Small animal Ophthalmology Flashcards
What makes up the uvea?
Iris
Ciliary body
Choroid
Path of aqueous humour?
Produces constantly by ciliary body
Drains through pupil into anterior chamber
Drained by drainage angle through pectinate ligaments
Determines intraocular pressure
Eye anatomy photo
Anterior space = between cornea and iris
Tarsal plates with tarsal glands
Conjunctiva lines lid and reflected back onto eye surface and continuous with cornea epithelium
Tapetum occupies upper half of back of eye sat behind retina
Retinal veins anastomose on surface of optic disc
What is the third eyelid? Appearance? Function?
Giant fold of conjunctiva Underside very hyperaemic due to lymphoid follicles May be pigmented Functions: - produces a part of the aqueous part of tears - surface protection - tear film distribution - immunological
Which animals don’t have a tapetum?
Pigs and rabbits
Horse eye anatomy differences?
Optic nerve more ventral - tapetum never reaches optic nerve
Eye flattened - not spherical
Retinal blood supply only around optic nerve (need rest of supply from choroid)
Granula iridica at top (and bottom) of pupil
Pectinate ligaments laterally and medially (grey lines) = drainage angle of aqueous
Ruminant eye anatomy differences?
Massive retinal blood vessels
Flattened eye
Bright tapetum
Rabbit eye anatomy differences?
Optic nerve head more dorsal
Massive retina and lens
Retinal blood vessels only run horizontally (may see choroidal vessels above and below)
Tooth roots in orbits
How does the pupil constrict and dilate?
Circular constrictor muscle - parasympathetic control (split into two parts in cats, medial and lateral parts stay put in horse)
Radial dilator muscle - sympathetic control
What is a mitotic and mydriatic drug?
Mitotic = constricts pupil Mydriatic = dilates pupil
What disinfectant is safe for the eye? Why antiseptic solution, not a surgical scrub solution? When would you just use saline?
Non lathering povidone iodine 1:50
Chlorhexidine is an irritant
Surgical scrubs are lathering
Saline if perforated eye as iodine is toxin to inside of eye
What suture material to use for eyelid surgery?
Absorbable
E.g. 5/0 vicryl in dogs, 6/0 vicryl in cats
What is the function of the tarsal plates? Benefit for eyelid surgery?
Stiffens the lid marginal areas
Contains tarsal glands
Secretes lipid portion of tears
Hold sutures much better than adjacent tissues
What is distichiasis? Is it a problem? Treatment options?
Hairs growing in an abnormal site from the tarsal glands within the tarsal plate and emerging at the lid margin Don't cause ulcers, some dogs not bothered but some are and need treatment No easy treatments Treatment options: - plucking - electrolysis - cryo - tarsoconjunctival resection
What are ectopic (conjunctival) cilia? Are they a problem? When to suspect? Treatment?
Emerge from the conjunctival surface and impinge directly on the eye (tiny stubble like hair)
Less common than distichiasis but far more painful and do cause shallow ulcers
Beware in young dogs (especially bulldogs) with a severely painful closed eye and no obvious cause
Treatment: easy - cut out! Good prognosis
What is entropion? What problem can it cause? Treatment?
In rolling of the lid margin so skin hairs impinge on eye (trichiasis)
Lateral 2/3 of eye margin - look for loss of lid margin
Can cause large masses of granulation tissue on eye with chronic hair contact - prognosis good once abrasion is removed
Entropion can be intermittent - test by turning lid in and see if dog flips it back
Treatment:
- skin and muscle excision (Hotz-Celsus procedure)
- lift lid up with finger
- first incision 2mm away from margin, second 3-5mm away tapered at both ends
- place middle suture first
- place deep suture if think area will be permanently wet to prevent wound breakdown (uncommon, lids heal well)
- degree of ectropion post-op is desirable, sorts out after couple of weeks
Define trichiasis?
Hair rubbing on eye
Should you clip for eye surgery?
Enucleation - full surgical clip
Eyelid surgery - surgical field only
Corneal, conjunctival or third eyelid surgery - no clipping
Innervation of the eyelids?
Orbicularis oculi muscle (VII nerve) encircles the lid margin to close the eye
Levator palpebrae superioris muscle (III nerve) and Muller’s muscle (smooth muscle, sympathetic) - raises upper eyelid
Why are SharPeis special? When to intervene?
Upper and lower lid problems
Can show lower lid entropion at a very early age
Downward angle to upper lid lashes due to convexity of the lid (most common problem in older SharPeis)
Excision surgery not advised in young puppies as may overcorrect
Can use tacking sutures as temporary measure until mature - but cut in and migrate away
When mature most need skin-muscle excisions on all four lids
What is ectropion? Problem?
