Glaucoma

Introduction

The glaucomas are a group of diseases in
which there is gradual loss of vision
(actually visual field) due to a form of optic neuropathy in which raised intraocular pressure is a risk factor.
Glaucoma is a common cause of blindness worldwide and once a patient is blind from glaucoma, vision cannot be restored.

Types

  1. Primary open-angle glaucoma
  2.  Primary closed-glaucoma (angle-closure)
  3. Secondary glaucoma
  4. Congenital glaucoma

Clinical features

  • The commonest type of glaucoma, chronic open angle glaucoma is generally symptomless except in the late stages when symptoms of visual loss present.
  • In Congenital glaucoma, there is enlarged eyeball(s) in the newborn, corneal oedema/opacity, photophobia and watering.
  • In Acute closed angle glaucoma, there is marked elevation of intraocular pressure with severe pain, reduction in vision, red eye, fixed mid-dilated pupil, shallow anterior chamber.

Investigations

  • Intraocular pressure measurement
  • Central and peripheral visual field test.
  • Fundoscopy to determine cup/disc ratio
  • Gonioscopy to view the angle of the eye

Management

Treatment objective:

  • Stop further loss of retinal ganglion cells¬† and nerve fibre layer by prompt treatment.

Drug treatment

  • Topical and Systemic drugs can be utilized in all forms of glaucoma but surgery may be the only treatment option in some glaucomas (drugs are used before surgery in these cases). These drugs include:
  • Betablockers e.g. Timolol
  • Parasympathomimetics e.g. Pilocarpine
  • Sympathomimetics e.g. Adrenalin, Dipivefrin
  • Carbonic Anhydrase Inhibitors e.g. Acetazolamide, Dorzolamide
  • Prostaglandin analogues e.g. Latanoprost
  • Hyperosmotic agents e.g. Mannitol, Glycerol

Surgical treatment

Available surgical procedures include:

  • Goniotomy (for Congenital glaucoma)
  • Trabeculectomy (for all forms of glaucoma)
  • Trabeculotomy
  • Laser Trabeculoplasty
  • Peripheral Iridectomy or Yag Laser
  • Iridotomy for acute closed angle glaucoma (to the affected eye as well as the normal fellow eye).
  • Laser photo-ablation of the ciliary body

Differential diagnosis

  • Ocular hypertension
  • Primary optic atrophy (pallor but no cupping of the disc)

Complications

  • Central Retinal Vein Occlusion
    Rubeosis Irides with resultant secondary glaucoma
  • Total blindness

Adverse drug reactions

  • Timolol can precipitate heart block, bradycardia and bronchospasms
  • Pilocarpine – Mioses, spasms of
    accommodation, retinal detachment
  • Acetazolamide – Paraesthesia, renal stone formation, Steven – Johnson syndrome, gastrointestinal disturbances, decreased libido, fatigue, weight loss.
  • Latanoprost -foreign body sensation, mild conjunctival hyperaemia and increased pigmentation of iris.

Contraindications

  • Timolol is contraindicated in Asthmatics and patients with heart block.
  • Acetazolamide is contraindicated in patients with pre-existing systemic acidosis, patients with sicke cell disease and allergy to sulphonamides.
  • Pilocarpine is contraindicated in eyes with previous retinal detachment, and pathological myopia.

Prevention

  • Early detection and prompt treatment.
  • Screening for glaucoma should be
    incorporated into the health plan of any nation.