Types of Glaucoma for NEET PG: Open-Angle vs Angle-Closure vs Congenital

Glaucoma is not one disease. It is a group of progressive optic neuropathies in which retinal ganglion cells are lost, the optic nerve is damaged structurally, and the visual field shows matching defects. Raised intraocular pressure (IOP) is the usual association, but glaucoma can occur at normal IOP (Aust Prescr 2026). Globally, glaucoma is one of the causes behind 7.7 million cases of preventable or unaddressed distance vision impairment or blindness (WHO).

The most useful way to sort glaucoma types is by the state of the drainage angle and the age of onset. This post compares primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG) and primary congenital glaucoma (PCG) side by side, then covers the secondary types, the optic disc, gonioscopy and treatment.

Key Takeaways

• Glaucoma types are first split into primary and secondary, then by whether the angle is open or closed, and by age of onset (congenital or childhood forms).

• POAG has an open angle and is chronic, painless and silent early. Angle-closure glaucoma has a closed or occludable angle and can present as a painful red eye with haloes.

• Acute angle closure is an ophthalmic emergency: lower IOP medically, then laser peripheral iridotomy, and treat the fellow eye too.

• Primary congenital glaucoma presents with cloudy cornea, enlarged corneal diameter and buphthalmos. Surgery (goniotomy or trabeculotomy) is the first-line treatment, and drugs only bridge.

• Gonioscopy views the angle directly, Humphrey perimetry is the functional gold standard, and Goldmann applanation tonometry is the reference method for measuring IOP.

How Are the Glaucoma Types Classified?

Glaucoma is classified broadly as primary or secondary (Aust Prescr 2026). Primary glaucomas arise without another eye disease driving the pressure rise. Secondary glaucomas follow a separate cause.

Within the primary group, the angle decides the label. In POAG the angle is structurally open. In PACG the angle closes, either gradually or suddenly, and aqueous outflow is impaired.

Childhood forms have their own scheme. The Congenital Glaucoma Research Network (CGRN) classification lists primary congenital glaucoma, infantile glaucoma, juvenile open-angle glaucoma (JOAG) and secondary childhood glaucoma (Indian J Ophthalmol 2019).

Secondary glaucoma types to know

Four secondary types are worth learning as pairs of cause and effect (Aust Prescr 2026):

• Neovascular: follows proliferative diabetic retinopathy or retinal vein occlusion.
• Pigmentary: pigment release affects the outflow pathway.
• Pseudoexfoliative: often higher IOP and faster progression than POAG.
• Uveitic: covers the steroid effect as well.

Primary Open-Angle Glaucoma: The Silent Type

Of all the glaucomas, POAG is the commonest. Its angle is structurally open, and the course is chronic and painless. Early disease is asymptomatic, and IOP may be raised or within the reference range (Aust Prescr 2026).

Because patients feel nothing, the disease is found by examination. In India, about 90% of glaucoma is undiagnosed, and the POAG to PACG ratio ranges from 1.8 to 10 across studies (Towards better management of glaucoma in India).

What counts as "normal" IOP?

Normal IOP is a statistical idea, not a disease threshold. It is the range within 2 standard deviations of the population mean, about 10 to 21 mmHg, and an IOP above 21 mmHg was the traditional criterion for "high" (Korea NHANES 2010-2011). This explains why glaucoma can exist with a "normal" reading.

Normal-tension glaucoma

In normal-tension glaucoma, a subtype of POAG, the IOP remains within the normal range. It is linked with migraine, Raynaud phenomenon, systemic hypotension and obstructive sleep apnoea (Aust Prescr 2026).

Angle-Closure Glaucoma: Acute, Subacute, Chronic and Latent

In angle-closure glaucoma the iris blocks the trabecular meshwork. The mechanism in the acute attack is pupillary block. The presentation depends on how fast the angle closes (Management of angle closure glaucoma).

• Acute: sudden IOP rise from total angle closure, with severe pain, red eye, blurred vision, haloes, headache, nausea and vomiting.
• Intermittent (subacute): the IOP rise aborts on its own, but recurrent episodes cause progressive peripheral anterior synechiae (PAS).
• Chronic: PAS permanently close the angle, and there are usually no symptoms.
• Latent: a narrow but open angle that has the potential to close.