Out turning of lid margin with conjunctival exposure
Mostly not a problem
Extreme = diamond eye - can result in entropion on upper and lower lateral edges - need to correct to get hairs out of eyes
What is upper lid trichiasis/entropion? Is it a problem? Treatment?
Not true entropion but definitely trichiasis
“Middle aged cocker spaniel upper eyelid syndrome”
Laxity of upper lid lashes which turn downwards and abrade eye causing discomfort and debility
Need Stades procedure rather than standard skin-muscle excision (not day one skill)
Eyelid “warts”/papillomas - significance?
Common and may remain unchanged for years
Check inside of lid and watch for growth and change
What is the most common eyelid tumour in the dog? Significance? Treatment?
Sebaceous adenoma/epithelioma
Arises from tarsal glands
Well defined mass requiring minimal clearance
Very low metastatic potential
Can bleed/ulcerate/irritate
Treatment - full thickness excision (check inside of lid):
- aim for perfect eyelid margin apposition
- knots must never contact the eye
- pentagonal by incising either side of tumour and then create a point or V incision if small
- remove as little lid margin as possible
- engage tarsal plate with at least one suture
- don’t use sliding grafts
- suturing conjunctiva as a spare layer risks knots contacting the eye - figure of 8 suture better at top and then simple interrupted
Significance of persistent scratching of the eye with periocular hair loss?
May be pruritus rather than eye pain
Scratching not common clinical sign for eye pain
What is cherry eye? Which breed mainly? Treatment options?
Prolapse of the nictitans gland of the third eyelid Mainly bulldogs Burying but preserving the gland (pocket technique): - preserves function - relatively expensive - failure rate Excision of the gland: - cheap - comes with guarantee won't come back - 30% of aqueous tear capacity lost
How to do the pocket technique for cherry eye?
2 curved incisions around gland and sutured over it
Adequate depth of the incisions to give a secure suture line (mucous membranes alone is too thin)
Blunt dissection through the incision closer to the eye to create some space for the gland
Strip a small area of conjunctiva off the apex of the swelling to allow adhesions to form
Tie first knot on outside
Problems with the third eyelid? Can you excise the third eyelid?
Cherry eye
Scrolling of the cartilage - far less common
Foreign bodies trapped underneath - turn out and removed (LA or sedation)
Only justified to excise third eyelid for neoplasia (especially cats, do badly without)
What conjunctiva of the eye is there? Normal colour?
Palpebral and outer third eyelid conjunctiva - dense pink Bulbar conjunctiva (covers globe) - white with discrete blood vessels
Normal appearance of eye mucus?
Off white-grey and darkens with time (may dry as black crusty lumps)
May accumulate in large amounts in dogs with deep medial pockets
Non specific conjunctivitis appearance? Treatment?
Diffuse redness without corneal, pupil or vision changes
Antibiotic responsive
Clears up in a few days
Never use oral antibiotics
Don’t do C+S
Occasionally do a snip biopsy of ventral conjunctiva in difficult cases
Fusidic acid - only effective against Staph
Broad spectrum drops
If persists then must be:
- something keeping it going (most commonly due to dry eye)
- or not conjunctivitis
Causes of a red eye?
Conjunctivitis Corneal ulcer or trauma Glaucoma Dislocated lens Uveitis Dry eye
Causes of dry eye in the dog? Which one causes the majority and how does it present?
Immune mediated inflammation of the glands with secondary loss of function (majority) - natural untreated pattern is gradual decline in tear values Sulphonamides Neurological (dry eye-dry nose syndrome) Trauma Distemper Chronic conjunctivitis/lid abnormalities Endocrine abnormalities
What produces and drains the tears?
Lipid part - tarsal glands
Aqueous part - lacrimal and third eyelid glands
Mucus part - conjunctival goblet cells
Tear duct openings on inside of medial upper and lower lids (lower more important) - join to form single tear duct (elongated Y) to nose
Clinical signs of dry eye?
Chronic conjuncitivits Dull appearance of ocular surface Mucopurulent discharge - tenacious and adherent Discomfort Corneal ulceration Corneal vascularisation and pigmentation
Diagnosis/monitoring and treatment for dry eye?
Schirmer tear test strips put on lateral lower lid for one minute (hold lids together) 20mm +/- 5 = normal 15mm = minimum 10-15mm = moderate dry eye <10mm = moderate to severe dry eye Re-measure each time comes in
Tear stimulants (for life):
- optimmune licensed (expensive, takes 3-4 weeks to reach maximum effect)
- tacrolimus skin ointment (expensive tube but lasts 6 months)/drops
Tear film replacements (poss for life):
- carbomer gel
- viscotears
- artelac nighttime gel
Reduce cyclosporin/tacrolimus treatment very cautiously (problem doesn’t usually go away)
What is follicular conjunctivitis?
