Glaucoma

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• Increased intra-ocular pressure structural damage and impaired function.
• Not a single disease process but a group of ocular disorders of varied etiology.
• Cause: always related to inadequate drainage, not to increased production, of aqueous.
• May be primary or secondary (more common in cats).
• Signs: ocular pain, episcleral vascular engorgement, globe enlargement, pupillary dilation and blindness.
• Diagnosis: measurement of intraocular pressure.
• Treatment: initial (emergency) to reduce intraocular hypertension.
• Restoration of iridocorneal angle function rarely possible, therefore long-term reduction of aqueous humor or creation of alternative drainage necessary.
• Prognosis: poor, whether surgical or medical treatment.

• Enlarged globe.
• Corneal edema.
• Dilated pupil.

• Vascularization.

• Pain and episcleral congestion .

• Middle-older age.

• Siamese .
• Persian .
• British shorthair .

• Obstructed aqueous drainage either through iridocorneal angle or through pupil (pupillary block).
• Primary: congenital narrowing of angle, later closed by age-related change.
• Secondary: antecendent disease process.

• Genetic/breed predisposition.

• Anterior uveitis may be FIV related or FeLV or toxoplasma .
• Corneal perforation.
• Neoplasia (lymphosarcoma or iris melanoma ).

• Lens luxation .

• Trauma.

Either Primary (open angle) which is rare and usually bilateral.
OR secondary to intra-ocular disease.

• Ciliary body processes produce aqueous humor flows through pupil into anterior chamber drains from eye via the iridocorneal angle.
• Glaucoma always due to inadequate drainage.
• Increased IOP damage to optic nerve blindness.
• The cat optic nerve is relatively resistant to degenerative changes.

Intra-ocular pressure (IOP) values

• Normal varies with breed and age: = 20.2 +- 5.5 mmHg.
• Up to 60 mmHg in acute glaucoma.

• Ocular pain .
• Episcleral congestion .
• Corneal edema .
• Pupillary dilation and fixation.
• Globe enlargement (later change).
• Loss of vision .

• Sudden onset ocular pain.
• Globe enlargement.

• Uveitis .
• Trauma.

• Dilated pupil.
• Increased intra-ocular pressure with later globe enlargement .
• Ocular pain.
• Blepharospasm.
• Serous ocular discharge .
• Episcleral congestion .
• Corneal edema and later pigmentation and vascularization .

• Exposure keratitis.
• Lens luxation.
• Retinal degeneration.

• Descemet's streaks or stria.
• Lens luxation/subluxation.
• "Cupping" of optic disk.
• Cataract .
• Intra-ocular hemorrhage .

• Applanation tonometry gives accurate measure of intra-ocular pressure (IOP) but equipment is costly.
• Tonopen is the best machine for veterinary use.

• Schiotz tonometry :
  • Readily available but limited accuracy.
  • Useful for comparing eyes and monitoring response to treatment.
  • Single measurement not diagnostic unless IOP >40-45 mmHg.
• Gonioscopy:
  • Clinical examination of the iridocorneal angle.
  • Easily accomplished in the conscious animal with topical anesthesia, using a Barkan-type low vacuum goniolens.
  • Allows examination of the pectinate ligament and estimation of the width of the ciliary cleft.
• Iridocorneal angle can be seen with standard ZOD bupe lens against anesthetized cornea if goniolens not available.

• Correct underlying cause.

• Medical (if <50 mmHg): Carbonic anhydrase inhibitors, eg dorzolamide topically TID-QID 1-3 mg/kg BID; miotics, eg 1-2% pilocarpine 2-4 times daily; beta blockers may reduce aqueous humor production.
• Prostaglandin analogue (latanaprost) SID in evening.
   Contra-indicated if glaucoma secondary to uveitis.
• If IOP >50 mmHg use osmotic agents, eg 20% mannitol 1-2 g/kg IV.
   Watch for renal failure in which use of mannitol is contra-indicated.
• Surgical: Anterior chamber paracentesis .
• Controversial, therefore may cause anterior chamber hemorrhage and acute pain.

• Treat anterior uveitis (if present) with topical antibiotics and corticosteroids.

• Surgical bypass of collapsed ciliary cleft, using modified Joseph or Ahmad drainage tube implant to produce alternative drainage.

• Corneoscleral trephination with peripheral iridectomy - also produces alternative drainage but less effective.

• Cyclodialysis - re-opening closed ciliary cleft by breaking down adhesions to separate ciliary body from the underlying sclera.

• Medication only - limited lasting value if extensive angle occlusion but dorzolamide can be useful long-term.
• Laser or cryotherapy to partially destroy aqueous production by ciliary body - difficult to assess correct amount of damage to ensure balance between production and drainage.
• Remove anterior luxated lens.
• Enucleation if glaucoma secondary to tumor or if medical therapy ineffective or painful eye with blindness.

• Side effects of drug therapy.

• Guarded unless underlying cause addressed.
• Often presented with chronic changes and if already blind, an eye which is painful may be enucleated. Often though, eyes are enlarged and blind but pain free.

• Reduced pain and intraocular pressure.

• Optic nerve/retinal degeneration already occurred irreversible vision loss.
• Phthisis bulbi.
• Subsequent closure of surgical channel/fistula by formation of post-operative adhesions.

• Recent references from PubMed.
• Sansom J (2000) Diseases involving the anterior chamber of the dog and cat. In Practice 22, 58-70.
• Cook C S (1997) Surgery for glaucoma. Vet Clin North Am Small Anim Pract 5, 1109-1120.
• Gelatt K N (1995) The role of tonometry in the clinical management of the glaucomas in companion animals. Vet Q 17 (Suppl 1), S45.
• Brooks D E (1990) Glaucoma in the dog and cat. Vet Clin North Am Small Anim Pract 20, 775-797.
• English R V P et al (1990) Intraocular disease associated with feline immunodeficiency virus infection in cats. JAVMA 196 (7), 1116-1119.
• Wilcock B P et al (1990) The causes of glaucoma in cats. Vet Pathol 27 (1), 35-40.
• McLaughlin S A et al (1987) Intraocular findings in three dogs and one cat with chronic glaucoma. JAVMA 191 (11), 1443-1445.
• Whitley R D et al (1984) Advances in feline ophthalmology. Vet Clin North Am Small Anim Pract 14 (6), 1271-1288.
• Bedford P (1983) Ocular disease in the cat. In Practice 5 (2), 64-70.

• Petersen-Jones S & Crispin S (2002) BSAVA Manual of Small Animal Ophthalmology. 2nd edn. British Small Animal Veterinary Association. ISBN 0 905214 54 4

• Dr Dennis E Brooks DVM PhD DipACVO, College of Veterinary Medicine, 2015 SW 16th Ave, University of Florida, PO Box 100126, Gainesville, FL 32610-0126, USA. Fax: 001 352 392 6125. E-mail: brooksd@mail.vetmed.ufl.edu.
• Dr David Williams MA Vet MB PhD CertVOphthal MRCVS, Department of Clinical Veterinary Medicine, Madingley Road, Cambridge CB3 0ES, UK.

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