Final Professional MBBS — Ophthalmology (complete, 12 chapters). Explanation-first answers with anatomical, optics, neuro & public-health diagrams, classifications, comparison tables, drug doses, clinical pearls and key-point recaps from Khurana's Comprehensive Ophthalmology, Parsons' Diseases of the Eye and Park's PSM.
12chapters144questions39High-Yield
THE CONCEPT
Glaucoma is a group of disorders in which a progressive optic neuropathy (loss of retinal ganglion-cell axons) produces characteristic optic-disc cupping and visual-field loss, usually — but not always — associated with raised intraocular pressure (IOP). Primary open-angle glaucoma (POAG) is the commonest form: a chronic, bilateral, painless, insidious disease in which the drainage angle is open but aqueous outflow is impaired within the trabecular meshwork.
Aqueous humour circulation
Ciliary body
(makes aqueous)
Angle: trabecular meshwork
→ Schlemm's canal (outflow)
Pupil
Lens
Aqueous: ciliary body → posterior chamber → pupil → anterior chamber → angle
Circulation of aqueous humour: secreted by the ciliary body into the posterior chamber, it flows through the pupil into the anterior chamber and drains at the angle through the trabecular meshwork into Schlemm's canal. Obstruction anywhere along the outflow raises intraocular pressure.
WHY THE PRESSURE RISES
Intraocular pressure depends on the balance between aqueous production (by the ciliary body) and its drainage (at the angle). In POAG there is increased resistance to outflow in the trabecular meshwork, so pressure rises even though the angle looks normal. Sustained pressure (and other factors such as poor optic-nerve perfusion) damages the axons at the optic disc.
RISK FACTORS
Key risk factors are raised IOP, increasing age, a positive family history, black ethnicity, high myopia, diabetes, and a thin central cornea. Because it is painless and symptomless until late, POAG is a major cause of irreversible blindness worldwide.
CLINICAL FEATURES & DISC CHANGES
The patient is typically asymptomatic until advanced, when peripheral field is lost and only central 'tunnel' vision remains. The optic disc shows progressive cupping — an enlarged cup-to-disc ratio, thinning/notching of the neuroretinal rim, bayoneting of vessels and disc haemorrhages.
Normal disc
cup/disc ratio ~0.3
Glaucomatous disc
deep, enlarged cup (≥0.6); vessels bayonet
Glaucomatous optic-disc cupping. As ganglion-cell axons are lost, the central cup enlarges (a rising cup-to-disc ratio, notch or thin neuroretinal rim) and the vessels bend sharply at the cup edge — the structural hallmark of glaucomatous optic-nerve damage.
INVESTIGATION & MANAGEMENT
Diagnosis rests on tonometry (IOP), gonioscopy (an open angle), optic-disc assessment, perimetry (visual fields) and OCT of the nerve-fibre layer. Treatment aims to lower IOP to a safe 'target':
Medical (first-line) — topical prostaglandin analogues (latanoprost — increase outflow), beta-blockers (timolol — reduce production), alpha-agonists, and carbonic-anhydrase inhibitors.
Surgery — trabeculectomy (a guarded filtration channel) or a drainage device, when medical/laser therapy fails.
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CLINICAL PEARL: POAG is a chronic, painless, bilateral optic neuropathy with an open angle and impaired trabecular outflow — the classic 'silent thief of sight'. It causes progressive cupping and peripheral field loss long before the patient notices, so screening at-risk groups matters. Diagnose with IOP, gonioscopy, discs, fields and OCT; treat by lowering IOP with prostaglandins first, then beta-blockers/other drops, laser trabeculoplasty, and trabeculectomy.
WHY POAG IS THE 'SILENT THIEF OF SIGHT'
The most dangerous feature of POAG is that it is asymptomatic until it is advanced. Because the disease first destroys peripheral, not central, vision, and because the fellow eye compensates for early gaps, patients notice nothing until a large amount of irreversible field has already been lost — by which time only 'tunnel' vision remains. There is no pain and no redness to raise the alarm. This silent, bilateral, gradual course is precisely why opportunistic case-finding and screening of at-risk groups (older age, family history, high myopia, black ethnicity) is so important, and why the emphasis is on early detection rather than waiting for symptoms.
THE PRINCIPLE OF THE 'TARGET PRESSURE'
A central idea in managing POAG is the 'target pressure'. Because the optic-nerve damage is irreversible, the goal of treatment is not to cure but to halt further loss, and the only proven way to do this is to lower the IOP. For each patient a target is set — a pressure judged low enough to stop progression — based on the starting pressure, the severity of existing damage, and the rate of progression. Treatment is then escalated (through drops, laser and surgery) until that target is reached and progression stops on serial fields and disc/OCT assessment. This individualised, progression-based approach guides lifelong follow-up.
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KEY POINTS / NUMBERS (viva)
POAG = chronic, painless, bilateral open-angle optic neuropathy; impaired trabecular outflow; leading cause of irreversible blindness.
Risk: raised IOP, age, family history, black ethnicity, high myopia, diabetes, thin cornea; asymptomatic → peripheral field loss/tunnel vision.
SOURCES: Khurana's Comprehensive Ophthalmology; Parsons' Diseases of the Eye.
THE CONCEPT
Acute primary angle-closure glaucoma is an ophthalmic emergency in which the peripheral iris suddenly blocks the drainage angle, obstructing aqueous outflow and causing a rapid, severe rise in intraocular pressure. Unlike the silent POAG, it is acutely painful and can blind the eye within hours to days if not treated promptly.
Open-angle
Angle open → aqueous
reaches the meshwork
(drainage resistance is IN the meshwork)
Angle-closure
Iris pushed forward,
blocks the angle
(iris covers the meshwork → sudden ↑IOP)
The drainage angle in the two main glaucomas. In open-angle glaucoma the angle is anatomically open but drainage is impaired within the trabecular meshwork; in angle-closure the peripheral iris is pushed forward and physically blocks the meshwork, obstructing outflow and causing a sudden pressure rise.