Numerous lymphoid follicles appear as circular raised pink swellings especially in the ventral fornix
Relatively mild condition with mild or no irritation only and no purulent discharge
Aetiology etc uncertain
What does poor lacrimal drainage of the eye cause? How to test? What to do if not draining?
Painless “wet eye”
Fluorescein drainage test
Flushing:
- local anaesthetic +/- sedation
- flush upper duct first, watch lower duct
- nose down, VN on nose watch
- then occlude lower duct and flush again to test flow to the nose
Tear ducts may be non patent - can cut open (but painless problem so not essential to fix)
What is the cornea? Layers?
Transparent window, continuous with sclera
4 layers: epithelium, collagen, endothelium, descemet’s membrane
What is a corneal ulcer? are they important? Do they heal well? what can it progress to?
A full thickness defect in the epithelium
Must take seriously as cause pain and potential for progression
Corneal epithelium heals rapidly if favourable conditions - heals from perimeter inwards
Corneal stroma (collagen) is susceptible to proteolysis/melting/keratomalacia by enzymatic destruction - turns superficial damage into a deep ulcer
Proteolytic enzymes may be released by:
- gram -ve bacteria
- inflammatory cells
- corneal cells
Enucleation needed if ulcer perforates (everything prolapses forwards, even if heals will have no vision)
Signs of a perforated corneal ulcer?
Sudden pain
Convex protrusion of brown/black tissue with overlying fibrinous material
Blood from the eye
Larger and more central is worse
Diagnosis of corneal ulcers?
Fluorescein = orange dye which turns green in alkaline conditions
Lipophobic so runs off an intact epithelium
Hydrophilic so adheres to exposed stroma
Flush with saline to avoid false positives (won’t flush it out of genuine ulcers)
Dark blue light helps
What does it mean if there’s a clear area in the middle of a corneal ulcer?
Descemet’s membrane doesn’t stain with fluorescein and doesn’t become oedematous so stays clear at all times
Worrying as very thin last layer of cornea - close to perforating
Causes of corneal ulcers?
Direct mechanical damage: eyelids, trauma, foreign bodies
Unhealthy superficial environment: dry eye, poor blink
Inherent corneal defects: indolent (boxer) ulcer
Unknown or multifactorial: brachycephalics
Which types of dog breeds have a higher incidence of corneal ulcers? Why are they worse?
Brachycephalics
Spread and deepen faster
Often require surgery
Potentially including enulcelation
Medical therapy for corneal ulcers? What not to use?
Topical antibiotics (q4-6h if needed):
- chloramphenicol if simple and non infected superficial ulcer (=prophylactic use): broad spectrum, safe for epithelial cells and good penetration, won’t work if pseudomonas
- ofloxacin if infected
- gentamicin if pseudomonas
- (fusidic acid licensed for conjunctivitis so higher on cascade but narrow spectrum)
Lubrication - covers exposed nerve endings so eye more comfortable
Systemic analgesia e.g. NSAIDs
Parasympatholytic for cycloplegia (as reflex uveitis -> pain):
- atropine most effective (contraindicated if dry eye as can exacerbate, use cyclopentalate instead)
- cyclopentalate
- tropicamide
- contraindicated if glaucoma
If need systemic antibiotics: tetracyclines (esp. if melting ulcer)
Serum if melting ulcer (and hospitalise, may need surgery)
Not:
- not topical steroids as can cause keratomalacia and inhibits healing
- not topical NSAIDs as delays healing
- not local anaesthetic for pain relief as only lasts 1 hour, toxic to epithelium and prevents blinking
When is corneal ulcer surgery needed? Methods?
May be required for deep ulcers - eye becoming fragile/weak due to stromal loss, risk of perforation
Specialist:
- conjunctival pedicle graft
- corneo-conjunctival transposition (strip of cornea, limbus and conjunctiva advanced over defect, better for future vision)
Third eyelid flap - may help in comfort and healing but mostly not necessary or not enough and interferes with monitoring
Advantages of natural healing (non surgical) for corneal ulcers?
Less painful
Better end result
Cheaper
Simpler
Why are blood vessels important for corneal ulcer healing?
They regress when healing is complete
Vascularised cornea does not get infected, melt or perforate
What are indolent “Boxer” ulcers? Presentation? Breeds?
= Spontaneous chronic corneal epithelial defects (SCCEDs)
Breeds - boxers, corgis, staffies
Epithelial only - no concavity/crater
Loose epithelium (under-run edges)
Stain well with fluorescin (runs under epithelium at edges)
Vascularisation varies from none to extreme
Very different treatments to normal corneal ulcer
Generally don’t get infected, deepen or melt
Don’t heal by themselves or with medical treatment alone, minor surgery always needed!
