Contributors: Dennis E Brooks, David L Williams, James Oliver

 Species: Feline   |   Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading


  • Cause: glaucoma represents a group of heterogeneous diseases characterized by pathologically elevated intraocular pressure resulting in retinal gangllion cell death. In cats, the most commn cause is intraocular inflammation.
  • Signs: discomfort, blindness, episcleral congestion, conjunctival hyperemia, corneal edema, mydriasis, buphthalmos, lens luxation.
  • Diagnosis: ophthalmic examination including tonometry.
  • Treatment: ocular hypotensive and inflammatory tonometry.
  • Prognosis: guarded.

Presenting Signs

  • Although glaucoma may present unilaterally the most common cause, uveiti  Anterior uvea: traumatic uveitis, is usually a bilateral condition.
  • Ocular discomfort.
  • Redness around eye (less pronounced in cats than dogs).
  • Clouding of eye (more likely due to intraocular inflammation in cats rather than corneal edema).
  • Visual deficits (might not be obvious to owner if contralateral eye retains vision).

Acute Presentation

  • Usually presents as a chronic problem rather than acutely.
  • Ocular discomfort.
  • Clouding of eye.
  • Dilated pupil.
  • Globe enlargement.
  • Visual deficits (might not be obvious to owner if contralateral eye retains vision).

Age Predisposition

Breed Predisposition

  • Primary (inherited) glaucoma is rare in cats but has been reported in the Siamese Siamese and Burmese Burmese.

Cost Considerations

  • Antiglaucoma medications can be costly.
  • Surgical treatments are expensive.

Special Risks



Predisposing Factors


  • Uveitis.
  • Systemic hypertension Hypertension.
  • Lymphoma.
  • Diffuse uveal melanoma.


  • 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 iridocornal angle.
    • The main components of this angle are the pectinate ligament and ciliary cleft which contains the sieve-like trabecular meshwork.
    • The vast majority of aqueous (//www.vetlexicon.com97%) filters through these structures and enters the angular aqueous plexus before entering the cleral venous plexus ('conventional' outflow).
    • Normal intraocular pressure in the cat is 10-25 mm Hg.
  • In cats, 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 cats 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:
      • Obstruction by red blood cells (trauma), white blood cells and inflammatory debris (acute and chronic uveitis).
      • Anterior synechiae (chronic uveitis).
    • Obstruction within ciliary cleft:
      • Collapse of ciliary cleft in all forms of glaucoma.
      • Neoplastic extension (in particular with diffuse uveal melanoma).
      • Obstruction by red blood cells (trauma), white blood cells and inflammatory debris (acute and chronic uveitis).
  • Elevation of intraocular pressure causes interruption of vascular supply to optic nerve head and axoplasmic flow within optic nerve axons.
  • Increase in glutamate levels may cause excitotoxicity-mediated retinal ganglion cell death.


  • Usually chronic in cats as a result of chronic uveitis.


Presenting Problems

  • Cloudy eye.
  • Visual deficits:
    • Cats may retain vision until late in disease process.
  • Enlarged eye.
  • Ocular discomfort:
    • Often difficult to assess in cats.

Client History

  • Change in appearance of eye.
  • Visual deficits.

Clinical Signs

  • Glaucoma is usually insidious in onset in cats and clinical signs can go unnoticed for some time.
  • Pain:
    • Signs of pain are usually less obvious in cats with glaucoma.
  • Corneal edema Eye: diffuse uveal melanoma and secondary glaucoma 01 :
    • Less often a feature of glaucoma in cats than dogs.
  • Corneal fibrosis and vascularization Eye: diffuse uveal melanoma and secondary glaucoma 02 :
    • Chronic changes.
  • Mydriasis Eye: diffuse uveal melanoma and secondary glaucoma 02 :
    • Results from paresis/paralysis of iris sphincter muscle.
    • Pupil may be normal size or even miotic in uveitis glaucoma which is common in cats.
  • Episcleral congestion:
    • Usually less marked in cats than in dogs.
    • Usually accompanied by conjunctival hyperemia.
  • Vision loss:
    • As a result of damage to retinal ganglion cells.
    • Cats may retain vision until late in the disease process.
  • Globe enlargement Eye: congenital glaucoma - Siamese  :
    • As a result of chronic elevation of intraocular pressure leading to globe stretching   Eye: glaucoma - congenital (buphthalmos DSH 9 weeks)  .
  • Intraocular hemorrhage:
    • Most commonly as result of hypertensive retinopathy in cats.
    • Also fairly common with intraocular neoplasia Eye: diffuse uveal melanoma and secondary glaucoma 03 .
  • Optic disk cupping:
    • Less obvious in cats owing to unmyelinated optic disk.
  • Retinal and optic nerve head atrophy.
  • Chronic uveitis:
    • Anterior and posterior synechiae.
    • Aqueous flare.
    • Keratic precipitates.
  • Lens luxation/subluxation:
    • Usually as a result of chronic anterior uveitis.
    • May occur with intraocular neoplasia Eye: diffuse uveal melanoma and secondary glaucoma 01 .
    • Cataract may be present Eye: luxated cataractous lens and secondary glaucoma .