THE MECHANISM — PUPILLARY BLOCK
It classically occurs in a predisposed eye — hypermetropic, with a shallow anterior chamber, a narrow angle and often an enlarging lens. The key event is relative pupillary block: aqueous cannot pass easily from the posterior to the anterior chamber through the pupil, so pressure builds behind the iris and bows its periphery forward to seal off the angle. A mid-dilated pupil (in dim light, stress or after mydriatics) is the typical trigger.
CLINICAL FEATURES
The patient presents with a sudden, painful red eye, markedly blurred vision, coloured haloes around lights, and often headache, nausea and vomiting (which can mimic a systemic illness). Signs are a hazy (oedematous) cornea, a mid-dilated, fixed, vertically-oval pupil, a shallow anterior chamber, ciliary congestion, and a stony-hard eye with very high IOP (often 50–70 mmHg).
MANAGEMENT
Treatment is urgent, aiming first to lower the pressure medically, then to relieve the block definitively:
Immediate medical — systemic acetazolamide (± IV mannitol), topical timolol, a topical alpha-agonist and pilocarpine (to constrict the pupil and pull the iris out of the angle), and topical steroids for inflammation.
Definitive — laser peripheral iridotomy (YAG PI) once the cornea clears, making a hole in the iris to bypass the pupillary block.
The fellow eye — a prophylactic laser iridotomy, because it is anatomically predisposed too.
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CLINICAL PEARL: Acute angle-closure is a painful red-eye emergency: a hard eye, hazy cornea, mid-dilated fixed oval pupil and haloes, with nausea/vomiting, in a hypermetrope with a shallow chamber. The mechanism is pupillary block. Bring the pressure down urgently with acetazolamide, timolol, pilocarpine (± mannitol), then perform a laser peripheral iridotomy — and treat the fellow eye prophylactically.
WHY MYDRIATICS MUST BE USED WITH CARE
An important practical warning follows from the mechanism. Because a mid-dilated pupil is what precipitates the attack, dilating the pupil (with mydriatic drops, or in dim light) can trigger acute angle-closure in a predisposed eye. This is why one must be cautious about pharmacological dilation in patients with shallow anterior chambers or narrow angles, and why some patients experience their first attack after entering a dark cinema, during stress, or after taking drugs with anticholinergic effects. Recognising the predisposed eye beforehand — and having treated it (or the fellow eye) with a prophylactic iridotomy — prevents this iatrogenic disaster.
A NOTE ON CHRONIC & INTERMITTENT ANGLE-CLOSURE
It is worth knowing that angle-closure is not always dramatic. Some patients have subacute (intermittent) attacks — brief episodes of blurring and haloes, often in the evening, that resolve spontaneously when the pupil constricts (e.g. on sleeping) — which are easily missed but warn of a closing angle. Others develop chronic angle-closure, in which repeated or gradual closure forms permanent peripheral anterior synechiae and produces a slowly rising pressure resembling POAG. Recognising these less acute presentations allows a preventive laser iridotomy before a full, sight-threatening acute attack occurs.
A NOTE ON THE STAGES OF ANGLE-CLOSURE
It helps to see acute angle-closure as one point on a spectrum. It begins as a primary angle-closure suspect (an occludable narrow angle but normal pressure and disc), may pass through intermittent (subacute) closure, and can present as the full acute attack or, if repeated, evolve into chronic angle-closure glaucoma with permanent synechiae and optic-nerve damage. A neglected acute attack can also leave the eye with a fixed dilated pupil, iris atrophy, glaukomflecken (small anterior lens opacities) and a cataract as tell-tale evidence of a previous episode. Recognising the earlier stages allows a preventive laser iridotomy before irreversible damage occurs, which is why screening narrow angles matters.
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KEY POINTS / NUMBERS (viva)
Acute angle-closure = emergency; peripheral iris blocks the angle → sudden severe IOP rise (often 50–70 mmHg).
Emergency medical treatment: acetazolamide (± IV mannitol), timolol, alpha-agonist, pilocarpine, topical steroid.
Definitive: laser peripheral iridotomy (bypasses pupillary block); do a prophylactic iridotomy on the predisposed fellow eye.
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SOURCES: Khurana's Comprehensive Ophthalmology; Parsons' Diseases of the Eye.
THE CONCEPT
Congenital (primary infantile) glaucoma is glaucoma present at or shortly after birth, caused by a developmental abnormality of the drainage angle (trabeculodysgenesis) that obstructs aqueous outflow. Because the infant eye is distensible, the raised pressure enlarges the whole globe, producing the classic 'ox-eye' — an important, treatable cause of childhood blindness.
PRESENTATION — THE CLASSIC TRIAD
The hallmark is a triad of watering (epiphora), photophobia and blepharospasm (lid squeezing), a baby who is uncomfortable in light. The most striking sign is buphthalmos (an abnormally large eye, 'ox-eye') from stretching of the young sclera.
SIGNS
Corneal enlargement and haze — a large, cloudy cornea (raised pressure causes oedema).
Haab's striae — horizontal breaks in Descemet's membrane from corneal stretching.
Deep anterior chamber, raised IOP, and glaucomatous optic-disc cupping (which can reverse in infants if pressure is controlled early).
INVESTIGATION & MANAGEMENT
Because infants cannot cooperate, examination under anaesthesia (EUA) is used to measure IOP, corneal diameter, and to perform gonioscopy and disc assessment. Treatment is primarily surgical (medical therapy is only a temporary adjunct):
Goniotomy or trabeculotomy — opening the abnormal angle to restore outflow (the definitive treatments).
Trabeculectomy / drainage devices — if angle surgery fails.
