Contributors: Dennis E Brooks, David L Williams, James Oliver
Species: Feline | Classification: Diseases
Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading
Introduction
- 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
- Depends on cause.
- Most common cause is anterior uveitis Anterior uvea: traumatic uveitis which can affect cats of any age.
Breed Predisposition
Cost Considerations
- Antiglaucoma medications can be costly.
- Surgical treatments are expensive.
Special Risks
- General anesthesia (if required for surgical treatment) Anesthesia: for ophthalmic surgery.
Pathogenesis
Etiology
- 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:
- Protozoal:
- Toxoplasmosis Toxoplasmosis.
- Fungal:
- Cryptococcosis Cryptococcosis.
- Histoplasmosis Histoplasmosis.
- Blastomycosis Respiratory fungal disease.
- Coccidiodomycosis Coccidioidomycosis.
- Idiopathic (lymphoplasmacytic uveitis):
- 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).
- Diffuse uveal melanoma Eye: uveal melanoma (primary)
- Intraocular hemorrhage:
- Usually as a result of hypertensive retinopathy.
- Primary:
- Rare.
- Siamese and Burmese may be predisposed.
Predisposing Factors
General
- Uveitis.
- Systemic hypertension Hypertension.
- Lymphoma.
- Diffuse uveal melanoma.
Pathophysiology
- 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).
- Pupil block:
- 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.
Timecourse
- Usually chronic in cats as a result of chronic uveitis.
Diagnosis
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
:
- 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
:
- Intraocular hemorrhage:
- 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:
Diagnostic Investigation
- 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
.
- Examination of the iridocorneal angle. Best performed using a specialized lens (goniolens) and magnification with illumination
- Schiotz tonometry Tonometry :
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).
Treatment
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:
- 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.
Monitoring
- 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
Treatment
- Additional antiglaucoma medications may be required.
Monitoring
- If treatment failure then enucleation Eye: enucleation is required for blind and painful eyes.
Outcomes
Prognosis
- 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
Publications
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.