimal groove - lateral nasal fold from maxillary processes
Solid tube of ectodermal cells form and gets buried in maxillary process
Two buds form from proximal end towards medial canthus, forming inferior and superior lacrimal puncta
Distal end enters ventral nasal meatus
Chord becomes duct by canalisation
Imperforate puncta can occur - usually lower one

Question 12

EOM

Answer 12

Neural crest –> secondary mesenchyme in orbit –> EOM

Question 13

Postnatal development

Answer 13

Retina: inner segments first week, outer segments by second week. Mature by 6 weeks.
Corneal oedema - impossible to examine fundus <2weeks, around this time tapetal and non-tapetal fundus cannot be differentiated on exam. ONH is small and fundus is dark and grey, vessels large
3-4 weeks tapetal fundus defined as paler area –> lilac/blue
7-8 weeks tapetal fundus granular in appearance
4 month - adult tapetal structure and colour

Question 14

Cornea - intro

Answer 14

1/6 outer tunic
Refracts and transmits light to retina, anterior surface contributes 48D of plus power towards convergence on the retina.
Oxygen derived from tear film, nutrition from aqueous humour.
Protects eye: chemical barrier through tight junctions superficially, subepithelial nerve plexus, fine nerve endings; do not impact clarity.
Immunoglobulins and anti-microbials provided in the tear film, blinking and epithelial desquamation, migrating Langerhans cells and macrophages from limbus
Tear film: 7um thick. Lipids - meibomian glands, aqueous - lacrimal glands, mucin - goblet cells.

Question 15

Epithelium

Answer 15

5-7 layers. Stratified, squamous, non-keratinised and non-secretory. 50-60um.
Outermost layer most differentiated, tight junctions, zona occludens, obliterate intercellular space. Anterior plasma membrane - microvilli
Superficial layer 3-4 layers flattened, nucleated, squames
Intermediate layer 2-3 layers interdigitating, wing and polygonal cells.
Basal columnar cells are adhered to 50nm thick basement membrane.
Basement membrane 40-60nm thick

Question 16

Epithelial cell adhesions

Answer 16

Superficial - tight junctions (barrier function) and desmosomes. Tight junctions/zona occludens completely encircle cell. Anastomosis lipid bilayer of adjoining membranes
Wing cells - beneath superficial cells. Desmosomes and gap junctions. Intercellular communication
Basal cells - desmosomes and gap junctions. Hemidesmosomes attach to basement membrane
Base membrane - specialised extracellular matrix, has a lamina lucida and lamina densa, laminin, collagen IV and proteoglycans Roles include: a) maintaining structure, b) anchorage, c) selective barrier d) filtration and temporary storage, e) involved in biological processes including embryonic development

Question 17

Stroma

Answer 17

500um thick. 90% of corneal thickness. Lamellae - flattened bundles of collagen fibrils. Highly organised. Stromal fibroblasts (keratocytes) reside between lamellae and secrete the lamellar stroma. Proteoglycan molecules cross-link the lamellae. Collagen I mostly, some II, V and VI.
Keratocytes perform constant remodelling as maintenance. Proteases enable this function. Over production by fibroblasts, bacteria and inflammatory cells results in melting ulcers.
Primates - Bowman’s layer - acellular layer in stroma
Stromal basement membrane = Descemet’s membrane and is secrete by the endothelium

Question 18

Endothelium

Answer 18

Low cuboidal, single-layered endothelium. No adhesive junctions with Descemet’s membrane. Interdigitation with other fellow cells, tight junctions and gap junctions (intercellular communication) with occasional desmosomes. Tight junctions only laterally so barrier is leaky.
Mitochondria +++, smooth and rough endoplastic reticulum, golgi apparatus.
Na+K- ATPase pump to maintain corneal hydration.
Does not self renew, enlarges to fill defects.

