Avian Ophthalmology

Question 1

What is the avian globe support by?

Describe the extraocular muscles of birds.

What are the three globe shapes adn what species have them?

Birds blink with which eyelid?

What are filoplumes?

The nictitating membrane is moved by what muscle and innervated by what nerve?

What ocular glands do birds have, what do they produce? Which are absent?

Answer 1

EAMS Rounds – Avian Ophthalmology

• Anatomy.
• Large, open orbit.
• Globe supported by:
  
  • Scleral ossicles – attachment for ciliary muscles
  • Scleral hyaline cartilage – support to posterior segment of the globe, unprotected in an open orbit
• Extraocular muscles NOT well developed
  
  • Retractor bulbi is absent
• Three globe shapes.
  
  • Tubular – Strigiformes
  • Globose – some raptors, crows
  • Flat – all other species; most common shape
• Lower eyelid more mobile than upper
  
  • Contains tarsal plate (cartilage)
• Filoplumes – avian eyelashes
• Nictitating membrane
  
  • Contraction of pyramidalis muscle (CN VI)
• Ocular glands
  
  • Lacrimal – minor tear production
    
    • Absent in owls and penguins
  • Harderian – major tear production
  • Meibomian – ABSENT

Question 2

Describe the structure of the avian cornea.

What is the funciton of crampton’s muscles? What birds are these most well developed in?

The iris is composed of what muscle types?

Which avian species has a vertical pupil?

How do birds supply nutrients to the back of their eye.

What group has a tapetum lucidum?

What avian species lacks a pectin?

Why do birds not have a consensual PLR?

Answer 2

Avian Eye Anatomy Continued

• Cornea – similar to mammals
  
  • Bowman’s layer
  • Crampton’s muscles – can alter the corneal surface and contribute to accommodation
    
    • Changes the most in diving birds
  • Striated and smooth muscle in iris – implications for mydriasis
  • Which avian species has a vertical pupil?
    
    • Black skimmer
• Avascular retina
  
  • Choroidal vessels may be seen on fundic exam
• Tapetum lucidum
  
  • Present in caprimulgiformes
    
    • Nightjar, frogmouth, potoos
• Which avian species lacks a pecten?
  
  • Kiwis
• Complete decussation of optic nerve fibers at optic chiasm and after pretectal nucleus – NO consensual PLR
  
  • Can sometimes be observed when light penetrates through thin intraorbital septum that separates the globes and stimulates contralateral retina
  • EXCEPT Tytonidae – septum is thick and complete

Question 3

Several studies have evaluated the microflora of the avian eye.

What are some of the most common bacteria in the eyes of terrestrial birds?

How do aquatic birds differ?

Answer 3

• gram-positive bacteria - most common normal flora among terrestrial birds
  
  • most common - coagulase-negative Staphylococcus
  • 2^nd most common - Streptococcus in psittacines, Corynebacterium in raptors
  • bustards - Micrococcus predominated followed by Staphylococcus
  • tawny owls - coagulase-positive Staphylococcus predominated, followed by Escherichia coli
  • blue-and-gold macaws
    
    • gram-positive organisms most prevalent (49%)
    • Bacillus subspecies most common, followed by Staphylococcus
    • higher fungal detection rate (28%) than previous reports
  • aquatic birds - gram-negative bacteria may predominate
  • healthy penguins – most common was Corynebacterium, followed by Staphylococcus
  • flamingos - Enterococcus subspecies (53%) and other gram-positive cocci (14%)

Question 4

Describe the common etiology for bacterial conjunctivitis in the follwoing taxxa.

Poultry

Passerines

Canada geese

Cranes

Answer 4

• bacterial conjunctivitis
  
  • primary vs secondary
  • poultry (previous reports)
    
    • fibrinopurulent blepharoconjunctivitis - combo of Staphylococcus hyicus, E coli, and Streptococcus
    • blepharoconjunctivitis and uveitis - Pasteurella multocida
  • mycoplasma gallisepticum
    
    • finches
      
      • tx - topical ciprofloxacin and oral tylosin in water
    • other species - chickens, blue jays, mockingbirds, starlings, canaries
  • Actinobacillus suis
    
    • Conjunctivitis, hyperkeratotic eyelids causing blindness in Canada goose
  • Mycobacterium - conjunctivitis reported in 2 emus
  • Streptococcus subspecies, Erysipelothrix, Clostridium, Mycobacterium, E coli, Pseudomonas, and Bordetella – all reported in passerines causing conjunctivitis
  • Salmonella and E coli septicemia - symblepharon in snowy owl chicks
  • Pseudomonas aeruginosa - ulcerative keratitis and corneal perforations in Siberian and whooping crane chicks
  • Chlamydophila psittaci
    
    • conjunctivitis with or without corneal involvement
    • local or systemic
    • chlamydophila associated with conjunctivitis reported in ducks

Question 5

What are teh clinical signs and lesions for the following viruses affecting avian eyes?

