17 - glaucoma

Be able to discuss the normal aqueous production/outflow pathways and discuss mechanisms by which the normal pathways may be interrupted, resulting in glaucoma.

normal

aqueous humor is produced by the ciliary body epitheilum

fluid enters posterior chamber → flows through pupil into anterior chamber

85% of fluid exits iridocorneal angle

15% of fluid exits through uveoscleral pathway

abnormal

  • pupillary block → flow is blocked at the pupil → posterior synechiae or lens luxation

  • iridocorneal angle obstruction → most common for secondary glaucoma → inflammatory debris, neoplasia, pre-iridal fibrovascular membranes

  • congenital → abnormal development of iridocorneal angle

  • compression/collapse of angle → intumescent cataract, iris bombe

List several breeds predisposed to primary glaucoma.

  • cocker spaniel

  • basset hound

  • beagle

  • samoyed

  • chow

  • shar pei

  • norweigian elkhound

  • arctic circle breeds

List major clinical signs which may be associated with acute glaucoma. What additional signs may be seen in chronic glaucoma? What is the range of normal intraocular pressure in most domestic species?

acute glaucoma

  • ocular pain

  • corneal edema

  • episcleral injection

  • mydriasis

  • congestion of iris

  • visual deficits

chronic glaucoma

  • buphthalmos

  • breaks in Descemet’s membrane (Haab’s striae)

  • lens subluxation or luxation

  • optic disc cupping

  • retinal degeneration

  • cataract formation

  • corneal fibrosis

intraocular pressure

15-25 mmHg

List and discuss causes of secondary glaucoma. How does uveitis lead to secondary glaucoma? How can intraocular neoplasia lead to secondary glaucoma?

  • uveitis → inflammatory debris, pre-iridial fibrovascular membrane, Iris bombe

  • lens luxation

  • intraocular neoplasia → physical ocupation of drainage angle, shed cells clog drain, secodnary uveitis

  • intumescent (swollen cataract)

  • hyphema

Outline a diagnosis and complete medical therapy regimen for treatment of acute glaucoma in a dog. Be able to discuss long-term therapy and prognosis for medical therapy of glaucoma.

diagnosis

  • tonometry > 25-30 mmHg

  • corneal edema

  • mydriasis

  • episcleral injection

  • ocular pain

treatment

  • 1 ggt latanoprost (prostaglandin analogue) + 1 drop dorzolamid/timolol ( beta blocker + carbonic anhydrase inhibitor) every 5 min for 30 min

  • repeat if IOP not <25 mmHg

  • after second round, if IOP not <25 mmHg, IV mannitol or aqueous paracentesis

  • if IOP < 25 mmHg with latanoprost/dorzolamide, send home with meds

    • latanoprost sid/bid in affected eye

    • dorzolamide/timolol TID/QID in affected eye

    • dorzolamide/timolol BID in unaffected eye

  • treat underlying disease if secondary

What surgical procedures exist, at the present time, for treatment of glaucoma for visual and nonvisual eyes? Know what surgical procedures are best for blind and painful eyes versus what surgical procedures are best for visual eyes. Know the major indications and contraindications for all surgical procedures for glaucoma

visual eyes

  • laser ciliary body ablation

    • destroys portion of ciliary body to decrease aqueous humor production

    • indicated for primary or secondary glaucoma after pressure spike is controlled

    • may develop cataracts, uveitis, hyphema

  • shunts

    • diverts aqueous humor to subconjunctival space or frontal sinus

    • indicated for primary glaucoma

non-visual, painful

  • chemical ciliary body ablation

    • gentamicin sulfate injection into vitreous

    • least invasive, least expensive

    • contraindicated in intraocular neoplasia or infection

    • may cause eye to shrink

  • enucleation

    • low complication rate

    • no long-term maintenance

  • intrascleral prosthesis

    • contents of eye removed and replaced iwth black silicone ball

    • contraindicated for neoplasia, infection, severe ocular surface disease

    • may develop KCS