Followed by refractive correction and amblyopia therapy, since these eyes are often anisometropic/amblyopic.
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CLINICAL PEARL: Suspect congenital glaucoma in any infant with the triad of watering, photophobia and blepharospasm, plus a large, hazy cornea and buphthalmos. Look for Haab's striae. It is caused by a developmental angle anomaly, assessed under anaesthesia (EUA), and treated surgically (goniotomy/trabeculotomy) — early treatment can even reverse the cupping and save useful vision.
WHY EARLY DIAGNOSIS IS SO IMPORTANT
The prognosis in congenital glaucoma depends heavily on how early it is recognised and treated. Prolonged high pressure not only enlarges the eye but causes permanent corneal scarring, optic-nerve cupping, high myopia and amblyopia. The encouraging point is that, unlike in adults, infant optic-disc cupping can partly reverse if the pressure is normalised early. This makes the classic triad of watering, photophobia and blepharospasm a red flag that demands urgent referral — a baby who avoids light and has a large or cloudy cornea should be assumed to have glaucoma until proven otherwise, because delay converts a treatable condition into lifelong blindness.
THE DIFFERENTIAL OF A CLOUDY/LARGE CORNEA IN INFANCY
Because the signs overlap with other conditions, it helps to know the differential. A watering eye in a baby is far more often due to a blocked nasolacrimal duct than glaucoma — but that causes watering and stickiness without photophobia, corneal haze or a large cornea. A cloudy cornea at birth may also be caused by birth trauma (forceps), metabolic mucopolysaccharidoses, or congenital corneal dystrophies. The presence of the full triad, a genuinely enlarged cornea (buphthalmos) and raised pressure on examination under anaesthesia point to glaucoma and separate it from these mimics, which is why EUA is central to the work-up.
A NOTE ON SECONDARY & SYNDROMIC INFANTILE GLAUCOMA
Not all infantile glaucoma is primary. It may be secondary or part of a syndrome, and recognising this guides wider care. It is associated with anterior-segment dysgeneses such as Axenfeld–Rieger anomaly and aniridia, with phakomatoses such as Sturge–Weber syndrome (a facial port-wine stain in the trigeminal distribution) and neurofibromatosis, and with congenital rubella. It can also follow congenital cataract surgery. Because these carry systemic and other ocular implications, a baby diagnosed with glaucoma needs a full ocular and general examination rather than treatment of the pressure alone, and often multidisciplinary follow-up.
A NOTE ON THE LONG-TERM FOLLOW-UP
Even after successful angle surgery, a child with congenital glaucoma needs lifelong monitoring, because the pressure can rise again years later and because these eyes are prone to high myopia, astigmatism, anisometropia and amblyopia from the earlier corneal and axial changes. Management therefore extends well beyond controlling the pressure to include regular refraction, spectacle/contact-lens correction and disciplined amblyopia therapy (patching) during the critical period of visual development. Parents must understand that surgery treats the glaucoma but that good vision depends equally on this long refractive and amblyopia rehabilitation — a point that distinguishes paediatric from adult glaucoma care.
Signs: enlarged hazy cornea, Haab's striae (Descemet's breaks), deep anterior chamber, raised IOP, disc cupping (reversible if treated early).
Assessed under anaesthesia (EUA); tonometry, corneal diameter, gonioscopy, disc.
Treatment is primarily surgical (goniotomy/trabeculotomy; trabeculectomy/tube if needed) + refractive correction and amblyopia therapy.
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
The one modifiable factor in glaucoma is intraocular pressure, so all treatment — medical, laser and surgical — aims to lower IOP to a 'target' at which optic-nerve damage stops progressing. The choice depends on the type of glaucoma, its severity, and the response to treatment; the two levers are reducing aqueous production and increasing its outflow.
Cholinergics (pilocarpine) — increase trabecular outflow and constrict the pupil (especially useful in angle-closure).
LASER THERAPY
Laser trabeculoplasty improves trabecular outflow in open-angle glaucoma; laser peripheral iridotomy relieves pupillary block in angle-closure; and cyclophotocoagulation reduces aqueous production (in refractory glaucoma).
SURGERY
When drops and laser fail to control pressure, surgery creates a new drainage route: trabeculectomy (a guarded fistula draining aqueous under the conjunctiva to form a 'bleb', often with antimetabolites like mitomycin-C), glaucoma drainage devices (tubes), and newer minimally-invasive glaucoma surgery (MIGS). Congenital glaucoma is treated by angle surgery (goniotomy/trabeculotomy).
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CLINICAL PEARL: Remember the drug classes by mechanism: prostaglandins (first-line; ↑ uveoscleral outflow), beta-blockers/alpha-agonists/carbonic-anhydrase inhibitors (↓ production), and pilocarpine (↑ trabecular outflow, ↓ pupil). Escalate through laser (trabeculoplasty for open-angle, iridotomy for angle-closure) to trabeculectomy. The whole strategy is simply to lower IOP to a target that halts progression, since the nerve damage itself is irreversible.
A NOTE ON ADHERENCE & THE PRACTICALITIES OF DROPS
A theme that determines real-world success is adherence to eye drops. Because glaucoma is lifelong, symptomless and treated with drops that themselves cause no felt benefit, many patients use them irregularly, allowing silent progression. Practical measures matter: choosing once-daily prostaglandins, minimising the number of bottles (using fixed-combination drops), teaching correct instillation and punctal occlusion (pressing the inner corner to reduce systemic absorption and improve local effect), and reviewing technique. Considering laser trabeculoplasty earlier can also reduce the drop burden. Recognising poor adherence as a common cause of 'treatment failure' is as important as the pharmacology itself.
