Cornea and Conjunctiva Disorders

• Learning objectives include identifying common cornea and conjunctiva disorders, formulating a diagnostic approach, and recommending appropriate management.

Corneal Anatomy

• The cornea and tear film consist of the tear film (lipid, aqueous, mucin layers), corneal layers (epithelium, stroma, Descemet's membrane, endothelium), anterior chamber, iris, pupil, and lens.

Corneal Transparency

• Corneal transparency is essential for light refraction and transmission and is achieved through several factors:
• Small diameter and lamellar arrangement of collagen fibers
• Absence of blood vessels and pigment
• Dehydration maintained by the endothelium
• A smooth optical surface
• Precorneal tear film quality

Major Corneal Pathological Reactions

• Corneal vascularisation manifests as red
• Corneal oedema appears as blue/grey
• Stromal malacia-melting presents as yellow/white
• Corneal fibrosis is scarring, appearing grey
• Corneal melanosis is black
• Stromal infiltration with white blood cells appears yellow/green
• Stromal mineral or lipid deposition is white

Corneal Oedema

• Corneal oedema involves excess fluid accumulation within the stroma, appearing blue and "fluffy" with indistinct borders.
• Diffuse, marked oedema with no fluorescein uptake indicates no pain/inflammation, normal IOP, and no aqueous flare, ruling out endothelial degeneration/dystrophy.
• Focal, mild oedema with positive fluorescein uptake indicates pain, inflammation, abnormal IOP, or aqueous flare, ruling out glaucoma, anterior uveitis, and anterior lens luxation, and suggesting corneal ulceration.

Corneomalacia - Stromal Melting

• Melting occurs when the stroma oozes and sags due to collagen destruction by proteinases from microorganisms, white blood cells (especially neutrophils), and corneal epithelial cells/keratocytes.
• Microorganisms causing it include gram-negative Pseudomonas spp. and gram-positive Streptococcus spp. and Staphylococcus pseudointermedius

Corneal Melanosis-Pigmentary Keratitis

• Pigmentary keratitis is a nonspecific response to chronic corneal irritation, which isn't a diagnosis by itself.
• Melanin gets deposited in the corneal epithelium and anterior stroma, with melanocytes migrating from the limbus.
• Insufficient corneal protection causes include lagophthalmos, KCS, ectropion, macropalpebral fissure, CN V/VII dysfunction, and qualitative tear film deficiency.
• Excessive corneal irritation causes include entropion, distichiasis, ectopic cilia, trichiasis, foreign bodies, blepharitis, eyelid mass, pannus, and herpes virus.

Corneal Diseases: Keratitis

• Ulcerative keratitis includes:
• Superficial corneal ulcer
• Spontaneous chronic corneal epithelial defect (SCCED)
• Stromal ulcer (superficial and deep)
• Descemetoceles
• Melting ulcers
• Ruptured ulcers
• Corneal foreign bodies
• Corneal sequestrum (cats only)
• Non-ulcerative keratitis includes:
• Chronic immune-mediated superficial keratoconjunctivitis (pannus)
• Keratoconjunctivitis sicca (KCS)
• Pigmentary keratitis/keratopathy
• Eosinophilic keratitis
• Corneal lipid/mineral dystrophy
• Corneal endothelial dystrophy
• Corneal degeneration
• Dermoid

Approach to Corneal Ulceration Case

• The approach to corneal ulceration involves ophthalmic examination, Schirmer tear test, swab for culture and sensitivity, fluorescein staining, and sample for cytology.

