Glaucoma

• 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.

• 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).

• 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).

• Depends on cause.
• Most common cause is anterior uveitis Anterior uvea: traumatic uveitis which can affect cats of any age.

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

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

• General anesthesia (if required for surgical treatment) Anesthesia: for ophthalmic surgery.

• Uveitis = most common cause of glaucoma in cats:
  • Idiopathic (lymphoplasmacytic uveitis):
    • Designated to cases where cause cannot be identified.
    • Most common cause of uveitis and secondary glaucoma.
  • Infectious:
    • Viral Uveitis: viral:
      • FIP Feline infectious peritonitis.
      • FIV Feline immunodeficiency virus disease.
      • FeLV Feline leukemia virus disease.
    • Protozoal:
      • Toxoplasmosis Toxoplasmosis.
    • Fungal:
      • Cryptococcosis Cryptococcosis.
      • Histoplasmosis Histoplasmosis.
      • Blastomycosis Respiratory fungal disease.
      • Coccidiodomycosis Coccidioidomycosis.
• Lens luxation Eye: lens luxation:
  • Usually secondary to anterior uveitis.
  • Primary is rare but has been reported.
• Neoplasia Eye: intraocular mass:
  • Diffuse uveal melanoma Eye: uveal melanoma (primary)   .
  • Lymphoma Lymphoma  (secondary).
• Intraocular hemorrhage:
  • Usually as a result of hypertensive retinopathy.
• Primary:
  • Rare.
  • Siamese and Burmese may be predisposed.

General

• 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.

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

• Change in appearance of eye.
• Visual deficits.

• 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  :
  • Less often a feature of glaucoma in cats than dogs.
• Corneal fibrosis and vascularization  :
  • Chronic changes.
• Mydriasis  :
  • 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   :
  • As a result of chronic elevation of intraocular pressure leading to globe stretching     .
• Intraocular hemorrhage:
  • Most commonly as result of hypertensive retinopathy in cats.
  • Also fairly common with intraocular neoplasia  .
• 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  .
  • Cataract may be present  .

• Ophthalmic examination Eye: examination for signs of above.

• Gonioscopy  Eye: gonioscopy :
  • Examination of the iridocorneal angle. Best performed using a specialized lens (goniolens) and magnification with illumination   .
  • 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  .
• Schiotz tonometry  Tonometry :
  • Rebound and applanation tonometers favored       .
  • NB restraint will increase intraocular pressure.
  • Compare both eyes.

Definitive diagnostic features

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

• Dependent on cause.

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

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:
  • NSAIDs Analgesia: NSAID.
  • Opioids Analgesia: opioid.

Anti-inflammatory medications

• Indicated when intraocular inflammation is a component.
• Corticosteroids:
  • Topical, eg prednisolone acetate Prednisolone 1%, dexamethasone phosphate   Dexamethasone 0.1%.

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.

Treatment

• Additional antiglaucoma medications may be required.

Monitoring

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

• Guarded but will depend on cause.

• Guarded.

• 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.

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 4 (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 1 (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.