Opthamology Flashcards
Persistent pupillary membrane
Foetal vasculature remnants that arise for the iris collarette and may stay in the iris of reach the cornea causing an opacity of either
Eyelid agenesis
Congenital
Abscess/cellulitis
Developmental
Strep or staph infection
Extra ocular polymyositis
Development Enlargement of the extra ocular muscles Bilated, very dilated pupil If not treated in time -> scarring -> permanently affected eye movement, optic nerve damage 2 weeks steroids
Blepharitis
Developmental
Trichiasis
Hairs from normal location contact the ocular surface
Not healthy for the eye - irritation to ulceration
Various causes
Distichiasis
Often multiple hairs - many present along eyelid margin of upper and lower eyelid
Arise from Meibomian glands
Ectopic cilium
Very irritating to cornea, frequently ulcerating, really early on
Usually associated with meibomian glands but do not ‘sprout’ through the gland opening
Come out through the conjunctiva of the bulbar surface of the eye and are nearly always located in the central upper eyelid of young dogs (
Ectropion
Developmental
Eyelid begins to fold out
Medial lower eyelid +/- canthus - brachycephalic dogs and cats esp pug
Upper eyelid - cockers, hounds etc. heavy eyes and forehead
Lateral upper and lower eyelid, lower canthus - Shar-pei
Lateral lower eyelid - young dogs, medium-to-big, old cats, blepharospasm
Dacryocystitis
Generally FB present but can be idiopathic
Idiopathic - unidentified debris
Infection of the lacrimal sac, secondary to obstruction of the nasolacrimal duct at the junction of lacrimal sac.
Pain, redness, and swelling over the inner aspect of the lower eyelid and epiphora.
Prolapsed gland of the third eyelid
Aka cherry eye - becomes inflamed
Developmental
LPI of the third eyelid
Lymphocytic-plasmacytic infiltrator if the third eyelid aka plasmoma
Developmental
Scrolled third eyelid
Part of T shaped cartilage grows excessively fast and folds
Corneal oedema
Developmental
Loss of epithelium - ulcer
Endothelial damage - increased IOP (glaucoma), inflammation (uveitis, low pressure), primary epithelial degeneration, contact (lens, surgery)
Vascularisation (developing vessels leak)
Corneal ulcer
Developmental
Fluorescein test
When corneal epithelium is missing
May develop red bed of granulation tissue
Corneal granulation tissue is formed by coalescing blood vessels (always arise at limbus and travel to trouble)
Eye muscles
Orbicularis - eyelid closure
Levator palpebral superioris - lift upper eyelid
Mueller’s muscle - supportive, upper eyelid
Nasolacrimal system
Blink brings tears back to medial canthus (puncta to collect tears)
Involves upper and lower punctum, canaliculi, lacrimal sac, nasolacrimal duct. nasal punctum
Jones test
Fluorescein drop on eye and wait for stain to come through nose
3rd eyelid/nictatins/nictating membrane
Leading edge cartiliginous core gland of the 3rd eyelid (30% tears)
Lacrimal gland
Below the dorsolateral orbital mm (70% of tear)
Subconjunctival tissues
Tennon’s capsule and the episclera (contain episcleral blood vessels - meander dont’ branch)
Episcleral vessal pattern
See typically with intraocular disease
Tear film
Lipid layer: on top, secreted by Meibomian glands, avoid evaporation of aqueous part
Aqueous layer: middle and most abundant, water, many solutes, defense mechanisms (immunoglobulin and lactoferrin)
Mucus layer: inner, secreted by corneal epithelial cells and goblet cells of the conjunctiva
Corneal epithelium
Few cells thick, most external layer
Basal cells in the deepest layer will ultimately shed as squamous cells in 1 week cycle
Basal cells act as stem cells
Cornea - Stroma
Thickest part
Several layers of collagen - each layer = lamella
Relative state of dehydration and GAGs keep orderly state of each lamella
Created by keratocytes
Corneal transparency
Achieved by lack of blood vessels and lack of myelin on corneal nerves
Cornea - Descemet’s membrane - surgical emergencies!
