Gonioscopy: Examining the Eye's Drainage Angle to Assess Glaucoma Risk

Key takeaways

• Gonioscopy classifies the angle, distinguishing open-angle from angle-closure disease, something eye pressure measurement alone cannot do.
• Gonioscopy does not measure eye pressure, image the optic nerve or test vision; it is one part of a glaucoma assessment, never the whole of it.
• Gonioscopy is subjective and operator-dependent. Grades reflect what one examiner saw under specific lighting and lens pressure, and can differ between examinations.
• A narrow angle is not a diagnosis of glaucoma. Many people with narrow angles never develop optic nerve damage; others need preventive laser treatment.
• Gonioscopy usually takes a few minutes per eye, and the numbing drops make it uncomfortable rather than painful.

At a glance

Also known as

• Angle examination / anterior chamber angle examination
• Goniscopy (common misspelling)
• "Glaucoma angle test" or "drainage angle check" in everyday clinic conversation in India
• Indirect gonioscopy (Goldmann, Zeiss, Posner, Sussman lenses); direct gonioscopy (Koeppe lens, mainly in theatre or for children under anaesthesia)

What gonioscopy is

Fluid called aqueous humour is produced continuously inside the eye and drains out through the trabecular meshwork, which sits in the angle formed where the iris meets the back of the cornea. That angle cannot be seen directly, because light from it is totally internally reflected at the corneal surface. A gonioscopy lens overcomes this, either with mirrors that redirect the view, or with a high-curvature contact lens that neutralises corneal refraction.

The examiner grades how widely the angle is open, identifies which anatomical landmarks are visible, and looks for abnormalities such as adhesions between iris and angle (peripheral anterior synechiae), pigment deposition, new blood vessels, recession after trauma, or angle abnormalities present from birth.

Indentation (compression) gonioscopy uses a small-diameter lens pressed gently on the cornea to push aqueous into the angle. This helps distinguish an angle that is merely crowded and closable from one permanently stuck shut by synechiae, an important distinction for treatment.

Why gonioscopy is done

• To classify glaucoma. Open-angle and angle-closure disease look similar on a pressure reading but are managed differently. Laser iridotomy helps angle closure; it does not help primary open-angle glaucoma.
• To assess angle-closure risk in people found to have shallow anterior chambers, hyperopia (long-sightedness), or a family history of acute angle closure.
• To find secondary causes of raised pressure: pigment dispersion, pseudoexfoliation material, angle recession after blunt trauma, neovascularisation in diabetic eye disease or retinal vein occlusion, inflammatory debris in uveitis, or blood after injury.
• Before dilating drops or certain medicines, where a clinician wants to know whether the angle is occludable.
• Before and after laser or surgery: planning laser iridotomy or iridoplasty, assessing the angle before minimally invasive glaucoma surgery or trabeculectomy, and checking angle status afterwards.
• To monitor known glaucoma, since angle appearance can change with age, cataract growth or treatment.

Who should have gonioscopy

• Anyone in whom glaucoma is diagnosed or suspected, gonioscopy is part of a standard glaucoma workup, not an optional extra.
• People with raised intraocular pressure on any measurement.
• People with a suspicious-looking optic disc or an abnormal visual field.
• People with a shallow anterior chamber on slit-lamp examination.
• Anyone with a first-degree relative who has had acute angle closure or has been advised laser iridotomy.
• People with blunt eye injury, long-standing uveitis, advanced diabetic retinopathy, retinal vein occlusion or previous intraocular surgery.
• People with intermittent brow ache, halos around lights in the dark, or transient blurring, symptoms that can suggest intermittent angle closure.

Gonioscopy is generally not a routine screening test for people with no risk factors and a normal eye examination. The decision rests with the examining ophthalmologist.