Only ulcer to ever debride!!
Surgery and treatment for indolent “Boxer” ulcers?
Anaesthesia - LA drops +/- sedation, or GA
Debridement to remove loose epithelia and disrupt hyaline layer
Use a cotton bud or scalpel blade (sedation needed), plus:
- nothing
- grid keratotomy: must be very fine scratches, barely visible
- diamond burr: can use contact lens for pain relief
- superficial keratectomy: heals very well, most scarring, most expensive, reserved for stubborn cases
- TKP
Cotton bud debridement only in cats as grid etc risks sequestrum
Supported by:
- topical b/s antibiotics plus lubricants
- contact lens
- third eyelid flap
Debridement must be thorough - rub firmly, and keep going until stops, if comes off it needs to come off
Only repeat if loose edges again
This is dangerous for stromal ulcers!
What are the two types of corneal foreign bodies?
Adherent to surface:
- shallow curvature
- embedded in/on surface with little penetration
- can be wiped off or squirted off with saline under LA
Intracorneal = thorns:
- easier with a reasonable amount protruding
- microsurgical problem in many cases
- needle(s) for removal (better than forceps)
What is pigmentary keratitis?
Common non specific response of the cornea to a variety of insults
Common in medial quadrant of brachycephalics
What is a dermoid?
A congenital malformation where a patch of skin grows on the ocular surface
Usually hairy - irritant to cornea so need to be removed
French bulldog speciality
What is pannus? Treatment?
Inflammatory and vascular tissue advances across the cornea always from the ventrolateral direction
Strong association with GSDs
Treatment: topical cyclosporin/tacrolimus or topical steroids
What is paracentral lipid dystrophy?
Painful fat deposition in eye
Not proven to be associated with hyperlipidaemia or any systemic disease (atypical peripheral lipid depositions may be associated with hyperlipidaemia)
Causes of uveitis?
Lots! Anterior uveitis more common than posterior
Spontaneous/idiopathic - rare in dogs, lymphoplasmacytic uveitis in cats
Deep or infected ulcers - reflex uveitis
Lens-induced uveitis (e.g. cataracts)
Corneal trauma/laceration
Remote sites of infection inc. pyometra
Post intraocular surgery
Specific intraocular infections - adenovirus in dogs (rare), FeLV, FeCoV, FIV?, TB in cats
Treatment for anterior uveitis?
Mydriatics (e.g. atropine) - relieve pain and reduce risk of adhesions
Topical steroids - reduce inflammation
Oral NSAIDs
What do uveal cysts look like and significance?
Look like little cannon balls
Most cases not significant
May affect vision
Ocular melanomas in dogs? Types? Behaviour?
Uveal - not much can do except enucleate
Limbial - debulk followed by cryotherapy (respond well)
Benign
Can cause pain and glaucoma as grow into eye
What is glaucoma? Significance?
Abnormal rise in intraocular pressure
Always a problem of aqueous flow or drainage (not overproduction)
Always serious because great pain and rapidly destroys retina and optic nerve
It is the ultimate reason for eye removal in most cases
Causes of secondary glaucoma? How bad it it?
Uncontrolled inflammation Tumours Trauma Anterior lens luxation Perforations Severe intraocular haemorrhage Chronic retinal detachment
Development of secondary glaucoma indicates the primary problem is out of control and is usually untreatable
Clinical signs of glaucoma?
Acute: (same day emergency but rarely seen/recognised) - red eye - pain and lethargy - steamy cornea - non responsive pupil (dilated) - blindness - globe hard but normal size Chronic: - red eye - pain variable - chronic corneal changes - non responsive pupil - irreversible blindness - globe hard and enlarged (easy to recognise but lost cause at this point)
What is primary closed angle glaucoma? Problems? Which breeds?
Congenital developmental abnormality of the drainage angle Sudden decompensation in middle age with an acute pressure rise - devastating Bilateral but not symmetrical problem Breeds: - English and Welsh Springers - English and American Cockers - Welsh Terrier - Golden retrievers - Flat coated retriever - Basset Hound - Dandie Dinmont Terrier - Great Dane
What are tonometry and gonioscopy?
Tonometry - measures intraocular pressure
Gonioscopy - assesses the drainage angle
Treatment for glaucoma?
Always topical carbonic anhydrase inhibitors (reduce production of aqueous humor) - Trusopt, Azopt
Possibly topical prostaglandin analogues, as long as no lens luxation or anterior uveitis (open drainage angle, increase unconventional pathway, constrict pupil) - e.g. latanoprost
(Beta blockers - timolol)?
