Glaucoma diagnostics: imaging techniques

Glaucoma diagnosis today relies on a three-pillar approach: assessment of intraocular pressure, anterior chamber angle anatomy, and structural and functional assessment of the optic nerve and macula. This means that the core trio of tests includes tonometry, gonioscopy, and standard automated perimetry, as well as optical coherence tomography of the optic nerve head and macula. This approach is reflected in the current guidelines of the American Academy of Ophthalmology and the European Glaucoma Society. [1]

The main goal of diagnosis is to confirm or rule out glaucomatous optic neuropathy and assess the risk of its progression. Not only a single photograph is important, but also a dynamic analysis: repeated measurements show whether the patient is losing nerve fibers and whether the visual field is deteriorating. In real-world practice, we use both structural markers from optical coherence tomography and functional markers from perimetry. [2]

Alongside classic technologies, new additions have emerged: anterior segment optical coherence tomography for angle objectification, optical coherence tomography angiography for assessing peripapillary perfusion, and home tonometry for 24-hour pressure profiling. These are not replacements for the basic trio, but rather tools that enhance them when clinically beneficial. [3]

Key principle: Diagnosis and treatment decisions rely on the consistency of multiple data sources. No single test alone establishes a diagnosis, and discrepancies between structure and function require additional verification and dynamic monitoring. [4]

Intraocular pressure: how to measure and how to interpret

Intraocular pressure measurement remains the most important modifiable factor in glaucoma management, but accuracy depends on the tonometry method and corneal properties. Goldmann applanation tonometry remains the standard of comparison, but dynamic contour tonometry is less dependent on corneal biomechanics, and rebound tonometers facilitate home monitoring. In the clinic, it is important to understand the limits of agreement between instruments—they "agree on average," but are not interchangeable in a given patient. [5]

Central corneal thickness is a strong independent predictor of ocular hypertension conversion to glaucoma and a source of systematic error for applanation. Attempts to "recalculate" pressure using correction tables have failed to improve prognostic models, so today corneal thickness is used not for arithmetic correction, but for risk assessment and pressure interpretation. [6]

Diurnal pressure fluctuations and nighttime peaks are discussed as possible factors for progression. Some studies find a link with worsening blood pressure, while others do not confirm an independent effect when taking into account average blood pressure levels. Practical conclusion: if there is a suspicion of fluctuations or a discrepancy between clinical and office data, home tonometry and stress tests are useful, but decisions should be made based on the totality of structural and functional data. [7]

Advances in home tonometry allow for a more complete picture of the circadian profile. Modern rebound devices demonstrate acceptable compliance with applanation and high patient acceptability. Contact lens sensors provide relative variability curves over the course of a day, which can be a useful adjunct in complex cases, although interpretation remains a task for specialized centers. [8]

Table 1. Tonometry methods: what to consider

Method	Contact	Dependence on the properties of the cornea	Strengths	Restrictions
Goldman's applanation	Contact	Significant	Standard of comparison, availability	The influence of corneal thickness and biomechanics
Dynamic contour tonometry	Contact	Smaller	Less corneal influence, high repeatability	Cost, availability
Rebound tonometry in the clinic	Contact	Moderate	Fast, without anesthesia	Not interchangeable with applanation in all patients
Home rebound tonometry	Contact	Moderate	Daily profiles, patient engagement	Teaching, interpretation
Contact lens sensors	Contact	Absolute mmHg is not digitized.	Continuous relative curves	Relative units, value and interpretation [9]

Anterior chamber angle: gonioscopy and anterior segment tomography

Gonioscopy remains the gold standard for assessing the anterior chamber angle and is mandatory for initial examination and follow-up. It reveals not only the angle width but also the presence of adhesions, pigment, and developmental anomalies, which is critical for differential diagnosis. [10]

Anterior segment optical coherence tomography (ASOT) objectively characterizes the angle configuration and is useful as an adjunct to screening, in unclear cases, and for documenting progression after laser and surgical interventions. Sensitivity for angle closure is high; however, it does not replace gonioscopy due to limitations in detecting adhesions and the need for clinical interpretation. [11]

In real-world practice, a reasonable strategy is to perform gonioscopy on everyone, adding anterior segmental tomography (AST) when indicated, especially in patients with an Asian phenotype, a small anterior chamber, hyperopia, and episodes of pain or iris halos. For triage in large cases, anterior segmental tomography (AST) helps filter out who needs to be seen by a glaucoma specialist more quickly. [12]

Let me remind you that false confidence is possible with a normal angle on optical coherence tomography. If clinical evidence suggests otherwise, we turn to gonioscopy, especially if a mixed mechanism for increased pressure is suspected. [13]

Table 2. When is it better to evaluate an angle?

