Centre for Applied Vision Research
  1. Visual Neuroscience and Psychophysics
  2. Ocular Optics and Instrumentation
  3. Ophthalmic Assessments and Patient Outcomes following Ophthalmic Interventions
  4. Visual Development and Plasticity
  5. Ophthalmic Public Health
  6. Measurement Techniques in Vision
    1. Individual tests
    2. Research & Case Studies

AVOT Vision

The AVOT (Advanced Vision and Optometric Tests) have emerged gradually from research studies carried out at the University over several years with support from research councils and government departments.

The tests were developed primarily to carry out research studies in camouflage, colour perception, rapid flicker and motion sensitivity, spatial vision under daylight and low light illumination, assessment of scattered light in the eye (i.e. the amount and angular distribution of forward light scatter in the eye) and performance in visual search tasks with measurement of eye movements and visual processing times. The Colour Assessment and Diagnosis (CAD) test was then developed further with support from aviation authorities and Transport for London and is the most researched and documented AVOT test.

The CAD test has now become the ‘gold standard’ for detection of congenital and acquired deficiencies and for establishing the severity of colour vision loss. However it is only one of several tests designed to assess different aspects of visual performance. There are other Advanced Vision and Optometric Tests (AVOT) developed and validated and offered by the centre to measure the quality of spatial vision, scattered light in the eye and the ability to see rapid flicker and motion perception.

To find out more information on the range of vision tests that are available to specific industries and job functions select an option below.

The Centre for Applied Vision Research has now made a new test available to screen adults and children for colour vision defiency.

The 'Colour Vision Screener' test can be used to identify those who may go on to benefit from taking the centre's CAD (Colour Assessment and Diagnosis) test, which provides an accurate diagnosis of colour vision loss.

(For further detail on the CAD test itself scroll below to the 'Medical Applications' tab.)

Colour Vision Screener

  1. The Colour Vision Screener test  can be downloaded here and is free to use.
  2. Colour Vision Screener: Instructions for use - (Note that this document also contains a list of CAD centres which contributed to the validation of the Colour Vision Screener test)
  3. Colour Vision Screener: Instructions for interpretation of results
  4. A short questionnaire for users of the Colour Vision Screener test

Disclaimer: The Colour Vision Screener is currently being validated for use with both calibrated and uncalibrated displays in a multi-centre study. The colour reproduction properties of uncalibrated visual displays can vary greatly in sRGB colour mode, even when the manufactures claim to support this colour mode for a particular display. Consequently, care should be taken in interpreting results obtained on uncalibrated 'home' displays, when the results of a full CAD test are not available.

Watch the narrated video for an overview of how to take the Colour Vision Screener test:


Focused Symposia

Colour in the Clinic - 4th November 2020

    14:00 Case presentation from the Medical Eye Unit - Sui Wong, Consultant Neurologist Guys and St Thomas' Hospital NHSFT

    14:40 Limits of what can be achieved in colour assessment John Barbur, City University

    15:00 Colour vision in posterior cortical atrophy Gordon Plant, University College London

    15:20 Nyctalopia and flashing lights Omar Mahroo, Moorfields Eye Hospital and Guys and St Thomas' NHSFT

    15:40 Break

    16:00 Photophobia and colour - the retina Christopher Tyler, City University

    16:20 Photophobia and colour - the cortex - Arnold Wilkins, University of Essex

Colour Assessment Workshop for Optometrists - 25th October 2019

The workshop is intended for Independent Optometrists with a programme focused on the latest advances in colour assessment and the provision of colour assessment services to fulfil current needs in healthcare and visually demanding occupations. The aim of the Workshop is to review current problems, to discuss the latest advances in colour assessment, to enable optometrists.

The tour of the Colour Research Laboratory includes explanations of current practices, interactive demonstrations and the opportunity to try out the latest colour assessment tests and protocols.

Colour in Health and Employment - 18th July 2019

Colour is used in abundance to enhance visual performance and to code information in many visually demanding occupations. As a result, screening for colour deficiency, and in particular, quantifying the severity of colour vision loss have become more important.

Colour in the Clinic - 5th December 2018

Research has revealed the importance of visual function testing, including colour vision, in the understanding of disorders affecting the retina, optic nerve and brain. We are also increasing our understanding of the importance of chromaticity in non-image forming visual functions which has implications for photophobia, migraine and light sensitivity. We are planning a workshop style meeting to stimulate discussion on how this increasing knowledge base can be applied in the clinical setting.