Question 19

Corneal innervation

Answer 19

CN V –> myelinated nerve leashes –> anterior stroma below Bowman’s layer.
Nerve sheath lost during penetration of basement membrane
Naked nerve endings send terminus up between cell layer, terminating at outer most squames.
300-400 more nerve endings cf. epidermis

Question 20

Corneal nutrition

Answer 20

Tear film - oxygen

Limbal vessels and aqueous humour - glucose and amino acids

Question 21

Limbus

Answer 21

Externally: junction of corneal and conjunctival epithelia
Anatomically: Schlemm’s canal, trabecular meshwork, outer region = epithelium, connective tissue (loosely arranged), down to corneo-scleral collagen
Epithelium 10-12 layers thick, non-secretory, junctions as per cornea. Basal cells (corneal epithelial stem cell) less columnar, >mitochondria, undulating extensions into matrix - additional adhesive strength and increased absorption. Less hemidesmosomes.
Unlike cornea, connective tissue has no keratin sulphates. Blood vessels and lymphatics loop into area along with unmyelinated nerves, provides peripheral cornea, conjunctiva, episclera, limbal sclera, peripheral uvea. Arterial supply: anterior ciliary arteries from rectus muscles, drained by venules passing over same direction.
Large radial folds form the palisades of vogt, these hold small vasculature. Limbal epithelial crypts reach down into palisades; protects stem cell population.

Question 22

Maintenance of resting state

Answer 22

Self renewing, constant state of healing
Squames shed into tear pool and replaced from cells moving centrally from limbus and anteriorly from basal layers.
Healing is an exaggeration of normal response.
X(proliferation of basal epithelial cells) + Y(contribution to mass by centripetal movement) = Z(epithelial loss).

Question 23

Epithelial wound healing 1

Answer 23

3 components contributing to continual process: cell migration, cell proliferation and cell adhesion
Latent phase: 4-6 hours following defect, wound becomes slightly larger from sloughing of necrotic cells. Increase synthesis of structural proteins. Actin filaments reorganised. Basal cells and squames in region thickened and separated. 2 hour post hemidesemosomal attachments disappear extending 50-70um beyond wound edge. Tight junctions severed, desmosomes stay. PMN cells arrived by tear film 3 hours post. Thinning of epithelium around wound edge. Ruffling and folding of plasma membrane near the free edge, finger like (filopodia) or broader coral (lamellipodia) - start of cell migration.

Question 24

epithelial healing 2

Answer 24

Linear phase: epithelial cells flatten, spread and move across defect. Glycogen serves as energy source. Basal and suprabasal cells participate. Actin at leading edge actively participate in cell motion.
Desmosomes intact, cells move as sheet. Hemidesmosomes lost.
Temporary adhesions; focal contacts aid migration - actin filament bundles. Intracellular mechanism draw trailing cells forward.
Fibrin & fibronectin –> epithelial cells release plasminogen activating factor. Plasminogen –> plasmin, lyses cell to substrate adhesions. Continues until wound closure.
Usually filled by single layer of cells initially, normal thickness restored by proliferation and upward movement.
Movement independent of proliferation but complementary. Wave of mitosis from periphery to wounds.

Question 25

Cell adhesion

Answer 25

Wound healing not complete until anchored down with new adhesions. ECM proteins appear on denuded surface and migrating cells develop focal contacts.
Hemidesmosomal attachments depend upon basement membrane and if intact at time of wounding. If intact fully adhered within 7 days. If not intact can take 6 weeks for basement membrane to be restored by epithelium and stroma.

Question 26

Stromal wound healing

Answer 26

Re-epithelialisation must be complete.
Fibroblasts lay down new collagen.
Arrangement is not regular and is opaque, with time remodelled and reduces in size

Question 27

Uveal tract

Answer 27

Anterior - iris and ciliary body
Posterior - choroid
The most immunologically reactive tissue in the eye

Question 28

Iris

Answer 28

Diaphragm between anterior and posterior chambers, narrow darker pupillary zone and wider pale peripheral zone. Junction = iris collarette. Posterior surface rests on lens centrally.
Histology - anterior border has no epithelium, fibroblasts and melanocytes above loosely arranged stroma. Sphincter in the stroma in pupillary zone. Posterior to stroma are two layers of epithelium - blood aqueous barrier, anterior is non-pigmented and continuous with inner pigmented epithelium of ciliary body, posterior pigmented epithelium is continuous with outer non-pigmented ciliary epithelium.
Blood supply - major arterial circle; raised tortuous line, arteries from medial and lateral branches of long posterior ciliary arteries enter at 9 and 3 positions. Venous; tortuous radial vessels–> anterior choroidal veins –> vortex veins

