John Barbur

John Barbur


John Barbur – Centre for Applied Vision Research, City, University of London, London, UK


Chromatic sensitivity in normal trichromats and in congenital and acquired deficiency – implications for employment


The spectral content of the light reflected from objects carries useful information about their chemical composition and surface properties. This can often be of advantage and the perception of ‘colour’ has evolved as important attribute of vision to achieve this aim. ‘Colour’ vision (CV), is of great value in enhancing our visual performance since it enables us to represent and use effortlessly information carried in the spectral composition of the light.

Not all of us benefit from normal CV and although colour perception is not a key requirement in everyday life, in some safety-critical jobs, it can be a matter of life and death. The correct interpretation of air traffic landing lights, railway signals and electrical wiring is a safety-critical task for which good colour perception is vital.

Normal trichromatic CV relies on the normal functioning of L, M and S cones. Some subjects do not have three functioning cone types or in some cases rely on pigments that differ in spectral responsivity to those found in normal trichromats. Congenital RG colour deficiency affects ~ 8% of men and less than 1% of women. The presence of anomalous red / green (RG) or yellow / blue (YB) signals leads to reduced chromatic sensitivity as well as changes in the perceived colour of objects. Many subjects with anomalous, trichromatic CV can still make use of their residual RG signals and their normal YB vision to perform the suprathreshold, colour-related tasks encountered in safety-critical, working environments as well as normal trichromats. Since these subjects should not be discriminated against on the basis of their colour deficiency, recently it has become more important to improve the sensitivity and specificity of our tests, and in particular, the ability to quantify accurately the severity of CV loss.

Recent advances in colour assessment make it possible to detect congenital / acquired deficiency with close to 100% sensitivity and specificity and, more importantly, to also quantify accurately the severity of CV loss. The Colour Assessment and Diagnosis (CAD) test achieves these aims, but the fully calibrated equipment needed is expensive and the full test requires ~ 14 minutes to complete. The development of a rapid, sensitive and inexpensive CV screener that can be administered quickly and efficiently would solve these problems. If such a screener was available for use within schools and visually demanding occupations, only ~10% of male subjects would require full colour assessment to establish accurately the class of deficiency and severity of loss.

A new CAD-Screener developed to fulfil these requirements will be described. The screener takes just under three minutes to complete. Only ~ 3.8% of the least affected deutans pass. All normal trichromats and all protans are detected with 100% sensitivity and specificity. Further work is needed to make the CAD-Screener available on the web and to extend its use in schools and occupations.

Short Bio

John Barbur trained in Physics at Imperial College London where he also studied Optics and Visual Science. John combines fundamental vision science with applied and clinical research, which underpins a long record of research achievement and wider impact. 

Work on camouflage led to insights into the processing of luminance and colour signals with important applications in colour vision assessment. New research instrumentation and measurement techniques, developed by John, led to new methods for investigating mesopic vision, pupillometry, eye movements, spatial, temporal and chromatic vision, colour constancy and the effects of scattered light in the eye. The P_SCAN system enabled the discovery of new components of the pupil response that require the processing of stimulus attributes such as colour or motion in central areas of the visual cortex. The system made possible studies of normal colour vision, congenital and acquired deficiency and ‘Blindsight’.


As a Fulbright Scholar, John worked with colleagues at the Center for Visual Science at the University of Rochester, New York. This work led to studies on mesopic optimization of visual efficiency, medical aspects of fitness to drive, minimisation of ‘glare’ in lighting installations and mesopic optimization of lighting for residential streets. These studies supported the development of several Advanced Vision and Optometric Tests (AVOT), initially for research studies and later for more precise assessment of vision and severity of vision loss in demanding working environments such as aviation, seafaring and rail transport. The CAD (Colour Assessment and Diagnosis) test is now used throughout the world to assess pilots, firefighters, seafarers, police officers and air traffic controllers. Other AVOT tests are also being used to detect changes in visual sensitivity and oculomotor responses in early-stage, degenerative disorders of the brain and / or the retina and to evaluate treatment effectiveness in clinical trials. John and his colleagues are currently working on the development of novel tests for non-invasive assessment of retinal function and the validation of a highly sensitive and specific colour vision screener for use on the web with direct impact in schools and occupations. The Centre for Applied Vision Research at City, University of London is now recognised internationally as a leading centre in visual psychophysics and colour vision research. 


Segreteria organizzativa locale

telefono: 0733/405124 (lunedì-martedì-venerdì 10.30-13.00); 347 2762464
Segreteria organizzativa GdC-AIC
Dr. Veronica Marchiafava

04 | 09 | 2019 pomeriggio

Seminario di apertura
“L’Archeometria per il colore nel restauro pittorico”

Istituto di Restauro Marche (IRM)
Montecassiano, MC

Programma di massima convegno

05 | 09 | 2019
09:00 | Registrazione

Saluti iniziali

09:30 – 13:00 | Invited Tutorial
13:00 – 14:00 | Intervallo
14:00 – 18:00 | Invited talk e sessioni
18:00 | Assemblea soci GdC-AIC

06 | 09 | 2019
09:00 – 13:00 | Invited talk e sessioni
13:00 – 14:00 | Intervallo
14.00 – 15.00 | Sessione poster
15:00 – 18:30 | Invited talk e sessioni

07 | 09 | 2019
09:30 – 12:00 | Invited talk e sessioni / Discussione / final remarks