What gonioscopy cannot detect or exclude

• Gonioscopy does not measure intraocular pressure. That requires tonometry.
• Gonioscopy does not assess the optic nerve. Optic disc examination, OCT of the retinal nerve fibre layer and visual field testing are separate.
• Gonioscopy cannot diagnose glaucoma on its own. Glaucoma is defined by characteristic optic nerve damage and corresponding field loss, an open angle does not exclude it, and a narrow angle does not confirm it.
• Gonioscopy does not detect normal-tension glaucoma or tell you whether vision is being lost.
• A normal gonioscopy does not exclude future angle closure. Angles narrow over time as the lens thickens with age.
• Gonioscopy cannot see behind the iris. Plateau iris configuration, ciliary body position and lens vault are better assessed with ultrasound biomicroscopy or anterior segment OCT.
• Gonioscopy cannot reliably grade an angle through a hazy cornea, in a very shallow chamber, or in an uncooperative patient.
• Gonioscopy does not quantify outflow resistance. An angle can look wide open and still drain poorly, this is exactly what happens in primary open-angle glaucoma.

If symptoms such as eye pain, halos or blurring continue despite a reported normal angle, return to your ophthalmologist. A negative finding describes what was seen on that day, under those conditions.

Related but different examinations

These tests answer different questions. None is universally superior, and a glaucoma assessment usually combines several. Which one comes first depends on the presenting problem: sudden painful red eye with halos points urgently towards angle assessment, while a routine finding of a suspicious optic disc may be investigated with imaging and fields alongside gonioscopy.

How to prepare

Preparation for gonioscopy is minimal, but arrangements differ between clinics. Your eye unit's written or verbal instructions take precedence over any general guidance here.

• Contact lenses: most units ask you to remove soft or rigid lenses before the examination. Bring your lens case and spectacles.
• Eye make-up: it is easier for the examiner if eye make-up is avoided on the day.
• Tell the clinic in advance about recent eye surgery or laser, corneal infection or ulcer, a recent eye injury, previous corneal transplant, or a known allergy to anaesthetic eye drops or preservatives.
• Bring your current eye drops and tablets, or a list of them. Do not start, stop or alter any prescribed medicine before the appointment, ask the prescriber if you are unsure.
• Eating and drinking: no fasting is needed for gonioscopy.
• Transport: gonioscopy alone does not usually affect driving, but if dilating drops or other tests are done in the same visit, vision may be blurred for some hours. Ask the clinic whether to arrange someone to accompany you.

If you are pregnant or breastfeeding

Gonioscopy itself involves only topical anaesthetic. Tell the clinic you are pregnant or breastfeeding so that any additional drops or medicines planned in the same visit can be reviewed.

Children

Slit-lamp gonioscopy needs cooperation that many young children cannot manage. In suspected childhood glaucoma, direct gonioscopy with a Koeppe-type lens is often performed under sedation or general anaesthesia as part of an examination under anaesthesia. Anaesthetic agents can alter eye pressure readings, which the ophthalmologist takes into account.

Older adults and people with tremor or neck problems

Sitting still at a slit lamp with the chin on a rest can be difficult. Tell the staff beforehand; positioning can often be adjusted, and handheld lenses can be used with the patient reclined.

People with dry eye, corneal disease or recent eye surgery

A contact lens on a fragile or recently operated cornea may need to be deferred or replaced by AS-OCT. Mention any corneal transplant, keratoconus, recent cataract or refractive surgery.

People taking blood thinners

Gonioscopy does not involve cutting or injection, so anticoagulants and antiplatelet medicines are not usually a barrier. Continue them as prescribed unless your own doctor advises otherwise.

What happens during gonioscopy

• Anaesthetic drops: a drop is instilled in each eye. A brief sting for a few seconds is common; the surface then feels numb.
• Positioning: you sit with your chin on the rest and forehead against the band of the slit lamp.
• Lens placement: the examiner steadies your eyelids and places the small mirrored lens gently on the front of the eye. Some lenses need a drop of clear coupling gel. You will feel contact and mild pressure, not pain.
• Viewing: the room light and slit beam are kept narrow and dim, because bright light makes the pupil constrict and can make a narrow angle look falsely open. The examiner rotates the lens to view all four quadrants and may ask you to look slightly in different directions.
• Indentation: if needed, gentle pressure is applied to see whether the angle opens. This can feel briefly odd and may cause transient blurring from corneal folds.
• Removal: the lens is removed, the eye may be rinsed, and the findings are recorded, often as a diagram of the four quadrants.