During progressive ulceration of the cornea, right before perforation this layer forms a descemetocele
Corneal endothelium
I cell thick layer
keeps cornea dehydrated - action of NaK-ATPase pump - takes fluid for aqueous humour -> stroma -> aqueous humour
Has almost no regenerative capabilities - limited ability to deal with cell loss
Sclera
White fibrous tunic, continuous with limbus and cornea - covered by subconjunctival connective tissue (episclera/Tennon’s capsule) and conjunctiva
Very thin near equator and optic disc
Several holes for nerve and blood vessels
Also contains the lamina - ribosa through which the axons of the ganglia exit the eye to form the optic nerve
Lamina Cribrosa
Hole in sclera which axons of the ganglion cells leave the eye to form the optic nerve
Synechia
Adhesions of the iris to other structures
Occur with inflammation of the iris - uveitis
Posterior synechiae - iris and lens
Anterior synechiae - iris and cornea, sudden loss of aqueous humour eg corneal perforation
Ciliary body
Has own musculature - focusing
When this musculature is contracted during disease can be source of pain
Has capacity to produce aqueous humour
NB involves action of carbonic anhydrase enzyme
Choroid - posterior uvea
Contain tapetum - reflects light inside the eye, better night vision, feeds outer retina (mostly the photoreceptors)
Horses have stars of Winslow all over tapetal fundi (end on capillaries that give tapetal fundus a subtle pin-prick spotted appearance)
Tapetum brighter in carnivores than herbivores
Iridocorneal angle
Outflow of the aqueous humour -> venous circulation (ultimately)
360 degree structure found between the iris and cornea
Zonules
Arise from ciliary body and attach to the lens. Anteriorly and posterior to the lens equator
Retinal epitheliam
Outermost layer
Retinal pigment epithelium (RPE) - nurses photoreceptors it is in contact with
Retina
9 neural layers
Outermost contain the photoreceptors, the rods and cones
Innermost layers contain the ganglion cells and the neural fibre layer which are an accumulation of axons - untimately form optic nerve
Retinal vasculature
Dogs, cats, farmed ungulates
Venules and arterioles that are generally paired
Dorsal, lateral and medial one - smaller ones branch from them
More subtle in horse
Optic nerve head, disc or papillae
Species differences
Various degrees of fluffy myelin
Dog: square/diamond shaped, anostomic branches of the retina on top
Cat: very round, no obvious myelin
Horses: oval, salmon colour
Vitreous body/gel
gelatinous structure fills large space in the psterior segment
Fundic reflex
Reflection of light we see coming back through the pupil
Usually yellow/green but can be orange
Red in atepetal animals
Pharmacology Mydriatic (short term)
Tropicamide
Pharmacology
Mydriatic/cycloplegic (long term)
Atropine
Pharmacology
Antibiotics
Fucidic acid
Chloramphenicol
Gentamycin
Fluoroquinolones (as Ciloxin and Exocin)
Triple antibiotic preparations:
e. g. neomycin, polymixin B, bacitracin
e. g. neomycin, polymixin B, gramicyclin (more common in USA)
Pharmacology
Steroids
Dexamethasone phosphate
Prednisolone acetate
Pharmacology
Immune-mediator
Optimmune
Pharmacology
NSAIDs
Flurbiprofen
Diclofenac
Pharmacology
Antihypertensive
Ca channel blocker (timolol - in Timoptic and Cosopt) Carbonic anhydrase inhibitors (dorzolamide - in Trusopt and Cosopt) Prostaglandin analogue (Iatanoprost)
Canine Lymphocytic-Plasmocytic Infiltrative
AKA corneal pannus, chronic superficial keratosis (CSK)
Especially greyhounds/lurchers, sunny/snowy countries
Cellular infiltrative and vascularisation +/- pigment
Dorsolateral corneoconjuctiva usually affected first
Primary immune mediated disease
Diagnosis: cytology
Treatment: Proxymetacaine 0.5% (topic anaesthetic)
-OOA: 30-60s
-DOA: 15-30mins
-Decrease blink, increase dryness, ulcer formation
Feline eosinophilic keratitis (EK)
also rabbits and horses
(Rabbits and horses)
Corneal inflammation with eosinophilic keratitis
Primary, immune-mediated, idiopathic
Fluorescein stain uptake - can be confused with ulcer
Dorso-lateral corneoconjunctival area normally affected first
