D R . H E A T H E R R E I D
T O R O N T O W I L D L I F E C E N T R E
T O R O N T O , O N
C A N A D A
Wildlife Ophthalmology
Why understand eyes?
Wildlife need to have excellent vision to survive in the wild
Eye related problems are common in wildlife admitted to rehabilitation centers
What we will cover
Anatomy of the eye
Differences between birds and mammals
The eye exam
Recognizing common problems
Prognosis
Treatment options
When to see the vet
Anatomy
Around the Eye:
Muscles & nerves
Skin
Eye lids
Nictitating eyelid
Conjunctiva & sclera
Tear glands & ducts
Ossicles (birds)
Anatomy
Front of the Eye:
Cornea
Iris
Pupil
Ciliary body
Anterior Chamber
Aqueous humor
Anatomy
Back of the Eye:
Lens
Retina
Optic nerve
Choroid
Pecten (birds)
Posterior Chamber
Vitreous humor
Mammal Eye Bird Eye
Fundus of the Eye
The Avian Eye - Differences
Small eye size in most birds and small pupil size makes it hard to examine
Can control the size of their pupil
Lower eyelid more developed
The nictitating membrane spreads the tears allowing birds to blink less
Moves horizontally across eye
The Avian Eye - Differences
Eyes are not as protected by skull
Less muscles around eye so less eye movement
Boney ossicles support the eye
Three main eye shapes; flat, globose & tubular
The Avian Eye - Differences
Four different color receptors compared to the three in mammals means better color detail
Can see in the ultraviolet range
Higher flicker rate – can detect lights that flicker at more than 100 flashes per second (humans detect at 50)
In some species the eye color changes with age
The Avian Eye - Differences
Red Eyed Vireo
Red Tailed Hawk Great Horned Owl
Mammal Eyes – Tapetum lucidum
Many animals have a special layer at the back of their eye that helps reflect light
Improves night vision, helping them see better in the dark
Some animals do not have a tapetum such as squirrels, birds, rabbits and primates
Cornea - Structure
Injuries to the cornea are common
Can range from scratches and abrasions to punctures into the eye
Can determine the depth of the injury by using fluorescein stain
The outer layer (epithelium) repels the stain
The middle layer (stroma) absorbs it, appearing green
Flourescein stain Corneal ulcer detected
Cornea - Structure
Eye Exam and Vision Assessment
Observe animal
Physical exam; include area around eyes
Assess reflexes; PLR , palpebral reflexes, menace response
Direct ophthalmoscope to assess structures in the front and back of the eyes
Pupillary Light Reflex - PLR
A reflex that controls the size of the pupil
Allows animal to adapt to different levels of light
Pupil gets smaller when bright light shines on the retina
In mammals there is a “consensual” PLR – opposite eye also constricts
Eye Exam and Vision Assessment
Pupillary Light Reflex - PLR
Eyes very sensitive to light – one pupil can be different size than other
Birds have some control over their pupil size
In birds there is no consensual PLR
PLR assesses the function of the retina and the brain.
Eye Exam and Vision Assessment
Measure tear production
Measure intraocular pressure
Eye Exam and Vision Assessment
Eye Exam and Vision Assessment
Take sample for culture and sensitivity if needed
Then stain eyes with fluorescein stain
Flush with sterile saline before assessing
Use cobalt blue light to better appreciate any stain uptake
Slit lamp biomicroscopy Indirect ophthalmoscopy
Eye Exam and Vision Assessment
Eye Exam and Vision Assessment
Assessment or Test Can you do it?
Physical Exam, examine area around the eyes Yes
Pupillary Light Reflex Yes
Other reflexes; e.g. palpepral reflexes, menace Yes
Culture or cytology (if required) Yes
Schwimmwer Tear Test Maybe
Intraocular Pressure No
Fluorescein stain Yes
Direct ophthalmoscopy Yes
Indirect ophthalmoscopy Maybe
Slit lamp biomicroscopy No
X-ray skull and orbital area Maybe
Ultrasound eyes No
Electroretinography No
Vision check – e.g. obstacle course, live prey testing Yes
Eye Exam and Vision Assessment
Your exam should consist of the below tests as a minimum Can make an exam sheet to use during your eye exam Complicated cases will need to be referred to your
veterinarian for further testing
Assessment or Test Can you do it?