Clinical task	The most informative	For what
Initial examination	Gonioscopy	Gold standard, synechiae, pigment, anomalies
Narrow angle screening	Anterior segmental tomography plus gonioscopy	High sensitivity and clinical verification
Documenting the dynamics	Anterior segmental tomography	Quantitative parameters before and after interventions
Unclear cases	Both methods	Summary of anatomy and clinical features [14]

Optic disc and macula: what optical coherence tomography can offer

Optical coherence tomography is a key structural test today. We analyze the thickness of the nerve fiber layer around the disc, the thickness of the ganglion cell complexes in the macula, and the parameters of the rim along the opening of Bruch's membrane. Together, this increases sensitivity in the early stages and improves monitoring. [15]

The "minimum rim width across the Bruch's membrane openings" parameter is particularly useful in patients with myopia, where the classic parameters are disc-dependent. It does not always exceed the nerve fiber thickness, but often complements it, reduces the dependence on disc size, and aids in early diagnosis. [16]

Interpretation requires attention to artifacts: decentration, segmentation errors, and quality loss due to opacities. Comparison with a reference baseline is useful, but for patients with high myopia and atypical anatomy, it is better to rely on their own baseline recording and reference layers rather than "red-green" maps. [17]

To monitor progression, the workflow includes event-based analysis using optical coherence tomography and trend analysis of the rate of thinning. The event-based approach often identifies clinically significant changes earlier, particularly in terms of three-dimensional rim parameters, but the final decision is made based on perimetry. [18]

Table 3. Optical coherence tomography in glaucoma: what to look for in the report

Block	What to look at	Why is this important?
Peripapillary nerve fiber layer	Global and sectoral profile, inferotemporal and supertemporal "forks"	Early changes in arcs
Macular ganglion cell complex	Minimum thickness and asymmetry	Sensitive to central defects
Rim on Bruch's membrane	Minimum rim width	Less dependent on disc size, useful for myopia
Quality and alignment	Quality index, segmentation artifacts	Exclusion of false pathology
Dynamics	Event plus trend analysis	Early detection of progression [19]

Field of View: How to Choose the Right Strategy

Standard automated perimetry remains the basic functional test. The 24-hyphen-2 and 30-hyphen-2 strategies cover the central 24 or 30 degrees, while the 10-hyphen-2 strategy focuses on the central 10 degrees, where many ganglion cells are concentrated. Accelerated "faster" algorithms reduce test time without significantly compromising diagnostic value in early glaucoma. [20]

The 24-hyphen-2-si grid adds central dots and helps detect early central defects faster than the classic 24-hyphen-2 grid. However, if macular involvement is suspected, the 10-hyphen-2 grid remains more detailed in the center, and the optimal strategy is to flexibly combine grids depending on the clinical presentation and optical coherence tomography data. [21]

Comparative studies show that the choice between ten-hyphen-two, twenty-four-hyphen-two, and twenty-four-hyphen-two-si depends on the question: detection of early central broken arcs, monitoring of typical Parris-Hodapp arcs, verification of questionable changes. When repeating, we use the same strategy to avoid confounding trends. [22]

When interpreting, we pay attention to the mean deviation and template loss indices, probability maps, and consistency with anatomy: an arcuate defect should correlate with thinning of the corresponding arc on optical coherence tomography. This increases confidence and reduces the risk of false-positive findings. [23]

Table 4. How to choose perimetry for a clinical task

Situation	Preferred grid	Comment
Screening and primary documentation	Twenty-four-hyphen-two or twenty-four-hyphen-two-si	Balance of coverage and time
Early central changes by optical coherence tomography	Ten-hyphen-two and twenty-four-hyphen-two-si	Macula plus periphery
Confirmation of arcuate defects	Twenty-four-hyphen-two	Comparability with the baseline and trends
Detailed monitoring of central vision	Ten-hyphen-two	Dense mesh in the center [24]

Additional techniques: when they are appropriate

Optical coherence tomography angiography allows for the assessment of peripapillary and macular vessel density. Decreased vascular density often accompanies structural atrophy and can be an additional marker of severity, but this method does not yet replace classical structural and functional tests in diagnosis and progression assessment. [25]

Electrophysiological tests such as pattern electroretinogram (PEG) and negative photoreceptor waveform (NPR) are being studied as markers of ganglion cell dysfunction. They are useful in complex differential situations, but their role in routine glaucoma practice is auxiliary. [26]