AVOT Recent Publications

• Barbur JL, Rodriguez‐Carmona M, Evans BE. Color vision assessment‐3. An efficient, two‐step, color assessment protocol. Color Research & Application. 2020. DOI: 10.1002/col.22599

• Rodriguez‐Carmona M, Evans BE, Barbur JL. Color vision assessment—2: Color assessment outcomes using single and multi‐test protocols. Color Research & Application. 2020. DOI: 10.1002/col.22598

• Evans BE, Rodriguez‐Carmona M, Barbur JL. Color vision assessment—1: Visual signals that affect the results of the Farnsworth D‐15 test. Color Research & Application 2020; DOI: 10.1002/col.22596

• Rodriguez-Carmona M, Evans B, Barbur JL. Assessment of chromatic sensitivity: 2. Color assessment outcomes using single and multi-test protocols Color Res Appl 2020;(in press).

• Hathibelagal AR, Bharadwaj SR, Yadav AR, Subramanian A, Sadler JRE, Barbur JL. Age-related change in flicker thresholds with rod- and cone-enhanced stimuli. PLoS One 2020;15:e0232784.

• Evans B, Rodriguez-Carmona M, Barbur JL. Assessment of chromatic sensitivity: 1. Visual signals that affect the outcome of color screening tests with emphasis on the Farnsworth D-15. Color Res Appl 2020; DOI: 10.1002/col.22596.

• Barbur JL, Rodriguez-Carmona M, Evans B. Assessment of chromatic sensitivity: 3. An efficient two-step color assessment protocol. Color Res Appl 2020; DOI: 10.1002/col.22599.

• Abdel-Hay A, Sivaprasad S, Subramanian A, Barbur JL. Acuity and colour vision changes post intravitreal dexamethasone implant injection in patients with diabetic macular oedema. PLoS One 2018;13:e0199693.

• Vemala R, Sivaprasad S, Barbur JL. Detection of Early Loss of Color Vision in Age-Related Macular Degeneration - With Emphasis on Drusen and Reticular Pseudodrusen. Invest Ophthalmol Vis Sci 2017;58:BIO247-BIO254.

• Rodriguez-Carmona M, Barbur JL. 3 - Variability in normal and defective colour vision: Consequences for occupational environments. In: Best J (ed), Colour Design (Second Edition): Woodhead Publishing; 2017:43-97.

• Rodriguez-Carmona M, Barbur J. Colour assessment outcomes–a new approach to grading the severity of color vision loss. Aerospace medicine and human performance 2017;88:298.

• Barbur JL, Rodriguez-Carmona M. Colour vision requirements in visually demanding occupations. Br Med Bull 2017;122:51-77.

• J. L. Barbur and M. Rodriguez-Carmona. “Color vision changes in normal aging”. In: Handbook of Color Psychology, Eds. A.J. Elliot, M. D. Fairchild and A. Franklin. 180-196, Cambridge University Press (2015).

• E. J. Patterson, G. Bargary and J. L. Barbur. “Understanding disability glare: light scatter and retinal illuminance as predictors of sensitivity to contrast”. J.Opt.Soc.Am.A, 32, 576-585 (2015).

• G. Bargary, Y. Jia and J. L. Barbur. “Mechanisms for discomfort glare in central vision”. Invest Ophthalmol Vis Sci, 56, 464-471 (2015).

Medical Applications

Diseases of the eye and/or systemic diseases that can affect vision include diabetes, glaucoma, multiple sclerosis, age-related macular degeneration (ARMD), ocular hypertension and optic neuritis. Research studies carried out at City, University of London over several decades led to the development of a series of tests that can be used to detect the earliest signs of ocular disease. The tests have direct application in optometry, neurology and ophthalmology and are also useful to those working in the public health arena.

Colour Vision Assessment - the CAD test

The CAD test screens for normal red/green (RG) colour vision in less than one minute. If loss of RG colour vision is detected, the program can be used to measure accurately the severity of RG colour vision loss and to diagnose the class of deficiency involved (i.e., protan- or deutan-like deficiency) in 9 minutes.

The CAD test can measure very small changes in the patient's chromatic sensitivity over time and this can be used to detect and then to monitor progression of disease and/or effects of treatment.

