Cambridge Color Test

A computerized color vision test using Landolt C rings embedded in pseudoisochromatic dot patterns. Identify the gap direction to screen for red-green and blue-yellow color blindness.

Cambridge Color Test

Identify the direction of the gap in the Landolt C ring hidden among colored dots. This test screens for both red-green and blue-yellow color vision deficiencies.

•Look at each plate and find the C-shaped gap
•Select the direction the gap is facing: Top, Bottom, Left, or Right
•If you cannot see the gap, click "I Can't See"

What is the Cambridge Color Test?

The Cambridge Colour Test (CCT) is a computerized color vision assessment developed at the University of Cambridge by J.D. Mollon, J.P. Reffin, and colleagues. It was designed as a modern alternative to traditional printed plate tests like the Ishihara, offering more precise and quantifiable measurements of color discrimination thresholds.

The test displays a Landolt C (a ring with a gap) embedded in a field of pseudoisochromatic colored dots. The target ring differs in chromaticity from the background dots, and the subject must identify the direction of the gap — up, down, left, or right. This forced-choice method eliminates the subjectivity of number-reading tests.

Because the stimulus is generated on a calibrated computer display rather than printed on paper, the CCT can precisely control chromaticity coordinates and adapt difficulty in real time using a staircase procedure. It tests along protan, deutan, and tritan confusion lines, making it capable of detecting all three major types of color vision deficiency.

How to Take the Test

1. Find the Gap

Look at the plate and locate the Landolt C ring — a circle with a gap — hidden among the colored dots. The ring and the background differ in color.

2. Choose Direction

Select which direction the gap is facing using the four arrow buttons: Top, Bottom, Left, or Right. If you cannot see the ring, press "I Can't See."

3. Get Your Results

After 12 plates, you'll receive an instant assessment of your color vision with a breakdown of each response.

Clinical CCT vs. This Online Version

The clinical Cambridge Colour Test uses a calibrated CRT monitor with precise chromaticity control (CIE 1976 u'v' coordinates) and an adaptive staircase algorithm to measure exact color discrimination thresholds. Our online version adapts the core methodology with the following differences:

Clinical CCT

- Calibrated CRT/LCD display
- Precise CIE chromaticity control
- Adaptive staircase procedure
- Measures exact thresholds (u'v' units)
- Tests protan, deutan, and tritan axes

This Online Version

- Uncalibrated screen
- Fixed-difficulty plates
- Pass/fail per plate (no staircase)
- Provides a screening score
- Results vary with screen calibration

Note: This online test is a screening tool only and cannot replace a clinical CCT examination. If you need a precise color discrimination threshold for research or diagnosis, consult an optometrist with calibrated testing equipment.

How the Cambridge Colour Test Works

The clinical CCT operates by presenting a Landolt C ring whose chromaticity differs from the background along specific confusion lines in CIE 1976 u'v' color space. These confusion lines correspond to the three types of cone photoreceptors:

Protan line — targets L-cone (long-wavelength) deficiency, detecting protanopia and protanomaly
Deutan line — targets M-cone (medium-wavelength) deficiency, detecting deuteranopia and deuteranomaly
Tritan line — targets S-cone (short-wavelength) deficiency, detecting tritanopia and tritanomaly

The test uses a four-alternative forced-choice (4AFC) paradigm — the subject must choose one of four gap directions. An adaptive staircase algorithm adjusts the chromaticity difference between the ring and background after each response, converging on the subject's discrimination threshold. This threshold, measured in u'v' units, provides a quantitative measure of color vision performance.

All dots in the display (both ring and background) vary randomly in size, and luminance is randomized to prevent the subject from using brightness cues rather than color differences. This pseudoisochromatic design ensures the test truly measures chromatic discrimination.

Understanding Your Score

11-12 Correct — Normal Vision

You can reliably distinguish the Landolt C ring from the background on all or nearly all plates. This suggests normal color discrimination.

9-10 Correct — Mild Deficiency

You may have difficulty with some chromaticity differences. This could indicate a mild color vision deficiency. Consider following up with a clinical test.

6-8 Correct — Moderate Deficiency

Significant difficulty distinguishing the target ring from the background. This suggests a moderate color vision deficiency and a professional assessment is recommended.

0-5 Correct — Strong Deficiency

Major difficulty identifying the Landolt C ring. This strongly suggests significant color vision impairment. Please consult an eye care professional for comprehensive testing.

Sources

Reffin, J.P., Astell, S. & Mollon, J.D. (1991). "Trials of a computer-controlled colour vision test that preserves the advantages of pseudoisochromatic plates." Colour Vision Deficiencies X, pp. 69-76.
Mollon, J.D. & Reffin, J.P. (1989). "A computer-controlled colour vision test." — Original description of the Cambridge Colour Test
National Eye Institute (NEI) — Overview of color blindness types, causes, and diagnosis
Ventura, D.F., et al. (2003). "Colour vision and colour vision loss." Principles and Practice of Clinical Electrophysiology of Vision, MIT Press.
PubMed — National Library of Medicine — Peer-reviewed research on computerized color vision testing

Frequently Asked Questions

The Cambridge Colour Test (CCT) is a computerized color vision assessment developed at the University of Cambridge. It uses a Landolt C ring (a circle with a gap) hidden among randomly colored dots. The test measures how well you can distinguish color differences along protan, deutan, and tritan confusion lines.

The Ishihara test uses printed plates where you identify numbers. The CCT uses a Landolt C ring and measures color discrimination thresholds quantitatively. The CCT can test along all three confusion lines (protan, deutan, tritan), while Ishihara primarily screens for red-green deficiency. The CCT also eliminates number-recognition as a variable.

Yes. Unlike many traditional plate tests, the CCT tests along the tritan confusion line in addition to protan and deutan lines. This makes it capable of detecting tritanopia and tritanomaly (blue-yellow color vision deficiency), which affects roughly 1 in 10,000 people.

Pseudoisochromatic means 'false same-color.' The test plates use dots that appear the same color to someone with a color vision deficiency but appear clearly different to someone with normal color vision. The target (Landolt C ring) is defined only by color differences, not by shape, size, or brightness cues.

No. This online version is a screening tool only. The clinical CCT requires a calibrated display and controlled testing conditions. If you need a certified color vision assessment for employment, licensing, or research, consult a qualified optometrist or vision scientist.

Screen color reproduction varies significantly between devices due to differences in display technology, color profiles, brightness settings, and ambient lighting. The clinical CCT uses a calibrated monitor to ensure precise chromaticity. For the most consistent online results, use a device with good color accuracy and test in consistent lighting conditions.