Cellular infiltrate with: neutrophils, plasma cells, clusters of eosinophils - white/pink in the form of plaque/clumps - lumpy cottage cheese
Treatment of EK and LPI
Topical use of immune modulators 4xday
Taper after many weeks (week 1: 4xd, weeks 2-4: 2xday etc)
Lowest dose possible for long term maintenance
Canine dry eye (KCS - keratoconjunctivitis sicca)
Primary KCS:
History: recurring persistent ocular surface problems
Signs: conjunctivitis, surface dullness, mucus discharge, ulcers, low STT-1
Treat: topical ciclosporin bid/sid, long term, Optimmune, surgery (C;CT, conjunctival pedical graft)
Usually primary and bilateral
Acute: young and older dosg, less mucus and less hyperema
Chronic: scarring, pigment changes, vascularisation
Other causes: Evaporative, anaesthesia and sedatives, Drug-related (sulfonamide, atropine), Neurogenic (affected nerve supply to lacrimal gland)
KCS improvement
If positive changes in at least 3/5
- Mucus production
- Redness
- Comfort
- Keratitis
- Tear readings
Lipid infiltrate
Reflective white crystals in superficial stroma
Primary form: most common, no vascularisation, several breeds eg CKCS, huskies
Secondary: degeneration, vascularisation, associated with chronic corneal problems and hyperthyroidism
Might be removed if affecting sight - not painful
Usually slowly progressive
Calcium infiltrate
Chalky non-reflective white crystals in superficial stroma - may adapt reticulated pattern
Secondary: (degeneration) associated with chronic, corneal problems, accompanied by vascularisation
May need to be removed via keratectomy if painful - can spiculate -> breaks through epithelium - painful
Difficult to tell apart from lipid in early cases
Corneal scar
Associated with chronic keratitis, ulceretive keratitis and surgery
May be accompanied by residual vascularisation and pigment
Whitish discoloration: non-reflective, non-crystalline, dull
Corneal abscess
Accumulation of WBCs
Enzymes can lead to rapid collagen melting
Not a pocket of fluid - cannot be drained
Pigment keratosis - pugs
Associated with medial canthal and lower eyelid entropion
Overexposure of the cornea and conjunctiva (macropalpebral fissure: big space between the eyelids)
Occasionally associated with dry eye (KCS)
Can be sight impairing by 2yo
Feline corneal sequestrum
Idiopathic and spontaneous - associated with chronic imitation, breed disposition (Persians, Himalayans)
Common in central cornea, medially with medial lower eyelid entropion
Progressive lesion - light tan discoloration of superficial stroma, intact epithelium
Pigment: melanin, iron, porphyris
Darkening of lesion, loss of epithelium, pain, vascularisation
Hardening and deepening of the lesion
Treat: surgically (keratectomy, bandage lens, tarsorrhaphy OR superficial keratectomy and grafting)
High recurrence rate
Tear readings (STT-1)
15mm/min and above - normal
10mm/min and less - low
First step of an opthalmic exam
1 min in each eye
Changes in the AC
Aqueous flare: Tyndall effect Keratic precipitates Hyphema - blood Hypopion - pus Posterior synechia and anterior synechia Anterior lens luxation Anterior presentation of the vitreous
Nuclear sclerosis vs cataracts
Direct opthalmoscopy
Nuclear sclerosis is transparent
Cataracts appear black
Tonometry
Glaucoma vs uveitis
IOP range is 12-22(24) mmHg
Uveitis
Inflammation of the uvea
Increases uveoscleral outflow and decrease IOP
Endothelial cell separation resulting in leakage of blood components - into the AC as keratic precipitate, hypophion, hyphaema, fibrin - around the lens as snow banking
Glaucoma
High IOP
Primary and secondary forms
Neurodegenerative disease: neural retina, ONH, leads to blindness, requires close monitoring
ICA (iridocorneal angle) closure/clogging - increases IOP
Primary or secondary
Miosis
Iris spasm with resulting pain (pupil constricts)
opposite = mydriasis
Development of PIFMs (periridal fibrovascular membranes)
Grow over iris and in pale irises are visible as rubeosis iridis
May lead to bleeding in the eye - hyphema
Closure/blockage of the ICA - a type of secondary glaucoma
Inflammation and infection in the retrobulbar area
- Stick injuries
- Originating from a middle ear abscess
