Shortwave perimetry: when it is used

Short-wavelength automated perimetry is a visual field test that uses blue test stimuli against a bright yellow background to selectively assess the short-wavelength cone pathway and associated retinal ganglion cells. Historically, this approach has been thought to allow earlier detection of functional defects in glaucoma compared to traditional white-on-white perimetry, particularly in patients with ophthalmoscopically normal optic discs but at risk for elevated intraocular pressure. Several longitudinal studies have shown that such defects can precede standard ones by 3–4 years, although the clinical significance of this “time advantage” depends on the quality of the test and associated factors. [1]

Today, standard automated perimetry remains the primary method for dynamic glaucoma monitoring, while short-wavelength automated perimetry is used selectively as an additional tool in specific clinical scenarios. The practical value of this method is limited by its higher variability, greater sensitivity to ocular opacities, and the need for careful standardization. This does not diminish its role in precise functional diagnostics, especially in patients suspected of having glaucoma, but it does require careful patient selection. [2]

In recent years, technical platforms for perimeter testing have evolved, with the emergence of shorter threshold testing algorithms and combined stimulus grids with additional points in vulnerable nerve fiber zones. However, the fundamental conclusions about the method's place in management tactics have remained similar: it doesn't replace white-on-white, but rather adds a layer of information. [3]

How the method works: physiology and technique

The yellow background in short-wavelength perimetry suppresses the sensitivity of the long- and medium-wavelength cone systems, allowing for selective stimulation of the short-wavelength cones and their associated pathway to the ganglion cells. This pathway is believed to be involved early in the glaucomatous process, so a decrease in thresholds in the blue-yellow mode may appear earlier than typical defects in the white stimulus. This principle is called selective perimetry, emphasizing the targeting of a specific channel of the visual system. [4]

The method is implemented in hardware on visual fields that support blue-on-yellow mode. The most common visual field analyzers utilize modern threshold testing algorithms, such as the Swedish Interactive Thresholding Algorithm, including a modification for short-wavelength mode. These algorithms reduce test duration and improve the clinical diagnostic utility of the test, while maintaining comparability of the indices with conventional reports. [5]

Modern test grids include the classic 24-2 and 30-2 grids, as well as the 24-2C grid, which includes points in strategically vulnerable nerve fiber bundles for glaucoma. This grid allows for better detection of early changes in the central zone with comparable examination duration and is already being used clinically. [6]

The key to good-quality data is standardized illumination, pupil diameter, correct refractive correction at the perimeter working distance, fixation control, and adherence to the patient training algorithm. Errors at any step lead to false diffuse or local defects, increasing the risk of misinterpretation of "early" changes. [7]

Table 1. Technical differences between visual field modes and clinical implications

Parameter	Shortwave perimetry	White-on-white perimetry	Clinical investigation
Stimulus	Blue on a yellow background	White on a white background	Selective shortwave path loading versus overall assessment of total sensitivity
Test duration	As a rule, more	As a rule, less	Fatigue has a stronger impact, and quality instruction is needed.
Threshold variability	Higher	Below	Re-confirmation of defects is required
Sensitivity to opacities	Expressed	Moderate	Cataracts and yellowing of the lens distort the thresholds more strongly.
Purpose	Early functional shifts in suspicious	Basic progression monitoring	A supplement, not a replacement, for the standard protocol

Diagnostic capabilities: what does it actually detect?