Tests for Corneal and Conjunctival Diseases

• Schirmer Tear Test 1 (STT) measures the aqueous component of tear film (mm/min) without local anaesthesia; place a test strip in the inferior conjunctival fornix for 60 seconds; dog result: 15-25mm/min, less than 5mm/min is diagnostic for KCS. Cat results vary
• Tonometry measures intraocular pressure using TonoPen (requires local anaesthesia) or TonoVet (doesn't require local anaesthesia); Dog result: 15-25mmHg, Cat result: 12-19mmHg
• Corneo-conjunctival cytology and culture involves collecting samples before topical treatment; use local anaesthesia (except for conjunctival swabs); Culture involves sterile swab rolling over the corneal lesion or lower conjunctival sac. Cytology involves scraping any lesions with the blunt end of a scalpel blade or cytobrush
• Ophthalmic dyes aids in assessing eye issues:
• Apply a drop of dye, gently move the eyelids to distribute it, and flush with saline to remove excess.
• Use cobalt blue light to enhance fluorescein, abnormal staining indicates corneal issues.
• Assess tear film quality with TFBUT (normal time about 20 seconds)

Common Causes of Corneal Ulcerative Disease

• Underlying etiologies and examples include:
• Eyelid abnormalities like eyelid agenesis (coloboma), entropion, blepharitis, eyelid neoplasia, and lagophthalmos
• Eyelash or hair abnormalities like ectopic cilia, distichiasis, trichiasis, and nasal fold trichiasis
• Tear film abnormalities like keratoconjunctivitis sicca, qualitative tear film abnormalities, facial nerve paralysis, and exposure keratitis
• Infections like primary/secondary bacterial (Pseudomonas), and melting ulcer
• Trauma like RTA, blunt trauma, cat scratches, foreign bodies, and thermal injury
• Dystrophy/degeneration like stromal corneal lipid/mineral accumulation, corneal oedema with glaucoma, and corneal endothelial dystrophy

Conditions Predisposing to Corneal Ulceration

• These conditions include neoplasia (meibomian adenoma), nasal fold trichiasis, trichiasis, lagophthalmos, entropion, and distichiasis.

Skull Conformation and Breed Predisposition to Corneal Ulcerative Disease

• Individual breeds with the highest corneal ulcerative disease (CUD) prevalence:
• Pug: 5.42%
• Boxer: 4.98%
• Shih Tzu: 3.45%
• Cavalier King Charles Spaniel: 2.49%
• Bulldog: 2.41%
• CUD prevalence in brachycephalic breeds: 3.76%, which is higher than in Spaniels 1.31%

Approach to Corneal Ulceration Case

• It involves ophthalmic examination and diagnosis via identifying eyelid abnormalities, eyelash/hair abnormalities, tear film abnormalities, infections, irritants, trauma, or dystrophy/degeneration.

Corneal Ulceration: First Assessment

• First assessment involves identifying and correcting/removing the primary cause.
• Complicated ulcers present for >7 days and/or involve the stroma
• Simple ulcers heal within 7 days and do not involve the stroma

Approach to Corneal Ulceration Treatment

• Medical treatment includes topical antibiotics, antivirals, artificial tears, collagenase inhibitors, and atropine (for reflex uveitis, not in KCS).
• Surgical treatment includes analgesics and contact lenses.
• Other surgical treatments include epithelial debridement, superficial keratectomy, conjunctival grafts, corneoscleral transposition, cyanoacrylate adhesives, and third eyelid flaps.

Superficial Chronic Corneal Epithelial Defect (SCCED)

• Synonyms: non-healing/indolent/Boxer/refractory ulcer, spontaneous chronic corneal epithelial defect.
• Characteristics: Develops without trauma, heals slowly, has blurred edges with fluorescein uptake underneath the epithelium, nonadherent epithelium, spontaneous occurrence, unilateral presentation (but can be bilateral), and abnormal adhesion of epithelial cells/stroma.
• Typically seen in Boxers, Corgis, and middle-aged/older animals.