Avian pox

Marek’s

Strigid Herpesvirus 1

Newcastle Disease Virus

West Nile Virus

Reticuloendotheliosis Virus

Answer 5

• Viral disease
  
  • Avian pox
    
    • Conjunctivitis, ocular discharge, facial or periocular proliferative lesions, ulcerative blepharitis and ocular crusts
    • generalized lesions or respiratory tract disease may be present
  • Herpesvirus
    
    • Mareks – usual involves uveal tissue but can cause keratitis
    • Stigid Herpesvirus 1
      
      • novel alphaherpesvirus
      • papillomatous conjunctivitis and chronic superficial ulcerative keratitis in GHOW
  • Newcastle disease virus and paramyxovirus 2
    
    • can cause conjunctivitis in passerine birds
  • West Nile Virus
    
    • chorioretinitis in raptors
    • no surface lesions
  • Reticuloendotheliosis virus
    
    • linked to ocular lymphoma in some birds

Question 6

What fungal infections have been documented causing ocular surface disease in birds?

How are they treated?

Answer 6

• Fungal disease
  
  • mycotic infections should be considered a differential in ocular surface disease
    
    • Aspergillus sp
    • Rhinosporidium - nodular blepharoconjunctivitis in mute & black swans
    • Scedosporium apiospermum - keratitis and uveitis in layer pullets
    • Ocular candidiasis
      
      • reported in ducks, budgerigar, a cormorant, a gull, and chickens
      • nictitating membrane and conjunctiva nodules, keratitis, uveitis
      • successful tx with oral ketoconazole and topical miconazole
  • Tx’s - oral itraconazole, topical miconazole, oral and topical voriconazole

Question 7

A variety of parasites have been documented infecting various avian species.

Name three helminths that may infect bird eyes.

How does plasmodium cause lesions?

What about cryptosporidium?

What about Encephalitozoon?

Answer 7

• Parasitic disease
  
  • spirurids, nematodes, trematodes
    
    • Philophthalmus gralli flukes - ostriches, greater rheas, waterfowl
    • Oxyspirura
      
      • conjunctivitis, keratitis, corneal fibrosis, and inflammatory damage to the lacrimal ducts, lacrimal glands, Harderian gland in bobwhite quail
      • found in 78% of lesser prairie chickens
      • under nictitating membrane of fulvous owl, no ocular pathology
    • Ceratospira
      
      • conjunctivitis and blepharitis in a Wompoo fruit dove
    • Thelazia - Senegal parrot and oriental white stork
    • Plasmodium – can cause swollen eyelids in canaries and poultry, ptosis in parakeets
    • Cryptosporidium
      
      • conjunctivitis in pheasants, duck, peacock
      • keratoconjunctivitis in a parakeet
      • conjunctivitis, corneal edema and bullae, uveitis in otus owls
    • Encephalitozoon hellem
      
      • umbrella cockatoo with persistent keratoconjunctivitis
    • Corneal protozoal infection - considered differential for corneal changes
      
      • uncommon

Question 8

What congenital eye defects have been reported in birds?

What dietary deficiencies may result in conjunctivitis in birds?

What types of corneal degeneration have been documented?

What birds get lipid keratopathies or degeneration?

What birds get avascular corneal crystalline deposits?

Answer 8

• Non-infectious
  
  • Congenital
    
    • partial eyelid agenesis reported in PEFA
    • Ectropion has been diagnosed in cockatiels
    • Congenital symblepharon reported in a red-vented cockatoo
    • Bilateral corneal dermoids reported in gosling and young blue-fronted Amazon
  • Trauma
    
    • keratitis, corneal fibrosis, eyelid abnormalities, other evidence of ocular trauma
    • very common in wild birds
      
      • blunt force > penetrating trauma (esp raptors)
• Nutritional
  
  • Hypovitaminosis A - eyelid swelling, keratitis, conjunctivitis
    
    • Dietary vs intestinal, pancreatic, or hepatic disease
  • Vitamin B5 (pantothenic acid) deficiency - conjunctivitis, facial dermatitis, and decreased hatchability in Japanese quail
• Corneal degeneration
  
  • Lipid keratopathy
    
    • common in parrots fed high-fat diets
    • secondary degeneration as inflammatory response to lipid
  • Corneal degeneration
    
    • observed clinically as a post-inflammatory change
  • Avascular corneal crystalline deposits - reported in cockatiels, parakeets, Amazon parrots, budgerigars, and finches
  • corneal dystrophy – single case in a parakeet
  • bilateral corneal keratopathy - axial stromal fibrosis in a BDOW
  • lipoidal corneal degeneration
    
    • cases in falcons
    • slowly progressive
    • may be age related
• Miscellaneous diseases
  
  • Keratoglobus of chickens
    
    • recessive sex-linked trait of females
    • starting around 5 weeks old
    • reported in at least 1 male chicken
    • also reported in a GHOW

Question 9

Identify SIX ways the avian eye differs from the mammalian eye.

Answer 9

Question 10

How is the avian eye innervated differently than the mammalian eye?

What are the three branches of the trigeminal nerve and what do they do?

Answer 10

Question 11

Compare and contrast evisceration vs enucleation.

When would you want to perform one over the other.

Describe the technique for evisceration.

Answer 11