Mannitol - option to remove volume of vitreous humour, but side effects
Systemic analgesia
Poss paracentesis
Options to add if chronic:
- aqueous shunt
- destruction of ciliary body
- intravitreal gentamicin
- enucleation
Lifelong treatment for primary glaucoma
What is primary lens luxation? Problems? Which breed is most prone?
An insidious degeneration of the apparatus supporting the lens so lens becomes loose
Affects both eyes but not simultaneously
If luxates anteriorly -> glaucoma, inflammation and secondary corneal oedema
Sub-central corneal oedema develops due to lens-cornea contact
Jack Russel Terrier with a sore eye has lens luxation until proven otherwise!
Also Tibetan Terrier, Parson Russel Terrier, Lancashire Heeler - DNA test available prior to breeding
Not always easy to diagnose - clear structure suspended in a clear fluid - shine torch in all directions
Emergency treatment for anterior lens luxation?
Antibiotic/steroid combination drops (maxitrol)
Trusopt/azopt topically
Can be effective short term
Surgery:
- lensectomy (expensive and guarded prognosis)
- or retropercussion = return lens to posterior chamber by external manipulation and then maintain a constricted pupil (prostaglandin analogue) to keep it there
If subluxated, remove lens or maintain constricted pupil with prostaglandin analogues to prevent anterior dislocation
What is a cataract? Most common cause?
= Any abnormal opacity in the lens (doesn’t always mean blindness)
Cataracts don’t affect the light reflex (scatter light but do transmit it)
Most common cause is diabetes
What does it mean if there is a poor pupillary light reflex (PLR?
Problem in afferent pathway (retina or optic nerve) or iris/pupil
Diabetic cataracts: Prevalence? Onset? Features of cataract? What to do?
75% of diabetics - warn owner might happen!
Relatively sudden onset but may develop at any stage of the condition (can go to sleep visual and wake up blind - scary for dog)
Typically total cataracts
Y shaped water clefts (due to osmosis)
Refer promptly - often emergencies, may need early surgery
Treatment for cataracts?
Phacoemulsification: - phaco probe irrigates, uses ultrasound to break up the cataract and aspirates the fragments - through a 2.85mm incision - expensive but good prognosis Artificial lenses
What is nuclear sclerosis?
Results from condensation of the nucleus on the lens with age
Causes blue/grey/hazy appearance of the pupil in all older animals = normal
Shows as a refractive ring within the lens but the lens transmits reflected light from tapetum (won’t reflect if cataracts)
What to use to dilate the pupil (small animals and horses) for a better fundic exam?
Tropicamide
Takes about 20 mins to work
Lasts several hours
Don’t use atropine as tastes bitter and lasts too long
What is the benefit of indirect ophthalmoscopy? How is it different?
Wide angle view so more of retina in one view (but less magnification)
Upside down and inverted left to right
What local anaesthetic drops can be used for the eye? When to use?
Proxymetacaine, Minims
To relax a painful eye to examine/test intraocular pressure etc
Standard questions for eye consult?
Time of onset? Cause? Pain? Is the eye still seeing? General health?
Be cautious and sceptical
What to do in an eye exam?
Hands off, lights on:
- signs of pain: squinting? eye fully open? sleepy look?
- discharge: watery, mucoid, purulent
- asymmetry: lids, third eyelids, globes
Menace response:
- no draught
- cats and some dogs not good at menace response
- no menace response in rabbits
- learned so limited/none below 12-16 weeks
Assess lids and lid movement
Protrude third eyelids
To check vision - drop cotton wool in front and see if responds
Lights off:
Pupillary light reflex
Examine lids, cornea and anterior chamber
Distant direct ophthalmology - look slightly up for tapetal reflex (opacities such as cataracts will cast a shadow), nuclear sclerosis vs cataracts
Close direct ophthalmology
Supplementary tests:
Schirmer tear test - before any others if it is indicated
Local anaesthetic if needed to relax a painful eye
Fluorescein - any corneal opacity or irregularity
Any painful eye should receive a fluorescein test and an IOP measurement
What is seen with Horner’s syndrome?
Protruded third eyelid Ptosis Miosis Ectropion of lower lid = loss of sympathetic drive to eye
What is seen with a nasal carcinoma which is invading the medial wall of the orbit?
Eye higher than other and displaced laterally
Protrusion of third eyelid
Bloody nasal discharge on same side
What is asteroid hyalosis?
Primary disease of the vitreous "The snowstorm in the vitreous" Can be incidental Far more common in diabetics Doesn't need treating
When does the tapetum form in puppies?
