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

| Breed/Species | Common Condition | Notes |
|---|---|---|
| Cocker Spaniel (Dog) | KCS, Glaucoma | Higher incidence; regular screening recommended |
| Poodle | Cataracts, Glaucoma | Hereditary conditions common |
| Beagle | Glaucoma | Screen breeding stock |
| Bulldog | KCS, Entropion | Brachycephalic anatomy predisposes |
| Labrador Retriever | Cataracts, Entropion | Hereditary cataracts; consider breeding assessment |
| Cat (all breeds) | FHV-1 Keratitis, Uveitis | FHV-1 endemic; systemic disease common cause |

## 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