Question 29

Iris colour and shape

Answer 29

Colour: determined by melanocyte numbers. Brown = lots, blue = less, albino = none but pigment due to glow of fundus.
Pupillary margin - posterior epithelial layers extend anteriorly around the pupil, physiological ectropion.
Shape of the pupil varies in different species. Dog and pig = round, cat = vertical. Herbivores e.g. horses = horizontally oval + corpora nigra

Question 30

Ciliary body

Answer 30

Posterior to iris, anterior to choroid. Secretes aqueous, nourishes lens, muscle for accommodation, lens zonules, vitreous face.
Histology - non-pigmented epithelium (secretes aqueous) is anterior extension of neuroretina, pigmented epithelium beneath is an extension of RPE. Gap between two layers closed with adhesion complexes. Pars plicata anteriorly, Pars plana posteriorly. Pars plicata - folds - ciliary processes, increase SA for aqueous production and anchor suspensory zonular fibres. Most anterior portion is ciliary cleft of irido corneal angle.

Question 31

Choroid

Answer 31

Between retina and sclera.
Vasculature
Bruch's membrane sits next to RPE
Choriocapillaris
Tapetum
Stroma and large vessels
Suprachoroid

Question 32

Lens

Answer 32

Capsule, lens epithelium and lens fibres
Divided into nucleus and cortex and anterior or posterior
Zonules originate on and between ciliary processes and insert onto lens anterior and poster to equator
Muscular action of ciliary body alters tension and optical power; dynamic accommodation
Firm attachment of vitreous to periphery - hyaloideocapsular ligament
Primary fibres - differentiate from posterior lens epithelium, elongate and fill nucleus, stimulate by retina. In adult no posterior lens fibres present.
Secondary - anterior epithelium actively divide, when these reach equator they elongate and become “secondary”. Compression of nucleus throughout life. Anterior capsule gets thicker –> nuclear sclerosis.
Lens suture - Merces inverted Y on back, Y on front
Developing lens nutrition - hyaloid artery, later from tunica vasculosa lentis

Question 33

Aqueous humour and IOP

Answer 33

Delivery of nutrients and removal of waste - lens, cornea, trabecular meshwork
Ciliary processes primarily active secretion, ciliary body by passive secretion
Blood-aqueous barrier reduces protein in aqueous to 0.5% of plasma and prevents many substances entering.
Fluid from capillaries –> stroma in processes –> epithelium and into posterior chamber
High concentrations of ascorbic acid as an energy dependent transport
NaK-ATPase pump in the non-pigmented epithelium involved with active production. Carbonic anhydrase catalyses CO2 and H2O to carbonic anhydrase. Which then dissociates and bicarb ions HCO3-, NA+ and H2O follow
Iridocorneal angle - “conventional drainage”, ciliary smooth muscle fibres contract to increase this, uveoscleral outflow “unconventional” - 3-15% of drainage.
Pectinate ligament and ciliary left including its trabecular meshwork make up majority of drainage apparatus.
Increase in IOP occurs from outflow resistance, not increased production

Question 34

IOP

Answer 34

Ref range: 15-25mmHg
Variations:
- instrument
- age of dog; increases with age
- position of patient; head back increases IOP
- restraint - vigorous increases IOP
- forced lid opening - increases IOP
- breed - terrier fluctant IOP
- obesity and BP

Question 35

Vitreous

Answer 35

Posterior segment, 2/3 globe, 99% water with collagen, HA, few cells (hyalocytes).
Anatomy: in contact with lens, zonules, pars plana, retina, optic disc. Attached at vitreous base, pars plana, ora ciliaris retinae, posterior lens capsule, around optic disc. Lens occupies depression - patella fossa.
Passage into and out of vitreous: boundaries with aqueous, retina and lens.
Blood-vitreal barrier: ABs e.g. penicillins, oxytetracycline, streptomycin - low liposolubilities and low penetration unless inflamed. Chloramphenicol - high permeability. Sulphonamides therapeutic in vitreous.
Intravitreal injections may be required in endophthalmitis