- Conjunctival FB that travel posteriorly
- Through general circulation
- Blunt trauma: bleeding haemorrhage
- Parasitic diseases
Neoplasia in the retrobulbar area
Anything in the orbit with the eye
Extraocular muscles, optic nerve (meninges. CSF), sympathetic and parasympathetic innervation, sensory nerves, blood vessels, lacrimal gland (dorsolaterally and gland of 3rd eyelid), zygomatic salivary gland, connective tissue
Epiphora
Increase tearing: Trigeminal (CN V) irritation: corneal ulcer, FB
Drainage problems: prolapse of the gland of the nictitans membrane, eyelid abnormality: entropion/ectropion. blockage of nasolacrimal system
Removal of eyelid masses
If affects less than 25% eyelid margin - wedge resection
Closure in 2 layers: subcutneous, skin with figure 8
More than 25% - referral
Entropion
After eyelid opening at 14 days - tacking sutures - temporary
Puppies -> young dogs - definitive therapy
Acquired: due to eyelid and skill extreme confirmations, elderly dogs and cats due to laxity of tissues and loss of retro-orbital fat
Symblepharon
Kittens, FHV-1 breaks epithelium on surface
Adhesions: nictitans membrane to conjunctiva of eyelid, eyelid to cornea
Causes of uveal problems
Infectious: Viral (FeLV, FIV), parasitic (Toxoplasma, Leishmania), Fungal (Cryptococcus), Bacterial (pyometra)
Immune-mediated: uveodermatologic syndrome aka VKH: Vogt-koyanagi-Haradi syndrome)
Neoplastic: Lymphoma, metastatic adenocarcinoma
Complicated ulcer: reflex uveitis, eye reacting to abnormal cornea
Treatment for uveal problems
Systemic anti-inflammatories: NSAIDs (caprofen, meloxicam), steroids (prednisolone)
Topical anti-inflamms (if no ulcer): steroid eyedrops (4xday prednisolone acetate or dexamethasone phosphate), cycloplegics (tropicamide)
Cataracts
Opacities of the lens impedes light transmission
Phacolytic - intact lens capsule - in cataracts
Phacoplastic - rupture of lens capsule - trauma
Can be sequel to uveitis - poor nourishment of the lens, altered chemistry of the aqueous humour
Only caused blindness when complete
White with distant direct opthalmoscopy
Dark with retroillumination
Vitreal diseases
Doberman, Pinscher, Schnauzer
Persistent hyaloid artery and primary vitreous
Usually young patients
Retinal dysplasia
Inherited in certain breeds (CKCS, ESS)
3 main types: retinal folds, geographic, retinal detachment (most severe)
Can lead to blindness
Progressive retinal atrophy
Inherited, certain breeds, genetic test available
Night blindness progressing to day blindness
Often starts at middle age, leads to cataracts (end stage)
No treatment, not painful
Retinal toxicity
High dose enrofloxacin in cats
Even at current recommended doses
Can also cause neuro clinical signs
SARDS (sudden acquired retinal degeneration syndrome)
Acute/subacute vision loss PLR may/may not be present Opthalmic exam otherwise unremarkable Diagnosis: ERG (electroretinography) IMR (immune-mediated retinopathy) similar to SARDS
Retinal detachment
Neuro-retina detaches from the retinal pigment epithelium
Two types: Inflammatory (retina is pushed by fluid -Bullous), Disinsertational (retina loses peripheral attachments - Rhetmatogenous)
Optic neuritis
Meningoencephalitis of unknown origin/aetiology
Infectious: distemper, ehrlichia, cryptococcus
Hyperaemia of the papilla, vascular congestion. peripapilary haemorrhages
Optic nerve neoplasia
Meningioma (most common)
Collie eye abnormality
Combo of two disease: choroidal hypoplasia (genetic test available) and optic nerve head coloboma
Can develop retinal detachment, hyphema or vitreal haemorrhage
Microphthalamia from birth
Usually bilateral
Rarely too striking
May be accompanied with other ocular defects e.g. cataracts
Micropthalamia from globe destruction
Sequelae to inflammation, Phthisis Bulbi (severe uveitis)
Targeted surgical destruction (excessive laser cycloablation)
Chemical abalation - injection of gentamycin into vitreal cavity
Primary glaucoma
Inherited, more likely to be(come) bilateral
Goniodysgenesis (abnormal ICA)
2 forms:
- Open angle (people, insiduous onset)
- Closed angle (dogs, unilateral, eye nearly exposed, very painful, rapid onset, likely to happen in other eye)