Longitudinal studies have shown that short-wavelength perimetry can detect defects before changes appear on standard perimetry; the time lag in some cohorts reached several years. However, the effect varies across risk groups, and the reproducibility of "early" maps requires control repeats. Therefore, the method is considered promising for confirming suspicions, but not sufficient for independent decisions about initiating therapy. [8]

Comparative studies yield mixed results: some show the advantage of short-wavelength vision in patients suspected of having glaucoma and in the early stages, while others find no superiority in detecting conversion to overt glaucoma or detecting defects in existing patients. The discrepancy is explained by differences in protocols, criteria for "abnormality," and the role of opacities in the optical media. [9]

Current clinical reviews emphasize that white-on-white assessment remains the basis for dynamic monitoring and treatment decision-making. Selective strategies are useful as an additional facet of assessment, especially in controversial cases, but they do not replace the basic method of monitoring progression. This approach is also reflected in international glaucoma guidelines. [10]

Of interest is the transfer of this technique to related fields: in some macular and vascular conditions, the sensitivity profile for the blue-yellow mode differs from that for the white mode. These observations expand the research field, but do not yet change the standards of daily practice. [11]

Table 2. Where

Clinical situation	Purpose of appointment	What does the standard add?
Suspected glaucoma with normal white field	Search for early dysfunction	Can detect subtle local defects
Unstable, "borderline" changes in white	Confirmation or denial	An independent defect map increases decision confidence
Structure-function imbalance	Comparison with tomography data	Helps to “translate” structural findings into functional ones
Research tasks	Sensitivity profiles in retinal conditions	Gives a different spectral cut of the function

Comparison with other methods: from white mode to structural tomography

When comparing short-wavelength imaging with standard perimetry, the former often depicts deeper and wider defects, but at the cost of greater variability and dependence on the condition of the medial environment. This necessitates repeating suspicious results before reaching a clinical conclusion. [12]

Shortwave mode shares selectivity and a desire for "early" sensitivity with frequency-doubled perimetry. In real-world practice, both technologies are more often used as a complement to, rather than as a primary method of treatment, since standard white mode remains the benchmark for assessing dynamics. The choice between them is determined by availability, test time, and the clinic's experience. [13]

Structural imaging techniques, such as optical coherence tomography of the nerve fiber layer and ganglion cell complex, often detect changes before any perimetric testing. In the early stages, tomography demonstrates high sensitivity to progression, and as the defects deepen, the role of functional monitoring increases. Therefore, the practical conclusion is that the best approach is to combine structural and functional assessment. [14]

The choice of visual field grid also affects the information content. Adding central dots to the 24-2C grid improves the "linkage" with macular nerve fiber bundle data and may be justified in early central complaints, while the 10-2 grid remains indispensable for detailed central assessment. [15]

Table 3.

Situation	What does tomography show?	What does the shortwave test add?	Practical solution
Suspicion without defects in white	Thinning of the nerve fiber layer or ganglion cell complex	Possible early local functional declines	Repeat the test, compare the zones, decide on the frequency of monitoring
Early central symptoms	Mild changes in the macular layers	Greater sensitivity to damage to the central fascicles	Consider 24-2C and 10-2 in dynamics
Severe cataract	Moderate reduction in tomography signal	A sharp "diffuse" decrease in thresholds and false defects	Rely on structure before cataract surgery
Progression in structure without dynamics in field	Persistent reduction in thickness	Ability to detect small threshold shifts	Increase the frequency of functional testing

Limitations and Artifacts: Why Blue Can Deceive

The key weakness of this method is its high sensitivity to opacities in the optical media, particularly age-related cataracts and generalized yellowness of the lens. The effect is a predominantly diffuse decrease in sensitivity, which is more pronounced with the blue-yellow test than with the white test, which can mask or imitate true local defects. Therefore, the lens status should always be considered, and after cataract extraction, the field should be re-shot to obtain an accurate baseline. [16]

Results are affected by pupil diameter and the quality of refractive correction at the perimeter working distance; miosis and defocus create false diffuse losses. Fatigue and the lack of a "learning effect" in novices increase local and global variability, which is especially critical for short-wavelength mode. At least two close-in sessions are required before drawing clinical conclusions. [17]

Comparative studies show statistically significantly higher repeatability for standard white-on-white perimetry compared to shortwave perimetry. Local variability increases where initial sensitivity is reduced; these are precisely the points most often found in the "zone of doubt" and require confirmation. This explains why "early" maps in shortwave mode are always re-verified. [18]