The CAD also tests for yellow/blue (YB) deficiency. Subjects born with congenital yellow/blue (YB) are very rare (about 1 in 20,000), but the prevalence of acquired YB sensitivity is much higher and increases with age. The presence of acquired loss of YB chromatic sensitivity can be detected with high sensitivity and the severity of colour vision loss can be quantified accurately in 3 minutes. YB loss is often associated with systemic and/or eye disease. Preliminary data suggests that in cases of ARMD and diabetes, the loss of chromatic sensitivity can be severe and often precedes early clinical signs of retinopathy, in some cases by several years.


Rapid flicker sensitivity is an important biomarker in glaucoma, multiple sclerosis, diabetes, ARMD and ocular hypertension. The Flicker-Plus test measures the patient’s rapid flicker thresholds at the fovea (along the line of sight), a region responsible for sharp vision, and also in each of the four quadrants, to assess near peripheral vision.

Training Opportunities - Advanced Colour Assessment

City Occupational Ltd (a spin out company of City) provides training on the use of Advanced Vision and Optometric Tests (AVOT) such as the CAD test. The training can be carried out either in London or on the customer's premises.

The training consists of lectures on colour vision and other aspects of visual performance that are relevant in visually-demanding occupations. The course is appropriate for customers who purchase the AVOT system and are likely to use the AVOT tests regularly within either clinical or occupational environments. In addition to lectures on fundamental aspects of vision, the course also includes hands on, practical, training sessions on the calibration of the system, the use of the tests and the interpretation of results. Handouts are provided and can be downloaded from the City Occupational website:

  1. Course Programme
  2. Colour Vision in Occupational Environments
  3. Colour Vision Assessment Course

Booking a course

Contact the AVOT centre or City Occupational to discuss your requirements and how best to train your personnel.

Workplace Applications

Visually demanding professions, such as the fire and police services and the maritime and aviation industries, specify minimum requirements for spatial vision as a prerequisite for entry. Others also require applicants to have normal trichromatic colour vision, preventing those with even mild colour vision loss from entering the profession.

Yet there is now a growing realisation that this approach based on the use of conventional colour assessment tests can be both unfair and unsafe. Applicants with mild congenital deficiency that can carry out suprathreshold, colour-related tasks as well as normal trichromats can fail and others that may not be safe to work in some environments can pass. This is because evidence-based, minimum colour vision requirements are not available in many environments and most conventional colour screening tests do not quantify accurately the severity of colour vision loss.

Accurate assessment of colour vision loss is important since congenital colour deficiency can range in severity from nearly normal trichromatic vision to complete absence of colour vision. Advances in colour vision assessment and the optimised use of colour in occupational environments have shown that people with mild loss of colour vision often have sufficient residual 'chromatic sensitivity' to be able to perform visually demanding, colour-related tasks as well as those with normal colour vision. So it is unacceptable to simply bar those with less than perfect colour vision from embarking on careers that may involve visually demanding, safety-critical, colour-related tasks.

The arbitrary relaxing of pass/fail criteria is equally inadequate unless properly quantified and proven to relate directly to visual performance in the most demanding, safety-critical, colour-related tasks.

Adequate scientific research studies need to be performed to identify and characterise the use of colour signals within occupational activities and to set safe limits for different professions that can be measured accurately using objective tests.

Limits of acceptable chromatic sensitivity loss have so far been established for commercial aviation, with the support of the Civil Aviation Authority (CAA), London Underground train drivers, with support from Transport for London, and air traffic controllers (with support from the Colt Foundation and the UK CAA). These limits are used in the CAD test to provide automatic pass/fail certification within these occupational environments.

Contact us to discuss the need for adequate but fair colour vision requirements within your industry and how we can help you to establish safe limits and a system that is accurate and reproducible.

For more information on each of the specific tests please select an option below.

Colour Vision Assessment (including CAD and additional tests)

As part of the Colour Vision Assessment, the CAD test relies on novel discoveries from studies in camouflage to isolate the use of colour signals. The test detects accurately both congenital and acquired colour vision deficiency, type of colour vision loss, whether it is normal trichromatic, deutan-, protan- or tritan- like deficiency, and also quantifies the severity of loss.

What is unique about CAD?

The test has high sensitivity which allows the detection of the mildest colour vision deficiencies. When the task involves only the detection of subjects with congenital colour deficiency and normal trichromats the test has 100% sensitivity and specificity. The test also classifies accurately the subject’s class of colour vision, including the presence of acquired deficiency. The availability of minimum colour vision requirements within selected occupations ensures that many mild congenital deficient pass and are therefore still able to take on jobs where the use of colour signals is safety critical.

