A Vision for 'Colour'
Ms Lakshmi Bodduluri takes us through available Colour Vision tests and explores how technology likely to shape the future of colour vision testing.
Ms Lakshmi Bodduluri is currently a postgraduate research student (PhD) at the School of Optometry and Vision Science, University of New South Wales. Her research involves the development and validation of an iPad colour vision test and applying this validated iPad test in children with type 1 Diabetes Mellitus. She received Bachelor’s degree in Optometry (B.S.Opt) from Bausch & Lomb School of Optometry (BITS-Pilani) after a one year of internship at the L V Prasad Eye Institute in the year 2010. Her research interests are colour vision, electrophysiology, diabetes mellitus and diabetic retinopathy.
About the author
Colour is often used as a means of communicating information through perception in our daily life. For example; red implies “stop” and green to “go”. Likewise in Optometry, black indicates “degeneration/dystrophy” and brown indicates “pigmentary changes” (colour coding). Hence colour matters! This article briefly describes the importance of colour vision assessment, different test types and future considerations in colour vision assessment.
Why test colour vision?
The importance of colour vision in our everyday tasks and in many occupations such as driving, railway, army and aviation etc. should not be underestimated.
Colour vision testing is not commonly included in routine eye examination. Colour vision tests are generally done only when we find an abnormal pupil response such as relative afferent pupillary defect: RAPD or when a patient comes with a prior diagnosis of any optic nerve/retina related conditions that can affect colour vision. Moreover, there are about 20% to 30% of people who are unaware that they have colour vision deficiency (CVD). This can lead to problems like when a student who completed the education may suddenly find that he/she can't pursue a career because of CVD. Therefore, there is an increasing need to include colour vision assessment in the routine eye examination as it helps the person with CVD to get proper counselling about the condition and the career options that they can opt for.
Along with the congenital CVDs, there are certain ocular (e.g.: optic nerve related conditions, age related macular degeneration and glaucoma) and systemic (e.g.: Diabetes Mellitus, Parkinson’s disease and multiple sclerosis) conditions that can affect colour vision. Therefore, assessing colour vision in routine clinical practice not only helps to identify congenital CV abnormalities and counsel the patients but also assists in identifying the early effects of any systemic or ocular diseases on visual functions.
Colour vision tests
There are a number of colour vision tests available to detect & diagnose the congenital and acquired colour vision deficiencies.
“Holmgren Wool test” (performed by matching different coloured “wool skeins”), introduced in 1875, was the first commercially available colour vision test developed for vocational purposes (for drivers in railway and maritime) to check the ability to differentiate coloured light signals.
Pseudoisochromatic (PIC) plate tests
The first clinical colour vision test developed is the “Stilling test” that used the pseudoisochromatic principle (i.e. discrimination of one colour in an opponent colour is compromised thus the pair of colours appear isochromatic and will be confused). PIC tests consist of a central test target, formed by circles of different colours and sizes, in the form of a numeral, an alphabet, a symbol or an optotype (Landolt C or Tumbling E). The examinee has to identify/trace (for children/illiterate) the target that they can see on each plate. The first successful commercially available and the most commonly used is the “Ishihara’s test”. Some other PIC plate tests are the American Optical Hardy-Rand-Rittler (AOHRR) test, Standard Pseudoisochromatic Plate (SPP) tests and Colour Vision Testing Made Easy (CVTME) test. The PIC plate tests are used mainly for screening purposes.
Arrangement tests
“Arrangement tests” require the examinee to arrange the colour caps in a sequence of either their hues (or saturation) or to group greys and colours. The Farnsworth-Munsell 100 Hue test (FM 100 Hue) is the first arrangement test. It is based on hue discrimination and, is commonly used clinical test due to its superior uses like detecting individuals with different degrees (normal, abnormal or supernormal) of colour discrimination and its ability to monitor for subtle colour vision changes secondary to any disease (acquired defects). Following the FM 100 Hue test are its shorter versions namely the FM Panel D15, Adams desaturated D15, Lanthony desaturated D15 and Lanthony New Colour test etc.
FM Panel D15
Other clinical tests
Anomaloscope, Medmont C-100 and the City University Test are some other colour vision tests. Of which, the anomaloscope is considered the gold standard for diagnosing anomalous and dichromatic colour vision deficiencies. It works on the principal of colour matching and the examinee has to match a semi-circle of a fixed colour (yellow or white) by mixing two other colours (red and green or blue and yellow).
Computerised colour vision tests
Cambridge Colour Test (CCT) and Colour Assessment and Diagnosis test (CAD) are two commercially available computer based tests that are based on the PIC principle. The CCT stimulus (a Landolt-like “C”) is formed by randomly distributed gray circles of varying size and luminance. The task for the examinee is to identify the orientation of “gap” in Landolt “C”. In CAD, the stimulus is a moving coloured square (formed by small squares) in the grey background that varies in luminance. The task here is to identify the direction in which the coloured square is moving. These tests are useful to not only detect colour vision defects rapidly but also allow more detailed assessment of colour discrimination. However, these tests use expensive technology and thus are used mostly for research than in clinical use.
Shortcomings of current tests
The current colour vision tests have their own limitations such as insensitive nature to blue-yellow or acquired colour defects (certain PIC plate tests), inability to detect anomalous colour vision or pass subjects with milder forms of colour vision abnormalities (FM Panel D15), specific testing conditions (ambient lighting), longer testing times (FM 100 Hue and anomaloscope tests) and need of expertise in administration and interpretation of the results. And, care needs to be taken in handling these tests in order to avoid fading of test plates or the coloured caps.
Although the computer based tests take care of the above mentioned limitations, they do have certain concerns like calibration of display monitor and the luminance & colour output of the monitors that are being used for testing.
Whats in future?
Technology is emerging as one of the biggest positives in the world of vision tests. Modern tablet computers are being used for the development of vision tests providing high quality vision assessment outside the traditional clinic or laboratory settings. Recent research showed that the vision tests when combined with gaming strategies can create more effective and engaging media for vision assessment, especially when testing younger population (DoDo game for colour vision screening: Watch YourTube video below).
In the essence, the future of vision testing may concentrate on development of more portable and easily accessible means of vision tests that can possibly address the need for specialized laboratory equipment (expensive) and longer testing times. Also, such robust tests coupled with simple instructions and techniques and, with user-friendly interfaces are likely to be accepted amongst eye care practitioners and become widely incorporated into clinical routine in the future.