Question 36

Retina

Answer 36

Bound anteriorly by vitreous body, posteriorly by choroid. Layer 2-10 make up neurosensory retina.
Anatomy: outside inward -
*RPE - next to choroid, pigmented except where they overlie tapetum, phagocytoses photoreceptor segments and provide metabolites to photoreceptors
*Visual cell layer - outer and inner segments of the photoreceptors, rods for dim lighting, shape and motion (95%) and cones for bright lighting, acuity and colour (5%), cones are concentrated in area centralis. Stacks of discs full of photopigment, mostly rhodopsin. Light –> photopigment change + chemical energy –> electrical activity –> visual cortex
*Outer limiting membrane - separates inner segments of visual cell layer from nuclei of photoreceptors.
*Outer nuclear layer - cell bodies and nuclei of photoreceptors, rod and cone axons and Muller cells
*Outer plexiform layer - branching terminal, synapse with dendrite of horizontal and bipolar cells
*Inner nuclear layer - cell bodies of horizontal, bipolar, amacrine and Muller Cells
*Inner plexiform layer - cell processes from inner nuclear layer synapse
*Ganglion cell layer - single layer ganglion cells, three types
*Nerve fibre layer - axons of ganglion cells, turn at right angles and course to posterior pole where ON exits, unmyelinated. Large retinal vessels.
*Inner limiting membrane - basement membrane, fused terminations of Muller cells.

Question 37

Vasculature

Answer 37

D&C: three main pairs of chorioretinal arterioles and veins, emanating from optic disc. Derived from short posterior ciliary arteries. Veins - larger, darker and less cf. arterioles. D - drain into the venous circle partly embedded in the disc, C - vessels leave at or near edge of disc, leaving central portion of disc free.
Holangiotic - dogs and cats large blood vessels in nerve fibre layer, ganglion cell and inner plexiform layers
Paurangiotic - horses 30 arterioles and venules radiating 360* from disc 4-6mm
Merangiotic - rabbits - horizontal band of vessels
Anangiotic - vasculature within restricted to e.g pecten in birds

Question 38

Phototransduction

Answer 38

light –> bleaches photons –> chemical reaction –> electrical signal at cell membrane –> CN II to brain
Photoreceptors stimulated by light–> nervous impulse modified cells in the inner nuclear layer –> ganglions, axons in nerve fibre layer –> CN II

Question 39

Phototransduction

Answer 39

light –> bleaches photons –> chemical reaction –> electrical signal at cell membrane –> CN II to brain
Photoreceptors stimulated by light–> nervous impulse modified cells in the inner nuclear layer –> ganglions, axons in nerve fibre layer –> CN II
light –> Rhodopsin –> opsin breaks off chromophore (11-cis retinal aldehyde) –> chromophore isomerised to all-trans retinal aldehyde (by product that in the end is shed and phagocytosed in RPE)
Cascade triggered, final step is hydrolysis of cGMP into GMP by phosphodiesterase. Drop in cGMP closes Na channels leading to hyperolarisation which is the neuronal signal.

Question 40

Retinal blood barrier

Answer 40

non-fenestrated retinal blood vessels and tight junctions of the RPE

Question 41

Fundus

Answer 41

Back of the eye ophthalmoscopically: retina, superimposed over choroid and sclera.
Differences in canine fundus - breed and individuals within the breed
Feline fundus less variation than dog

Question 42

Tapetum

Answer 42

k9 - semi-circular to triangular; granular and is yellow, green, orange or blue. Absence of tapetum common in Merle collies and RPE may be +/- pigment in dorsal region.
Feline - highly reflective, triangular; yellow-green, sometimes blue. Absence of tapetum rare in cat, but may be the case in colour dilute cats, thin tapetum may be seen with the choroidal vessels visible.