Who can benefit from it?

The CAD test includes clear certification limits for pilots, TfL train drivers and air traffic controllers. The test also relies on age corrected ‘normal’ limits from 6 to 85 years of age, which makes the test particularly useful in clinical applications.

Other relevant tests

In addition to the CAD test, the full colour vision assessment includes a range of other traditional tests that are still accepted in several occupations.

These tests include Ishihara pseudo-isochromatic plates (38-, 24- and 14-plate Editions), Farnsworth D-15, Holmes-Wright Lantern (type A and B), Nagel Anomaloscope, City (2nd Edition) plates and American Optical (Hardy, Rand and Rittler) AO-HRR plates.

Having completed these tests, you may also be referred to or choose to take the PAPI or CRATO tests.

Run the video below for a simulation.


What is unique about ACAD?

Many people who suffer from severe loss of colour vision as a result of unusual genetically inherited eye diseases in addition to severe loss of spatial vision The very poor visual acuity can cause problems with conventional colour vision tests and makes the assessment difficult on the CAD test.

City produced the ACAD, or Achromatopsia Colour Assessment and Diagnosis test to tackle this problem. Although other clinics use the CAD test, the full range of tests is only available at City. It can be taken in place of or in addition to the CAD test as part of the colour vision assessment.

Who can benefit from it?

Like CAD, this test measures red/green and yellow/blue chromatic sensitivity, but uses larger, spatially separated stimuli and eliminates the element of dynamic luminance contrast noise making it accessible for low vision patients. The test is visually more exciting and interesting and also works well with young children.


Spatial vision can be affected by changes in the optics of the eye or by retinal disease, so this test is a useful method of determining if you have normal, healthy spatial vision appropriate to your age. The test is also often used as a follow up after refractive surgery to quantify the success of the operation. It is also extremely useful when used in conjunction with the CAD test to distinguish between changes in the optics of the eye or changes in the retina.

What is unique about Acuity-Plus?

The Acuity-Plus test offers highly detailed measures of Visual Acuity (VA) and Functional Contrast Sensitivity (FCS) and therefore produces more accurate results than the typical Snellen chart. The test can also be used to investigate the applicant’s sensitivity to visual crowding.

Who can benefit from it?

Everyone can benefit from the use of this test which provides a more detailed description of one’s spatial vision under both photopic (daylight) and high mesopic (twilight) conditions. The test measuring visual acuity (VA) and functional contrast sensitivity (FCS) and reveals the presence of large higher order aberrations, increased scatter in the eye and / or residual, uncorrected refractive errors. Assessment of spatial vision under mesopic lighting conditions is recommended for anyone with particular interest or concerns about their night vision. Specifically, it is relevant to people in careers that require all round good vision such as pilots, seafarers and police officers, and can be taken in conjunction with a CAD and Flicker-Plus tests to determine the overall quality of one’s vision.

Acuity Plus

Other relevant tests

Other tests that are often useful to carry out in conjunction with Acuity-Plus, are the Light Scatter and the Aberrometry assessment tests. These provide information on higher order optical aberrations and light scatter in the eye.

Aberrometry Assessment

By measuring the wavefront aberrations across the eye this test can provide an indication of the changes in retinal image quality that can be caused by higher order optical aberrations or abnormalities.

Who can benefit from it?

The Aberrometry Assessment generally provides information on the quality of the optics of the eye, so it is a useful test when assessing unexplained loss of spatial vision.

Other relevant tests

This test is often used as a means of checking the results of refractive surgery, but can also be used in conjunction with results from the Light Scatter, Acuity Plus and CAD tests to help decide if any decreased visual performance is a result of degraded retinal images or the presence of early stage retinal disease.

Light Scatter

Poor spatial vision is often caused by an increased light scatter, therefore it is important to know how much light is scattered by the optics of the eye. Large amounts of scattered light also cause ‘disability glare’ which is characterised by visual discomfort and the failure to see fine spatial detail in low contrast environments.

What is unique about Light Scatter?

Unlike similar available tests, City’s unique Light Scatter test uses several scatter rings to measure both the amount and angular distribution of scattered light in the eye. The test is totally non-invasive and easy to use.

Who can benefit from using this test?

Scattered light increases with advancing age and can affect night driving and other tasks when bright objects are seen against a dark background. Equally if bright lights distort your vision, you may benefit from taking this test. It is particularly relevant for those employed in the transport industry and having to drive at night.

