VCS Test: Free Online Visual Contrast Sensitivity Screening
The VCS test measures how well you distinguish faint differences between light and dark, and that ability turns out to be one of the earliest measurable casualties of biotoxin exposure. A person whose contrast sensitivity has dropped in a specific band will usually notice nothing in daily life, which is what makes the measurement worth taking rather than guessing at.
Testing takes about fifteen minutes, runs in a browser after a short screen calibration, and produces a result immediately. The test on this site is free, needs no account, and scores your result against the pattern associated with biotoxin exposure from water-damaged buildings.
Who this test is for
You suspect your house or office is impacting your health.
Symptoms that ease when you are away from home or work, and return when you go back, are the pattern worth measuring. The test gives you one objective data point instead of a guess.
You have a diagnosis that never quite fitted.
Contrast sensitivity is one of the few markers in this area that moves within weeks, so it can be used to test a hypothesis rather than only to describe a state.
You are a clinician or a researcher.
The protocol, the pass thresholds at 6 and 12 cycles per degree, the scoring, and the limits of what a result supports are all set out on this page.
What a VCS test measures
Contrast sensitivity differs from visual acuity, and the distinction matters for understanding what the test detects. Acuity, the figure an optician reports as 20/20, describes the smallest detail you can resolve at high contrast. Contrast sensitivity describes the faintest difference between light and dark you can detect at a given level of detail. Someone can hold perfect acuity while losing a substantial amount of contrast sensitivity, which is why this deficit passes unnoticed.
The test presents circular patches containing striped patterns, called sine-wave gratings, at five spatial frequencies and nine contrast levels each. Spatial frequency describes how fine the stripes are, expressed in cycles per degree of visual angle. Each patch is tilted vertically, fifteen degrees left, or fifteen degrees right, and identifying that orientation confirms you can resolve the pattern at that contrast.
Plotting the faintest contrast you can resolve at each spatial frequency produces a contrast sensitivity function, or CSF curve. In biotoxin-related illness the curve shows a characteristic dip in its middle range rather than falling uniformly, and that shape is what the screening looks for.
The science behind visual contrast sensitivity testing
The protocol derives from the Functional Acuity Contrast Test, developed by Arthur Ginsburg and subsequently adapted for biotoxin screening through the clinical work of Dr Ritchie Shoemaker across roughly three decades of patient data.
The physiological chain runs through blood flow. In people who cannot clear biotoxins efficiently, exposure triggers a persistent innate immune response involving complement fragment C4a, which constricts small blood vessels and reduces perfusion. The capillary networks supplying the retina and optic nerve head are particularly susceptible, and reduced perfusion there impairs the magnocellular pathway, the visual channel responsible for mid-range spatial frequencies. Researchers have correlated these deficits with hypoperfusion measured directly by laser flowmetry.
That mechanism explains the two features which make the test useful. Deficits concentrate at 6 and 12 cycles per degree rather than spreading evenly, producing a recognisable signature. And because the cause is perfusion rather than structural damage, the deficit reverses as inflammation settles, with meaningful improvement often visible within two weeks of effective treatment and decline reappearing within days of re-exposure.
The full research background sets out the biotoxin pathway in more detail, including where the evidence is strong and where it remains contested.
We publish mold related research work as well as cite other people's work. Our paper on consumer interpretation of mold and biotoxin lab reports carries a registered DOI, is archived on Zenodo under CC BY 4.0, and is indexed in OpenAIRE, and this screening tool is cited by name in the wider literature on biotoxin exposure and early screening. See the papers and the citations.
How the test works, step by step
Screen calibration, roughly two minutes. Because every display differs in pixel density and gamma, gratings would render at the wrong physical size and the wrong contrast without correction. Calibration establishes your screen’s pixel density by matching an on-screen outline to a standard credit card, then determines its gamma by adjusting two grey patches until they blend. An uncalibrated contrast test produces results that cannot be interpreted against reference data.
