Introduction

• Cause: glaucoma represents a group of heterogenous diseases which, in dogs, are characterized by pathologically elevated intraocular pressure resulting in retinal ganglion cell death.
• Signs: ocular pain, blindness, episcleral congestion, conjunctival hyperemia, corneal edema, mydriasis.
• Diagnosis: ophthalmic examination including gonioscopy and tonometry.
• Treatment: ocular hypertensive medications and surgical options.
• Prognosis: guarded.
  Print off the owner factsheet on Glaucoma Glaucoma to give to your client.

Pathogenesis

Etiology

• Primary glaucoma.
• Uveitis Uveitis.
• Lens luxation Lens: luxation.
• Intraocular neoplasm Eye: intraocular neoplasia.
• Intraocular hemorrhage.
• Ocular melanosis Eye: uveal melanoma.

Predisposing factors

General

• Breeds predisposed to primary closed angle and lens angle glaucoma.
• Breeds predisposed to primary lens luxation.

Specific

• Presence of goniodysgenesis.
• Homozygosity for known mutations for primary open angle glaucoma and primary lens luxation.
• Uveitis.
• Cataracts Cataract.
• Previous intraocular surgery.
• Intraocular hemorrhage.
• Ocular melanosis.

Pathophysiology

• See also Glaucoma: secondary to anterior uveitis Glaucoma: secondary to anterior uveitis , Glaucoma: due to lens luxation Glaucoma: due to lens luxation , Glaucoma: primary closed angle Glaucoma: primary closed angle and Glaucoma: primary open angle Glaucoma: primary open angle.
• Normal intraocular pressure is a balance between aqueous humor production and outflow:
  • Aqueous humor is produced by the ciliary body processes by active secretion (mainly) and ultrafiltration.
  • Aqueous humor then traverses the posterior chamber via the pupil into the anterior chamber.
  • From the anterior chamber, the majority of aqueous drains via the iridocorneal angle.
  • The main components of this angle are the pectinate ligament and ciliary cleft which contains the sieve-like trabecular meshwork.
  • The majority of aqueous (~85%) filters through these structures and enters the angular aqueous plexus before entering the scleral venous plexus ('conventional' outflow).
  • A minority of aqueous (~15%) bypasses the aqueous plexus and reaches the scleral venous plexus via the choroid and suprachoroidal space.
  • Normal intraocular pressure in the dog is 10-25 mm Hg.
• In dogs, the only consistent risk factor for glaucoma amongst the group of heterogenous diseases is pathologically elevated intraocular pressure.
• Overproduction of aqueous humor is not a recognized phenomenon in dogs and, thus, all known forms of glaucoma relate to obstruction to aqueous humor outflow.
• Aqueous humor obstruction can occur at any point from its release into the posterior chamber to its ultimate drainage into the angular aqueous plexus and include the following:
  • Pupil block:
    • Iris bombe. Peripheral synechiae (adhesions between posterior iris and anterior lens capsule) for 360° in chronic uveitis.
    • Lens luxation and subluxation.
    • Vitreous prolapse (following lens removal or lens luxation).
  • Obstruction of entrance to iridocorneal angle:
    • Severe goniodysgenesis (pectinate ligament dysplasia) in primary closed angle glaucoma.
    • Obstruction by red blood cells (trauma), white blood cells and inflammatory debris (acute and chronic uveitis).
    • Anterior synechiae (chronic uveitis).
  • Obstruction within ciliary cleft:
    • Severe goniodysgenesis in primary closed angle glaucoma.
    • Undefined anatomical and biochemical changes in primary open angle glaucoma.
    • Collapse of ciliary cleft in all forms of glaucoma.
    • Neoplastic extension.
    • Obstruction by red blood cells (trauma), white blood cells and inflammatory debris (acute and chronic uveitis).
• Elevation of intraocular pressure causes interruption of vacular supply to optic nerve head and axoplasmic flow within optic nerve axons.
• Increase in glutamate levels may cause excitotoxicity-mediated retinal ganglion cell death.

Timecourse

• Variable dependent on cause.
• Acute in primary closed angle glaucoma and primary lens luxation.
• Chronic in anterior uveitis, neoplasia and ocular melanosis .

Diagnosis

Treatment

Prevention

Outcomes