6 weeks - retina is blue colour
9 weeks - green coming through
12 weeks - full tapetum (varies in appearance - solid, broken up, green, yellow, red, blue, dogs with blue eyes often don’t have a tapetum, may or may not reach optic disc)
Which part of the eye is most vascular?
Choroid
What is hyperreflectivity of the eye? Possible genetic cause?
Light passes through the retina before being reflected from the tapetum
So indicates the tapetum is being seen through a thinned retina
Generalised progressive retinal atrophy (GPRA):
- adult onset progressive hereditary pan-retinal degeneration resulting in total blindness
- mostly English Cocker, Miniature poodle, Labrador
- hyperreflectivity and vascular attenuation
- DNA tests
- can lead to secondary cataracts which in time will obscure the primary lesion (but with GPRA get dilated non responsive pupils and don’t with cataracts alone)
What is collie eye anomaly?
Congenital and progressive Pale area lateral to the optic disc with abnormal blood vessels Common in rough collies and shelties Blindness Serious breeders should use eye scheme
What can be seen in the eye with hypertension?
Retinal haemorrhages
Big grey folds - detached retina
More common in cats
What is “Post-inflammatory retinopathy”?
Hyperreflective retinal scars due to (presumed) resolved inflammation
Which breeds have excessive myelination of the optic nerve head?
Golden retrievers mostly
Looks large and swollen
What can cause abnormal optic disc swelling?
Optic neuritis/meningitis
Or raised intracranial pressure
Clinical signs of orbital abscess/cellulitis? What causes it? Treatment?
Pain opening mouth
Pushes third eyelid across
Cause uncertain - poss micro foreign bodies
Maximum doses of antibiotics and anti-inflammatories
IVFT if not eating
Clinical signs of an orbital tumour?
Gradual painless displacement of the globe - look from above to assess anterior displacement
Third eyelid pushed across
Swelling
CT/MRI to confirm or tissue for histology if accessible
(Watch out for nasal discharge on same side as could be nasal carcinoma invading medial orbit instead) - check nasal airflow
Prolapse of the globe - when seen? Management? Complications?
Trauma - dog attacks
Often brachycephalics
Management:
- replace globe quickly to prevent the lids going into spasm behind the equator (GA)
- suture the lids closed for 2 weeks - sutures must not rub the cornea
- antibiotics and NSAIDs
But poor prognosis
Complications even with correct management:
- avulsion of medial rectus muscle -> squint
- traction on optic nerve -> blindness
- traction on trigeminal nerve -> loss of corneal sensation so don’t blink -> dry eye
Method for trans-palpebral enucleation?
Alliss tissue forceps
Cautery may help
Encircling incision through full thickness of skin
Section the canthal ligaments early
Work close to the sclera
Don’t leave conjunctival tissue or foreign material behind
Close with a good seal
Warning - excessive traction on optic nerve in cats can damage the opposite optic nerve at the chasm so don’t pull
Most common lid tumour of cats?
SCC - pale areas
May be nodular and tumour-like or erosive
How does entropion present in cats?
Young cats - especially British Shorthairs, lid may be too long and requires shortening by maybe 3mm
What is chemosis in cats?
Swelling of conjunctiva
Occurs readily in cats
Looks dramatic
No prognostic significance (will go away)
Treatment of Chlamydophila felis infection affecting the eyes in cats?
Doxyxyline or synulox
What is symblepharon in cats?
Permanent adhesion of ocular surfaces following herpes infection as kittens (e.g. third eyelid sticking to eyelids)
Very variable
Often pain free and functionally minor - leave alone
Some may need correction - difficult
What is epiphora in cats?
Poor tear drainage in brachycephalic cats
A few have medial entropion which can be corrected
Most cases are anatomically normal and little can be done - flushing has little benefit
What is a corneal sequestrum in cats? Treatment?
Delayed healing of a corneal ulcer may lead to necrosis of the exposed stroma
Necrotic stroma turns brown/black
This acts as a foreign body and causes pain
Some will eventually get undermined by granulation tissue and slough and heal without surgery
Most do require surgery but:
- difficult to judge depth of lesion
- may be difficult
- reconstruction may be needed e.g. grafting
What is lymphoplasmacytic uveitis in cats? Which cats? Cause?
Clinical signs? Significance?
Most common form of uveitis in cats
Older males with a “street” history
FIV and Bartonella suggested but unproven
Relatively low grade but chronic
Clinical signs:
- spots or sheets of exudate on the posterior cornea
- “keratic precipitates”
- prominent blood vessels on the iris surface
- grey nodules in the iris (lymphoid follicles)
- vitreous opacities
Can lead to serious secondary changes - cataracts, glaucoma, lens luxation
What are lens luxation and glaucoma usually secondary to in the cat?