The blood flow assessment methods described in detail in the original article are of scientific interest, but are not part of the standard glaucoma diagnostic algorithm. We rely on tonometry, gonioscopy, optical coherence tomography, and perimetry for clinical decision making. [27]

Home tonometry and contact sensors can add valuable information about the circadian pressure profile, especially when there are discrepancies between clinic and office figures, but interpretation of the curves requires experience and should always be balanced against structure and function.[28]

Table 5. Technologies from the original article: place today

Technology	Routine role in glaucoma	Comment
Green laser retinal thickness analyzer	No	A historical technique, superseded by optical coherence tomography
Scanning laser ophthalmoscopic angiography	No	Invasive dyes, niche applications
Pulse ocular blood flow	No	Research application
Laser Doppler velocimetry and flowmetry	No	Complex interpretation, limited clinical utility
Spectral retinal oximetry	No	Scientific tasks do not affect the standard of conduct

Monitoring progression and frequency of follow-up

For structural optical coherence tomography data, an event-based approach and trend analysis are used. The event-based approach allows for the detection of changes beyond age-related thinning and intervisit variability, and often provides early warning signs, especially along the three-dimensional rim. For reliability, we compare the findings with perimetry. [29]

For the visual field, software algorithms are used that compare current maps with the database and estimate the rate of deterioration of the mean deviation index. Repeatability is important: tests must be comparable in strategy and quality. Consistent progression in structure and function is the most compelling argument for changing treatment tactics. [30]

The frequency of visits and the range of tests are determined by stage, risk, and life expectancy. Patients with high risk and advanced stages require more frequent assessments, as reflected in the Academy's consolidated benchmarks. For patients with ocular hypertension without overt glaucoma, risk calculators based on large studies are useful. [31]

The target pressure level is a dynamic value, aimed at a reduction of twenty to thirty percent from the initial level and subsequent adjustment based on the observed dynamics of structure and function. This is a practical compromise between the effectiveness and safety of therapy. [32]

Table 6. Progression: what we consider significant

Data source	Event	Comment
Optical coherence tomography	A decrease in the thickness of the nerve fiber layer or rim that is outside the range of variability	We confirm by re-recording and checking the artifacts
Perimetry	Repeatable defect according to probability maps and index	Requires consistent dough quality
Coherence	Coincidence of localization by structure and function	The most important criterion for changing tactics
Pressure	Increase in average values or expansion of the amplitude of oscillations	Reason for intensification of therapy in case of proven progression [33]

A practical algorithm for examining a patient with suspected glaucoma

First visit. We collect risk factors, measure pressure, perform gonioscopy, photograph the optic disc, perform optical coherence tomography of the disc and macula, and perform perimetry using a 24-dash-2 or 24-dash-2-si grid. We record the thickness of the central cornea to assess risk and interpret pressure. [34]

If in doubt, if optical coherence tomography indicates central changes, add a ten-hyphen-two. If the angle is narrow, supplement the assessment with anterior segment tomography. If clinical and office measurements disagree, consider home tonometry. [35]

Risk stratification. We use a risk calculator for ocular hypertension, taking into account pressure, age, corneal thickness, cup ratio, and visual field, to select the frequency of observations and the threshold for initiating treatment. [36]

Dynamics. We repeat the same tests at agreed-upon intervals, analyze events and trends, and look for consistency between structure and function. If progression is confirmed, we reduce the target pressure and intensify therapy. [37]

Table 7. Common pitfalls and how to avoid them

Trap	What's happening	How to prevent
Red zone overestimation in optical coherence tomography	False positives due to artifacts and non-standard anatomy	Check quality, segmentation and compare with your own baseline visit
Incomplete angle estimation	Mixed pressure boosting mechanism failure	Perform gonioscopy on everyone, supplemented with anterior segment tomography as indicated
Changing perimetry strategies	Uninterpretable trends	Keep one strategy for the trend, add a second one according to the indications
A literal "correction" of pressure for corneal thickness	Wrong decisions	Use corneal thickness for risk stratification rather than arithmetic correction
Focus on a single visit	Random variability	Confirm findings with replication and multimodal agreement [38]

Brief conclusions

Modern glaucoma diagnostics is a systemic, multi-layered process. We rely on tonometry, gonioscopy, optical coherence tomography of the disc and macula, and standard perimetry, adding anterior segment tomography, optical coherence tomography-angiography, and home tonometry as indicated. Decisions are made based on the consistency of structure and function and the observed dynamics. [39]