Gonioscopy: Why is it needed for glaucoma?

Gonioscopy is an examination of the anterior chamber angle using a contact lens with mirrors and a slit lamp. This method allows direct visualization of the structures of the eye's drainage system and assessment of the angle's openness, adhesions, pigment, newly formed vessels, and other key features that determine glaucoma risk and management. International guidelines emphasize that gonioscopy remains the "gold standard" for angle assessment, and any imaging technologies are a complement, not a substitute. [1]

In practice, gonioscopy helps differentiate open-angle glaucoma from closed-angle glaucoma and identify secondary causes of increased intraocular pressure, such as pigment dispersion, pseudoexfoliation, or angle neovascularization. This is not only a diagnostic test but also a routing test: its results determine further investigations and the type of treatment, including the choice of medications and surgical interventions. [2]

Despite the rapid development of anterior segment optical coherence tomography and ultrasound biomicroscopy, high-quality gonioscopy remains more informative for recognizing adhesions, assessing the true iris insertion line, and dynamic phenomena such as hidden angle closure with changing illumination or pressure. The European Glaucoma Society guidelines explicitly state that instrumental images of the angle do not replace clinical gonioscopy. [3]

However, real-world clinical practice shows that this method is underutilized: according to large registries, gonioscopy is performed on far fewer patients presenting for the first time with glaucoma. Expert reviews remind us that a decrease in the frequency of performance does not mean a decrease in its value – competent gonioscopy remains critical for safe diagnosis and treatment selection. [4]

Table 1. What does gonioscopy give to the doctor and the patient?

Clinical task	What does gonioscopy show?	How does it affect tactics?
Distinguish an open angle from a closed one	Visibility of the trabecular meshwork and ciliary body	Choosing between laser iridotomy, medications, and surgery
Find secondary causes	Pigment, pseudoexfoliative material, neovascularization	Treatment of the cause and correction of antiglaucoma therapy
Assess the adhesions	Peripheral anterior synechiae	Prognosis and choice of intervention
Confirm the dynamics of the angle	Difference in darkness and indentation	Prevention of acute episodes and monitoring plan

What you need to know about the anatomy of the anterior chamber angle

The anterior chamber angle is the area between the posterior corneal surface and the anterior iris surface, containing key elements of aqueous outflow: Schwalbe's line, trabecular meshwork, Schlemm's canal, and the ciliary body plexus. The visibility of these structures and their relationships determine the angle's appearance in a given patient. For accurate interpretation, it is important to confidently recognize landmarks and understand normal variations. [5]

The superior-inferior quadrants often appear narrower due to the influence of gravity on the position of the iris and lighting conditions, while the temporal and nasal quadrants may appear wider. This is why a complete four-mirror examination is preferable to a selective one. Furthermore, the distribution of pigmentation and the presence of special lines, such as the Sampaolesi line, provide diagnostic information. [6]

The Sampaolesi line is a dark pigment accumulation anterior to the Schwalbe line. It is characteristic of pigment dispersion and pseudoexfoliation, but can also be found in other conditions. Its detection increases suspicion for secondary glaucoma and requires a more thorough examination of the trabecular meshwork and pupillary margin of the iris. [7]

Gonioscopy allows for the assessment of not only the angle width, but also the shape of the iris insertion, the peripheral iris contour, the presence of adhesions and synechiae, hemorrhages, and vascular changes in the angle area. This is critical, as the same angle width with different iris insertion patterns and trabecular meshwork conditions implies a different risk of closure and different prognosis. [8]

Table 2. Angle structures: how to recognize them and what they mean

Structure	What does it look like?	Clinical clue
Schwalbe Line	A thin, bright arc at the border of the cornea	Landmark of the anterior border of the angle
Trabecular meshwork	Grayish-brown stripes, may be pigmented	The place of main resistance to outflow
Schlemm's Canal	A thin translucent line, sometimes with blood	Blood in the canal with increased venous pressure
Ciliary body	A dark stripe at the base of the iris	A clearly visible sign of a wide angle

