ophthalmology-exam

name: ophthalmology-exam description: Schirmer tear test values and interpretation, fluorescein staining, tonometry with normal IOP ranges, common conditions by species (KCS, glaucoma, cataracts, ulcers, entropion, cherry eye), breed predispositions.

Ophthalmology Exam

Overview

Systematic ophthalmic examination with diagnostic reference values. Covers tear production (Schirmer test), intraocular pressure (tonometry), corneal integrity (fluorescein), and species-specific disease differentials with breed predispositions.

When to Use

• User presents ocular pathology or performs routine ophthalmic examination
• User needs diagnostic values, IOP interpretation, tear production assessment
• Keywords: eye, Schirmer, tonometry, IOP, fluorescein, keratitis, KCS, glaucoma, cataract, corneal ulcer, uveitis, entropion, cherry eye

Schirmer Tear Test (STT)

Normal Values

• Dogs: 15-25 mm/minute (STT-1); STT-2 rarely used
• Cats: 10-20 mm/minute (STT-1); lower baseline than dogs
• Horses: 30-40 mm/minute

Interpretation

• STT-1: ≥15 mm/min (dogs) or ≥10 mm/min (cats) = normal
• KCS Range: 5-14 mm/min = mild-moderate; <5 mm/min = severe KCS
• Stimulus STT (STT-2): Reflex tear production; >25 mm/min suggests adequate reflex function despite low basal production

Limitations: Single STT-1 <5 mm/min diagnostic for KCS, but sequential testing more reliable; environmental factors (stress, time of day) affect values

Intraocular Pressure (IOP) - Tonometry

Normal Ranges (Applanation Tonometry)

• Dogs: 12-22 mmHg (mean 15-18)
• Cats: 12-20 mmHg (mean 15-17); typically 2-3 mmHg lower than dogs
• Rabbits: 12-22 mmHg

Glaucoma Thresholds

• IOP >25-30 mmHg warrants investigation for glaucoma

• 35 mmHg with clinical signs (pain, mydriasis, corneal edema, lens subluxation) = acute glaucoma emergency

• Baseline IOP varies by individual; serial measurements more useful than single value

Rebound Tonometry: Non-contact; convenient but 1-3 mmHg higher than applanation; acceptable for screening

Technique: Applanation (gold standard); requires anesthesia/topical blocks in fractious animals; avoid if corneal ulcer suspected (contraindicated)

Fluorescein Staining

Technique: 0.5-1% sterile fluorescein strip or solution; examine under cobalt-blue light (Wood's lamp, slit lamp)

• Positive stain (green): Indicates loss of corneal epithelium (ulceration, erosion, foreign body)
• Negative stain (punctate dark spots in epithelium): Desquamated epithelial cells, superficial keratitis, KCS changes

Differential Diagnosis by Staining Pattern

• Central ulcer: Melting ulcer, deep stromal involvement; risk of perforation
• Dendritic pattern: Suspected herpesvirus (feline, equine)
• Punctate staining: KCS, superficial keratitis, early ulceration

Precautions: Do not apply pressure; avoid excessive fluorescein (causes false staining); irrigate eyes post-exam to prevent dye absorption

Common Conditions by Species

Dogs

1. Keratoconjunctivitis Sicca (KCS)

   • Prevalence: 1-5%; breeds: Cocker spaniels, Bulldogs, West Highland terriers
   • Diagnosis: STT-1 <15 mm/min (ideally <10); history of chronic conjunctivitis, xerosis
   • Treatment: Artificial tears (TID-QID minimum), cyclosporine (0.5% BID-TID; onset 4-6 weeks), tacrolimus ophthalmic, pilocarpine (rarely used)

2. Glaucoma

   • Acute: IOP >35 mmHg, mydriasis, pain (blepharospasm, photophobia), corneal edema, red eye
   • Chronic: Gradual blindness, buphthalmos (large eye), cupped optic disc
   • Breeds predisposed: Beagles, Cocker spaniels (primary); secondary in uveitis, anterior lens luxation