Uveitis
What is seen with ocular tuberculosis in the cats?
Thickening - can biopsy
Uveitis
Uveal melanomas in cats - what is the most common type? Significance? Diagnosis difficulty? Treatment?
Diffuse anterior uveal melanoma is most common type
A higher proportion of melanomas will metastasise than in the dog
Patches of superficial pigment are common and benign in older cats - can also occur in young cats and progress/enlarge - so distinguishing between benign pigment patches and true melanoma is difficult
Thickening is very suggestive of a melanoma
Enucleation
What to do if removing a progressive non-diagnosed eye from a cat?
Non-pigmented thickening in the cat eye requires histology for diagnosis
Work up for systemic disease including chest X ray
Submit eye for pathology
What form of cataracts are most common in the cat?
Primary cataracts rare
Congenital and secondary more common
Difference between dogs and cats with retinal detachment from systemic hypertension?
Dogs usually have something major wrong with them
Cats often systemically well even with alarmingly high BP
What is hyphaema? Cause?
Bleeding into the anterior chamber
Hyphaema in a teenage cat is almost pathognomic for hypertension unless there has been trauma
Check other eye
Which cat breeds have hereditary pan-retinal atrophy?
Siamese and Balinese
Same as GPRA in dogs
(Hyperreflectivity and loss of vessels)
What can baytril cause in cats’ eyes?
Overdose (single or prolonged doses) can cause rapid and irreversible retinal blindness in cats
May be reversible if baytril stopped immediately
Only happens in cats
What has usually happened to a cat’s eye with severe blunt trauma?
Total hyphaemia
Also usually ruptured posteriorly with massive internal damage
What is the problem with penetrating (cat claw injuries) injuries in cats?
Cat corneas seal and heal well
But intraocular damage leads to serious complications
Management of an acute/traumatised cat eye?
Local anaesthetic drops and wait Flush the eye - don't pull a clot off the cornea Start medication immediately: - topical and oral antibiotics - mydriatics Re-examine soon
What is the most common eye problem in cats?
Teat duct blockage Mostly due to pasteurella Secondary corneal damage Primary lesion in molar misalignment (PM2_ with damage to the duct Prognosis guarded
What can cause tumour-like abscessation in rabbit eyes?
Encephalitozoon cuniculi
What to be careful of in rabbits with enucleation?
Can lead to sudden profuse and dangerous haemorrhage from the orbital sinuses
Be careful and work close to sclera
What do OD, OS and OU mean?
OD: right eye
OS: left eye
OU: both eyes
What to check for with palpebral reflex in brachycephalics?
Check can completely shut eyelids
How to check PLR of eye if can’t see pupil e.g. hympaema?
Watch other eye - if constricts, then both back of eyes are fine
What does it suggest if there is a negative PLR to red and blue light?
- ve red: suggests retina problem
- ve blue: suggests optic nerve problem
When to do a schirmir tear test?
In all eye cases
Always do if ulcer etc to check for dry eye
Only not if very deep ulcer
What can affect a schirmir tear test result?
Conjunctivitis can affect but still test - if low, recheck when resolved as could be dry eye
Superficial ulcer - should have high reading as lacrimation so concern if <20 - retest when resolved
How does uveitis affect IOP?
Lowers it because inflammation of ciliary body so reduced aqueous humour production (if normal IOP, probably glaucoma and uveitis)
If >5mmHg less than other eye, possibly uveitis (match with clinical signs)
Most accurate tool to monitor response of uveitis to treatment
What can influence a false IOP reading?
Neck pressure e.g. tight restraint
-> Increases BP -> increases IOP
Will drop after release pressure
(Therefore, harnesses best for dogs with ocular problems)
Keratomalacia/melting ulcers: Diagnostics?
C+S but takes time for results and need to treat quickly, so also do cytology to guide immediate antibiotic selection
What is electroretinography (ERG) used for?
Good for SARDS, optic neuritis and sudden blindness with no obvious reason
Important for cataract surgery assessment
Sedation -> dark adapted for 20 mins -> contact lens placed -> electrodes placed -> bright light flashed 8 times
What are green and blue on an ophthalmoscope useful for?
Green - blood vessels
Blue - fluorescein
What to use the slit beam for on an opthalmoscope/slit lamp?
Beam at different angle to where looking at eye
Uveitis: aqueous flare
Depths of ulcers
Looking to see if pigment is raised in cats (more concern if is)
How are cataracts classified?
Aetiology Size: - Incipient = tiny - Immature = bigger but not entire lens - Mature = entire lens Location: - E.g. posterior polar subcapsular
Lens anatomy and growth? SIgnficiance of growth for cataracts?
