Wildlife Ophthalmology
DR. HEATHER REID TORONTO WILDLIFE CENTRE TORONTO, ON CANADA 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
Fundus of the Eye
Mammal Eye Bird 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)
The Avian Eye - Differences
In some species the eye color changes with age
Red Eyed Vireo
Great Horned Owl Red Tailed Hawk 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 Cornea - Structure
Flourescein stain Corneal ulcer detected 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
Eye Exam and Vision Assessment
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 Measure intraocular production pressure 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 Eye Exam and Vision Assessment
Slit lamp biomicroscopy Indirect ophthalmoscopy 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 The red eye squinting, swollen, entire eye, around eye, tearing part of eye, front of eye, back of eye The white or cloudy eye whole eye, partial, Other conditions; front of eye, back of eye 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
The Painful Eye – Corneal Ulcer
Three questions to answer: Timeline for healing:
Uncomplicated 1) Why is there an ulcer? superficial ulcers 2) How deep is the ulcer? should heal within 3-5 days with treatment 3) Is it healing as Deeper ulcers should expected? 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 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
The White or Cloudy Eye
Corneal edema
Cornea becomes “leaky” and water enters Causes include corneal ulcers, trauma, uveitis, glaucoma Treat the underlying cause!
The White or Cloudy Eye
Cataracts
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
The White or Cloudy Eye - Uveitis
Causes Principle of therapy
Infection – viral, Treat the underlying bacterial, fungal cause e.g. topical Blunt trauma – can antibiotics lead to leaky vessels Treat the inflammation Other – cancer, – topical or oral problem with the steroids immune system, unknown cause, breed Treat the pain – topical related (dogs) or oral pain medication
The White or Cloudy Eye - Uveitis
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 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
The Red 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 Poor prognosis if present (stain eye!) bleeding continues or Topical NSAIDs if ulcer recurs, in cases of is present glaucoma, or if retina Topical atropine detaches (mammals) if uveitis present and normal eye pressure
The Red Eye
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
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
The Red Eye
Conjunctivis – Distemper Virus
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
Other Conditions
Missing Eye Irreparably Damaged Eye
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 Topical antibiotics Direct ophthalmoscope Topical steroids Fluorescein strips or Topical NSAIDs drops + saline flush Topical antibiotic + Culture swabs steroid combinations Exam sheet Atropine +/- Tonopen Topical anesthetic +/- STT strips 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]