Finally, the choice of grid and algorithm affects the duration and quality of the data. Faster algorithms reduce fatigue but do not eliminate the physical limitations of the method. The right balance between speed and accuracy is selected individually, based on the purpose of the visit. [19]

Table 4. Sources of false positives and what to do about them

Problem	What does it look like on the map?	What to check	What to do
Cataract	Diffuse general decrease in thresholds	Visual acuity, slit lamp, cataract status	Repeat after surgery, rely on the structure
Small pupil	Pseudo-diffusion losses	Pupil diameter before the test	Drug dilation as indicated, repeat
Defocus	Scattering of defects	Correction for perimeter distance	Correct lenses in a trial frame
Beginner's fatigue	Chaotic local foci	Test time, breaks	Short breaks, repeat another day

How the study is conducted

Preparation begins with a refraction check and selection of correction for the perimeter working distance. It is important to assess the pupil diameter and the condition of the ocular media; in cases of severe cataracts, it is preferable to first consider surgery and then create a basic visual field map. The patient is explained the test principle, shown test flashes, and helped to achieve a comfortable posture, as stable fixation is the key factor in quality. [20]

The choice of grid is based on the clinical task: 24-2 is a universal start, 24-2C is when additional points on vulnerable fascicles are important, and 10-2 is when early central changes are suspected. It is algorithmically advisable to use modern shortened strategies that reduce fatigue and maintain index comparability. [21]

During the test, fixation, false-positive and false-negative responses, eyelid condition, and tear film are monitored. If monitoring is impossible, it is better to stop and reschedule the test rather than obtain misleading data. Upon completion, reliability indices are assessed before proceeding to clinical interpretation of the charts. [22]

For suspicious or newly identified defects, a confirmatory repeat is planned, if possible within 2-8 weeks, using the same protocol, the same correction, and similar conditions. Only consistent changes over several visits justify a change in diagnosis or treatment strategy. [23]

Table 5. Mini-protocol for conducting a qualitative test

Step	What to do	For what
Check refraction and pupil diameter	Select a correction, evaluate miosis	Reduction of diffusion loss artifacts
Select a grid	24-2 as a base, 24-2C for risk of central involvement, 10-2 for central complaints	Increase clinical relevance
Educate the patient	Test bursts, emphasis on a calm pace	Reduce fatigue and false responses
Monitor reliability	Fixation, false responses, artifacts	Eliminate data defects
Repetition plan	Confirmation of suspicious cards	Turn a "find" into evidence

Interpretation: From Gray Card to Solution

The report includes several representations: a grayscale field, deviations from the age norm for all points, pattern deviations, probability maps, and global indices. The key principle is to look at the consistency between representations, not rely on the grayscale image alone. Any "picture beauty" is secondary to reliability and clinical significance. [24]

Global indices include average visual field depression, a local pattern instability index, and an integral functional state index. All of these are meaningful only with benign reliability indices and over time. The short-wavelength mode is characterized by a somewhat more "pessimistic" display, so directly comparing such indices with standard ones is inappropriate. [25]

Typical glaucomatous patterns—arcuate scotomas, nasal steps, paracentral foci—often appear deeper in short-wavelength mode than in white light. This helps identify weak spots early, but requires confirming the stability of the defect with a repeat to rule out fatigue or optical media artifacts. [26]

Comparison with tomography and the optic disc completes the picture. If the structural and functional changes coincide in location, confidence is higher. If they diverge, quality factors and the influence of the cataract are checked first, and then the examination is repeated in the same manner. [27]

Table 6. Interpretation of global indices and typical patterns

Index or pattern	What does it mean?	What to look out for	Next steps
Decreased average sensitivity	Diffuse loss or artifact	Cataract, pupil, correction	Checking quality factors, repeat
Increased local instability	Local defects	Consistency on maps and in dynamics	Repetition and comparison with structure
Arcuate scotoma	Lesion of the arcuate fasciculi	Top-bottom consistency, boundaries	Dynamics, comparison with 24-2C and 10-2 grids
Bow stage	Early sign of glaucoma	Eliminate artifacts	Confirm by repetition, take into account the structure