How long does gonioscopy take

The lens is usually on the eye for only a minute or two per eye. Allow a few extra minutes for drops to take effect and for findings to be discussed. As part of a full glaucoma consultation with pressure measurement, imaging and possibly visual fields, the whole visit commonly runs to an hour or more, and longer if dilating drops are used. Actual timings vary by clinic and by how busy the unit is.

Understanding your gonioscopy report

Findings are usually recorded per quadrant (superior, inferior, nasal, temporal) of each eye, and describe both how open the angle is and what is present in it.

What the examiner is naming

From front to back, the visible landmarks are Schwalbe's line, the anterior and posterior trabecular meshwork, the scleral spur, the ciliary body band, and the iris root. In broad terms, the more of these structures visible, the wider the angle. Seeing only Schwalbe's line suggests a very narrow angle.

Grading systems

Several systems are in use, and different clinics prefer different ones:

• Shaffer system: grades the angular width of the angle recess on a scale where higher numbers mean a wider, more open angle and 0 means closed.
• Spaeth system: records three things separately: the level of iris insertion, the angular width, and the peripheral iris contour (steep, regular or queer/concave). It is more descriptive and often preferred in specialist glaucoma clinics.
• Scheie system: grades by which structures are visible, with, confusingly, higher grades meaning a narrower angle. Always check which system your report uses.

Reports may also note pigmentation of the trabecular meshwork, peripheral anterior synechiae and their extent in clock hours, new vessels, angle recession, blood, or membranes.

Grades are descriptive, not a verdict

Gonioscopy grading is subjective and operator-dependent. It varies with lighting, the amount of pressure on the lens, pupil size, the patient's accommodation and the examiner's experience. The same eye can be graded differently by two clinicians or on two days. Patients often read a low grade as "I have glaucoma", that is not what the grade means. A narrow or occludable angle describes anatomical risk; glaucoma is diagnosed only when there is optic nerve damage with matching visual field loss.

Equally, an open angle does not reassure you about the optic nerve. Interpretation belongs to the ophthalmologist who examined you, in the context of your pressure, disc appearance, fields, corneal thickness and symptoms.

When gonioscopy results can be misleading

Factors that can make an angle look falsely open (wider than it is)

• Bright room or slit-lamp light, which constricts the pupil and pulls the peripheral iris away from the angle.
• Unintentional pressure on the cornea with the lens, artificially deepening the angle, a particular risk with small-diameter indentation lenses.
• A long slit beam crossing the pupil, triggering the light reflex.
• Recent dilating drops or examination shortly after mydriasis.
• The patient looking towards the mirror, which rotates the eye and widens the apparent recess.

Factors that can make an angle look falsely narrow or closed

• Accommodation: fixating on a near target thickens the lens and shallows the angle.
• Corneal oedema or haze, common during an acute pressure rise, obscuring landmarks.
• Prominent iris processes or heavy pigmentation being mistaken for synechiae; only indentation gonioscopy distinguishes these reliably.
• A steeply convex iris hiding the recess even when the angle is technically open.
• Squeezing the eyelids or poor lens coupling distorting the view.

Situations where gonioscopy may be unobtainable

Corneal scarring, active infection, severe dry eye, recent surgery, nystagmus, or inability to sit at the slit lamp. In these cases AS-OCT, UBM or examination under anaesthesia may be used instead.

Risks and safety

Gonioscopy is a low-risk office examination, but it is not without any risk, and the risk profile differs by technique.

Indirect (contact) gonioscopy at the slit lamp

Possible effects include transient stinging from the drops, brief blurring from coupling gel, minor corneal surface abrasion, temporary corneal folds after indentation, and reactive redness. Serious complications are uncommon. Because the corneal surface is numb, avoid rubbing the eye until sensation returns, usually within about half an hour. Infection transmission is minimised by cleaning and disinfecting lenses between patients according to the unit's protocol.

Indentation gonioscopy

Carries the same risks with slightly more corneal manipulation. In eyes with a very shallow chamber, high pressure or recent surgery, the examiner will judge whether indentation is appropriate.

Direct gonioscopy under anaesthesia

The examination adds little risk in itself, but sedation or general anaesthesia carries its own risks, which the anaesthetist will discuss separately. This route is mainly used in infants and young children.

