Cornea & Sclera Disorders Flashcards
Duration of antimicrobial use for corneal ulcerations?
Until the epithelium has healed/scarred over- determined via fluoroscopy
What are cycloplegic drugs?
Drugs that relax the ciliary muscles -> mydriasis + paralysis of lens accommodation
(“-plegic” = paralysis)
What drugs are contraindicated in corneal ulcerations?
Corticosteroids
(DELAY HEALING OF CORNEAL EPITHELIUM! Potential negatives of corticosteroids include: worsening of the infection, corneal thinning, perforation, increased intra-ocular pressure, and cataract development.)
Surgery for removal of necrotic/infected cornea?
Keratectomy
Surgical intervention that provides structural support to ulcerated cornea?
Corneal or biomaterial graft
Surgical intervention that speeds the healing of ulcerated cornea?
Conjunctival flap/graft
Functions of conjunctival flaps (4)
1. Mechanical support
2. Immediate blood supply
3. Fibroblast source
4. Epithelial cell source
Fibroblasts synthesize ECM & collagen -> structural framework for connective tissue
“SCCED”
Spontaneous Chronic Corneal Epithelial Defect
Superficial, non-healing ulcer
Idiopathic, non-infected
Main mechanical consequence of SCCED?
Epithelium cannot stick to the corneal stroma (-> loose lip / ridge appearance)
Treatment for SCCED
- Debridement
- SX = Keratotomy or keratectomy
- Manage as a superficial ulcer until healed
What virus causes keratitis in dogs and cats?
Herpesvirus
FHV-1, Canine Herpes
Dendritic ulcers/erosions
What is the most common bovine ocular disease?
- Inciting cause?
- Transmission?
- Prevention and treatment?
Infectious Bovine Keratoconjunctivitis (Bovine Pink Eye)
- Bacterial: Moraxella bovis
- Direct contact; mechanical vectors (Face Fly)
- Fly control, environmental and nutritional considerations; difficult to treat a heard of cattle with topical ABX
Cattle can usually heal eye on own! (unlike some cats, most dogs)
common source of transmission = feedlots!
What is this? Risks?
Corneal Foreign Body – risk for perforation so removal is imperative
Partial vs. Full Thickness corneal laceration / perforation - definition and treatment
Partial = does NOT rupture globe -> managed medically if SF (i.e. < 50% corneal thickness)
Full = DOES rupture globe -> managed with surgery
What has happened?
Perforation -> iris herniates out and plugs the perforated hole -> iris sticks to the cornea -> heals itself
Identify
Corneal Abscess
- Infection occurs within the corneal stroma (intra-stromal cellular accumulation); corneal epithelium still intact
Infected vs. Non-infected, sterile abscesses (e.g., puncture wound)
Corneal abscess healing depends on what?
Vascularization
Treatment used for this focal abscess?
Focal abscess -> conjunctival flap graft
Pigmentary Keratitis
- signalment
- cause
- tx
- brachycephalic dogs
- underlying cause that results in chronic irritation
- tx = address underlying cause, and topical cyclosporine or tacrolimus may help clear pigment
Proper medical terms for the “center” and “off-center” of cornea:
Axial and paraxial regions
What is the cornea comprised of?
Corneal epithelium -> corneal stroma (90% of cornea) -> Descement’s Membrane -> corneal endothelium
- avascular; lamellar collagen arranement
- “modified skin that is optically transparent”
Descement’s Membrane
Acellular, eosinophilic band that separates corneal stroma and corneal endothelium layers
Function of corneal endothelium
pump fluid out of the cornea –> cornea normally stays in a dehydrated state in order to be optically transparent
4 main pathologies of the cornea:
- Edema
- Vascularization
- Pigmentation
- Scarring / Fibrosis
Neovascularization occurs in response to disease
Diffusely cloudy cornea =
edema
What type of vascularization occurs in deeper, inflammatory conditions in the eye?
More “straight” vessels
Image = Uveitis
360º vascularization pattern
What type of vascularization occurs in superficial ocular disease
Superficial disease = Branching vascularization
?
Pigmentation of the cornea
Dermoid - inciting cause
Congenital corneal disorder
Persistent Pupillary Membrane
- inciting cause
- description
- Congenital Corneal Disorder
- Inherited failure of the uveal tract to regress appropriately during embryologic and immediate postnatal development
Persistent pupillary membranes (PPMs) occur secondary to the incomplete resorption of embryonic lenticular vasculature, a process which is usually complete by several weeks after birth but which may continue for several months in some dogs. Occasionally, the remnants of this process may be recognized as a collection of fine, punctate, tan to brown spots on the axial anterior lens capsule. PPMs may extend from iris to iris, iris to lens, iris to corneal endothelium and/or extend to float feely into the anterior chamber. The condition may be unilateral but is more commonly bilateral. Large or multiple PPMs may result in corneal opacification (due to endothelial damage, traction & fibrosis) and/or secondary cataract formation. Commonly affected dog breeds include the Basenji, Pembroke Welsh Corgie, Mastiff & Chow Chow.
Conjunctival hyperemia / chemosis
Vasodilatory response of micro-vasculature of the cornea in response to inflammation (looks red, swollen), such as allergic conjunctivitis
How does cornea heal to an epithelial defect?
Epithelial sliding and mitosis - no scarring
How does cornea heal to corneal stroma defect?