Physical Exam, examine area around the eyes Yes
Pupillary Light Reflex Yes
Other reflexes; e.g. palpepral reflexes, menace Yes
Fluorescein stain Yes
Direct ophthalmoscopy Yes
Culture or cytology (if required) Yes
Vision check – e.g. obstacle course, live prey testing Yes
Problems with the Eye
The painful eye
squinting, swollen, tearing
The white or cloudy eye
whole eye, partial, front of eye, back of eye
The red eye
entire eye, around eye, part of eye, front of eye, back of eye
Other conditions;
trauma around the eye, the missing eye, the blind eye
The Painful Eye
The Painful Eye
Quick Differentials:
Injury to cornea – ulcer
Injury to structures around the eye
Increased pressure within the eye – glaucoma
Severe uveitis – inflammation within the eye
The Painful Eye – Corneal Ulcer
Superficial erosion – damage to the surface layer
Partial thickness ulceration – variable depth into stroma
Descemetocoele – deep ulcer, to the level of Descemet’s membrane
Perforation – right through all layers
Three questions to answer: Timeline for healing:
1) Why is there an ulcer?
2) How deep is the ulcer?
3) Is it healing as expected?
Uncomplicated superficial ulcers should heal within 3-5 days with treatment
Deeper ulcers should stop taking up stain within 5-7 days although defect may be visible for longer
The Painful Eye – Corneal Ulcer
Treatment
Corneal ulcers are very painful = pain medication e.g. oral meloxicam
There is a risk that it will become deeper and rupture = prevent infection with topical antibiotics
Drops vs. ointment
The Painful Eye – Corneal Ulcer
The White or Cloudy Eye
The White or Cloudy Eye
Quick Differentials
Corneal edema – from injury to cornea or uveitis
Scar tissue on cornea – from injury to cornea
Hypopyon = pus in the front of the eye
Cataracts – lenses are not clear
Uveitis – inflammation in the front of the eye
Corneal edema
The White or Cloudy Eye
Cornea becomes “leaky” and water enters
Causes include corneal ulcers, trauma, uveitis, glaucoma
Treat the underlying cause!
Cataracts
The White or Cloudy Eye
Four main causes:
Congenital
Trauma
Geriatric
Disease
The White or Cloudy Eye - Cataracts
Treatment is surgery to remove the lens
In wildlife it is very difficult to replace the lens so vision is compromised
Solution for animals that don’t rely on perfect vision
The White or Cloudy Eye - Cataracts
Exceptions:
Very young dark-eyed owls have naturally bluish lenses that become clear as they age
Dehydrated baby squirrels may have cloudy lenses that resolve once rehydrated
The White or Cloudy Eye - Uveitis
Inflammation of the front of the eye
Symptoms: pain, squinting, redness, aqueous flare, small pupil size, changes to iris color
Causes
Infection – viral, bacterial, fungal
Blunt trauma – can lead to leaky vessels
Other – cancer, problem with the immune system, unknown cause, breed related (dogs)
Treat the underlying cause e.g. topical antibiotics
Treat the inflammation – topical or oral steroids
Treat the pain – topical or oral pain medication
The White or Cloudy Eye - Uveitis
Principle of therapy
Use steroids with caution!
ALWAYS use fluorescein stain to make sure there is no corneal ulcer present
Steroids interfere with ulcer healing so DON’T USE if an ulcer is present
Can use topical NSAIDs instead
Many antibiotic & steroid combinations available
The White or Cloudy Eye - Uveitis
Open up the pupil
Pupil is often very small because the iris muscle is in spasm
Painful and interferes with normal fluid movement in the eye affecting the eye pressure
Dilate the pupil (in mammals) with atropine, tropicamide or phenylephrine drops.