Secondary glaucoma
Something affected the ICA (outflow from eye)
Blood, fibrin, PFIMs, WBCs, Neoplasia (primary and metastatic), Inflammation (uveitis) - cataracts, Infectious (FIP, leishmania), Hyphema, Lens luxation, Intraocular/metastatic neoplasia, Trauma
Dogs, horses, cats
Feline glaucoma
Primary form in Burmese
Often secondary and associated with uveitis
- FIV, FeLV, FIP and toxoplasma
- Idiopathic (most common)
Feline glaucoma - clinical signs
Moderate IOP and higher
Mid-dilated, non-responsive pupils (+/- anisochoria)
Conjunctival and episcleral vessel congestion
+/- vision problems (-ve menace response/vision maze test)
High IOP on tonometry (do a cure over 30 hours - best)
Len luxation
Phacodonesis - lens jiggle
Iridodonesis - iris jiggle
Anterior presentation of vitreous mucus like strand floating in AC
Posterior luxation:
- Deep AC: iris normally rests on lens and so bow forward, if lens falls backwards the AC deepens
- Cataract formation, lens induced uveitis, lens adhesion to the retina
Anterior luxation:
- Lens falls forwards though pupil
- Pupil block glaucoma
Inherited disease: terriers esp
Corneal healing by sliding
1-2mm/day, centripetal movement
Depends on corneal health - disease will interfere with Existence of limbal basal stem cells
Age and species
Limbal stem cells act as a barrier to conjunctival overgrowth
Keratocytes - build up collagen and GAGs
Monocytes, macrophages, neutrophils, leukocytes - clean up and destroy
Making a healing plan
Re-examine based on findings (3d, 5d)
Postive changes seen? Expectations?
No? Where is the imbalance?
Common problems: Tear film (quantitative or qualitative)
Eyelids and 3rd eyelid - problems with blinking
Repair process - brachycephalic effect, secondary infection, ‘melting’
Taking to long to heal
Lack of re-epithelialisation
Stromal wall is deepening
Stromal is devitalising (melting)
ACT! SOMETHING IS WRONG
Tarsorrhaphy
Horizontal mattress suture through eyelids
Use stents made of IV tubing to protect eyelids
With/without bandage lens
Sutures engage the holding layer (tarsal plate)
Descemetocoele
Right before a perforation happens
Partial bulging of Decemet’s membrane
- does not uptake fluorescein
- wall of oedematous stroma around it does
Clear centre - no stroma to have oedema, may appear black
Surgical emergency
CLCT for central ulcers
Corneolimboconjunctival transposition uses clear peripheral cornea
Allows for clearer visual axis after healing than other techniques
Conjunctival pedicle graft for peripheral ulcers
Slightly faster to perform than CLCT
Does not clear much over time but not that important peripherally
Superficial chronic corneal epithelial defects (SCCEDs)
Loose epithelial edges - underrunning of fluorescein - pulse saline test (local anaesthetic)
+/- corneal oedema, ocular pain, vascularisation
Always rule out other causes of ulcers
Treat: debride, grid keratotomy/superficial scrape (not in cats), keratectomy, diamond burring
FHV-1
Lives in trigeminal ganglion and corneal tissue - only infection that causes an ulcer
Associated with cat flu and symblepharon
Ulcer can look like a dendrite or geographic
Feline Acute Bullous Keratopathy
Very new Acute development of corneal oedema - cornea becomes soft - risk of melting and perforation ensues Rapid referral
Anterior uveal cysts
Not always a problem unless numerous
Remain behind iris, push it forward, close ICA, cause glaucoma (Golden Retrievers,Great Dane)
Accumulate in AC, over visual axis
Can disturb patient - fly catching behaviour
Anterior uveal melanoma
Benign melanosis leads to AUM in cat
Treat: usually enucleation, metastasis is uncommon and usually happens years later
Look at speed of progression and age of patient
Conjunctiva
Continuous with skin of eyelid
Stratified squamous epithelium
Goblet cells: secret deepest, mucus, layer of tear film which adheres tears to surface of globe
Cornea - layers
(Conjunctiva) Bowman's capsule Thick transparent fibrous layer Descernet's membrane Endothelium
The aqueous
Nutrient for lens and cornea - maintain IOP (25mmHg)
Replaced several times/day (2ml/min)