Non-contact alternatives

AS-OCT avoids touching the eye altogether and so avoids abrasion and infection risk, but it provides different information and is not an equivalent substitute in every situation.

Results vary depending on individual clinical circumstances.

Special situations

Pregnancy

Gonioscopy can be performed during pregnancy. Topical anaesthetic exposure is small. Tell the team you are pregnant, since glaucoma medicines and any planned additional drops need separate consideration by the prescriber.

Children and infants

Congenital and developmental glaucoma have distinctive angle appearances. Cooperative older children may manage slit-lamp gonioscopy; infants usually require examination under anaesthesia. Corneal clouding, a large eye and watering with light sensitivity in a baby need prompt specialist assessment.

Older adults

Angles narrow with age as the crystalline lens thickens, so an angle that was open a decade ago may not be now. Cataract surgery often deepens the angle, and repeat gonioscopy after surgery is common.

People with diabetes

Advanced diabetic retinopathy can lead to new blood vessels in the angle (neovascular glaucoma). Gonioscopy is important in these eyes even when pressure is normal, because vessels in the angle may appear before pressure rises.

People with hypermetropia (long sight) or small eyes

Shorter eyes tend to have shallower chambers and a higher risk of angle closure. This group is more likely to be advised gonioscopy and, sometimes, prophylactic laser iridotomy.

People who have had eye trauma

Blunt injury, including cricket ball and firecracker injuries, can cause angle recession that raises pressure years later. Gonioscopy documents this, and lifelong periodic pressure checks are usually advised.

People with uveitis

Inflammation can produce synechiae that progressively close the angle. Gonioscopy helps distinguish steroid-induced pressure rise from inflammatory angle closure, a distinction that changes treatment.

Gonioscopy in the Indian context

• Angle-closure disease carries substantial weight in India. Primary angle-closure glaucoma is proportionally more common in Asian populations than in European ones, which makes angle assessment central rather than peripheral in Indian glaucoma practice. Population-based data from Indian studies, including the Chennai Glaucoma Study and the Andhra Pradesh Eye Disease Study, have reported a substantial burden of both open-angle and angle-closure disease, much of it previously undiagnosed.
• Glaucoma is frequently silent until late. Open-angle glaucoma causes no pain and no early visual symptom, so many people in India present with advanced field loss. Gonioscopy at the first glaucoma-suspect visit helps ensure the mechanism is identified early.
• Terminology you may hear: clinics may call it the "angle test", "glaucoma angle check" or simply "kala motia" assessment, "kala motia" is the common Hindi term for glaucoma, distinct from "safed motia" (cataract). The two are different conditions and need different treatment.
• Self-medication with steroid eye drops bought over the counter for redness or allergy is a recognised cause of raised eye pressure in India. Tell your ophthalmologist about any drops you have used, including those advised by a pharmacy or a relative.
• Trauma-related angle recession is relatively frequent, reflecting sports injuries, road traffic injuries and festival-related firecracker injuries.
• Access: gonioscopy needs only a lens and a slit lamp, so it is available in most ophthalmology departments and many standalone eye clinics, including in smaller towns. AS-OCT and UBM are concentrated in larger centres.
• Consent and records: personal and health data collected at registration are handled under the Digital Personal Data Protection Act, 2023. You may ask the hospital how your records and images are stored and shared.

Cost and insurance in India

Gonioscopy is usually billed either as part of a comprehensive ophthalmology or glaucoma consultation, or as a small additional charge. It is generally one of the less expensive elements of a glaucoma workup, because it requires no consumables beyond drops and gel.

What influences the cost

• City and type of facility: metro tertiary hospitals, tier-2 city hospitals, charitable eye hospitals and standalone clinics price differently.
• Whether it is bundled into a glaucoma evaluation package with tonometry, pachymetry, OCT and visual fields, or charged separately.
• Consultant seniority and whether a glaucoma subspecialist performs the examination.
• Additional imaging: AS-OCT or UBM add significantly more than gonioscopy itself.
• Examination under anaesthesia for children, which involves theatre and anaesthetist charges and costs far more than an office examination.
• Repeat examinations during long-term glaucoma follow-up.

