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VetOphtho Veterinary Ophthalmology Resource

website·Indexed 31 days ago

https://vetophtho.org/

A comprehensive clinical resource for veterinary ophthalmology covering anatomy, physiology, and pathology of the eye. Topics include the cornea, lens, retina, optic nerve, and lacrimal system, as well as guidance on glaucoma, cataracts, conjunctivitis, and neuro-ophthalmology. The site provides detailed information on diagnostic techniques like tonometry and gonioscopy, surgical instrumentation, ophthalmic medications, and clinical management for both large and small animal patients.

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What's inside VetOphtho

  1. Use Cross-linked hyaluronan (Remend) for corneal ulcers

    Cross-linked hyaluronan (Remend) can be used to accelerate the resolution of corneal ulcers and encourage a more normal epithelial architecture.

  2. Understand fundus histology and physiology

    The fundus consists of the retina, choroid, and sclera.

    • Retina: Comprises approximately 60 cell types. The 'neurosensory retina' includes everything except the Retinal Pigment Epithelium (RPE). Signal transduction flows from photoreceptors (rods for dim light/movement; cones for bright light/color) $\rightarrow$ bipolar cells $\rightarrow$ ganglion cells. The optic nerve is the collection of ganglion cell axons.
    • Choroid: A highly vascular uveal tract layer between the retina and sclera. It contains the tapetum (if present) and provides significant nutrition to the retina in dogs.
    • Sclera: The outermost layer; relatively acellular, avascular, and nonpigmented.

  3. Understand aqueous humor outflow pathways

    Aqueous humor is produced by the nonpigmented epithelium of the ciliary body and drains via two primary pathways to maintain an intraocular pressure (IOP) of approximately 8-18 mmHg. According to Pascal’s law, IOP is equal throughout the eye (anterior chamber, posterior chamber, and vitreous cavity).

    Conventional (Trabecular) Outflow: Nonpigmented epithelium of ciliary body $\rightarrow$ Posterior chamber $\rightarrow$ Pupil $\rightarrow$ Anterior chamber $\rightarrow$ Iridocorneal angle (Pectinate ligaments $\rightarrow$ Trabecular Meshwork) $\rightarrow$ Intrascleral venous plexus $\rightarrow$ Systemic circulation.

    Unconventional (Uveoscleral) Outflow: Nonpigmented epithelium of ciliary body $\rightarrow$ Absorption directly into uveal tissue $\rightarrow$ Supraciliary space $\rightarrow$ Sclera $\rightarrow$ Systemic circulation.

  4. Understand eyelid anatomy and the role of the eyelid margin

    The eyelids protect the globe and distribute the tear film. They consist of haired skin on the exterior and conjunctiva on the interior. The eyelid margin is the critical junction between the skin and conjunctiva where Meibomian gland openings reside. These glands exude the lipid layer of the tear film. Any abnormality at the eyelid margin (e.g., distichia or entropion) can lead to corneal ulcers, keratitis, and discomfort.

  5. Understand the anatomy and physiology of the nasolacrimal system

    The tear film is composed of aqueous (produced by the lacrimal gland and gland of the third eyelid), lipid (produced by tarsal/Meibomian glands), and mucin (produced by goblet cells). During blinking, tears move from lateral to medial, draining through the lacrimal puncta, into the canaliculi, then the lacrimal sac, and finally through the nasolacrimal duct to exit via the nose or pharynx.

  6. Understand the functional anatomy of the orbit

    The orbit consists of the bone and muscle surrounding and protecting the eye. It contains the globe, fat, extraocular muscles, associated nerves, vasculature, the lacrimal gland, and a portion of the zygomatic gland. The space behind the eye is the 'retrobulbar space'.

    Skull conformation (cephalic index) significantly impacts ocular health:

    • Dolicocephalic, Mesacephalic, and Brachycephalic: These represent a gradient of decreasing orbital volume.
    • Brachycephalic risks: Shallower orbits lead to exophthalmia (protrusion) and lagophthalmia (incomplete eyelid closure), increasing the risk of trauma, ulceration, and conjunctivitis. These dogs also typically have lowered corneal sensitivity, which can delay reaction times to trauma and reduce tear production.