The visual test, roughly six minutes. Each eye is tested separately while the other is covered. You identify the orientation of each grating, or indicate that you cannot see it, working through decreasing contrast at each spatial frequency. Testing at a given frequency stops once your threshold has been located rather than continuing through every remaining patch.
Symptom questionnaire, roughly seven minutes. Fifty-one questions across nine domains cover the thirty-seven symptoms Shoemaker identified, organised into thirteen clusters, with each rated for both frequency and severity. Rating both allows the score to serve as a baseline for tracking change rather than only a snapshot.
Report. Per-eye CSF curves, cluster analysis of your symptom responses, an exposure pattern assessment distinguishing mold, Lyme, post-viral, and heavy metal patterns, and suggested next steps including which laboratory tests would be informative.
The screening runs in your browser and takes about fifteen minutes from calibration to result.
Start the test nowWhether your eyes qualify
The scoring assumes your visual system is otherwise healthy, so certain conditions affect how much weight a result carries.
Acuity. Results are interpretable when each eye tested reaches at least 20/50 corrected or uncorrected, equivalent to 6/15 metric or LogMAR 0.40. If you wear a current prescription and feel it works, you almost certainly meet that threshold. Where one eye falls below it, testing the other alone still produces a usable result. Where both do, an in-person assessment is the better route.
Corrective lenses. Wearing your usual glasses or contacts is appropriate if you would normally need them at the testing distance. Glasses are marginally preferable to contacts, since some contact lenses affect contrast sensitivity slightly.
Lenses to avoid. Polarised lenses improve contrast sensitivity across all spatial frequencies and will skew results upward. Blue-light filters and yellow-tinted lenses marketed for contrast enhancement will do the same. Neither belongs in a screening test.
Prism lenses and monovision contacts introduce complications, since prism can lower baseline contrast sensitivity and monovision gives each eye a different focal length. Testing remains useful for tracking change over time, though a single positive or negative determination carries less weight, and mentioning either to a clinician reviewing your result is worthwhile.
Ocular conditions. Cataracts, glaucoma, macular degeneration, and nystagmus all reduce contrast sensitivity independently of any biotoxin exposure. A positive result in someone with these conditions cannot be attributed confidently to biotoxins, though serial testing still tracks change reliably against that person’s own baseline.
Age. Contrast sensitivity rises through childhood, peaks in adulthood, and declines in later life, particularly above 6 cycles per degree. Reference data accounts for this, but it explains why an older adult may sit closer to threshold without any exposure at all.
Screen and device requirements
Display quality determines whether calibration can succeed, and some devices simply cannot render the required contrast steps accurately.
High pixel density draws the gratings small and sharp, which allows a comfortable testing distance.
Reliable where the panel is reasonably current and brightness sits at a normal working level.
Panel quality is generally lower and output drifts out of specification within a few years, with Apple hardware the usual exception.
A device manufactured within the past four or five years is a reasonable guideline.
Pixel density also determines your testing distance, which is why the figure the calibration gives you may differ from the eighteen inches quoted for printed charts. Lower pixel density requires larger gratings, which in turn requires sitting further back to preserve the correct spatial frequency at your eye.
Room conditions matter less than people expect but still matter. Dim ambient lighting rather than darkness, no glare or reflection on the screen, brightness set between 50 and 70 percent, native resolution, and browser zoom off. Automatic brightness adjustment and any accessibility contrast settings should be disabled, since both will interfere with calibration.
If gamma calibration reports a value outside the normal range, the display is operating outside manufacturer specification. Checking that brightness and contrast sit at midrange settings resolves most cases, and testing on a newer device resolves the rest.
Start your testHow to read your VCS test results
Results are reported by column, each corresponding to a spatial frequency, and the pattern across columns carries more meaning than any single value.
Columns A and B, at 1.5 and 3 cycles per degree, sit at the low-frequency end. Deficits confined here have been associated anecdotally with nutritional deficiency rather than biotoxin exposure.