SCCED - Medical Treatment

• Medical treatment includes:
• Topical antibiotics if the cornea is compromised (chloramphenicol, chlortetracycline)
• Tear replacement therapy (Remend, Vizoovet, Oculeze), but beware of dry eye
• Atropine- considered in individual base (e.g., reflex uveitis)
• Pain control using systemic/topical NSAIDs.
• Prevention of self-trauma. Requires re-examination in 7 days

SCCED - Surgical Treatment

• It is characterised by a thin hyaline membrane on the anterior stroma that prevents adhesion of new epithelium.
• It occurs most commonly in middle-aged to older animals, where medical treatment is seldom successful. Prophylactic antibiotics are needed every 6-12 hours if the cornea is compromised.
• A procedure is usually needed to remove or destroy the hyaline membrane

Stromal Corneal Ulceration - Management

• Broad spectrum topical antibiotic therapy (Fluoroquinolones) recommended.
• Avoid ointments, increased risk of anterior uveitis if used.
• Can use antiproteolytic agents using autologous serum.
• N-Acetylcysteine (Stromease), EDTA, Tetracyclines can be helpful.
• Cytoplegic-topical 1% Atropine but avoid in KCS.
• Systemic NSAID +/- more potent analgesia can be useful.
• DO NOT USE TOPICAL CORTICOSTEROIDS, leads to higher risk of infections
• Surgery can be helpful

Melting Ulcer - Ophthalmic Emergency

• Pseudomonas aeruginosa, B-haemolytic Streptococcus spp., and Staphylococcus pseudointermedius are commonly associated with collagenolysis
• Cytology: Pseudomonas - rods, Streptococcus, Staohylococcus spp. - cocci
• Antibiotic treatments:
• Pseudomonas: fluoroquinolones, gentamycin, polymyxinB
• Streptococcus spp. : chloramphenicol, cephalexin
• Staphylococcus pseudointermedius: amoxicillin/clavulanic acid, cephalexin, and cefazolin
• MRSP (methicillin-resistant S. pseudintermedius) cases have increased in dogs since 2006, it's vital to collect a sample for culture.

Melting Ulcer - Ocular Emergency

• Loading dose: 1 drop q5min for 6-12 doses, then 1 drop q1-2h for 24-48h for medications to properly work.
• Ciprofloxacin-Ciloxan is usually a first choice
• Ofloxacin-Exocin is used for cases where other antibiotics are ineffective
• Use of Chloramphenicol can be helpful
• Autologous serum is an anti-collagenase against serine proteases and MMPs.
• EDTA and N-acetyl cysteine are can act against MMPs
• Use systemic antibiotics is increased risk of globe rupture present.
• Cytoplegic-topical 1% Atropine is helpful- not helpful in KCS
• Pain relief is achieved via analgesia: NSAID, stronger if required.

Chronic Superficial Keratitis (Pannus, Überreiter's Syndrome)

• It is an immune-mediated progressive superficial keratitis with a genetic basis.
• It is bilateral, leads to potential blindness, where the temporal limbus appears as a red vascularised conjunctival lesion.
• Occurs if the lesion progresses to the temporal cornea as a fleshy vascularized lesion, where then corneal vascularization, granulation & pigmentation appears at the nasal limbus.
• Cholesterol deposits form within the stroma and the third eyelid thickens where females are more commonly affected
• No cure, requires life-long therapy:
• Initially topical corticosteroid (1% prednisolone, 0.1% dexamethasone) 3-4x daily
• Topical cyclosporine (0.2-2%) with or without corticosteroids 2x daily
• For refractory cases:
• Subconjunctival injection of corticosteroids
• β-radiation
• Superficial keratectomy

Corneal Lacerations- Non Penetrating

• Common ocular emergency
• Caused by cat claws, thorns, nails etc.
• It can be partial thickness where it punctures or lacerations the eye
• If large enough, can lead to a corneal flap
• Medical treatment consists of stromal exposure management with regular re-examinations, if the cornea is small.
• Direct suturing or through use of a conjunctival graft.

Corneal Lacerations-Full Thickness

• Occurs when there is no iris prolapse and no lens injury
• Other presentations can be there is iris prolapse with possible lens injury.
• During cornea laceration, sudden decompression of anterior chamber leads to the production and extravasation of proteins like fibrinogen from the iris and ciliary body where fibrin acts as a plug to coat the corneal defect.
• Prolapsed iris (if there) may either be visible or hard to see if under coagulated fibrin

FHV-1 Keratitis in Cats

• Keratotomy must never be performed, can lead to corneal sequestration
• It is a primary ocular pathogen
• Always has FHV-1 involvement unless proven otherwise.
• Shows tropism in the conjunctiva and commonly causes corneal disease.
• Presents in dendritic and geographic ulcerations and marked different clinical presentations.
• Remains latent in ganglia via tigeminal nerve where recrudescence may be present and has subclinical shedding properties
• Best standard for testing is PCR

FHV-1 Keratitis in Cats- Clinical Signs

• Frequently unilateral, with epiphora (crying in one eye).
• Clinical signs include blepharospasm, dendritic lesions-short lasting, geographic ulceration, qualitative tear film disease, and stromal keratitis (caused by immune mediated inflammation).