Question 43

Non-tapetal region

Answer 43

Surrounds tapetal fundus, is dark brown-black in the dog. Paler chocolate coat with light brown iris - choroid vessels may be visible giving tigroid appearance.
Transition between tapetal and non-tapetal fundus appears to be more gradual in longer coated breeds cf. shorter coated breeds.
Islands of tapetal tissue can be see in the tapetal fundus also.
Cats - junction between the two areas distinct

Question 44

Optic disc/ONH

Answer 44

K9 - close or at junction between tapetal and non-tapetal fundus. White due to myelination of fibres prior to leaving globe. Circle, oval or triangular. Edge - smooth, defined or indented.
Myelinated fibres may extend onto retina in some breeds - Golden Retriever.
Centre - small grey area - physiological pit; the origin of hyaloid vasculature.
Hyper-reflective ring or band can be seen as a normal finding around disc - conus, retinal layer incomplete in this area
Feline - small and roughly circular, cupped and has a well-defined edge. Almost always within tapetal region, slightly lateral and ventral to the posterior pole of the eye. Disc is grey and unmyelinated.

Question 45

Electroretinography

Answer 45

Eye is stimulated by light, electrical potential picked up at surface of the globe (corneal electrode). Amplified and recorded = ERG - a summation of potential waves generated by different sites in the retina.
Eye should be adapted to darkness and usually performed UGA.
Rod dominated response.
Uses: prior to phaco, opaque ocular media, early PRA detection, differentiate SARDs from central causes of blindness.

Question 46

Immune responses and the eye

Answer 46

Immune recognises molecules opposed to infectious agents.
Altered immune response due to interactions between immune cells and resident cells in eye; ACAID or Anterior Chamber Associated Immune Deviation.

Question 47

General immune response

Answer 47

1 - Local destruction/inflammation; antigen presentation.
Cytotoxic effects of organism –> tissue destruction and inflammation, resident cells release pro-inflammatory molecules (PGs, LTs, PAF, TNFa, IFNs) –> chemokines which attracts neuts, monocytes, dendritic cells, NK cells. 2 arms - a) non-specific destruction of pathogen, b) initiation of stronger and specific antigen response
2 - Activation of T-helper cells
3 - Clonal expansion
4 - Migration
5 - effector cells eliminate the antigen - antigen specific B cells, and NK cells, macrophages and granulocytes
6 - shut down; definitive signal is antigen clearance

Question 48

Ocular immune system

Answer 48

Conjunctiva associated lymphoid tissue (CALT): collections of lymphoid tissue in the superficial substantia propia, primary centre for ocular surface, only lymphatic drainage of the eye.
ACAID -
1) effectors produced are limited, result of spleen as primary site for antigen presentation a) depression of DTH, B) minimal production of complement fixing antibody c) NK cell function impaired in the eye
2) deviant response is antigen specific
3) deviant response is systemic due to decreased DTH response and complement-fixing antibody, re-presentation of same antigen at other sites does not elicit response
4) antigen presentation at anterior chamber can down regulate existing response, CD8+ suppressor cells are produced.
5) most antigen capable of generating deviant response
6) ACAID influenced by light
7) Spleen is an essential part of ACAID, splenectomy –> ACAID failure

Question 49

Why ACAID?

Answer 49

Prevent excessive inflammation. Cytotoxic lymphocytes eliminate antigen with minimal inflammation. Cons - limits ability to eliminate pathogen.

Question 50

Blood eye barriers

Answer 50

Blood-retinal barrier - endothelial portion: endothelium of the retinal capillaries, non-fenestrated, tight junctions to prevent inward and outward movement. Epithelial portion: RPE. The most permeable point of the BRB is the ONH. Choroidal fluid can pass into the nerve. Choroidal capillaries are highly permeable and pass nutrients readily into the RPE and into the rest of the retina.
Blood aqueous barrier - ciliary vessels have high protein permeability, epithelial = non-pigmented ciliary epithelium, proteins pass into the aqueous by pinocytosis. Endothelial = tight junctions, and contribute to BAB of iris. Free passage of some substances from aqueous into tissues and blood stream. Lens removal can result in increase of passage of some drugs from anterior chamber into vitreous and retina. BAB –> modified aqueous –> proteins and prostaglandins, aqueous flare. Plasmoid aqueous clots easily due to fibrinogen (can see after IO sx). Intraocular surgery –> loss of aqueous –> PGs –> breakdown of BAB. May be reduced with PG inhibitors e.g. NSAIDs.
All types of uveitis - signs attributed to blood ocular barrier disruption.
Acute vascular permeability mediate by histamine, maintained by serotonin, plasmin, kinins, PGs etc. Slugging and stasis of blood, cellular infiltrate - swollen and congested iris