  7. Administer emergency medical therapy for canine glaucoma

    Emergency therapy focuses on rapidly lowering intraocular pressure (IOP) to preserve vision. If vision maintenance is the goal, treat as an emergency. Available options include:

    • Prostanoids (Latanoprost, bimatoprost, travaprost): Very potent and rapid acting (effect within 1-2 hours). They likely reduce aqueous production and increase both trabecular and uveoscleral outflow.
    • Carbonic Anhydrase Inhibitors (CAIs): Reduce aqueous production.
      • Topical: Dorzolamide (potent, effect within 1-2 hours).
      • Systemic: Methazolamide, dichlorphenamide (associated with more side effects).
      • Combination: CoSopt (contains both dorzolamide and timolol).
    • Osmotic Diuretics (Mannitol): Very potent with rapid onset (30 minutes) but short duration (6 hours). Works by dehydrating the eye to reduce ocular volume.
    # Mannitol Administration
Dosage: 1 gm/# slowly IV over 30-60 minutes
Constraint: Withhold oral water for 2 hours

  8. Manage stromal ulcers and descemetoceles

    Stromal ulcers occur when an ulcer extends beyond the epithelium into the superficial, mid, or deep stroma, creating a 'divot' and an uneven corneal surface. Treatment depends on the presence of infection, 'melting' (collagenolysis), and the inciting cause.

    A descemetocele is a deep ulcer extending through the stroma to Descemet’s membrane. A key diagnostic feature is that the walls of the descemetocele take up fluorescein stain, while the floor does not. Due to the high risk of perforation, surgical intervention is required.

  9. Identify and treat Feline Corneal Sequestrum (Nigrum)

    A corneal sequestrum is an area of focal corneal stromal necrosis in the center of the cornea, seen only in cats (predisposition in brachycephalics). Etiology may include tear film abnormalities, herpesvirus, or chronic trauma.

    Diagnosis: Based on clinical appearance (black area on the cornea).

    Treatment:

    • Aggressive: Lamellar keratectomy, potentially followed by a conjunctival (NM) flap; subsequently treated as an ulcer. Preferred if the condition is painful.
    • Conservative: Allow the sequestrum to slough spontaneously over several months.

  10. Diagnose and treat Neurogenic KCS

    Neurogenic KCS results from damage to the parasympathetic fiber pathway to the lacrimal gland. Because these fibers travel near the middle ear and branch to the nasal gland before the lacrimal gland, two key diagnostic indicators are:

    1. History of middle ear disease or otitis media (common in Cocker Spaniels or swimming Labs).
    2. Xeromycteria (dry nostrils), appearing as a plug of dried mucous in the nose, indicating a lesion in the common pathway to both glands.

    Treatment focuses on the underlying cause (e.g., hypothyroidism, otitis media) or increasing parasympathetic tone using pilocarpine.

  11. Treat Pannus (Chronic Superficial Keratitis)

    Pannus is an immune-mediated, bilateral vascularized and pigmented corneal lesion, common in German Shepherds. It is controllable but generally not curable.

    Treatment Protocol

    1. Initial Phase: Topical dexamethasone or prednisone TID to QID.
    2. Maintenance: Taper to a controlling dose (often once daily or every other day). Response may take 3-4 weeks.
    3. Alternatives: Cyclosporine or tacrolimus for maintenance.
    4. Severe Cases: Radiation therapy may be used.

    Monitoring: Use the level of vascularization to determine if the lesion is active or quiescent.

  12. Treat allergic conjunctivitis in dogs

    Treatment for allergic conjunctivitis typically proceeds without a firm diagnosis but requires a complete ophthalmic exam (including STT, IOP, and stain). If the animal has active atopy, treating the systemic allergy may also resolve the conjunctivitis. Treatment usually continues for approximately 2 weeks past clinical resolution or the end of the allergy season.

    Medication progression typically follows this order:

    1. Topical anti-histamines: e.g., Zaditor (brand) or Ketotifen (generic) BID-TID.
    2. Topical NSAIDs: e.g., Ketorolac BID-TID.
    3. Topical Cyclosporine (Optimmune): Used for immune-modulatory effects or to increase tear production to flush allergens. Use q12-24h to avoid epiphora.
    4. Topical Steroids: (e.g., Dexamethasone, NPD, or NPB-HC). Used for severe or persistent cases. If only steroids resolve the redness, reconsider the diagnosis toward immune-mediated disease.

    Note: Primary bacterial conjunctivitis is rare; avoid using antibiotics like gentamicin or tobramycin unless secondary bacterial overgrowth is confirmed, as this can lead to resistant bacteria.