3. Cataracts

   • Breed-related (hereditary): Poodles, Labrador retrievers, Miniature schnauzers
   • Diagnosis: Lens opacity on direct/indirect ophthalmoscopy; shadows in pupil
   • Treatment: Surgical (phacoemulsification) for vision-threatening; medical treatment not effective

4. Corneal Ulcers

   • Classification: Superficial vs. deep vs. perforating
   • Fluorescein positive: Indicates epithelial loss
   • Melting ulcer: Stromal collagenase activity; risk of rapid progression/perforation; requires intensive care

5. Entropion

   • Inversion of eyelid margin; irritates cornea
   • Breeds: Labrador retrievers, Chow Chows, Basset hounds, Rottweilers
   • Treatment: Surgical correction (blepharoplasty)

Cats

1. Herpes Simplex Keratitis (Feline Herpesvirus-1, FHV-1)

   • Presentation: Conjunctivitis, keratitis, dendritic ulcers (fluorescein-positive)
   • Diagnosis: PCR, viral culture (less sensitive); clinical presentation in endemic regions
   • Treatment: Antiviral ointment (idoxuridine, vidarabine 5×/day), L-lysine (250-500 mg BID oral)

2. Keratoconjunctivitis Sicca

   • Less common than in dogs; associated with FIV, Chlamydia infection
   • Diagnosis: STT-1 <10 mm/min
   • Treatment: Same as canine (cyclosporine, artificial tears)

3. Glaucoma

   • Secondary to uveitis common; primary glaucoma less common than dogs
   • Associated conditions: Anterior uveitis, inflammatory disease, lymphoma
   • IOP threshold: >20 mmHg warrants investigation; >25-30 mmHg with signs = acute glaucoma

4. Cataracts

   • Less common hereditary form than in dogs; diabetes-related common (rapid onset)
   • Diagnosis: Lens opacity
   • Treatment: Surgical (phacoemulsification) if vision desired; medical management less effective

5. Anterior Uveitis

   • Often secondary to systemic disease (FIV, FeLV, toxoplasmosis, fungal)
   • Signs: Pain (blepharospasm, photophobia), corneal edema, iris color change, hyphema (blood in AC)
   • Topical: Atropine (dilates pupil, improves comfort); dexamethasone/betamethasone QID (caution: avoid if corneal ulcer)

Exotic Species

• Rabbits: Cataracts common; KCS rare; dacryocystitis (blocked tear duct) frequent; need specialized anesthesia for tonometry
• Reptiles: Spectacle (brille, transparent covering); retained spectacle common; no eyelids in snakes

Breed Predispositions

Workflow

1. Examine external eye (lids, lashes, conjunctiva, sclera)
2. Perform Schirmer tear test (STT-1) prior to fluorescein (dye interferes)
3. Apply fluorescein; examine corneal surface under light
4. Tonometry (applanation if ulcer ruled out)
5. Direct and indirect ophthalmoscopy (dilate with tropicamide 1% if indicated)
6. Assess accommodation, pupillary light reflex, consensual response

Key Species Differences

• Dogs: Higher baseline IOP (15-18 mmHg); STT values 15-25 mm/min; breed-specific screening available (OFA, CERF)
• Cats: Lower tear production (10-20 mm/min); IOP slightly lower (15-17 mmHg); FHV-1 endemic; secondary uveitis common
• Exotics: Specialized anesthesia required; reference ranges differ significantly

Limitations

• Single IOP measurement insufficient for glaucoma diagnosis; serial measurements, fundic assessment essential
• Fluorescein staining does not assess depth of ulceration (ultrasound or clinical assessment needed)
• Some breed predispositions lack sufficient statistical data; breeding decisions should use multi-generational pedigree assessment
• Ophthalmic examination in conscious fractious animals may be incomplete; sedation/anesthesia may be required
• Referral to board-certified ophthalmologist recommended for glaucoma, anterior uveitis, corneal melting, and surgical candidates