Canis ISSN: 2398-2942

Glaucoma

Contributor(s): Dennis E Brooks, David L Williams, James Oliver

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

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 Eye: ocular melanosis and secondary glaucoma - Cairn terrier.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information


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