Ocular

Question 1

What are the 3 tunics of the eye? What structures are in each? What is the function of each?

Answer 1

1. FIBROUS: cornea, sclera; shape, protection, light refraction
2. VASCULAR/UVEA: iris, ciliary body, choroid; pigmented and vascular for light reflection, scattering, nutrition, and waste removal
3. NERVOUS: retina, optic nerve; electric and chemical signaling to brain

Question 2

What is the purpose of the aqueous humor, lens, and vitreous humor?

Answer 2

light refraction and internal pressure maintenance (must be transparent!)

Question 3

Eye anatomy:

Answer 3

Question 4

What are 6 common clinical presentations of ocular disease?

Answer 4

1. blindness resulting from alterations in the cornea, lends, or humors, damage to the retina or optic nerve, and extraocular lesions in the brain’s occipital lobes
2. conjunctival discharge
3. swelling and pain (chemosis)
4. sensitivity to light
5. excessive (epiphora) or decreased lacrimation due to damage to the glands
6. opacity of the cornea or lens

Question 5

What is exophthalmos? Proptosis? Buphthalmos? Enophthalmos? Hyphema? Hypopyon?

Answer 5

• protrusion of eyes within the orbit
• protrusion of eyes out of the orbit, typically due to fractures or space-occupying lesions
• enlargement of the eyes
• sunken in eyes, typically caused by orbital fractures or muscle atropy
• blood in anterior chamber
• pus in anterior chamber

Question 6

What is this?

Answer 6

buphthalmos - enlarged eye

Question 7

What is this?

Answer 7

proptosis - protrusion of eye out of orbit

Question 8

What is this?

Answer 8

exophthalmos - protrusion of eye within orbit

Question 9

What is this? What are some possible differential diagnoses?

Answer 9

hyphema - blood in anterior chamber

hypertension caused by hyperthyroidism or CKD

Question 10

What is this?

Answer 10

hypopyon - pus in anterior chamber

Question 11

What is the most common cause of congenital ocular abnormalities?

Answer 11

infectious, nutritional, or genetic teratogens that cause defective cell signaling during organogenesis in embryonic development

Question 12

What is microphthalmia?

Answer 12

congenital/hereditary anomaly where one or both eyes are abnormally small and are histologically malformed and disorganized

Question 13

What is synophthalmos?

Answer 13

congenital/hereditary anomaly where two eyes are present in a singular orbit caused by incomplete separation of the paired globes

Question 14

What is cyclopia?

Answer 14

congenital/hereditary anomaly where there is a singular, central eye

Question 15

What is the most common cause of cyclopia and synophthalmos in sheep? When in embryonic development is this able to happen?

Answer 15

ingestion of Veratrum californicum, which contains cyclopamine and jervine that are able to cause the failure of the prosencephalon to divide into the 2 lobes of the cerebral hemispheres

day 14-15 of gestation, when this division is beginning to occur

Question 16

What vasculature is present in the embryonic eye? How does this develop during gestation?

Answer 16

hyaloid artery branches and supplies blood to different structures of the eye

these vessels should regress 2-4 weeks after birth

Question 17

What is persistent pupillary membrane? How does it affect the animal?

Answer 17

persistence of the vascular fetal structure that covers the pupil and causes uveal/vascularized strands to develop across the pupil iris-to-iris, iris-to-lens, or iris-to-cornea

most common in cats —> does not progress, is not painful, and does not affect vision

Question 18

What are the 5 layers of the normal cornea?

Answer 18

1. epithelium - nonkeratinized stratified squamous
2. basement membrane
3. stroma - parallel collagen fibers (clear spaces that look like edema are common artifacts upon fixation)
4. Descement’s membrane - produced by endothelium
5. endothelium

Question 19

What part of the eye is most susceptible to damage?

Answer 19

cornea —> outermost, exposed layer

(allow light to enter)

Question 20

What are 5 common responses of the cornea to injury?

Answer 20

1. edema - opacity
2. inflammation - keratitis
3. vascularization*
4. pigmentation*
5. fibrosis*

*chronic, lymphoplasmacytic

Question 21

Chronic corneal damage:

Answer 21

• inflammation
• vascularization
• pigmentation
• results in opacity, pigmentation, and vision effects

Question 22

Keratitis and healing:

Answer 22

• opacity, pigmentation, vascularization
• decreased opacity and vascularization

Question 23

What are 4 common causes of keratitis? What specific bacterium and virus cause this?

Answer 23

1. irritation - entropion, eyelid masses, particulate material
2. desiccation/exposure - lagophthalmos (incompletely closed eyelids common in brachycephalic breeds), buphthalmos (glaucoma), exophthalmos (orbital masses)
3. repeated corneal ulceration
4. trauma

Moraxella bovis, feline herpesvirus-1

Question 24

What is indicative of acute keratitis?

Answer 24

accumulation of neutrophils cause keratomalacia (melting ulcer) due to excretion of proteases and metalloproteases

• endogenous: inflammation
• exogenous: bacteria, fungi

(basophilic band = neutrophils)

Question 25

What is indicative of chronic keratitis?

