Glaucoma
Glaucoma questions reward a disciplined sequence: pressure, angle, disc, field and nerve fibre layer. The examiner wants to see that you gonioscope every patient before calling it open-angle, and that you can distinguish a glaucomatous field from a cataract or a neurological one.
Core rules
- Open-angle glaucoma is a progressive optic neuropathy; IOP is the only modifiable risk factor, but a third of patients have pressures below 21 mmHg at diagnosis.
- Gonioscopy is mandatory. Shaffer grading describes angle width; look for peripheral anterior synechiae, pigment and a plateau configuration.
- Disc signs: vertical cup-to-disc ratio, neuroretinal rim thinning (inferior, superior, nasal, temporal - the ISNT rule), disc haemorrhage, beta-zone atrophy and bayoneting.
- Visual field: arcuate scotoma, nasal step, paracentral defects, respecting the horizontal midline. A defect that crosses the midline suggests neurological disease.
- OCT retinal nerve fibre layer is useful for progression but is confounded by myopia, media opacity and peripapillary atrophy.
- First-line medical therapy is usually a prostaglandin analogue once nightly, which increases uveoscleral outflow. Avoid beta blockers in asthma and heart block; alpha agonists cause follicular conjunctivitis; carbonic anhydrase inhibitors are avoided in sulfa allergy and sickle cell disease.
- Acute angle closure: immediate topical beta blocker, pilocarpine after the pressure falls, systemic acetazolamide, mannitol if needed, then laser peripheral iridotomy to both eyes.
Worked example
A 64-year-old woman presents with a painful red right eye, nausea and halos. Vision is 6/60, the pupil is fixed and mid-dilated, and IOP is 54 mmHg. The left anterior chamber is shallow. You treat with topical timolol, oral acetazolamide and intravenous mannitol, defer pilocarpine until the iris sphincter is not ischaemic, then perform a laser iridotomy in the right eye and prophylactically in the left. The reasoning is that the fellow eye has the same crowded anatomy and is at risk even if it has never had an attack.
Traps
Missing angle closure because the eye is white, attributing a nasal step to cataract, and forgetting that steroid-induced pressure rise can occur weeks after drops stop.