Equipment and machinery

Goniolenses are used for contact examination. The classic three-mirror Goldmann lens is convenient for static assessment but is not suitable for rapid indentation. Four-mirror Zeiss lenses and their analogs allow dynamic gonioscopy with gentle pressure on the cornea, which helps distinguish temporary, appositional closure from true synechiae. The choice of lens depends on the purpose of the examination and the experience of the physician. [9]

The algorithm is as follows: a narrow, short slit is used, minimal illumination is applied, the patient's gaze is directed forward, a lens with a viscous contact solution is placed on the bubble-free cornea, and a sequential examination begins along all meridians. In doubtful cases, a dark room and dynamic gonioscopy with light indentation are used. Local anesthetic is administered beforehand. [10]

The illumination and position of the slit lamp affect the results. A beam that is too bright causes miosis and artifactually "opens" the angle. A slit that is too wide "illuminates" the iris and creates the false impression of greater visibility of the structures. The correct technique requires a short, narrow, weak beam that does not hit the pupil. [11]

If it is necessary to check for occult angle closure, gonioscopy is performed in the dark and then indentation is performed. With appositional closure, gentle pressure temporarily opens the angle; with synechiae, this does not occur. This approach is recommended by angle-closure disease guidelines. [12]

Table 3. Technique of execution

Stage	What to check	If there is a problem
Preparation	Anesthesia, contact gel without bubbles	Repeat lens installation
Lighting	Narrow, short, weak slit	Reduce brightness and width
Meridian Walk	Nasal, temporal, superior, inferior sectors	View all quadrants
Dynamics	Dark room, indentation according to indications	Repeat and document the photo

How to describe an angle: scales and standards

The most common scale is the Shaffer scale. It evaluates the estimated angle between the peripheral iris and the trabecular meshwork in degrees and assigns a score from 0 to 4: 0 = closed, 1 = extremely narrow, 2 = narrow, 3 = moderately open, and 4 = wide open. Values of 0-1 correspond to a high risk of closure, 2 = borderline, and 3-4 = usually safe, all other things being equal. [13]

The Spaeth classification is more detailed: it describes the location of the true iris insertion relative to the angle structures, the angle magnitude in degrees, and the profile of the peripheral iris. This protocol better aligns with ultrasound biomicroscopy data and helps standardize descriptions in scientific and clinical papers. [14]

The Scheie scale is less common and describes the degree of angle openness from "wide open" to "closed." In practice, the Shaffer scale is often used for brevity, and in research or controversial cases, Spaeth parameters are added to more accurately capture the configuration. [15]

It is important to record not only the score but also any findings: pigment, nodules, lines, adhesions, blood in the canal, and the angle's response to indentation. Documenting the angle with photographs improves reproducibility and assists colleagues in subsequent follow-up. [16]

Table 4. Shaffer Scale: Quick Reference Points

Score	Angle estimation	Approximate value	Risk of closure
4	Wide open	≥40°	Minimum
3	Moderately open	25-35°	Short
2	Narrow	20°	Border
1	Very narrow	≤10°	High
0	Closed	0°	Critical

Table 5. Spaeth protocol components

Component	What to record	Example of a recording
Iris insertion	Regarding the trabecula and ciliary body	A, B, C, D or E by insertion level
The magnitude of the angle	In degrees	20°, 30°, 40°, etc.
Peripheral iris contour	Flat, convex, concave	b - flat, s - convex, d - concave
Additions	Pigment, synechiae, vessels	Comments with localization

What to look for in different types of glaucoma

When closed-angle disease is suspected, the key goals are to confirm angle narrowness, differentiate transient iris adherence from adhesions, and identify risk factors such as plateau iris or a large lens. Guidelines recommend darkroom and dynamic gonioscopy for maximum sensitivity. If adhesions are present, the treatment plan and prognosis change. [17]

In open-angle glaucoma, the uniformity of trabecular meshwork pigmentation, the presence of Sampaolesi's lines, pupillary margin defects, and other signs of pigment dispersion or pseudoexfoliation are assessed. Severe trabecular darkening and pigment dusting increase the likelihood of secondary open-angle glaucoma and require appropriate management. [18]