A NOTE ON THE SYSTEMIC SIDE-EFFECTS OF GLAUCOMA DRUGS
Although given as drops, glaucoma medicines are absorbed systemically and have important side-effects to remember. Beta-blockers (timolol) can cause bronchospasm, bradycardia and heart block — hence caution in asthma, COPD and cardiac disease. Carbonic-anhydrase inhibitors (oral acetazolamide) cause paraesthesiae, malaise, renal stones and electrolyte disturbance. Alpha-agonists (brimonidine) can cause drowsiness and are avoided in infants. Prostaglandins are largely local (iris and lash pigmentation, hyperaemia), and pilocarpine causes brow-ache and a small, dim pupil. Knowing these guides safe prescribing and explains why the drug is tailored to the individual patient.
A NOTE ON MATCHING TREATMENT TO THE GLAUCOMA TYPE
A unifying principle is that the treatment ladder is tailored to the type of glaucoma, not applied uniformly. Open-angle glaucoma is usually controlled first with drops (or laser trabeculoplasty), reserving trabeculectomy for failure. Angle-closure requires laser iridotomy to relieve the block (drops alone are insufficient). Congenital glaucoma is primarily surgical (goniotomy/trabeculotomy). Secondary glaucomas demand treatment of the underlying cause alongside pressure control. Thus, although 'lower the IOP' is the common aim, the correct first step depends entirely on the mechanism — which is why establishing the type (by gonioscopy and examination) precedes choosing therapy.
A NOTE ON EMERGENCY PRESSURE-LOWERING
It is worth separating the chronic ladder from the emergency lowering of a dangerously high pressure (as in an acute attack or neovascular glaucoma). Acutely, one combines oral or intravenous acetazolamide and intravenous hyperosmotics (mannitol) to pull water out of the eye rapidly, with topical timolol, an alpha-agonist and (in angle-closure) pilocarpine, buying time until definitive treatment. This differs from the measured, long-term approach to chronic glaucoma, where a single drop is added and its effect assessed over weeks. Knowing both — the slow escalation for chronic disease and the rapid combination for a pressure emergency — is essential in practice.
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KEY POINTS / NUMBERS (viva)
Goal: lower IOP to a target that halts progression (nerve damage is irreversible). Levers: ↓ production or ↑ outflow.
Secondary glaucoma is a rise in intraocular pressure that is caused by another identifiable ocular or systemic disorder, rather than arising primarily. The underlying condition obstructs aqueous outflow (or, occasionally, increases production), so management must address both the pressure and its cause. It can be open-angle or angle-closure depending on the mechanism.
IMPORTANT TYPES
Neovascular glaucoma — new vessels (from diabetic retinopathy or a central retinal vein occlusion — ischaemia driving VEGF) grow over the angle and block it; painful and difficult to treat (needs pan-retinal photocoagulation/anti-VEGF plus pressure control).
Lens-induced glaucoma — phacomorphic (a swollen intumescent cataract causing angle closure) and phacolytic (leaked proteins from a hypermature cataract blocking the meshwork); cured by cataract surgery.
Inflammatory (uveitic) glaucoma — from trabecular obstruction by inflammatory cells, or synechiae.
Pseudoexfoliation and pigment-dispersion glaucoma — material or pigment clogging the meshwork.
Traumatic (angle-recession) glaucoma — after blunt injury damages the angle.
PRINCIPLES OF MANAGEMENT
The two aims are to control the IOP (with the usual medical/laser/surgical measures) and to treat the underlying cause — for example, cataract surgery for lens-induced glaucoma, pan-retinal photocoagulation/anti-VEGF for neovascular glaucoma, steroids-plus-pressure-control for uveitic glaucoma, and stopping the steroid in steroid-induced glaucoma. Recognising a secondary cause is essential because treating it may itself resolve the glaucoma.
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CLINICAL PEARL: Always ask whether a glaucoma is secondary, because the cause guides the cure. Key patterns: neovascular (diabetes/CRVO ischaemia → new vessels over the angle), lens-induced (phacomorphic/phacolytic → treat with cataract surgery), uveitic, steroid-induced (stop the steroid), pseudoexfoliative/pigmentary, and traumatic angle-recession. Manage by controlling the pressure AND treating the underlying disorder.
A NOTE ON NEOVASCULAR GLAUCOMA IN DETAIL
Neovascular glaucoma deserves emphasis because it is painful, aggressive and hard to treat. The sequence is instructive: a severely ischaemic retina (from proliferative diabetic retinopathy or an ischaemic central retinal vein occlusion) releases VEGF, which diffuses forward and drives a fibrovascular membrane to grow over the iris (rubeosis iridis) and the drainage angle, first blocking it and then contracting to pull it closed. The result is a very high, painful pressure with a red eye. Management must tackle the ischaemic drive (pan-retinal photocoagulation and/or anti-VEGF injections) as well as the pressure (drops, and often a tube or cyclodestruction), and prevention rests on treating the underlying retinal ischaemia early.
A NOTE ON STEROID-INDUCED GLAUCOMA
A commonly-tested and preventable secondary glaucoma is the steroid-induced type. In susceptible individuals ('steroid responders'), prolonged corticosteroids — most often topical eye drops, but also periocular, inhaled, nasal or systemic — raise outflow resistance in the trabecular meshwork and elevate IOP, usually after some weeks of use. It is frequently symptomless and can cause glaucomatous damage if unrecognised. The key messages are to use ocular steroids only with a clear indication, at the lowest effective dose, and to monitor the IOP, and that stopping the steroid usually (though not always) reverses the pressure rise. This makes it a genuinely avoidable cause of glaucoma.
