Glaucoma
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Direct answer
Glaucoma is a progressive optic neuropathy with characteristic cupping of the optic disc and visual field loss, of which raised intraocular pressure is the chief modifiable risk — not the definition, since normal-tension glaucoma exists and ocular hypertension may never damage a nerve. Primary open-angle glaucoma is silent: a painless eye with pressures above 21 mmHg, cup-disc ratio above 0.6, and arcuate field defects discovered late. Primary angle-closure glaucoma is dramatic: a painful, red eye with a hazy cornea, haloes, a fixed semidilated pupil and pressure of 40 to 60 mmHg — an emergency lowered medically then cured by laser peripheral iridotomy. Congenital glaucoma shows the triad of watering, photophobia and buphthalmos in an infant.
What you must remember
- Normal intraocular pressure is 10 to 21 mmHg by applanation; the danger level is individualised — therapy targets the pressure at which the field stops progressing.
- Open-angle field sequence: paracentral scotoma, then nasal step, arcuate Bjerrum scotoma, ring scotoma and finally tubular vision with a preserved central island.
- Disc signs: vertical cupping, rim notching, disc haemorrhage, bayoneting of vessels; an asymmetry of 0.2 or more between the two cups is itself suspicious.
- First-line drops for open-angle disease: prostaglandin analogues such as latanoprost once nightly (side effects — increased iris pigmentation and lash growth), or beta-blockers such as timolol.
- Timolol is contraindicated in asthma, chronic obstructive pulmonary disease, bradycardia and heart block; brimonidine is contraindicated below two years of age because of apnoea.
- Acute angle closure is broken with intravenous acetazolamide, topical timolol and apraclonidine, hyperosmotic mannitol, then pilocarpine 2 per cent once the ischaemic sphincter recovers below about 40 mmHg; definitive treatment is laser peripheral iridotomy in both eyes.
- Trabeculectomy, frequently with mitomycin C, is the standard operation when drops fail; steroid-induced glaucoma resolves on withdrawing the drop.
- Congenital glaucoma: buphthalmos with enlarged corneal diameter above 12 mm, Haab striae and raised pressure; treated by goniotomy or trabeculotomy, not drops alone.
The acute attack, managed minute by minute
A 58-year-old woman presents at night with severe right-sided eye pain, headache, vomiting and blurred vision with rainbow rings around lights. The right eye is injected, the cornea is steamy, the anterior chamber is shallow, and the pupil is fixed and oval at mid-dilation; pressure measures 52 mmHg. Diagnosis: acute primary angle closure from pupillary block. Order the treatment as the exam expects it. Immediately, intravenous acetazolamide 500 mg and topical timolol 0.5 per cent plus apraclonidine lower secretion and pressure; intravenous mannitol shrinks the vitreous if pressure resists. Antiemetics and analgesia treat the symptoms that make this mimic a migraine or an abdomen. Only when pressure has fallen — the cornea clears and the ischaemic sphincter pupillae can respond — does pilocarpine 2 per cent constrict the pupil and pull the iris from the angle; giving pilocarpine first is the classic wrong answer. Once the attack is broken, laser peripheral iridotomy in both eyes removes the pupillary block permanently, and the fellow eye is prophylactically treated at the same sitting. Step back and the teaching point is symmetrical: chronic open-angle glaucoma steals sight silently and needs screening, while angle closure announces itself and needs an emergency pathway memorised to the minute.
Where candidates slip
The recurring MCQ trap is sequence: pilocarpine before the pressure is lowered does nothing, because an ischaemic sphincter cannot constrict. The second trap is systemic: prescribing timolol to the asthmatic in the same prescription, or brimonidine to an infant, converts eye drops into a systemic hazard. Third, candidates call glaucoma a disease of high pressure; examiners now reward the optic-neuropathy definition, because normal-tension glaucoma and ocular hypertension break the pressure equals disease equation. In the Indian clinic setting, steroid drops bought freely for unrelated red eyes remain the commonest iatrogenic cause of a pressure spike, worth remembering both for the exam and for counselling.
Frequently asked questions
Why is pilocarpine delayed in acute angle-closure glaucoma?
The ischaemic sphincter pupillae cannot respond until pressure falls below roughly 40 mmHg, so medical decompression with acetazolamide, timolol and mannitol comes first.
What is the definitive treatment of primary angle-closure glaucoma?
Laser peripheral iridotomy, which relieves pupillary block in the affected and the fellow eye, performed once the acute attack is controlled.
Which antiglaucoma drop is contraindicated in asthma?
Topical beta-blockers such as timolol, which can precipitate bronchospasm; bradycardia and heart block are the cardiac contraindications.
How does congenital glaucoma present?
The triad of epiphora, photophobia and blepharospasm in an infant with an enlarged globe (buphthalmos), corneal diameter above 12 mm, Haab striae and raised pressure.
What field defect appears earliest in open-angle glaucoma?
A paracentral scotoma or nasal step in the arcuate field bundle, progressing to an arcuate Bjerrum scotoma and eventually tubular vision.
What is the role of mitomycin C in trabeculectomy?
An antifibrotic applied intraoperatively to limit subconjunctival scarring and keep the filtration bleb functioning, especially in high-risk eyes.