FHV-1 Keratitis in Cats- Treatment

• Keratotomy should not be performed in cats as results in corneal sequestration
• Topical antibiotic (Chloramphenicol, Fusidic acid) and Famciclovir 90mg/kg q12h are useful.
• Other management options include topical ganciclovir (Virgan) q 6-8h for 21d, autologous serum, and tear replacement therapy.
• Environmental modifications (stress or overcrowding reduction) is key.

Feline Eosinophilic Keratitis

• Traditionally treated with ophthalmic or systemic corticosteroids, involvement of FHV-1 presents dilemma as immunomodulatory drugs can lead to recrudescence from latent disease- consider antivirals first.
• It is seen as proliferative keratoconjunctivitis from immune response and white/pink deposits that are slowly developing
• Affects conjunctiva, epithelium, and superficial stroma and found at the limbus
• May be part of an eosinophilic granuloma complex that has associations with FHV-1. use a brush to diagnose eosinophils
• Not curable and requires medical managment like Famciclovir and topical steroids. Can also use autologous serum and lubricants. Takes weeks to month to resolve

Corneal Sequestrum

• Treat like FHV-1 unless other cause is identified.
• Not age or breed specific can can involve early clincal discolouration with late stage firm brown lesions.
• Brachycephalic breeds predisposed due reduction in corneal sesitivity
• Treat via medical or surgical (medical is complex though)

Conjunctiva - Normal Commensal Flora

• There is normal flora that exists in the conjunctiva layers of the eye
• Made of non-keratinized stratified squamous epithelium and a goblet cell (mucoid layer of precorneal tear film). The substantial propria also helps compose the structural layer.
• Also conjunctival assocaited lymphoid tissue (CALT) that aids in production.
• 46-90% in dogs, 40% in cats.
• Dogs are made of Staphylococcus spp, bacillis, and corynebacterium
• Cats are made of staphylococcus felis

Conjunctivitis

• Defined through hyperermia and chemosis due to normal IOP. The mucus membranes can be very sensitive in this case
• Conjunctival is a vision threatening disease because of the potential for ocular diseases
• Needs differentiation among uveitis, orbital, glacoma disease
• The deficiency is caused dueto a low mucin production and felines usually suffer from FHV

Clinical Sign of Conjunctivitus

• This is characterised with haemorrhaging and edema to the eye along with discharge through the eyes to potentially cause even for pruiritis (itchy eyes)

Approach to Conjunctivitis

• There are 2 tear test including the Schirmer Tear Test and the fluorescein test and based on levels (normal vs increased), a normal eye examination can be perforemd
• Also should conduct eye examintations to determine severity and type fo disease present.

Treatment

• Surface should be through for evaluation
• Antibiotic prescriptions should be used to combat any potential infections

General Recommendations Bacteria

• To properly treat , can provide prevention and soaks and potentially use collard on the elizabethans

Kerato Conjuicntivits (KCS)

• A quantitative measure of the tear film through a schirmer test and diagnosis of break thru
• Clinical signs may include discharge and swelling may cause dry corners and ulceritive disease
• Through a low SFT score an assessment can be performed through different test types the amount/type of treatmanent can be selected based on reading levels and severity

Cyclospirne A

• helps inhibit the spread of t-cells thru Lacrimal which will helps the stimulare Lacrimal and normalize goblet cells
• with treatmant can see result for 50%

Opcular AMs

• Are usually based on staphs bacteria with the intention of stopping the spread for the disease early on with medication