Ocular Flashcards
What are the 3 tunics of the eye? What structures are in each? What is the function of each?
- FIBROUS: cornea, sclera; shape, protection, light refraction
- VASCULAR/UVEA: iris, ciliary body, choroid; pigmented and vascular for light reflection, scattering, nutrition, and waste removal
- NERVOUS: retina, optic nerve; electric and chemical signaling to brain
What is the purpose of the aqueous humor, lens, and vitreous humor?
light refraction and internal pressure maintenance (must be transparent!)
Eye anatomy:
What are 6 common clinical presentations of ocular disease?
- 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
- conjunctival discharge
- swelling and pain (chemosis)
- sensitivity to light
- excessive (epiphora) or decreased lacrimation due to damage to the glands
- opacity of the cornea or lens
What is exophthalmos? Proptosis? Buphthalmos? Enophthalmos? Hyphema? Hypopyon?
- 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
What is this?
buphthalmos - enlarged eye
What is this?
proptosis - protrusion of eye out of orbit
What is this?
exophthalmos - protrusion of eye within orbit
What is this? What are some possible differential diagnoses?
hyphema - blood in anterior chamber
hypertension caused by hyperthyroidism or CKD
What is this?
hypopyon - pus in anterior chamber
What is the most common cause of congenital ocular abnormalities?
infectious, nutritional, or genetic teratogens that cause defective cell signaling during organogenesis in embryonic development
What is microphthalmia?
congenital/hereditary anomaly where one or both eyes are abnormally small and are histologically malformed and disorganized
What is synophthalmos?
congenital/hereditary anomaly where two eyes are present in a singular orbit caused by incomplete separation of the paired globes
What is cyclopia?
congenital/hereditary anomaly where there is a singular, central eye
What is the most common cause of cyclopia and synophthalmos in sheep? When in embryonic development is this able to happen?
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
What vasculature is present in the embryonic eye? How does this develop during gestation?
hyaloid artery branches and supplies blood to different structures of the eye
these vessels should regress 2-4 weeks after birth
What is persistent pupillary membrane? How does it affect the animal?
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
What are the 5 layers of the normal cornea?
- epithelium - nonkeratinized stratified squamous
- basement membrane
- stroma - parallel collagen fibers (clear spaces that look like edema are common artifacts upon fixation)
- Descement’s membrane - produced by endothelium
- endothelium
What part of the eye is most susceptible to damage?
cornea —> outermost, exposed layer
(allow light to enter)
What are 5 common responses of the cornea to injury?
- edema - opacity
- inflammation - keratitis
- vascularization*
- pigmentation*
- fibrosis*
*chronic, lymphoplasmacytic
Chronic corneal damage:
- inflammation
- vascularization
- pigmentation
- results in opacity, pigmentation, and vision effects
Keratitis and healing:
- opacity, pigmentation, vascularization
- decreased opacity and vascularization
What are 4 common causes of keratitis? What specific bacterium and virus cause this?
- irritation - entropion, eyelid masses, particulate material
- desiccation/exposure - lagophthalmos (incompletely closed eyelids common in brachycephalic breeds), buphthalmos (glaucoma), exophthalmos (orbital masses)
- repeated corneal ulceration
- trauma
Moraxella bovis, feline herpesvirus-1
What is indicative of acute keratitis?
accumulation of neutrophils cause keratomalacia (melting ulcer) due to excretion of proteases and metalloproteases
- endogenous: inflammation
- exogenous: bacteria, fungi
(basophilic band = neutrophils)
What is indicative of chronic keratitis?
lymphoplasmacytic inflammation leads to epidermalization (eye becomes “skin-like”) —> acanthosis, melanosis, vascularization, stromal scarring (fibrosis)
What is chronic superficial keratitis/conjunctivitis? What is the most likely etiology? What animal is predisposed?
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
What are boxer ulcers? At what age does it most commonly develop? What is the most likely cause?
indolent (lazy) ulcer that is a non-healing, superficial corneal erosion
middle to older age
spontaneous or traumatic defect in epithelial adhesion to stroma
What are the 2 histological characteristics of boxer ulcers?
- non-adherent hyperplastic epithelium
- clefts between epithelium and stroma
What is eosinophilic keratitis?
proliferative, placoid lesions of white material common in cats and horses
What cytology is indicative of eosinophilic keratitis?
impression smear = EOSINOPHILS. granules, epithelial cells, mast cells
What is corneal sequestrum? What is the likely cause? How does it affect the eyes?
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
What is the most common cause of fungal/mycotic keratitis? In what animals is this most common?
opportunistic Aspergillus or Fusarium infection of corneal wounds being treated with antibiotics or corticosteroids
horses in warm and humid climates
What lesion is characteristic of fungal/mycotic keratitis? What tropism does it typically have? What does this cause?
destructive, deep stromal, ulcerative suppurative keratitis with keratomalacia (liquefaction)
Descement’s membrane —> ruptures, causing exudate spillage into the anterior chamber (endophthalmitis)
Fungal/mycotic keratitis, keratomalacia:
What causes corneal degeneration? What 3 metabolic disorders are most common?
accumulation of lipids and calcium
- high fat diets - amphibians, reptiles, and birds fed high amounts of crickets and mealworms
- hyperadrenocorticism, hypothyroidism, diabetes
- hypercalcemia
What is characteristic in the histology of lipid keratopathy?
- cholesterol clefts
- oil red O stained fat droplets
What is the most common origin of corneal neoplasms?
extension from adjacent tissue (conjunctiva)
In what animals is squamous cell carcinoma of the eyes most common? What is the cause?
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
What is the most common cause of corneal neoplasms in dogs? What is a major risk factor?
dogs with chronic keratitis develop hyperplasia, which develops into dysplasia and neoplasia
use of immuno-modulating drugs
What is corneal dermoid?
congenital, non-neoplastic, choristoma - where normal tissue not usually found in the eye is present
What a staphyloma? What is it commonly lined by? What is thought to be the cause?
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
Staphyloma:
outpouching, can include cornea
What is granulomatous/necrotizing scleritis? What is characteristic? In what animals is it most common?
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
What is the most prevalent scleral disease of dogs? How does it look grossly?
nodular granulomatous episcleritis (NGE)
firm, painless, moveable, smooth, gray-pink mass/swelling
What is characteristic of the histology of nodular granulomatous episcleritis (NGE)? What does it commonly respond well to?
discrete granulomas lacking collagenolysis
immunosuppressive therapy
What is the most common neoplasm of the sclera? What must it be differentiated from in cats?
limbal melanocytoma —> benign (no metastasis), large, extension into cornea, most common in dogs
iris melanoma extension
What is characteristic of the histology in limbal melanocytoma?
heavy pigmentation with minimal atypia and absent mitoses
- benign!
