Canis ISSN: 2398-2942

Glaucoma: primary closed angle

Synonym(s): Angle closure glaucoma

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

Introduction

  • Cause: inherited abnormality of the anterior chamber aqueous outflow pathway. Specifically, there is dysplasia of the pectinate ligament at the opening of the iridocorneal (drainage) angle and/or narrowing of this angle. Collectively these anomalies are termed goniodysgenesis. It was originally thought that these were congenital abnormalites but it is now known that the iridocorneal angle can become narrowed with age and that pectinate ligament 'dysplasia' can be progressive (Pearl et al, 2015). These abnormalities are highly associated with the risk of glaucoma and may be markers for further abnormalities deeper within the aqueous outflow pathways.
  • Signs: sudden onset blindness and pain associated with acute elevation of intraocular pressure.
  • Treatment: medical and surgical options exist but the prognosis for restoration of vision is poor following onset of acute glaucoma.
  • Prognosis: poor.

Pathogenesis

Etiology

  • Primary closed angle glaucoma is always associated with goniodysgenesis.
  • Goniodysgenesis is the term applied to abnormalities affecting the irdiocorneal angle. These abnormalities manifest as dysplasia of the pectinate ligament and/or narrowing of the opening of the iridocorneal angle. The normal pectinate ligament is composed for sparse fine fibers which extend from the iris base to the peripheral inner cornea Eye: gonioscopy - normal iridocorneal angle 02. When the ligament is dysplastic, the fibers are broader and may appear as sheets of mesodermal tissue spanning the angle Eye: goniodysgenesis - Cocker spaniel.
  • These abnormalities were originally thought to be congenital (or at least existing by 8 weeks of age). It is now known, however, that these changes can be progressive with age.
  • Typically a disease of middle age but age of onset varies dramatically depending on the extent of abnormalities of the iridiocorneal angle.

Specific

  • Goniodysgenesis.
  • Breed.

Pathophysiology

  • Normal intraocular pressure is a balance between aqueous humor production from the ciliary processes and outflow from the eye. The majority (~85%) of outflow is via the iridiocorneal angle into the angular aqueous plexus and scleral venous circulation (conventional pathway).
  • A relatively small (~15%) amount of aqueous humor bypasses the aqueous plexus, draining via the cilliary cleft into the choroid and suprachoroidal space before entering the scleral venous plexus.
  • Dogs which develop primary closed angle glaucoma have severe goniodysgenesis and eventually suffer an obstruction to aqueous humor outflow in the irdiocorneal angle.
  • The precise physiologival mechanism for the acute disruption in aqueous humor outflow is not understood but the iridiocorneal angle quickly becomes collapsed and usually irreversibly so.
  • The sudden and marked elevation of IOP causes retinal ganglion cell and optic nerve degeneration.

Timecourse

  • Goniodysgenesis is usually an early life abnormality which may be gradually progressive.
  • Glaucoma is acute in onset.
  • Disease occurs in adults who are typically middle aged but this is very variable.

Epidemiology

  • Relates to breed distribution within a given population.

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

  • Recent references from PubMed and VetMedResource.
  • Pearl R, Gould D, Speiss B (2015) Progression of pectinate ligament dysplasia over time in two populations of Flat-Coated Retrievers. Vet Ophthmol 18, 6-12 PubMed.
  • Tsai et al (2013) The effect of topical latanoprost on anterior segment anatomic relationships in normal dogs. Vet Ophthmol 16 (5), 370-376 PubMed.
  • Miller P E et al (2000) The efficacy of topical prophylactic antiglaucoma therapy in primary closed angle glaucoma in dogs: a multicenter clinical trial. JAAHA 36 (5), 431-438 PubMed.
  • Nasisse M P, Davidson M G, English R V et al (1990) Treatment of glaucoma by use of transcleral neodymium:yttrium aluminium garnet laser cyclophotocoagulation in dogs. JAVMA 197, 350-353 PubMed.

Other sources of information

  • Bras I D, Robbin T E, Wymanet al(2005) Diode endoscopic cyclophotocoagulation in canine and feline glaucoma(abstract). 36th Proceedings of the American College of Veterinary Ophthamologists, p 50.
  • Cook C S (1997) Surgery for glaucoma. Vet Clin North Am Small Anim Practice 27, 1109-1129.


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