Angle neovascularization—thin newly formed vessels on the trabecular meshwork—indicates severe ischemic pathology and a high risk of secondary closure. This finding requires investigation of the underlying cause, typically diabetic retinopathy or retinal vascular occlusions, and an immediate change in management. [19]

Blood in the Schlemm's canal during gonioscopy indicates increased episcleral venous pressure and is found, for example, in carotid-cavernous fistulas. This sign helps link the ophthalmological picture with a systemic vascular problem and refer the patient for further examination. [20]

Table 6. Typical findings and their meaning

Find	What could it be?	What to do
Sampaolesi Line	Pigment dispersion, pseudoexfoliative process	Check the pupillary margin, trabecula, pressure
Peripheral anterior synechiae	Past episodes of closure or inflammation	Changes prognosis, discuss laser and surgery
Angle neovascularization	Retinal ischemia, diabetes, occlusions	Urgently find the cause and adjust the plan
Blood in the Schlemm's canal	High venous pressure	Look for a vascular cause and refer to specialists

Appositional vs. Synechial Closure: How to Tell the Difference

Appositional closure is a temporary adhesion of the peripheral iris to the trabecular meshwork without adhesions. It is often triggered by darkness or medicated mydriasis and may resolve with lens indentation. This pattern of reaction suggests the potential for prevention with laser iridotomy and behavioral interventions. [21]

Synechial closure is a persistent adhesion of the iris to the drainage structures. It does not "separate" upon indentation and is associated with a poorer prognosis for fluid outflow and a higher risk of increased pressure. In these cases, surgical options and more stringent risk factor control are often considered. [22]

Dynamic gonioscopy is the primary tool for distinguishing between these two variants. Proper pressure technique, using minimal force through a four-mirror lens, allows the difference to be safely and clearly observed and recorded on the chart. [23]

Additionally, documentation of photographs of the angle helps, which increases the reproducibility of the description and facilitates team decision-making, especially in multidisciplinary clinics. [24]

Table 7. Appositional and synechial closure: visual cues

Sign	Oppositional	Synechial
Reaction to indentation	The corner is temporarily open	The corner remains closed
Story	Provocation by darkness or mydriasis	Frequent episodes or inflammation
Forecast	Better with prevention	Worse, higher risk of persistent high blood pressure
Tactics	Preventive laser iridotomy according to indications	Surgical options and strict control

Common mistakes and how to avoid them

A slit that is too bright and wide causes miosis and artifactually "opens" the angle. This creates a false sense of security in the patient, risking closure. The solution is minimal illumination, a narrow slit, and a short beam, as recommended in educational reviews of gonioscopy technique. [25]

Bubbles in the contact fluid, lens decentration, excessive pressure, and failure to examine all four quadrants lead to missed diagnoses. A systematic checklist and mandatory data quality recording significantly reduce the likelihood of error. [26]

Underestimating secondary features—for example, the Sampaolesi line, varying degrees of pigment in the sectors, and thin newly formed vessels—leads to missed secondary glaucomas and delayed treatment. Targeted screening for these markers should be part of the routine for every at-risk patient. [27]

Finally, a real problem is the rare use of gonioscopy in everyday practice. Recent publications have called for a "return to gonioscopy" as a key skill, as well as for the wider use of goniophotography for training and monitoring. [28]

Table 8. Anti-artifact protocol

Error	What does it look like?	How to fix
The light is too bright	The angle appears wider	Reduce brightness, narrow the gap
Bubbles under the lens	They interfere with seeing landmarks	Remove, add gel, reinstall
Skipping quadrants	Incomplete picture	Inspect all sectors systematically
Strong pressure	False opening of the angle	Use light indentation

When to add anterior segment imaging techniques

Anterior segment optical coherence tomography and ultrasound biomicroscopy are useful for quantifying angle width, confirming plateau iris, visualizing ciliary processes, or analyzing postoperative configuration. However, these methods do not replace gonioscopy for resolving adhesions and microvascular changes. [29]