Nucleus, cortex and capsule
Grows from equator (outside) - creates Y shaped suture at front and back of lens (may see on ophthalmoscope)
So middle of lens older than outside - if cataract tight in centre, likely always had and won’t get bigger, while if on periphery likely new and may get bigger as lens grows
Why can diabetes lead to cataracts?
Hexokinase in glucose involved in converting glucose to energy
Lots of glucose, limited hexokinase
When hexokinase saturated, alternative pathway used which involves aldose reductase
Aldose reductase involved in formation of insoluble products from glucose -> cataracs
Osmosis into lens -> swollen lens - capsule can only stretch so much
If a lens capsule ruptures when diabetic cataracts, where likely ruptures? How to tell?
At weakest point = equator
Likely diagnosis if Y shaped water cleft has shifted to the side
Why do all cataracts cause lens-induced uveitis? Types of LIU? Treatment?
Lens forms in womb before immune system so only capsule recognised by immune system
Especially problem if lens ruptures
LIU can be:
- phacolytic: low level inflammation, treat with anti-inflammatories
- phacoclastic: big release of lens Ags, e.g. if diabetic cataract, cat claw or thorn, must take cataract out within ~14d or will lose eye
What to do in cataracts case?
Always offer referral!! Ie for poss surgery (except incipient ones old dogs have probably always had)
Always put on anti-inflammatories as lens-induced uveitis
What 3 very important things must know about cats and ophthalmology?
- Baytril overdoses -> retinal blindness
- Dentals - elevator going into eye if not careful
- Enucleations - short optic nerve, blind other eye if not careful, ok to cut and then ligate
What are the extra-ocular muscles and their functions?
Dorsal rectus Ventral rectus LAteral rectus Medial rectus Dorsal oblique Ventral oblique Retractor bulbus
For which 2 main ocular diseases are prostaglandin analogues contraindicated? Why?
Anterior uveitis
Anterior lens luxation
Because it constricts the pupil!
What does cycloplegic mean? Which drugs have this effect?
Paralysis of the ciliary body - stops it spasming
Parasympatholytics:
- atropine
- cyclopentolate
- tropicamide (very minimal, basically doesn’t)
(all are mydriatics too)
Topical drug to use for FHV-1?
Ganciclovir
How do Tonopen and Tonovet work? When not to use?
Tonopen:
- measures pressure from how hard needs to press
- must use local anaesthetic
- don’t use if descemetocele (risk of rupture)
Tonovet:
- rebound tonometry
- measures pressure of rebound
Normal IOP (mmHg) and STT (mm/min) in dogs and cats?
Dog: - IOP 10-25 - STT 15-25 Cat: - IOP 10-25 - STT 3-30
What to do when taking a jugular blood sample from a patient with an ulcer? Why?
Take from jugular vein opposite side to eye ulcer
Prevents increased IOP to eye with ulcer
Why is one drop of medication sufficient in the eye?
Can’t hold any more - will just be wasted
What is TPA? What is it used for?
Tissue plasminogen activator
Plasminogen -> plasmin -> fibrinolysis
Use if significant fibrin causing increased IOP
How may distichiasis/ectopic cilia present?
Recurrent conjunctivitis and ulcer in same place of cornea each time
How thick is the cornea?
500-600um
Function of the corneal endothelium?
Actively pumps water out of cornea
So if damaged -> corneal oedema
Innervation of the cornea?
Trigeminal nerve
How quick should a superficial ulcer take to heal? Significance?
Whole corneal epithelium would take 10-14 days to heal
So should be less than this!
If >14 days, not just a simple superficial ulcer (stromal ulcers take weeks)
When do blood vessels start appearing at the limbus for corneal ulcers? Rate of growth?
Start appearing at limbus at 5-7 days
Grow in by 0.5mm/day
What suggests a corneal ulcer involves infection?
Ill defined, infiltration around ulcer
What to do if a corneal ulcer is not healing with antibiotics?
Repeat exam to check didn’t miss anything e.g. entropion, dry eye, distichiasis
Refer if just getting deeper
Signs of uveitis? Appearance on exam?
Pain - blepharospasm, photophobia, lacrimation etc (more evident if anterior uveitis)
Reduced vision
May have corneal oedema due to endothelial damage (in acute uveitis)
Particles in suspension in anterior chamber (or aqueous humour not transparent) = pathognomic
Material in anterior chamber (hypopyon, fibrin etc)
Chronic:
- posterior synechiae
- no corneal involvement if chronic
- changes to lens e.g. subluxation as damage to zonules (can get vitreous in anterior chamber), cataracts
- “iris bombe” with cataract and glaucoma
Pilocarpine: When used?
Neuro exams..
Sodium chloride drops: when used?
Reduces corneal oedema
Use for corneal conditions
