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 Veterinary@torontowildlifecentre.com