Signs of an acute attack

The eye shows conjunctival injection, corneal oedema, a mid-dilated fixed pupil, a hard globe and a shallow anterior chamber (Management of angle closure glaucoma). IOP in an acute attack has been reported at about 50 to 80 mmHg (Emergency management: angle-closure glaucoma).

A useful reasoning step: a painful red eye with haloes, a fixed mid-dilated pupil and a hard globe points to acute angle closure, not conjunctivitis or iritis. The red eye comparison lays out how to separate them.

Risk factors and triggers

Risk factors are female sex, East Asian descent, hypermetropia with short axial length, a shallow chamber, a thick lens, older age and a family history (Emergency management: angle-closure glaucoma; Acute angle closure glaucoma). Mydriatic and anticholinergic drugs, and dim light, can trigger an attack in an eye with an occludable angle (Systemic medications as triggers, 2026).

The ISGEO staging

The ISGEO scheme stages the primary angle-closure spectrum by gonioscopy, pressure and optic nerve status (Management of angle closure glaucoma):

Primary Congenital Glaucoma: Glaucoma in the Infant Eye

Primary congenital glaucoma presents in infancy, with a classic triad of epiphora, photophobia and blepharospasm that can nevertheless be absent. A cloudy cornea and buphthalmos are the most common presenting signs, seen in over 40% of cases (Review on the Management of Primary Congenital Glaucoma).

An infant's eye stretches under pressure. That is why corneal diameter matters. A normal horizontal corneal diameter is 9.5 to 10.5 mm in a newborn and 10 to 11.5 mm at 1 year, and more than 12 mm in a newborn should raise suspicion (Review on the Management of Primary Congenital Glaucoma).

Diagnostic criteria in childhood glaucoma

The childhood glaucoma criteria include IOP above 21 mmHg, Haab's striae, and an enlarged corneal diameter: 11 mm or more in a newborn, above 12 mm under 1 year, and above 13 mm at any age.

A cup-disc asymmetry of 0.2 or more, or a progressive rise in cup-disc ratio (CDR), also counts (Indian J Ophthalmol 2019).

Genetics and epidemiology

Most cases are sporadic. Familial cases make up 10 to 40%, usually autosomal recessive, with the gene CYP1B1 on 2p21 and a male predominance of about 65%. Incidence is 1 in 10,000 to 1 in 70,000 in the West, but 1 in 1,250 to 1 in 3,300 in populations with consanguinity, including southern India (Review on the Management of Primary Congenital Glaucoma).

In India, PCG occurs in about 1 in 3,300 live births and accounts for 4.2% of childhood blindness. In one South Indian tertiary cohort it made up 37.6% of childhood glaucoma and was bilateral in 85% (Indian J Ophthalmol 2019).

Glaucoma Types Compared: POAG vs PACG vs Congenital

This table pulls the three primary types into one view. Redraw it from memory as a revision exercise.

Sources for the table: Aust Prescr 2026, Management of angle closure glaucoma, Review on the Management of Primary Congenital Glaucoma, Indian J Ophthalmol 2019.

Cup Disc Ratio and Optic Disc Changes

The optic disc is where glaucoma is seen. On examination, look for rim thinning, the cup-to-disc ratio, Drance haemorrhage, retinal nerve fibre layer (RNFL) dropout and peripapillary atrophy (Aust Prescr 2026).

In adults, the rim thins first inferotemporally, then superotemporally, and the nasal rim is affected last. The cup enlarges vertically or obliquely (J Curr Glaucoma Pract 2022). A quick memory aid: inferotemporal first, then superotemporal, nasal last, so a vertically oval cup is the pattern to look for.

In primary congenital glaucoma, the cup enlarges circumferentially, and cupping can reverse after IOP control, though not in every case (Review on the Management of Primary Congenital Glaucoma). A reversible cup is a feature of the infant eye.

Function is tested separately. Humphrey automated perimetry is the functional gold standard, and optical coherence tomography (OCT) shows RNFL and rim thinning (Aust Prescr 2026).

Gonioscopy and Tonometry in Glaucoma Types

To measure IOP, Goldmann applanation tonometry remains the gold standard, while gonioscopy gives a direct view of the angle and OCT is only an adjunct (Aust Prescr 2026). Gonioscopy is what separates an open angle from a closed one, so it decides which glaucoma type you are dealing with.