Columns C and D, at 6 and 12 cycles per degree, are the biotoxin-relevant range. Deficits concentrated here, particularly when both eyes are affected, produce the signature the screening is designed to detect.
| Column | Cycles per degree | What a deficit there reads as |
|---|---|---|
| A | 1.5 | Low frequency. A deficit confined here has been associated anecdotally with nutritional deficiency. |
| B | 3 | Low frequency. Read together with column A rather than on its own. |
| C | 6 | Biotoxin-relevant. Deficits here, in both eyes, carry the most weight. |
| D | 12 | Biotoxin-relevant. The second half of the signature the screening detects. |
| E | 18 | Responds to biotoxins but also to many other influences, so it supports fewer conclusions alone. |
Your report plots your measured curve against the reference curve for healthy individuals, with error bars indicating the normal range. A curve tracking above the reference indicates contrast sensitivity better than the reference population. A curve dipping below it in the middle columns is the finding that matters.
What your VCS test score means
Numeric scores are best read as a baseline for comparison rather than as a verdict, since the positive or negative determination depends on the pattern of misses across columns rather than on a total. Where you also hold laboratory results, the test interpreter reads mycotoxin panels, ERMI and HERTSMI-2 scores, and CIRS blood markers alongside a VCS result.
How accurate the VCS test is
Reported sensitivity sits near 92 percent for detecting CIRS-pattern illness, with a false positive rate below 1 percent in unexposed populations. Pairing the visual result with the symptom questionnaire raises combined screening accuracy to approximately 98.5 percent, drawn from Shoemaker's clinical data across tens of thousands of patients.
The false negative rate of roughly 8 percent is the figure worth understanding, because it is not randomly distributed. False negatives concentrate in people whose baseline contrast sensitivity is unusually high, since contrast sensitivity can be trained. Artists, photographers, pilots, professional athletes, competitive gamers, and adolescents are all over-represented. Someone in those groups with a negative result and a symptom pattern that tracks their building has reason to keep investigating.
These figures describe screening performance rather than diagnostic performance, so a positive result indicates a pattern consistent with biotoxin exposure rather than confirming a condition. They also derive from a large body of clinical data rather than from a single independent blinded trial.
Start your testWhat else can lower contrast sensitivity
A positive result narrows the field without naming a cause, since contrast sensitivity responds to a range of influences beyond mold.
Biotoxin sources other than mold produce the same signature, including Lyme disease and its co-infections, cyanobacteria, and dinoflagellates such as Pfiesteria and Ciguatera. Non-biological causes include heavy metals, volatile organic compounds, certain medications, alcohol, and nutritional deficiency. Ocular pathology, as covered above, acts independently.
This breadth is why the screening pairs the visual measurement with a symptom questionnaire and an exposure history. The visual deficit establishes that the pathway is affected, and the exposure history is what narrows down by what.
Retesting and tracking treatment
Because deficits reverse as inflammation resolves, serial testing measures response in a way a one-off result cannot. Clinical practice commonly involves weekly testing during early treatment, when response to an intervention is the open question, with the interval stretching to fortnightly or monthly as improvement holds.
Re-exposure produces the reverse. Contrast sensitivity typically declines within three to five days of returning to a contaminated environment, which makes serial testing a practical way to evaluate whether a remediated building is genuinely clear or whether a new location is contributing.
Testing here is free and unlimited, so no cost consideration limits how often you retest.
What to do with your result
A positive result supports treating biotoxin exposure as a live hypothesis rather than confirming it. The productive next steps involve establishing exposure and characterising the response: reviewing symptoms against the pattern associated with mold toxicity, investigating the building through ERMI or HERTSMI-2 dust testing, and discussing inflammatory markers such as C4a, TGF-beta1, MMP-9, MSH, and VIP with a clinician familiar with reading them together.
A negative result carries useful information too. Where symptoms do not track a particular building and no dampness history exists, it argues for redirecting investigation elsewhere before spending on laboratory work. Where symptoms clearly follow a location, the false negative profile above is worth weighing before concluding anything.