Answer 25

lymphoplasmacytic inflammation leads to epidermalization (eye becomes "skin-like") ---> acanthosis, melanosis, vascularization, stromal scarring (fibrosis)

Question 26

What is chronic superficial keratitis/conjunctivitis? What is the most likely etiology? What animal is predisposed?

Answer 26

pannus - fleshy gray-pink superficial tissue formation in the limbus where the sclera meets the cornea (no ulceration!) immune-mediated reaction to UV light modifying cornea-specific antigens German Shepherds

Question 27

What are boxer ulcers? At what age does it most commonly develop? What is the most likely cause?

Answer 27

indolent (lazy) ulcer that is a non-healing, superficial corneal erosion middle to older age spontaneous or traumatic defect in epithelial adhesion to stroma

Question 28

What are the 2 histological characteristics of boxer ulcers?

Answer 28

1. non-adherent hyperplastic epithelium 2. clefts between epithelium and stroma

Question 29

What is eosinophilic keratitis?

Answer 29

proliferative, placoid lesions of white material common in cats and horses

Question 30

What cytology is indicative of eosinophilic keratitis?

Answer 30

impression smear = EOSINOPHILS. granules, epithelial cells, mast cells

Question 31

What is corneal sequestrum? What is the likely cause? How does it affect the eyes?

Answer 31

amber/black stromal pigmentation commonly seen in Persian and Siamese cats corneal disease: injury (trauma) and FeHV-1 - stromal hyalinization (necrosis) causes epithelium to slough off - prone to bacterial colonization

Question 32

What is the most common cause of fungal/mycotic keratitis? In what animals is this most common?

Answer 32

opportunistic Aspergillus or Fusarium infection of corneal wounds being treated with antibiotics or corticosteroids horses in warm and humid climates

Question 33

What lesion is characteristic of fungal/mycotic keratitis? What tropism does it typically have? What does this cause?

Answer 33

destructive, deep stromal, ulcerative suppurative keratitis with keratomalacia (liquefaction) Descement's membrane ---> ruptures, causing exudate spillage into the anterior chamber (endophthalmitis)

Question 34

Fungal/mycotic keratitis, keratomalacia:

Answer 34

Question 35

What causes corneal degeneration? What 3 metabolic disorders are most common?

Answer 35

accumulation of lipids and calcium 1. high fat diets - amphibians, reptiles, and birds fed high amounts of crickets and mealworms 2. hyperadrenocorticism, hypothyroidism, diabetes 3. hypercalcemia

Question 36

What is characteristic in the histology of lipid keratopathy?

Answer 36

- cholesterol clefts - oil red O stained fat droplets

Question 37

What is the most common origin of corneal neoplasms?

Answer 37

extension from adjacent tissue (conjunctiva)

Question 38

In what animals is squamous cell carcinoma of the eyes most common? What is the cause?

Answer 38

horses, Hereford cattle, cats unpigmented skin around the eye is damaged by UV light and it extends from the conjunctiva or eyelids - ulceration and discharge

Question 39

What is the most common cause of corneal neoplasms in dogs? What is a major risk factor?

Answer 39

dogs with chronic keratitis develop hyperplasia, which develops into dysplasia and neoplasia use of immuno-modulating drugs

Question 40

What is corneal dermoid?

Answer 40

congenital, non-neoplastic, choristoma - where normal tissue not usually found in the eye is present

Question 41

What a staphyloma? What is it commonly lined by? What is thought to be the cause?

Answer 41

circumscribed outpouching of the sclera due to weakening or thinning uveal tissue ---> pigmentation from choroid makes it look like a melanocytic tumor increased intraocular pressure from glaucoma, trauma, or scleritis

Question 42

Staphyloma:

Answer 42

outpouching, can include cornea

Question 43

What is granulomatous/necrotizing scleritis? What is characteristic? In what animals is it most common?

Answer 43

idiopathic painful, rapidly-progressive inflammation that can involve the entire sclera, along with the uvea and retina, leaving the contralateral eye at risk robust inflammation containing epithelioid macrophages, multinucleated giant cells, and collagenolysis dogs

Question 44

What is the most prevalent scleral disease of dogs? How does it look grossly?

Answer 44

nodular granulomatous episcleritis (NGE) firm, painless, moveable, smooth, gray-pink mass/swelling

Question 45

What is characteristic of the histology of nodular granulomatous episcleritis (NGE)? What does it commonly respond well to?

Answer 45

discrete granulomas lacking collagenolysis immunosuppressive therapy

Question 46

What is the most common neoplasm of the sclera? What must it be differentiated from in cats?

Answer 46

limbal melanocytoma ---> benign (no metastasis), large, extension into cornea, most common in dogs iris melanoma extension

Question 47

What is characteristic of the histology in limbal melanocytoma?

Answer 47

heavy pigmentation with minimal atypia and absent mitoses - benign!