Epithelial sliding & mitosis -> keratocyte proliferation -> collagen deposition & scarring
Risk factors for corneal ulcer progression:
5
- abnormal tear production
- absent blinking
- brachcycephalic breed / conformation exophthalmos
- adnexal abnormality
- ulcer appears infected
Type of corneal ulcer: No depression / divot on the cornea; tiny “ridge” of epithelium missing
Superficial corneal ulcer
“blue edema” from partial loss of epithelium
Identify type of ulcer
Corneal Stroma Ulcer: ridge present, deep depression upon cornea
This horse has a secondary fungal infection (the white plaque) due to a corneal ulcer. Why is there a lack of edema present?
NO EDEMA b/c the fungal infection has invaded the stroma -> no place for the ECF to accumulate in and cause edema
Corneal edema is defined as the increase in the thickness of cornea due to the accumulation of extracellular fluid in epithelium and stroma resulting in loss of corneal transparency
Identify
Descemetocele — the only structure left maintaining the integrity of the globe= the basement membrane / Descemet’s Membrane. Occurs due to extreme thinning of the stroma in severe corneal ulcers
Chronic Superficial Keratitis (Pannus)
- Inciting cause
- Common breed
- Possible etiology
- Clinical signs
- Treatment
- Immune-mediated
- German Shepherds
- Etiologies: UV radiation, high-altitude regions (b/c higher UV radiation)
- Clinical Signs: Corneal vascularization/pigmentation beginning from lateral limbus; corneal hyperemia; thickening or depigmentation of nictitans (3rd eyelid); non-painful
- Bilateral
- Topical corticosteroid tx, life-long
A pannus is an extensive ingrowth of tissue from the limbus onto the peripheral cornea
Equine Immune-Mediated Keratitis
- Typical presentation
- The 4 classifications
Can be unilateral or bilateral
1. Epithelial
2. Superficial Stromal
3. Mid-Stromal
4. Endothelial
What are 3 ways a superficial stromal Equine IMMK be surgically treated?
- Lesion excision;
- Cyclosporine implants (dilutes cyclosporine slowly, approx. 1-year duration of efficacy);
- Photodynamic therapy (inject dye into cornea and use laser to activate the dye)
Lipid Keratopathy
- Definition
- Clinical Appearance
- Causes (3)
-Accumulation of cholesterol within the corneal layers => cloudy spots on the cornea // “sparkly” appearance
- Non-painful!
Causes:
1. Lipid dystrophy (genetic, bilateral)
2. Lipid degeneration (lipid deposits b/c of local, non-inherited metabolic issue. e.g., = hx of or active corneal/scleral disease)
3. Lipid keratopathy (systemic lipid metabolism abnormality//elevated levels of systemic cholesterol. Cushing’s, chronic corticosteroid use, diabetes, hypothyroidism)
Lipid Dystrophy
- round-oval in shape
- central cornea
Corneal dystrophy is an inherited, or genetic condition and is most commonly seen in dogs. This condition is rarely seen in cats. It is usually present in both eyes. It is not painful and has a minimal effect on vision. Some commonly affected breeds include Beagles, Cavalier King Charles Spaniels, Siberian Huskies, Alaskan Malamutes, Samoyeds, American Cocker Spaniels, Labrador Retrievers, and Collies.
Lipid Degeneration
Occurs secondary to inflammation in the eye and is usually associated with other eye diseases, such as anterior uveitis (inflammation of the iris, choroid, and ciliary body), keratitis (inflammation of the cornea), or scleritis (inflammation of the sclera or white of the eye) Sometimes lipid accumulation is associated with trauma, such as after corneal ulceration that healed with lipid deposits. This is seen more frequently in dogs than cats.
Corneal Mineralization / Calcific (Band) Keratopathy
- Definition / appearance
- Causes (3 main ones)
Deposition of calcium hydroxyapatite into sub-epithelium of cornea => band-like, horizontal plaque across the cornea
Causes:
1. Senescence
2. Secondary to systemic Ca/P ratio imbalance (e.g., high calcium/ phosphorus ratios // hyperadrenocorticism)
3. Horses with chronic, recurrent uveitis
Endothelial Dystrophy / Degeneration
- Etiology
- Clinical Signs
Reminder: Endothelium pumps out fluid from the cornea (maintains a dehydrated state!
Etiology: abnormal corneal endothelium development, + age-related endothelial degeneration
Clinical signs: progressive, severe corneal edema. Bilateral
Corneal endothelial Dystrophy or Endothelial Degeneration is a disease of the internal layer of the cornea. In a normal cornea, endothelial cells work as a pump to remove fluid from the cornea. This maintains the cornea’s clear appearance.
When endothelial dystrophy is present, endothelial cells are gradually lost. This means fluid is no longer removed from the cornea. This results in corneal edema (swelling), cloudiness of the cornea, and decreased or “blurred” vision.
With chronic (long-term) edema, the fluid accumulates, forming pockets, known as bullae. These bullae can rupture through the outer layer of the cornea (the epithelium), forming a corneal ulcer. These ulcers are very painful, may be recurrent, and often non-healing.
Eosinophilic Keratitis / Keratoconjunctivitis
- Species
- Diagnosis
- Treatment
- Prognosis
- Cats & Horses
- Eosinophils visualized (scrape the tissue -> cytology)
- Anti-inflammatory medications, +/- Topical corticosteroids, antihistamines (horses)
- Long-term treatment, but prognosis can be excellent with it
Feline Corneal Sequestrum
- Clinical Features
- Etiology / Pathogenesis
- Painful, focal region of stromal pigmentation & necrosis (brown-black pigmentation)
- History of Chronic, non-healing ulcer
- Associated with a brachycephalic breed disposition (such as Persians) and often an active feline herpes virus infection
Neoplastic Corneoscleral Masses
- Origin / pathogenesis
- Originates from the limbus (corneosclero junction) // vascularized areas
- Image: melanoma originating from melanocytes growing into the cornea
