The science
What contrast sensitivity measures.
A short, cited tour of why this test exists, what your curve means, and what we deliberately don’t claim.
More than “can you read this row?”
Visual acuity — the 20/20 chart — asks one question: how small a high-contrast letter can you resolve? Contrast sensitivity asks the whole map: how faint a pattern can you see, across a range of pattern sizes. The result is a curve, the contrast sensitivity function (CSF), plotted against spatial frequency (in cycles per degree of visual angle, cpd). For healthy young adults the curve peaks around 3–6 cpd at a sensitivity of roughly 200–500 and falls off above ~10 cpd[1,2].
Your CSF, drawn in one picture.
The classic Campbell-Robson chart shows stripes that get finer left to right (higher spatial frequency) and fainter top to bottom (lower contrast). The boundary between “I can see the stripes” and “I can’t” traces out roughly your contrast sensitivity function — peaking near the middle of the spatial-frequency range.
The same psychophysics sits behind the clinical Pelli-Robson chart[1] and grating tests like FACT and CSV-1000. What changes between tests is the stimulus (letters vs. gratings), the contrast resolution, and how threshold is found.
Contrast sensitivity loss isn’t specific — but it’s sensitive.
CS dips can show up in many conditions, often before letter-chart acuity moves. A dip is a screening signal, not a diagnosis. Forthcoming blog posts go deeper on each of these.
- Cataract
Intraocular scatter from lens opacities lowers contrast sensitivity — often well before the standard letter chart catches it. Night-driving complaints typically arrive first.
- Glaucoma
Magnocellular pathway damage can show up as mid-frequency contrast sensitivity loss earlier than visual-field defects, which is why some clinicians use CS as one of several early signals.
- Multiple sclerosis
Low-contrast acuity at 2.5% and 1.25% has been added to the MS Functional Composite for clinical trials — it is a recognized, sensitive measure of optic-nerve and central-pathway involvement.
- Post-concussion / mTBI
First- and second-order CSF disruptions are documented after mild TBI, sometimes persisting after symptoms resolve and while letter-chart acuity reads 20/20.
- Age-related macular degeneration
AMD reduces contrast sensitivity at the spatial frequencies that matter for reading and face recognition, often before central acuity falls noticeably.
The honest limits of an online test.
The contested case is mold/CIRS. A specific 6–12 cpd contrast-sensitivity pattern has been associated with biotoxin exposure in the Shoemaker framework, and this association is widely repeated inside that patient community. The independent, adequately-blinded evidence base for the specificity claim is small, and reviewers point out that VCS cannot distinguish the proposed pattern from cataract, glaucoma, refractive error, dry eye, fatigue, or an uncalibrated screen.
We make no claim that this test detects mold exposure, CIRS, or any other specific etiology. We do not replace an eye exam, an OCT, a visual field, or a neuro-ophthalmic evaluation. If something on your curve concerns you, the next step is a clinician who knows your case.
Want more depth?
The methodology page lays out the exact stimulus, calibration, and threshold procedure. The blog goes deeper on each condition.
References on this page.
- [1] Pelli D, Robson J, Wilkins A. The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences. 1988;2(3):187–199.
- [2] Mäntyjärvi M, Laitinen T. Normal values for the Pelli-Robson contrast sensitivity test. Journal of Cataract and Refractive Surgery. 2001;27(2):261–266.
- [3] Lesmes LA, Lu ZL, Baek J, Albright TD. Bayesian adaptive estimation of the contrast sensitivity function: the quick CSF method. Journal of Vision. 2010;10(3):17. PMC4439013.
- [4] Watson AB, Pelli DG. QUEST: a Bayesian adaptive psychometric method. Perception & Psychophysics. 1983;33(2):113–120.
- [5] Allard R, Faubert J. The noisy-bit method for digital displays: converting a 256 luminance resolution into a continuous resolution. Behavior Research Methods. 2008;40(3):735–743.