Ocular exam
What tests make up the ocular minimum database? What are normal values for each?
STT: normal >15mm/min in dogs, >9 mm/min in cats
IOP: normal 10-20 mmHg in eyes without anterior uveitis, <10 mmHg in eyes with anterior uveitis or significantly lower than a contralateral eye without uveitis
Fluorescein stain
What medications cause mydriasis?
Atropine
Tropicamide
What is proptosis?
Proptosis is defined as the forward displacement of the globe to the extent that the eyelids are trapped behind the globe equator.
Blindness can occur due to disease in these 5 anatomic locations.
Assess menace, visual tracking (cotton ball test), maze test
Clinical signs - mydriasis or anisocoria, normal/decreased/absent PLR, lack of menace, bumping into objects
1) Cornea - loss of transparency
2) Lens - cataract
3) Retina - detachment, hemorrhage, inflammation/cellular infiltrate
4) Optic nerve and tracts
5) Brain
What is the mechanism of action of timolol?
Nonselective beta-adrenergic receptor blocking agent
Blockade of ciliary body beta-receptors reduces IOP by decreasing aqueous humor production
Use with caution in patients with AV block, bradycardia, heart failure, asthma, chronic bronchitis
What is the difference and why is it important to differentiate episcleral from conjunctival hyperemia?
Episcleral vessels - stout, easily identifiable vessels, course perpendicular to limbus, usually stop before reaching limbus
--> Associated with intraocular disease: anterior uveitis, glaucoma
Conjunctival blood vessels - extremely fine, branching, cross limbus
--> External or surface disease: conjunctivitis, KCS
What are two medications that can cause blindness?
Ivermectin toxicity in dogs
Enrofloxacin in cats --> retinal degeneration
Why does lateral strabismus often occur with proptosis of the eye?
Bonus: What cranial nerve controls medial rectus muscle?
What is the pathognomonic signs of anterior uveitis?
Aqueous flare
--> Also see keratic precipitates (fibrin and WBC aggregates on the posterior cornea), hyphema (RBCs), and hypopyon (WBCs)
What is the treatment for primary anterior lens luxation?
Reduce IOP:
- Dorzolamide
- Mannitol
- Why not latanoprost?
Prompt referral for surgical removal
What are differentials for subconjunctival hemorrhage?
direct ocular trauma, coagulopathy, strangulation, chronic emesis, rarely constipation
What class of medications is linked to the development of KCS?
Systemic sulfa derivatives
Up to 50% of affected dogs develop KCS within 30 days of treatment, can be permanent
Recommend STT every 2-3 days in ICU
Discontinue medication, start cyclosporine ointment and increased frequency of artificial tear lubrication
What is the prognosis for return of vision?
What are long-term complications?
20% of globes retain some functional vision.
Complications -
Lateral strabismus
KCS
Corneal ulceration
Glaucoma
Eventual need for enucleation
What ocular changes can be seen with glaucoma?
Primary glaucoma - rapid increase in intraocular pressure without uveitis or lens luxation
Blepharospasm, corneal edema, epiphora, episcleral injection, corneal edema, mydriasis, and blindness
IOP >25 mmHg
What is the treatment for a simple, epithelial only corneal ulcer?
1) Identify precipitating cause
2) Prevent infection - topical antibiotic TID-QID
3) Artificial tear preparation to maximize lubrication
4) Topical atropine 1% to reduce iridociliary spasm - CAUTION has potential to lower tear production in all patients - need pre-treatment STT
5) Systemic pain control
6) E-collar
What factors lead to exposure keratopathy and corneal ulceration?
- Abnormal tear film - quantity or quality
--> Outer lipid layer, a middle aqueous layer, and inner mucin layer
- Ability to blink fully
--> impacted by sedation, general anesthesia, diminished consciousness and reflexes
- Complete closure of the eyelids while sleeping
What is the mechanism of action of latanoprost?
prostaglandin analogue
increases outflow of aqueous humor
causes miosis
generally not indicated for use in cats - it does not lower IOP in normal feline eyes and glaucoma in cats is frequently secondary to anterior uveitis
What are negative prognostic factors for retention of the globe? What factors create the most favorable prognosis?
Negative prognostic factors:
- Globe is ruptured
- Three or more rectus muscles are torn
- Hyphema
- Facial fractures
- Owner unable to provide long-term post-operative care
Favorable factors:
- Vision is present
- Minimal damage to extraocular muscles
- Absence of hyphema
- Normal fundic exam
What conditions can cause anterior lens luxation?
Primary anterior lens luxation - heritable degeneration of lens zonules - small terrier breeds
Glaucoma with secondary lens luxation
Uveitis with secondary lens luxation
What are signs that a corneal ulcer is infected?
Depth - stromal loss
Stromal infiltrate
Corneal malacia
Reflex uveitis
What are two conditions that can lead to miosis?
Horner's syndrome
--> Enophthalmos, ptosis, and/or third eyelid protrusion
Anterior uveitis
--> episcleral hyperemia, low IOP, and/or aqueous flare
What is the mechanism of action of dorzolamide?
decreases production of aqueous humor
What is your treatment plan for a proptosed globe that can be replaced?
Temporary tarsorrhaphy (or enucleate)
Oral antibiotic for potential cellulitis/infection
Topical antibiotic for corneal ulceration
Systemic pain medication
Sutures in place for at least 2-3 weeks as cellulitis resolves
E-collar
What are your differential diagnoses for anterior uveitis?
Local disease - r/o trauma (ulcer, blunt force trauma, foreign body), primary neoplasia, lens induced uveitis from cataract (immune-mediated)
Systemic disease - r/o neoplasia, immune-mediated disease, infection, idiopathic (>50% of cases)
What exam findings are typical in a dog with SARDS?
Sudden onset of complete blindness
No significant pain or inflammation
PLR may be slow or incomplete
Absent dazzle and menace
Unremarkable fundic exam
Diagnosis confirmed with electroretinograph