A NOTE ON MALIGNANT (AQUEOUS-MISDIRECTION) GLAUCOMA
A rare but important secondary type worth knowing is malignant glaucoma (aqueous misdirection / ciliary-block glaucoma), classically occurring after intraocular (often glaucoma or cataract) surgery in a small, hypermetropic eye. Aqueous is misdirected posteriorly into or behind the vitreous, pushing the lens–iris diaphragm forward and producing a uniformly shallow (flat) anterior chamber with a high pressure — despite a patent iridotomy, which distinguishes it from pupillary-block closure. It is managed with cycloplegics, aqueous suppressants and, if needed, disruption of the anterior vitreous face (laser or vitrectomy). Recognising it matters because the intuitive treatment (miotics) makes it worse.
A NOTE ON WHY IDENTIFYING THE CAUSE CHANGES EVERYTHING
The overarching lesson of the secondary glaucomas is that the label 'glaucoma' is only the starting point — the treatment, and often the cure, lies in the cause. A phacomorphic or phacolytic glaucoma is cured by removing the cataract; a steroid-induced rise resolves on stopping the steroid; a neovascular glaucoma will not settle until the retinal ischaemia is treated. Missing the underlying disorder means treating the pressure endlessly while the true problem persists (and, in cases like an intraocular tumour presenting as glaucoma, missing something dangerous). This is why every glaucoma assessment includes a deliberate search for a secondary cause before the diagnosis of a 'primary' glaucoma is accepted.
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KEY POINTS / NUMBERS (viva)
Secondary glaucoma = raised IOP caused by another ocular/systemic disorder; open- or angle-closure by mechanism; treat pressure AND cause.
Manage by controlling IOP (medical/laser/surgical) and treating the underlying condition.
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
Tonometry is the measurement of intraocular pressure (IOP), a cornerstone of glaucoma diagnosis and monitoring. The normal range is about 10–21 mmHg. Most methods estimate pressure from the force needed to flatten (applanate) or indent the cornea.
METHODS
Goldmann applanation tonometry — the gold standard; measures the force to flatten a fixed corneal area at the slit lamp (after topical anaesthetic and fluorescein).
Non-contact ('air-puff') tonometry — uses a puff of air; convenient for screening, no contact.
Schiotz (indentation) tonometry — an older portable device measuring corneal indentation by a weighted plunger.
Perkins (portable applanation) and rebound (iCare) — useful in children and the bedbound.
A KEY CAVEAT
IOP readings are affected by central corneal thickness — a thick cornea overestimates and a thin cornea underestimates the true pressure — so pachymetry is measured alongside tonometry when assessing glaucoma.
A NOTE ON THE LIMITATIONS OF A SINGLE READING
An important clinical caveat is that a single IOP reading can be misleading. Pressure shows a diurnal variation (usually highest in the early morning), so a normal reading in clinic does not exclude damaging peaks at other times — which is one reason normal-tension glaucoma can be missed and why diurnal phasing (repeated measurements through the day) is sometimes done. Equally, a raised reading alone does not diagnose glaucoma without disc and field changes. Interpreting tonometry in the context of corneal thickness, the disc, the fields and repeated measurements — rather than in isolation — is the mark of sound glaucoma assessment.
THE BOTTOM LINE
Tonometry measures intraocular pressure (normal ~10–21 mmHg), best by Goldmann applanation, but must be interpreted with corneal thickness and alongside the disc and fields rather than as a single figure.
IN PRACTICE
For screening and in special situations, the choice of tonometer matters: non-contact devices allow quick technician screening, portable applanation and rebound tonometers suit children and the bedbound, and only Goldmann is relied upon for treatment decisions — always remembering to disinfect contact tips to avoid cross-infection.
MECHANISM RECAP
All the common methods share one idea — relating pressure to how the cornea resists a force — which is also why they share one weakness: they are all influenced by corneal properties (thickness, curvature and rigidity). A very thick or scarred cornea reads falsely high and a thin or post-refractive-surgery cornea falsely low, so tonometry is calibrated against the individual cornea and, where the reading and the clinical picture disagree, it is the disc and field that decide.
A related concept is the ocular pulse and the diurnal curve: since pressure varies with the cardiac cycle and across the day, a low clinic reading never fully excludes damaging peaks, and in suspicious cases (a glaucomatous disc with 'normal' pressure) repeated or home tonometry may unmask them. Interpreting a number this way — as one point on a fluctuating curve, adjusted for the cornea — is what separates a meaningful pressure from a misleading one.
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KEY POINTS TO REMEMBER
Tonometry = measurement of intraocular pressure; normal ~10–21 mmHg.
Goldmann applanation tonometry is the gold standard (slit-lamp, anaesthetic + fluorescein).
Readings depend on central corneal thickness (thick over-, thin under-estimates) — measure pachymetry too.
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
Gonioscopy is the examination of the drainage (iridocorneal) angle of the anterior chamber using a special mirrored contact lens (a goniolens) at the slit lamp. It is essential in glaucoma because the angle cannot be seen directly — light from it is totally internally reflected at the cornea — so a lens is needed to view it.
WHY IT MATTERS
Gonioscopy is what distinguishes open-angle from angle-closure glaucoma, which is fundamental because their management differs completely. It allows the examiner to grade the angle width, identify a narrow or closed angle, and detect abnormalities such as peripheral anterior synechiae, new vessels (in neovascular glaucoma), angle recession (after trauma) and pigment or exfoliative deposits.
STRUCTURES SEEN
From the front backward, the angle structures are Schwalbe's line, the trabecular meshwork (containing Schlemm's canal), the scleral spur, the ciliary body band and the iris root — and how many of these are visible defines whether the angle is open or closed.
A NOTE ON WHY GONIOSCOPY IS INDISPENSABLE
The reason gonioscopy cannot be skipped is that open-angle and angle-closure glaucoma can look identical on pressure and disc examination, yet need completely different treatment — drops/trabeculoplasty for the open angle, but a laser iridotomy for the closed one. Giving a patient with an occludable angle only drops, or dilating their pupil unaware, risks precipitating an acute attack. Gonioscopy is also the only way to detect the tell-tale angle signs of secondary glaucomas — new vessels, recession, synechiae, pigment or exfoliation. It is therefore a mandatory part of assessing every glaucoma patient, not an optional refinement.