Blockage: no nutrition for cornea -> glaucoma *especially canal of Schlemm)
Lens
Deriviative of the optic placade Onion structure of lens fibres - live cells Cuboidal epithelium Capsule, with rostral and caudal sutures Softer cortex, firmer nucleus
The vitreous
Secreted by ciliary until mature
Gelatinous: water, hyaluronic acid and collagen
Hyaloid canal: remnant of blood vessels present during development
The uveal tract
Choroid:
- Tapetum lucidum (inner - nearest retina)
- Vascular
- Black/connective (outer - nearest sclera)
Ciliary body: aqueous, vitreous, lens accommodation
Iris: for pupil size (iridic granules)
Adnexa
3 layers of tear film
- Deep mucus: from conjunctival goblet cells - adheres tears to conjunctiva
- Middle aqueous: from main and 3rd eyelid lacrimal glands, cleanses, IgA, oxygenates, fills optic defects
- Superficial oily layer: from tarsal glands (modified sebaceous) prevent evaporation)
Eyelids
Outer layers: palpebral skin, sweat glands, ciliary glands, sebaceous glands and striated muscles (levator palpebral and obicularis oculi)
Inner layers: tarsal plate, dorsal and ventral tarsal smooth muscles, palpebral conjunctiva and tarsal (meibomian glands)
Bulbar conjunctiva: blends with corneal surface and form conjunctival sac
Lacrimal gland
Dorsolateral aspect of the eye on the lacrimal fossa of the frontal bone
Produces most of lacrimal fluid
Innervated by sympathetic nerves form dorsal cervical ganglion
Parasympathetic innervation: arise in facial nerve -> synapse in pterygopalatine ganglion -> via maxillary branch of trigeminal -> lacrimal gland
Sclera
Tough fibrous coat - attachment for the extra-ocular muscles
Perforated at the posterior aspect by optic nerve at lamina cribosa
Most anterior portion of sclera bulges to form the cornea
Corneal-scleral junction forms a trabeculae meshwork which contains canal of Schlemm
Retina
10 layers of cells
- Outermost is pigment retinal epithelium upon which photosensitive layer rests
9 neural layers:
- Outermost contain photoreceptors (rods and cones)
- Innermost contain ganglion cells and the neural fibre)
Cataracts
Structural alteration in layers of lens causing opacity
Blood supply to eye
Opthalmic artery - branch of internal carotid
- Central artery to retina
- Short posterior ciliary artery to choroid
- Large posterior ciliary artery to ciliary body and iris
- Anterior ciliary artery arising from vessels of rectus muscles
Carnivore orbit
Open (unlike in herbivores)
Incomplete bony orbital rim and ventral part of the orbital cup is made of soft tissue that is continuous with the soft tissues of the posterior oral and oropharyngeal areas and not bone
Periorbita
Connective tissue that extends from the periosteum of the orbital rim to the sub-conjunctival tissues of the eye forming a connective tissue bridge between the 2 structures
Surgical landmark during transpalpebral enucleation
Medial canthus and medial canthal ligament
True, wide, very short ligament that tightly adheres the medial canthus to the orbital rim medially
Lateral canthus and lateral canthal ligament
Not a true ligament
More of a long tendinous - connective tissue band
Cilia
Lashes
- None of the bottom of small animals or equine
- Dogs and horses have lashes in the upper eyelids
- Cats have hairs that resemble lashes
Vibrissae
Long hairs attached to sensitive touch receptors
Horses have vibrissae around their eyes
Meibomian glands
Embedded in tarsal plate, all along eyelid length (upper and lower)
Opening at eyelid edge - secrete meibomium (oily product spread onto tear film)
Material can become impacted within the gland which can burst and lead to granuloma formation
- Chalazion gland can beceom infected -> internal stye (internal hordeolum)
Glands of Zeisse Moll
Less important gland
Skin hairs and cilia
When infected - external stye (external hordeolum)
Tarsal plate
Poorly developed fibrous structure (4-5mm wide) running along eyelids length - eyelid rigidity
Surgical landmark - several eyelid procedures
Holding layer of suturing techniques - figure of 8
Holds meibomian glands
Conjunctival lining
Upper eyelid: Conjunctival lining folds and turns around to create fornix before it reaches the globe and it fuses with the eye at the limbis