Practical indications

In patients with suspected glaucoma and a normal white field, a short-wavelength test can increase sensitivity for early focal defects, especially in the presence of structural thinning on imaging. Consistent results facilitate decisions on surveillance frequency and target pressure. [28]

In patients with unstable white-mode maps, the blue-yellow test serves as an independent check. Coincidence of lesions increases the reliability of the clinical conclusion, while discrepancies require verification of quality factors and, possibly, repetitions in both modes. [29]

The method has also been used in studies of systemic metabolic conditions without overt retinopathy, seeking subtle functional shifts. These studies are interesting, but have not yet established routine indications and should be interpreted with caution. [30]

In cases of severe cataracts, corneal opacities, and vitreous opacities, structural imaging and white mode are prioritized until surgery is considered. After cataract removal, it makes sense to re-record the base map in both modes. [31]

Table 7. Indications and contraindications

Situation	Shown	With caution	Not shown
Suspected glaucoma	Yes, as an addition	-	-
Initial glaucoma	Yes, to clarify the localization	At low quality	-
Severe cataract	-	After surgery	Before surgery as the main method
Impossibility of fixation control	-	-	Visit without test, postponement

Selecting a grid and strategy

The 24-2 grid remains a universal basis for most tasks. Adding points to the 24-2C increases sensitivity to central vulnerable areas and is appropriate for early involvement of the macular bundles or complaints of "dips" near the fixation point. For detailed central assessment, the 10-2 is used, especially if suspicions are concentrated near the center. [32]

It makes algorithmic sense to use modern shortened strategies that reduce test time and improve tolerability without significantly compromising diagnostic value. However, no accelerated strategy compensates for the impact of cataracts or poor fixation, so quality remains paramount. [33]

When deciding on the frequency of repetitions, clinical risk is taken into account: the higher the probability of progression in structure or in the white field, the shorter the intervals between functional tests, including in short-wave mode. In controversial cases, it is preferable to alternate short-wave and white fields, seeking confirmation of stable local patterns. [34]

In a report with a complex clinical problem, it is useful to have consistent grids and strategies over time. Unnecessarily changing grids complicates comparisons and can mask or create the appearance of progression. [35]

Table 8. How to choose a field of view grid for a task

Clinical objective	Recommended grid	Why
Basic assessment of the periphery and arcuate zones	24-2	Standardized coverage with best comparability
Search for early central foci	24-2C	Additional points in vulnerable bundles
Detailed central assessment	10-2	Dense central mesh for paracentral defects
Long-term observation	Consistent mesh	Comparability over time is more important than a one-time "perfect" grid

Recent updates and horizons

Technological innovations include the expanded use of the 24-2C grid and further optimization of algorithms that reduce test time. These changes increase the procedure's tolerability and improve integration with the clinical workflow. However, the fundamental limitations of the short-wavelength mode remain, so it remains a complementary, rather than a basic, tool. [36]

Alternative functional testing formats are also being developed, including virtual reality and online perimetry. These demonstrate good correlation with standard automated perimetry and may expand the availability of monitoring, but for now they complement rather than replace clinical instruments. In the future, these technologies will likely be incorporated into hybrid monitoring protocols. [37]

Recent clinical guidelines emphasize an integrative approach: imaging structure, white-field function, and, if necessary, clarifying selective tests. This strategy minimizes the risk of misinterpretation of "early" maps and allows for personalized visit frequency and intervention thresholds. [38]

For everyday practice, this means targeting the short-wavelength test where it adds confidence, not just for show. The key is benign conditions and confirmation by repeat testing. Then the additional sensitivity of the method becomes a clinical benefit, not a source of false alarms. [39]