Other relevant tests

The Acuity-Plus test as well as a Light Scatter test may be recommended as well in order to understand what causes poor vision by separating increased high order aberrations and residual refractive errors from scattered light.

Light scatter


The test measures rapid flicker thresholds at the fovea (a region responsible for sharp central vision), as well as in each of the four quadrants. Flicker thresholds measured with the Flicker-Plus test can be very low in normal vision, but can also be highly elevated in older people or in the presence of glaucoma, hypertension or other diseases that affect the retina. The test interleaves all retinal locations and uses the same calibrated display system that runs all other AVOT tests.

Who can benefit from it?

Rapid flicker sensitivity is an important biomarker in glaucoma, multiple sclerosis, diabetes, ARMD and ocular hypertension. Anyone with health concerns or clinically diagnosed conditions may benefit from taking this test.

Other relevant tests

Taking Flicker-Plus together with CAD can provide more specific results regarding changes in the retina in ocular disease. The tests are also useful to detect and quantify subtle changes linked to side effects of accidental exposure or to plan treatment with certain drugs.


MAP (Macular Assessment Profile)

The MAP test measures the spatial distribution of macular pigment (MP) in the eye. This is of particular interest due to its properties as an absorber of blue (short wavelength) light and for acting an anti-oxidant. High macular pigment levels may help to protect against age-related macular degeneration.

What is unique about MAP?

Unlike versions of this test offered by other clinics, City’s MAP test employs improved techniques that allow the accurate measurement of the spatial profile of the MP along any meridian. The test also yields an estimate of the lens absorption of short wavelength light with respect to the average absorption of young subjects (up to 20 years of age).

Who can benefit from it?

Older people for whom this test can act as an early warning sign of an increased probability of developing degenerative diseases of the retina.

Other relevant tests

You may also want to take the CAD test in conjunction with MAP test, if you are concerned about age-related changes in the retina.

EMAIL (Eye Movements and Intrinsic Latency)

This Eye Movement And Intrinsic Latency test measures oculomotor parameters such as eye movement latencies, saccade durations and visual processing times, all of which are affected by anxiety and fatigue. In addition to intrinsic latencies, EMAIL also tests simple reaction times and decision processing response times.

What is unique about EMAIL?

This test is the only one of its kind and is carried out without the need for any eye-tracking equipment.

Who can benefit from it?

These are important functions for anyone in a safety-critical, visually-demanding occupation. The beneficiaries include commercial pilots, train drivers, air traffic controllers and even firefighters.

PAPI (Precision Approach Path Indicator Lights)

The PAPI test has been developed at City as a practical simulation of the conditions in which pilots must be able to identify the red and white coloured PAPI lights used to guide them along the correct angle of approach for landing on a runway.

What is unique about PAPI?

This test simulates the geometry, landing conditions, spectral composition of the real PAPI lights and the intensity levels a pilot is expected to experience from an approach distance of 5.5km. The PAPI apparatus provides the closest approximation for the real PAPI lights and is used to establish the applicant’s ability to perform this task.

Who can benefit from it?

Pilots with loss of colour vision that falls close to the pass / fail limits established for commercial aviation.

CRATO (Colour Requirements for Air Traffic Operators)

Colour is used extensively in air traffic control, as well as other visually demanding occupations. Colour signals can make targets more conspicuous, aid in segmentation and grouping operations and can also be used to signal specific information by means of colour naming. This test measures how colour signals affect visual performance by measuring the mean time needed to find a coloured target on a screen or to recognise a particular colour in complex scenes defined by other objects and colours.

What is unique about CRATO?

CRATO tests dynamic vision and the use of colour signals over a large visual field. This test is available as part of the Colour Assessment offered at City.

Who can benefit from it?

Subjects with colour vision deficiencies, school children and others wanting to assess their ability to use colour in complex visual scenes.

Other relevant tests

Applicants may be referred to take the CRATO test following results from the CAD test.

Collaborating in Excellence

City Occupational Ltd is a joint venture between City, University of London and the UK CAA to make available Advanced Vision & Optometric Tests (AVOT) with applications in occupational medicine, public health and applied vision research. CAA International Limited, a subsidiary of the UK CAA, has licenced City Occupational to use, in these commercial applications, the findings of the research funded by the UK CAA relating to minimum colour vision requirements.