Insurance

Outpatient diagnostic tests are often not covered by standard indemnity health insurance in India unless the policy includes an OPD benefit, or the test forms part of an approved day-care or inpatient admission. Cover for glaucoma-related surgery differs from cover for outpatient diagnostics, and waiting periods for pre-existing conditions may apply. Check specifics with your insurer or the hospital's insurance desk before the visit. Government schemes and state eye-care programmes may cover eligible patients; eligibility criteria vary.

Myths and facts

Frequently asked questions

Does gonioscopy hurt?

Gonioscopy is generally not painful. Anaesthetic drops numb the eye surface first; they sting briefly. Most people feel pressure or a sense of contact while the lens rests on the eye. Mild grittiness or watering can follow for a short time once the numbness wears off, and that usually settles on its own.

How long does gonioscopy take?

The lens is typically on each eye for only a minute or two, so the examination itself is brief. Allow additional time for the drops to work and for your ophthalmologist to explain the findings. Within a full glaucoma consultation involving pressure checks, imaging and visual fields, the overall visit is considerably longer.

Will my eyes be dilated for gonioscopy?

Usually not before the angle is assessed. Dilating drops widen the pupil and can distort the appearance of the angle, and in a very narrow angle they may briefly raise pressure. The examination is generally done in a dim room with a short slit beam. Dilation may follow afterwards for retinal examination if your ophthalmologist decides it is safe.

Can I drive home after gonioscopy?

After gonioscopy alone, vision usually returns to baseline quickly, though coupling gel can blur things briefly. If dilating drops or other tests are performed in the same visit, vision and glare sensitivity may be affected for several hours. Ask the clinic in advance whether you should arrange transport or bring a companion.

What does a Shaffer grade of 1 or 2 mean for me?

A lower Shaffer grade means the angle appeared narrow on that examination. It flags a risk of angle closure and may prompt discussion of laser iridotomy or closer monitoring. It does not by itself mean you have glaucoma or will lose vision. Your ophthalmologist interprets the grade alongside pressure, optic disc and visual fields.

Is gonioscopy safe if I have had cataract or LASIK surgery?

Gonioscopy is commonly performed after cataract surgery, and the angle often appears deeper afterwards. Timing after recent surgery matters, and your surgeon will advise when the cornea and wound are ready for a contact lens examination. After LASIK, mention it so the examiner is aware of the corneal flap. Individual circumstances vary.

Why do I need gonioscopy if I have no symptoms?

Both open-angle glaucoma and chronic angle closure can progress silently, with no pain and no noticeable visual change until damage is advanced. If you have risk factors such as raised pressure, a family history, long-sightedness or a shallow chamber, angle assessment allows earlier decisions about monitoring or preventive laser treatment.

How often should gonioscopy be repeated?

There is no single interval that suits everyone. People with known glaucoma, narrow angles, previous laser, uveitis or past trauma are usually reassessed more often, and angles are commonly rechecked after cataract surgery. Your ophthalmologist sets the interval based on your angle findings, pressure control and rate of change.

Can gonioscopy be done if my cornea is cloudy?

A hazy or oedematous cornea, as occurs during an acute pressure rise, can make the angle impossible to see clearly. Clinicians may first lower the pressure or use glycerine drops to clear the cornea temporarily, or turn to anterior segment OCT or ultrasound biomicroscopy. The angle is usually re-examined once the cornea clears.

Sources

• American Academy of Ophthalmology, Preferred Practice Pattern guidelines on Primary Open-Angle Glaucoma and Primary Angle-Closure Disease.
• European Glaucoma Society, Terminology and Guidelines for Glaucoma.
• World Glaucoma Association consensus statements on angle-closure and angle-closure glaucoma.
• All India Ophthalmological Society and Glaucoma Society of India educational resources on gonioscopy technique and grading.
• Published population-based Indian epidemiological studies of glaucoma, including the Chennai Glaucoma Study, the Andhra Pradesh Eye Disease Study and the Aravind Comprehensive Eye Survey.
• Shaffer, Spaeth and Scheie angle grading systems as described in standard ophthalmology texts.
• Digital Personal Data Protection Act, 2023 (Government of India), for handling of patient data.