For choosing between the available laboratory options, our comparison of the VCS test and urine mycotoxin panels covers what each measures and which to spend money on first.
How this test compares with other VCS options
Three routes to a VCS test exist, and they differ in cost, access, and what they return.
| Option | Cost | Account | Symptom assessment | Repeat testing |
|---|---|---|---|---|
| This test | Free | None | Included | Unlimited |
| VCSTest.com | Free, contribution for detail | Required | Not included | By contribution |
| Surviving Mold | Fee for results | Required | Not included | Per result fee |
| In-office FACT chart | Appointment | Not applicable | Practitioner led | Per visit |
This test is free with no account required, no email address, and no limit on retesting. Calibration covers pixel density and gamma, both eyes are tested separately, and the fifty-one-question symptom assessment runs alongside the visual test so the combined screening accuracy applies rather than the visual figure alone.
VCSTest.com operates on a free-or-by-contribution model, providing an initial test with limited results after registration, with detailed results, a printable PDF, and repeat testing available for a contribution. It offers healthcare provider accounts, results forwarding, and EHR integration, which suits clinical practice.
Surviving Mold hosts the test associated with Shoemaker’s own protocol, free to take with a fee for results.
In-office FACT chart testing uses the physical chart the online tests are modelled on, administered by a practitioner under controlled lighting, which removes calibration variables at the cost of requiring an appointment.
The practical differences come down to whether you want a symptom assessment scored alongside the visual result, whether you need results forwarded to a clinician automatically, and whether repeat testing needs to be free.
Start the test nowFrequently asked questions
What is a VCS test?
A visual contrast sensitivity test measures your ability to detect faint differences between light and dark at several levels of visual detail. Applied to biotoxin screening, it looks for a characteristic deficit at 6 and 12 cycles per degree, which reflects reduced blood flow to the optic nerve caused by inflammation.
Is the VCS test free?
The test on this site is free, requires no account or email address, and can be repeated as often as you like. Other providers operate contribution or fee models for detailed results.
How accurate is the VCS test?
Sensitivity is around 92 percent for CIRS-pattern illness with a false positive rate under 1 percent, rising to approximately 98.5 percent combined screening accuracy when paired with the symptom questionnaire. The false negative rate of roughly 8 percent concentrates in people with unusually high baseline contrast sensitivity.
Can I take the VCS test if I wear glasses?
Yes, and you should wear your usual correction if you would normally need it at the testing distance. Polarised lenses, blue-light filters, and tinted lenses meant to enhance contrast will skew results and should be removed.
Can I take the VCS test on my phone?
Yes, and newer phones and tablets are the preferred devices because high pixel density allows accurate rendering at a comfortable distance. Laptops are the least reliable option, since panel output drifts from specification within a few years.
What does a positive VCS test mean?
It indicates a contrast sensitivity deficit in the pattern associated with biotoxin exposure. It supports further investigation rather than confirming a cause, since Lyme co-infections, heavy metals, certain medications, and ocular conditions can produce similar deficits.
How often should I retake the VCS test?
Weekly during early treatment, when the question is whether an intervention is working, stretching to fortnightly or monthly as improvement holds. Since deficits reappear within three to five days of re-exposure, retesting also indicates whether an environment is genuinely clear.
Does the VCS test diagnose mold illness?
No. It is a screening instrument that identifies a pattern warranting investigation. Diagnosis involves exposure history, symptom assessment, laboratory markers, and clinical judgement.
Why does the test need screen calibration?
Displays vary in pixel density and gamma, so identical instructions render gratings at different physical sizes and contrast levels on different screens. Calibration corrects for both, and results from an uncalibrated contrast test cannot be compared against reference data.
What is the difference between this and the Surviving Mold VCS test?
Surviving Mold hosts the test associated with Shoemaker’s protocol, free to take with a fee for results. This test is free throughout, requires no registration, includes the fifty-one-question symptom assessment scored alongside the visual result, and places no limit on retesting.