Lower eyelid: ventral fold between eyelid and lower eyelid
Then cover 3rd eyelid and after this forms another fold - ventral fornix between 3rd eyelid and the globe
Then covers ventral globe and fuses with eye at limbis
Iris
Constrictor and dilator muscle to open/close pupil
Constrictor (stronger) - during disease processes, it can be contracted (miosis)
Area of iris next to pupil - pupillary zone
Peripheral area - ciliary zone
Area between - iris collarette
Lens - suture lines
At confluence of the lens fibres, in the shape of a Y in the anterior part of the lens and an upside down Y in the posterior part of the lens in cats and dogs
Lens cortex
Youngest part of the lens produced by the lens epithelial cells as they form fibres throughout the life at the lens
Fibres will lose their cell nuclei and form part of the nucleus which is more and more compacted with age (harder and blueish - nuclear sclerosis)
Retinal vasculature
Dogs, cats, farmed ungulates - contain venules and arterioles that are generally paired
Dorsal, lateral and medial ones - smaller vessels branch off
Much subtler in horses - few short blood vessels emanating from the optic disc only
Optic nerve
Structure that arises from the optic disc/papilla and contains fibres from the nasal (medial) and lateral retina
Fundic reflex
Aka tapetal reflex
The reflection of light in response to an external light
Atapetal animals have a red reflex
Visual signal pathway
Rods and cones Inner retina Ganglion cells Nerve fibre layer Optic disc Optic nerve Optic chiasm Lateral geniculate nucleus Optic radiation Visual cortex
PLR pathway
Rods and cones Inner retina Nerve fibre layer Optic disc Optics nerve Optic chiasm Optic tract Area of the pre-tectal nucleus Parasympathetic fibres of the oculomotor nerve with ciliary ganglion to pupillary musculature
Secretory control of lacrimal glands
Mostly parasympathetic
Facial nerve -> pterygopalatine fossa -> travel with and are distributed by trigeminal
Blepharospasm
Eyes closed tightly can lead to secondary entropion -> spastic entropion
- 1 drop of proxymetacaine: if entropion persists, surgical correction (if not, investigate source of pain)
Symblepharon
Kittens, FHV1 breaks epithelium on surface
Adhesions: nictitans membrane to conjunctiva of eyelid
Adhesions: eyelid to cornea
Causes of uveal problems
Systemic hypertension
Infectious: viral (FeLV, FIV), parasitic (Toxoplasma, Leishmania), fungal (Cryptococcus), bacterial (Pyometra)
Immune-mediated: uveodermatologic syndrome (aka VKH: Vogt-Koyanagi-Haradi syndrome)
Neoplasia: lymphoma, metastatic adenocarcinoma
Complicated ulcers: reflex uveitis, eye reacting to abnormal cornea
Causes of cataracts
Inherited: breed, rarely congenital
Congenital: rarely inherited, always nuclear
Trauma: FB, cat scratches, might need removal of the lens via phacoemulsification and suture the corneal defect
Metabolic: Diabetic dogs, increased glucose concentration (sorbitol cannot leave lens)
Nutritional: uncommon, inappropriate milk replacements
PRA (progressive retinal atrophy): retinal degeration -> releases toxins (glutamate) -> cataracts
Senile: generally affect cortex, wedge shaped
Extraocular polymyositis
Bilateral protruding eyes
Very dilated pupils - optic nerve damage
2 weeks of cortical steroid
If not treated in time - scarring - permanent effects on oular movement
Buphthalmia - enlarged eye
Increased IOP - glaucoma (primary or secondary)
- Conjunctival and episcleral vessel congestion
- Corneal oedema
- Haab’s striae: stretch marks, breaks in Descemet’s membrane
- Zonular tears
- Corneal over exposure
Control IOP
Remove cause if secondary (treat inflammation, remove lens from AC, remove eye)
Anti-hypertensive drugs ( beta blockers, carbonic anhydrase inhibitors, prostaglandin analogue)
Marcus Gunn sign
Pre-chiasmal, unilateral, afferent lesion
Retina, optic nerve, optic nerve head
Facial nerve paralysis
Viral, otitis media, ear canal avulsion, ear canal neoplasia, TECA with LBO, idiopathy, part of a polyneuropathy
- Loss of blink
- Cats: chronic otitis media treatment
Treat: tarsorrhaphy for 1-2m
