glaucoma

see also:

• ophthalmology

• aqueous humor is produced by the ciliary body in the posterior chamber of the eye. It diffuses from the posterior chamber, through the pupil, and into the anterior chamber. From the anterior chamber, the fluid is drained into the vascular system via the trabecular meshwork and Schlemm canal contained within the angle.
• glaucoma is the traditional name for ocular hypertension (raised intraocular pressures or IOP)
• there are 2 main types of glaucoma:
  • open angle glaucoma:
    • this presents in those over 40yrs of age as an insidious loss of visual fields and is painless
  • closed angle glaucoma
    • this presents as an acute onset, very painful, unilateral red eye when drainage system of the eye becomes occluded, usually precipitated when the eye is dilated in those at anatomic risk.
    • this is an ocular emergency

• usually presents suddenly as an acutely painful, red eye with reduced visual acuity
• arises when an eye becomes dilated and if there are anatomic risk factors, aqueous flow from the posterior chamber to the anterior chamber is obstructed or altogether blocked by the apposition and contact between the lens and the iris, this then increases posterior chamber pressures which exacerbates the situation by further closing an already narrow angle and preventing drainage
• anatomic risk factors:
  • narrow angle
  • shallower anterior chambers
  • thinner ciliary bodies
  • a thinner iris
  • anteriorly situated thicker lens
  • a shorter axial eye length
  • perhaps increased iris thickness and cross-sectional area are also associated with increased risk.
• may be precipitated by pupil dilatation via either:
  • increased ocular sympathetic tone:
    • emotional stress
    • sympathomimetics
    • low light conditions
  • anti-muscarinic anticholinergic agents which cause mydriasis
• diagnostic criteria:
  • at least 2 of the following symptoms:
    • ocular pain
    • nausea/vomiting
    • a history of intermittent blurring of vision with halos
  • and at least 3 of the following signs:
    • IOP greater than 21 mm Hg
    • conjunctival injection
    • corneal epithelial edema
    • mid-dilated nonreactive pupil
    • shallow chamber in the presence of occlusion

• emergent ophthalmology consult
• lie down (lens falls away from the iris decreasing pupillary block)
• do NOT use eye shades as you want pupils to constrict and not stay dilated in the dark
• analgesia
• anti-emetics to avoid vomiting which will increase IOP
• decrease aqueous humor production and to enhance opening of the angle by:
  • acetazolamide
    • should be given as a stat dose of 500 mg IV followed by 500 mg PO
  • beta adrenergic blockers such as timolol eye drops
• decrease the inflammatory reaction and reduce optic nerve damage via topical steroids:
• traditionally, 1 hour after onset of above Rx:
  • pilocarpine eye drops every 15 minutes for 2 doses to open the angle
    • this could result in reducing the depth of the anterior chamber and worsening the clinical situation in a paradoxical reaction, but seems to be still recommended Rx
    • if the IOP is not reduced 30 minutes after the second dose of pilocarpine, consult with ophthalmology to discuss further options such as osmotic agents (eg. oral glycerol if non-diabetic, or iv mannitol)

• chronic, painless condition in which the persistent high intra-ocular pressures result in characteristic pattern of “tunnel vision” blindness if left untreated.
• 4-10% of the population older than 40 years, are currently without detectable signs of glaucomatous damage using present-day clinical testing, but they are at risk due to IOP of 21 mm Hg or higher.
  • 0.5-1% per year of those individuals with elevated IOP will develop glaucoma over a period of 5-10 years
  • visual field loss can be expected to develop in about 3% of subjects over 10 years of follow up without treatment. Risk increases with age and IOP.
• hence routine testing of ocular pressures in middle age and the elderly to ensure permanent damage is prevented.

• timolol eye drops
• consider tafluprost, a new PG F2 receptor agonist which is thought to increase uveoscleral outflow
• regular IOP testing