Gonioscopy shows how much of the trabecular meshwork is visible. In the ISGEO scheme, angle-closure suspects are defined by 180 to 270 degrees of posterior trabecular meshwork not being visible (Management of angle closure glaucoma).

How Is Each Type of Glaucoma Treated?

Open-angle glaucoma

Medical options span prostaglandin analogues, beta blockers, alpha-2 agonists, carbonic anhydrase inhibitors and cholinergics. A prostaglandin analogue once daily is first line. Its side effects are red eye, irreversible iris pigmentation, eyelash growth and periorbitopathy (Aust Prescr 2026).

Bradycardia and bronchospasm are possible with timolol, which is contraindicated in asthma, COPD and heart block. Brimonidine, dorzolamide and brinzolamide are adjuncts. Pilocarpine causes miosis and brow ache and is contraindicated in uveitis.

For selected open-angle patients, selective laser trabeculoplasty (SLT) offers a first-line alternative. Trabeculectomy and drainage devices are used for advanced or refractory disease, while minimally invasive glaucoma surgery (MIGS) has a modest effect (Aust Prescr 2026).

Acute angle closure: the emergency sequence

Acute angle closure needs same-day ophthalmic assessment (Aust Prescr 2026). The sequence in the emergency review is (Emergency management: angle-closure glaucoma):

1. Lie the patient flat.
2. Give acetazolamide 500 mg, IV preferred.
3. Add a topical beta blocker, alpha agonist or prostaglandin analogue.
4. Give analgesia, a topical steroid and an antiemetic.
5. About 1 hour later, give pilocarpine 2% or 4%, two doses 15 minutes apart.
6. Use a hyperosmotic agent if IOP is still dangerously high.

Hyperosmotic doses are oral glycerol 1.0 to 1.5 g/kg (contraindicated in diabetes), isosorbide 1.5 to 2.0 g/kg, and IV mannitol 1 to 2 g/kg (Emergency management: angle-closure glaucoma).

Drugs only buy time. The definitive treatment is laser peripheral iridotomy (argon or Nd:YAG), and the fellow eye is at risk, so iridotomy is done in both eyes. Cataract or lens extraction is used when the lens drives the mechanism (Management of angle closure glaucoma).

One exception: in drug-induced angle closure without pupillary block, caused by effusion, pilocarpine and iridotomy may be ineffective or harmful (Systemic medications as triggers, 2026).

Primary congenital glaucoma

Surgery is first line: goniotomy or trabeculotomy when corneal diameter is under 13 mm, with goniotomy needing a clear cornea. Some centres use combined trabeculotomy-trabeculectomy first. After goniotomy, 72% have normal IOP after one procedure and 88 to 94% after two. Fewer than 10% are controlled by medical therapy, so drugs serve only as a bridge (Review on the Management of Primary Congenital Glaucoma).

During examination under anaesthesia, succinylcholine and ketamine raise IOP, which can mislead the reading (Review on the Management of Primary Congenital Glaucoma).

Quick Self-Test on Glaucoma Types

Cover the table above and answer from memory:

• Which type has a circumferential cup that can reverse? (Primary congenital glaucoma.)
• Which stage of the ISGEO scheme first requires glaucomatous optic neuropathy with matching field loss? (PACG.)
• Which rim sector thins first in adult glaucoma? (Inferotemporal, then superotemporal, nasal last.)
• Which procedure is definitive for an acute attack, and which eye gets it? (Laser peripheral iridotomy, both eyes.)

Common Mistakes When Comparing Glaucoma Types

These are reasoning errors worth guarding against:

• Equating glaucoma with high IOP. POAG and normal-tension glaucoma can occur at pressures in the reference range.
• Using pilocarpine or a dilating drop without checking the angle. Mydriatics can trigger angle closure in an occludable eye.
• Treating only the affected eye in angle closure. The fellow eye needs an iridotomy.
• Mixing up the cup patterns. Adult cupping is vertical or oblique, congenital cupping is circumferential.
• Giving glycerol to a diabetic patient, or timolol to an asthmatic.

Conclusion

Glaucoma types sort neatly once you ask three questions: is the angle open or closed, when did it start, and is there a separate cause? POAG is silent and chronic, angle closure can be an emergency treated with drugs first and an iridotomy second, and congenital glaucoma is a surgical disease of the infant eye. Test yourself with the glaucoma practice questions, and use the wider NEET PG question bank to mix glaucoma with other ophthalmology topics.