THE BOTTOM LINE
Gonioscopy views the drainage angle with a mirrored lens and is indispensable for distinguishing open-angle from angle-closure glaucoma and detecting secondary angle pathology.
IN PRACTICE
Angles are graded (for example by the Shaffer or Van Herick systems) to record how occludable they are, and indentation gonioscopy can distinguish a merely narrow (appositionally closed) angle from one permanently sealed by synechiae — a distinction that changes whether a simple iridotomy will suffice.
MECHANISM RECAP
The need for a special lens arises from simple optics: the critical angle at the cornea–air interface causes light from the angle to be totally internally reflected, so the angle is invisible on ordinary examination. A goniolens — either a direct (Koeppe) lens or, more commonly, an indirect mirrored (Goldmann/Zeiss) lens — overcomes this, letting the clinician see and grade the angle that determines the entire classification and treatment of the glaucoma.
In the acute setting, gonioscopy of the fellow eye is especially valuable during a suspected acute angle-closure attack, because the congested attacking eye may be too hazy to examine — an occludable angle in the other eye supports the diagnosis and mandates prophylactic treatment of that eye too. This simple manoeuvre often clinches an emergency diagnosis and prevents a second, avoidable attack.
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KEY POINTS TO REMEMBER
Gonioscopy = examination of the anterior-chamber drainage angle with a mirrored contact lens (the angle can't be seen directly).
Distinguishes open-angle from angle-closure glaucoma — fundamental, as their management differs.
Glaucoma damages the optic nerve by progressive loss of retinal ganglion-cell axons, and this is seen at the disc as 'cupping' — an enlargement and deepening of the central cup at the expense of the surrounding neuroretinal rim. Recognising these changes is central to diagnosing and monitoring glaucoma.
Normal disc
cup/disc ratio ~0.3
Glaucomatous disc
deep, enlarged cup (≥0.6); vessels bayonet
Glaucomatous optic-disc cupping. As ganglion-cell axons are lost, the central cup enlarges (a rising cup-to-disc ratio, notch or thin neuroretinal rim) and the vessels bend sharply at the cup edge — the structural hallmark of glaucomatous optic-nerve damage.
KEY SIGNS OF GLAUCOMATOUS CUPPING
Increased cup-to-disc ratio (e.g. ≥0.6, or progressive enlargement) and asymmetry between the two eyes.
Thinning or notching of the neuroretinal rim (violating the normal 'ISNT' rule — rim thickest Inferior > Superior > Nasal > Temporal).
Bayoneting of vessels (they bend sharply as they cross the steep cup edge) and nasal shift of vessels.
Disc (splinter) haemorrhages and peripapillary atrophy.
ASSESSMENT
The disc is assessed by ophthalmoscopy and, increasingly, OCT of the retinal-nerve-fibre layer, which quantifies and tracks the loss objectively over time.
A NOTE ON STRUCTURE VERSUS FUNCTION
A useful concept is that disc cupping represents the structural damage of glaucoma, while the visual field (perimetry) shows the functional loss, and the two are monitored together. Often structural change (disc/OCT nerve-fibre thinning) is detectable before a reproducible field defect appears ('pre-perimetric' glaucoma), while in advanced disease the field is more useful for tracking further loss. Comparing serial disc photographs/OCT with serial fields therefore gives the fullest picture of whether glaucoma is progressing, which is the key question that drives treatment decisions. Neither structure nor function alone tells the whole story.
THE BOTTOM LINE
Glaucomatous cupping is the structural sign of ganglion-cell loss (rising cup:disc ratio, rim notching, disc haemorrhage), assessed by ophthalmoscopy and OCT and tracked for progression.
IN PRACTICE
In practice the disc is examined stereoscopically at the slit lamp with the pupil dilated, and findings are documented with photographs or OCT so that subtle progressive rim thinning or an enlarging cup can be detected over years — since it is change over time, more than any single appearance, that confirms glaucoma.
MECHANISM RECAP
Because the cup simply reflects how much neuroretinal rim (axon tissue) remains, a large cup in a large disc can be physiological while a modest cup in a small disc can be pathological — which is why the size of the disc is taken into account, and why inter-eye asymmetry and the ISNT rule are used rather than the cup:disc ratio alone. It is loss of rim tissue, not the cup number itself, that signifies glaucoma.
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KEY POINTS TO REMEMBER
Glaucomatous cupping = enlargement/deepening of the optic cup from loss of ganglion-cell axons (thinning neuroretinal rim).
Signs: increased cup:disc ratio (≥0.6) and inter-eye asymmetry, rim thinning/notching (breaks the ISNT rule).
Bayoneting and nasal shift of vessels, disc (splinter) haemorrhages, peripapillary atrophy.
Assess by ophthalmoscopy and OCT of the retinal-nerve-fibre layer (objective monitoring).
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
Perimetry is the measurement of the visual field, and it detects the functional damage of glaucoma — the field loss that mirrors the optic-nerve damage. It is essential both for diagnosis and, crucially, for monitoring progression over time.
CHARACTERISTIC GLAUCOMATOUS FIELD DEFECTS
Glaucoma damages nerve fibres in a pattern that produces typical defects: an enlarged blind spot, paracentral scotomas, and arcuate (Bjerrum) scotomas that follow the arc of the nerve-fibre bundles, later forming a nasal step (Rönne's). As damage advances these coalesce, leaving only a central and temporal island ('tunnel vision'), with central acuity preserved until very late.
METHODS
Automated static perimetry (e.g. the Humphrey field analyser) is the standard, testing sensitivity at many points; manual kinetic (Goldmann) perimetry is also used. Serial fields are compared to detect progression, guiding treatment intensity.