Diagnostic Investigation

  • Gonioscopy  Eye: gonioscopy :
    • Examination of the iridocorneal angle. Best performed using a specialized lens (goniolens) and magnification with illumination  Gonioscopy: examination .
    • Useful to assess for neoplastic extension (eg difuse iris melanoma), prsence of inflammatory debris and goniodysgenesis (rare in cats).
    • In the normal cat, the iridocorneal angle is spanned by sparse, thin, widely separated pectinate ligaments fibers Gonioscopy: normal iridiocorneal angle .
  • Schiotz tonometry  Tonometry :
    • Rebound and applanation tonometers favored  Tonometry: applanation tonometer   Tonometry: rebound tonometer  .
    • NB restraint will increase intraocular pressure.
    • Compare both eyes.

Definitive diagnostic features

  • Raised intraocular pressure (>25 mm Hg) in presence of compatible clinical signs.

Histopathology Findings

  • Dependent on cause.

Differential Diagnosis

  • Pharmacological pupil dilation.
  • Other causes of blindness Blindness  (cataract, retinal disease, CNS disease).


Standard Treatment

Medical management

Ocular antihypertensive medications

  • Carbonic anhydrase inhibitors (eg dorzolamide Dorzolamide 2%). Used topically, these agents reduce aqueous humor production by inhibiting carbonic anhydrase within the ciliary epithelium and are the most useful drugs for feline glaucoma. They are usually used 2-3 times daily.
  • Beta-blockers (eg timolol Timolol 0.5%). These drugs also increase aqueous outflow and are usually used 2-3 times daily. Side effects include miosis, bradycardia and hypotension.
  • Prostaglandin analogues, although very useful in canine glaucoma, are ineffective in feline glaucoma owing to differences in presence and distribution of prostanoid receptors in the feline eye.
  • Analgesia:

Anti-inflammatory medications

  • Indicated when intraocular inflammation is a component.
  • Corticosteroids:

May cause IOP elevation in some cats.

  • Systemic, eg prednisolone (in absence of presence of systemic infection).
  • NSAIDs:
    • Topical, eg ketorolac trometamol 0.5%.
    • Systemic, eg meloxicam Meloxicam.
  • Tissue plasminogen activator (tPA):
    • Injected intracamerally to dissolve fibrin clots.

Surgical therapy

  • The same surgical approaches used to treat glaucoma can potentially be used in cats with glaucoma but are rarely employed. Blind eyes with elevated intraocular pressure (and therefore likely a source of pain) should be enucleated. Evisceration and intraocular prosthesis placement is rarely performed in cats owing to the risk of intraocular sarcoma development.


  • Any case of chronic uveitis should be monitored for possible glaucoma development.
  • As the most common cause of feline glaucoma is uveitis and uveitis in cats is often bilateral, both eyes should be monitored.
  • If there is a change in treatment then re-examination is performed after one week to ensure satisfactory response to treatment is indicated.

Subsequent Management


  • Additional antiglaucoma medications may be required.


  • If treatment failure then enucleation Eye: enucleation is required for blind and painful eyes.



  • Guarded but will depend on cause.

Expected Response to Treatment

  • Guarded.

Reasons for Treatment Failure

  • Most cats with glaucoma present quite late in disease process.
  • Irreversible collapse of ciliary cleft.
  • Irreversible retinal and optic nerve degeneration.
  • Poor response to human antiglaucoma medication.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dietrich U, Chandler M, Cooper T et al (2007) Effects of topical 2% dorzolamide hydrochloride alone and in combination with 0.5% timolol maleate on intraocular pressure in normal feline eyes. Vet Ophthalmol 10 (Suppl 1), 95-100 PubMed.
  • Rainbow M & Dziezyc J (2003) Effects of twice daily application of 2% dorzolamide on intraocular pressure in normal cats. Vet Ophthalmol 6 (2), 147-150 PubMed.
  • Hampson E C, Smith R I & Bernays M E (2002) Primary glaucoma in Burmese cats. Aust Vet J 80 (11), 672-680 PubMed.
  • Blocker T & Van Der Woerdt T (2001) The feline glaucomas: 82 cases (1995-1999). Vet Ophthalmol (2), 81-85 PubMed.
  • Olivero D K, Riis R, Dutton A G et al (1991) Feline lens displacement a retrospective analysis of 345 cases. Progress in Vet Comp Ophthalmol (4), 239-244 VetMedResource.

Other sources of information

  • Gould D & McLellan G (2014) BSAVA Manual of Small Animal Ophthalmology. 3rd edn. British Small Animal Veterinary Association. pp 293-294.
  • Gelatt K, Gilger B, Kern T (2013) Veterinary Ophthalmology. 5th edn. pp 1514-1518. 

Other Sources of Information