More drastic solution is a subconjuctival injection of these agents (by veterinarian)
The White or Cloudy Eye - Uveitis
The Red Eye
The Red Eye
Quick Differentials
Hyphema = blood in the front of the eye
Retinal hemorrhage – blood in the back of the eye
Conjunctivitis – inflamed conjunctiva around eye
Glaucoma / uveitis – inflamed tissue in and around the eye
Hyphema – Blood in the Front Eye
Blood in the anterior
chamber Most common cause is
trauma May be difficult to see
all structures in eye May need to wait for
clot to form and resolve Ultrasound is an option
The Red Eye
Retinal Hemorrhage – Blood in the Back Eye
Blood in back of eye in
the posterior chamber Causes include trauma,
clotting disorders, infection, tumor
Often see bleeding around pecten in birds after trauma
Danger of retinal detachment
The Red Eye
Blood in the Eye - Treatment
Topical steroids if corneal ulcer not present (stain eye!)
Topical NSAIDs if ulcer is present
Topical atropine (mammals) if uveitis present and normal eye pressure
The Red Eye
Poor prognosis if bleeding continues or recurs, in cases of glaucoma, or if retina detaches
Conjunctivis
Conjunctiva is the
tissue that lines the inside of the eyelids and the white part of the eye
Conjunctivitis is an inflammation of these tissues
Swelling is also present Irritating but not
painful
The Red Eye
Conjunctivis - Bacterial
Purulent discharge
from eyes, can crust shut if extreme
Treatment: topical antibiotic
NO steroids – can make infection worse
Culture if not responding to treatment
The Red Eye
Finch Conjunctivis
The Red Eye
Common infectious disease of finches
Caused by Mycoplasma gallisepticum
Primarily a respiratory problem
Treatment is topical antibiotics - ciprofloxacin and oral tylosin in the drinking water
Concern about carriers
Conjunctivis – Distemper Virus
The Red Eye
Infectious viral disease of canids, mustelids, skunks and raccoons
Caused by Canine Distemper Virus
No treatment once infected
Prevent with vaccination
Poor prognosis
The Red Eye - Glaucoma
Increased intra-ocular pressure - EMERGENCY
Symptoms – extremely painful condition, red eye, blindness
Causes – secondary to intra-ocular inflammation, tumor, inherited disease (dogs)
Affects the flow of fluid within the eye.
The Red Eye - Normal!
Other Conditions – Pox Infections
Viral infection that causes nodular lesions
If nodules are close to the eye can cause irritation to the eye including corneal ulcers
In extreme cases lose vision in eye
Can recover with supportive care
Other Conditions – Wounds
Wounds to structures around eyes – lids, conjunctiva
Concern if the wound affects the function of the eye - e.g. can no longer close eye
Surgery has the best outcome
Other Conditions – Mange
Parasitic infection with Sarcoptes mange mites
Skin becomes thickened and crusty
Skin around the eye is often affected
Can cause corneal irritation or ulceration
Treat for secondary bacterial infection
Other Conditions – Species specific
Overweight Virginia
opossums have fat deposits that build up around their eyes so they look cross-eyed
Aquatic animals, like beavers, muskrats, and water birds can develop crusty eyes when kept out of water.
Owls that are blind in one eye have been noted to have tuft down on that side
Missing Eye Irreparably Damaged Eye
Other Conditions
Conditions you can treat
Treatment by the Wildlife Rehabilitator
Simple corneal ulcers
Hyphema from trauma
Retinal hemorrhage from trauma
Trauma around eye that doesn’t affect lids, glands, etc.
Conjunctivitis
Conditions for your Veterinarian
Deep corneal ulcers
Non-healing ulcers
“Complicated” eyes
Uveitis
Suspected glaucoma
Lacerations & punctures
Hypopyon
Anything you aren’t sure about!
Equipment and Medications to have:
Bright pen light
Direct ophthalmoscope
Fluorescein strips or drops + saline flush
Culture swabs
Exam sheet
+/- Tonopen
+/- STT strips
Topical antibiotics
Topical steroids
Topical NSAIDs
Topical antibiotic + steroid combinations
Atropine
Topical anesthetic
Oral pain medication
Oral antibiotics
Assess Visual Function
Evaluate behavior from a distance
Food intake – can it find food? Can it hunt?
Movement in enclosure - reluctant to climb, jump, swim, fly?
Head posture – is there one eye used more than the other?
Startle reaction – is there an exaggerated response?
Dr. Heather Reid Toronto Wildlife Centre 60 Carl Hall Road, Unit 4 Toronto, ON M3K 2C1 (416) 631-0662 x 3206 [email protected]