Guidelines emphasize the complementarity of approaches: clinical gonioscopy determines the angle type and secondary features, while visualization helps standardize measurements and communicate across specialists. This "union" of methods increases accuracy and reduces risks. [30]

Scientific reviews show reasonable agreement between gonioscopy and optical coherence tomography classifications, particularly with regard to wide and narrow angles. Disagreements often concern borderline situations, where dynamic indentation testing and clinical context are important. [31]

A separate area is goniophotography and videogonioscopy. Recording the angle of the image facilitates training, quality control, and monitoring, especially in network clinics and during physician rotations. [32]

Table 9. When gonioscopy is sufficient and when to add visualization

Clinical task	Gonioscopy is sufficient	It's worth adding visualization
Confirm the narrowness of the angle	Yes, with a dark room and indentation	In case of controversial configuration or plateau iris
The sought-after cause of increased pressure	Yes, assessment of pigment, adhesions, vessels	If ciliary abnormalities are suspected
Post-intervention monitoring	Yes, with a stable picture	For quantitative dynamics and planning

Gonioscopy and microinvasive surgery: what is important to consider

Before microinvasive antiglaucoma surgery, a thorough assessment of the angle is required: width, pigmentation, landmarks of the trabecular meshwork and Schlemm's canal, and potential obstructions. This increases the chance of choosing the right intervention and reduces the risk of intraoperative surprises. [33]

During and after procedures, gonioscopy helps document the position of implants and the condition of the trabecular meshwork, as well as evaluate the effectiveness of procedures such as circumferential transluminal trabeculotomy. Recent publications detail techniques based on angle visualization. [34]

Even with ideal surgical technique, the outcome depends on the "biology" of the angle: severe pigmentation, adhesions, and cicatricial changes worsen the prognosis. Therefore, preoperative gonioscopy with photographic documentation is a mandatory part of the preparation. [35]

Finally, in patients with secondary mechanisms, such as pigment dispersion, surgical and postoperative follow-up strategies are adjusted based on gonioscopy findings and systemic risk factors. [36]

Table 10. Preoperative angle inspection checklist

Paragraph	For what	What to record
Iris width and insertion	Choice of access and technology	Scale, photographs
Trabecular pigmentation	Forecast and benchmarks	Localization and severity
Adhesions and vessels	Risk of complications	Length and activity
Reaction to indentation	Dynamic reserve	Apposition against synechiae

Practical protocol for the office

Step 1. Indications. Gonioscopy is mandatory during the initial examination of any patient with suspected glaucoma or elevated intraocular pressure, as well as before pupil dilation in at-risk patients. This is reflected in leading guidelines. [37]

Step 2. Execution. Use minimal illumination, a narrow, short beam, examine all quadrants, and perform darkroom and dynamic tests if necessary. Record the scale and all findings, including the reaction to indentation. [38]

Step 3. Documentation. Take photographs of the angle, especially for atypical findings or before interventions. This will improve reproducibility and facilitate team discussion. [39]

Step 4. Decisions. For narrow or closed angles, discuss prophylactic laser iridotomy or surgical options according to current strategies. For secondary signs, treat the underlying cause and adjust antiglaucoma therapy. Plan monitoring based on risk and stage. [40]

Table 11. From discovery to action

Find	First decision	Additionally
Narrow angle without adhesions	Preventive iridotomy according to indications	Dynamic test in the dark
Synechiae	Consider surgical options	Strengthen control of risk factors
Pigment dispersion	Pressure control, photo documentation	Search for accompanying features
Neovascularization	Systematic search for the cause	Urgent revision of tactics

Brief conclusion

Gonioscopy is an indispensable clinical skill and tool that safely and quickly provides critical information about angle type and secondary mechanisms. Proper technique, clear description according to standards, and photographic documentation make this single procedure the foundation for a correct diagnosis and rational management of glaucoma patients. [41]