A NOTE ON THE ANATOMICAL BASIS OF THE DEFECTS
The characteristic shapes of glaucomatous field defects are explained by the anatomy of the retinal nerve-fibre layer. The axons run in arcuate bundles that arch above and below the fovea and respect the horizontal midline (the temporal raphe). Damage to a bundle therefore produces an arcuate (Bjerrum) scotoma that mirrors this arc, and because the upper and lower fibres meet at the horizontal, defects characteristically step across the nasal horizontal midline (the nasal step). Understanding this makes the otherwise odd-looking defects logical, and explains why central vision — served by the tightly-packed papillomacular fibres — is spared until late.
THE BOTTOM LINE
Perimetry reveals the functional field loss of glaucoma — arcuate scotomas and nasal steps progressing to tunnel vision — and serial fields are the key measure of progression.
IN PRACTICE
Reliable perimetry depends on a cooperative, well-instructed patient, and early fields can be affected by learning effects and false results, so a defect is generally confirmed on repeat testing before treatment is escalated, and results are always interpreted alongside the disc and pressure.
MECHANISM RECAP
Perimetry probes vision point by point against a background, comparing the patient's sensitivity with age-matched norms, so its output is best read through summary indices and probability plots rather than raw numbers. Because it depends on subjective responses, fatigue and attention affect it — reinforcing that a single field is a snapshot, and it is the trend across reliable, repeated fields that reveals true glaucomatous progression.
A practical pitfall is the artefactual field defect — lens-rim, ptosis or an uncorrected refractive error can mimic or mask glaucomatous loss — so the patient is refracted for the test distance and lids/lenses positioned correctly. Reading the reliability indices first, before interpreting any defect, prevents these artefacts from being mistaken for progression.
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KEY POINTS TO REMEMBER
Perimetry = measurement of the visual field; detects the functional (field) loss of glaucoma and monitors progression.
Advanced disease → tunnel vision (central/temporal island); central acuity preserved until late.
Automated static perimetry (Humphrey) is standard; serial fields track progression and guide treatment.
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
Trabeculectomy is the standard glaucoma filtration surgery, performed when medical and laser treatment fail to control intraocular pressure. It works by creating a new, guarded drainage channel for aqueous to bypass the blocked trabecular meshwork.
THE PRINCIPLE
A partial-thickness scleral flap is fashioned and a small block of trabecular tissue removed, allowing aqueous to drain from the anterior chamber into the subconjunctival space, where it collects as a 'bleb' and is absorbed. A peripheral iridectomy is done to prevent the iris blocking the opening. Antimetabolites (mitomycin-C or 5-fluorouracil) are often applied to reduce scarring and keep the drainage working.
COMPLICATIONS
These include a shallow anterior chamber and hypotony (over-drainage), bleb leak or failure from scarring, cataract, and — a lifelong risk — bleb-related infection (blebitis/endophthalmitis).
A NOTE ON THE ROLE OF ANTIMETABOLITES & MIGS
Two developments have shaped modern filtration surgery. The use of antimetabolites (mitomycin-C, 5-fluorouracil) to suppress subconjunctival scarring dramatically improved trabeculectomy success — the commonest reason a bleb fails being fibrosis — though at the cost of a higher risk of a very thin, leaky, infection-prone bleb. More recently, minimally-invasive glaucoma surgery (MIGS) — small devices/stents that enhance outflow with less tissue disruption — has offered a safer, quicker option for milder glaucoma, often combined with cataract surgery, albeit with more modest pressure-lowering than trabeculectomy. Choosing between them balances the pressure target against the surgical risk.
THE BOTTOM LINE
Trabeculectomy is guarded filtration surgery that drains aqueous to a subconjunctival bleb when medical/laser therapy fails, improved by antimetabolites but at risk of hypotony, bleb failure and infection.
IN PRACTICE
After surgery the bleb is nurtured with intensive topical steroids to limit scarring and may need adjustment (suture release, needling) to fine-tune drainage, and patients are warned that a leaking or infected bleb causing a sudden painful red eye needs immediate attention for the rest of their lives.
MECHANISM RECAP
The essence of the operation is to convert an eye that cannot drain into one that drains in a controlled way, with the scleral flap acting as a one-way valve that resists over-drainage. Everything that determines success — antimetabolite use, flap tension, suture management and post-operative bleb care — is aimed at achieving that delicate balance between too little flow (failure) and too much (hypotony).
An alternative worth naming for refractory or high-risk cases is the glaucoma drainage tube (e.g. Ahmed or Baerveldt implant), which shunts aqueous to a plate placed under the conjunctiva far from the limbus; it is favoured when a trabeculectomy has failed or is likely to fail (as in neovascular or uveitic glaucoma), completing the surgical armamentarium alongside trabeculectomy and MIGS.
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KEY POINTS TO REMEMBER
Trabeculectomy = filtration surgery creating a guarded drainage channel when medical/laser therapy fails.
Scleral flap + removal of trabecular block → aqueous drains subconjunctivally as a 'bleb'; peripheral iridectomy prevents iris blockage.
Antimetabolites (mitomycin-C, 5-FU) reduce scarring and improve success.
Complications: hypotony/shallow AC (over-drainage), bleb leak/failure, cataract, bleb-related infection (blebitis/endophthalmitis).
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SOURCES: Khurana's Comprehensive Ophthalmology.
TWO REVEALING EXTREMES
These two conditions show that intraocular pressure and glaucomatous damage are related but not identical. Ocular hypertension is a raised IOP (>21 mmHg) WITHOUT any optic-disc or visual-field damage — a risk factor for, but not yet, glaucoma. Normal-tension glaucoma is the opposite: typical glaucomatous disc cupping and field loss occurring WITH an IOP in the normal range (≤21 mmHg).
IMPLICATIONS
Ocular hypertension is monitored (and treated if the risk of conversion is high — e.g. very high pressure or a thin cornea), not automatically treated. Normal-tension glaucoma implies factors beyond pressure (poor optic-nerve perfusion, vascular dysregulation), but treatment is still to lower the IOP further from its 'normal' baseline, which slows progression. Both underline that glaucoma is an optic neuropathy, not merely 'high pressure'.
A NOTE ON WHY THESE CONDITIONS RESHAPED THE DEFINITION
Ocular hypertension and normal-tension glaucoma are the reason the modern definition of glaucoma emphasises the optic neuropathy, not the pressure. If high pressure alone were 'glaucoma', ocular hypertensives would all have the disease (they do not), and normal-tension patients would be missed (they have genuine glaucoma). Landmark studies also showed that lowering pressure benefits both groups — reducing conversion in ocular hypertension and slowing progression in normal-tension glaucoma — cementing IOP as the key modifiable risk factor even when it is 'normal'. Together they teach that glaucoma is diagnosed on the disc and field, with pressure as a major but not defining factor.
THE BOTTOM LINE
Ocular hypertension (high IOP, no damage) and normal-tension glaucoma (damage at normal IOP) show that glaucoma is an optic neuropathy, with pressure a major but not defining factor — and lowering IOP helps both.
IN PRACTICE
Deciding whether to treat an ocular hypertensive uses the overall risk of conversion — higher with very raised pressure, a thin cornea, older age, a large cup and a family history — so that high-risk eyes are treated while low-risk eyes are simply monitored, sparing them lifelong drops.
MECHANISM RECAP
Both conditions are really statements about where a patient sits on the relationship between pressure and nerve damage: the ocular hypertensive has the risk factor without the disease, while the normal-tension patient has the disease without the obvious risk factor. Managing each is about individualised risk — watching the one and lowering pressure in the other — and both are followed with the same disc and field tools used for all glaucoma.
A memorable clinical rule follows from these two: never diagnose glaucoma from pressure alone, and never dismiss it because the pressure is 'normal' — always examine the disc and field. This is why an apparently healthy person with a raised pressure is watched, while a normal-pressure patient with a suspicious, asymmetric or notched disc is fully investigated for normal-tension glaucoma.
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KEY POINTS TO REMEMBER
Ocular hypertension = IOP >21 mmHg with NO disc/field damage; a risk factor for glaucoma, monitored (treat if high conversion risk).
Normal-tension glaucoma = typical glaucomatous cupping and field loss WITH IOP ≤21 mmHg.
Normal-tension implies non-pressure factors (poor optic-nerve perfusion/vascular dysregulation), but treatment still lowers IOP further.
Together they show glaucoma is an optic neuropathy, not simply 'raised pressure'.
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SOURCES: Khurana's Comprehensive Ophthalmology.
THE CONCEPT
Aqueous humour is the clear fluid filling the anterior and posterior chambers of the eye. Understanding it is the key to understanding glaucoma, because intraocular pressure is set by the balance between its production and drainage.
FORMATION & CIRCULATION
It is secreted by the ciliary processes (ciliary body) into the posterior chamber, flows through the pupil into the anterior chamber, and drains at the angle. Outflow is by two routes: the main trabecular (conventional) pathway — through the trabecular meshwork into Schlemm's canal — and the uveoscleral (unconventional) pathway (targeted by prostaglandin drugs).
FUNCTIONS & RELEVANCE
Aqueous nourishes the avascular cornea and lens, removes their waste, and maintains intraocular pressure and the shape of the globe. Obstruction of its outflow raises IOP and causes glaucoma, while its production and outflow pathways are precisely where glaucoma drugs act.
A NOTE ON THE BLOOD–AQUEOUS BARRIER
A further point of interest is that aqueous humour is not a simple filtrate of blood but is actively secreted across the ciliary epithelium, which maintains a blood–aqueous barrier. This is why normal aqueous is protein-poor and crystal-clear, giving the optically empty anterior chamber needed for vision. When this barrier breaks down in inflammation (uveitis), protein and cells leak into the aqueous, producing the 'flare' and cells seen at the slit lamp. Understanding active secretion also explains why drugs that inhibit the ciliary epithelium's carbonic anhydrase or beta-receptors reduce aqueous production and thereby lower intraocular pressure.
THE BOTTOM LINE
Aqueous humour is actively secreted by the ciliary body, circulates to drain at the angle, nourishes the avascular cornea and lens and sets the intraocular pressure — so its outflow obstruction causes glaucoma.
IN PRACTICE
Clinically, the depth and clarity of the anterior chamber and the level of aqueous production and outflow underlie every glaucoma decision, and drugs are chosen precisely for where they act on this circulation — suppressing ciliary production or enhancing trabecular or uveoscleral outflow.
MECHANISM RECAP
Aqueous is produced continuously at a steady rate and must drain at the same rate to keep pressure constant, so glaucoma is fundamentally a plumbing problem of outflow rather than over-production. This is why almost all treatment targets outflow or, failing that, throttles production — and why understanding the aqueous circulation makes the logic of every glaucoma drug and operation immediately clear.
Finally, the small volume yet constant turnover of aqueous (a few microlitres per minute, replacing the anterior-chamber volume several times a day) explains why drugs delivered into the eye are cleared steadily and why intraocular pressure responds within hours to agents that alter its production or outflow — the physiological basis of medical glaucoma therapy.
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KEY POINTS TO REMEMBER
Aqueous humour = clear fluid in the anterior and posterior chambers; IOP = balance of its production and drainage.
Secreted by ciliary processes → posterior chamber → pupil → anterior chamber → drains at the angle.
Outflow: trabecular (conventional) via meshwork → Schlemm's canal; and uveoscleral (unconventional, targeted by prostaglandins).