The prevalence of colour vision defect is estimated at 8% in males (or one out of every 12) and between 0.4 and 0.5% in females (or 1 out of every 200).1,2 A classic text, Birch,2 explains that the most likely form of colour abnormal vision is inherited, via an X-linked form of inheritance.
A boy may inherit just one X chromosome, so has a 50% chance of expressing the trait whenever the mother is a carrier (the daughter of a male colour defective) or will inherit the trait when it is the rare occasion of the mother being colour defective. So it is typically a boy who gets the disorder and inherits it from his maternal grandfather. Deuteranomalous trichromatism is the most common type of congenital colour vision defect.2
The Vischeck
Lillo et al have described the Vischeck tool.3 This might be thought of as software that allows an individual to view what might be seen by a colour abnormal individual (a patient) with either a protanopic or deuteranopic (dichromatic) type of defect. In truth, while these defects are not the most common types of defects (this being anomalous trichromatism), it may still prove useful to be aware of Vischeck in high street practice as the tool provides a demonstration of the lived experience of a person with abnormal colour vision. However, this is not the aim of this paper.
This project utilised the Vischeck, a tool that was developed by Dr Bob Dougherty and Dr Alex Wade. The tool is available free of charge to the public online.7 In the authors’ opinion, the Vischeck tool is exceptional because it allows someone to understand the lived experience of a person with a colour vision defect.
A sweet solution
Most optometrists screening for colour vision defects use the Ishihara Test or the City University Colour Vision test. Neither of these tests include a recognisable intrinsic reward. Colour vision screening is important because colour names are the first things a child learns2 and colour vision issues may have a long-standing impact for children, especially if parents and teachers are not made aware of the problem.
In the United Kingdom, a recent study states that many students and teachers lack an understanding and awareness about abnormal colour vision.4 Surprisingly, colour vision also has an occupational context as it was thought to have led to one of the greatest railway disasters in Europe called the Lagerlunda Incident (railway incident) which occurred in Sweden in November of 1875.5 More information on this subject of colour vision and occupations is available from the Association of Optometrists online.6
We wondered whether coloured sweets to detect colour vision defects could ever be approved by the College of Optometrists and satisfy the competency 3.1.4; ‘Identifies abnormal colour vision and appreciates its significance.’7
Aims
The aim of this project was to use photographs to identify a potential cheap, quick and widely accessible sweet to be used in a colour vision test with paediatric applications. The test is essentially a quick sorting task, using either a packet of M&Ms or Skittles (Fruits) sweets. The idea was to identify a suitable sweet for a colour vision test that can be completed in under three minutes under the supervision of a nurse, teacher, dispensing optician, contact lens optician, optometrist, pre-registration optometrist, physician or orthoptist.
The child would be told to sort out a number of sweets presented to them according to their colour. Using the Vischeck, we were able to predict which sweets of different colours would be confused and seen as the same colour by a protanope and a deteranope. In this way, it might be possible to detect the defect by simply seeing the grouped patterns of sweets from any patient.
The test would also be used as a reward to encourage good behaviour during the eye exam, such as perhaps prior to the instillation of drops. Currently, there are no other colour vision tests that present an intrinsic reward. In fact, most colour vision tests are costly, not durable and require very specific instructions often poorly understood by the paediatric population and parents. The sweets are widely available for approximately £1 on the high street.
Figure 1: (a) Normal colour, (b) as through deuteranope filter and (c) through a protanope filter
Methods
Eight photos were run through the Vischeck tool out of 12 photos in total. The four normal and eight filter images are shown in figures 1 to 4.
Results and discussion
M&Ms and Skittles appear good candidates for this cheap and cost-effective colour vision screening test. The Skittles orange and green appear to be likely confused when run through the protanope and deuteranope simulated defects. The M&Ms red and brown appear most likely to be confused when run through the protanope simulated defect. Photographic lighting conditions were not considered. Future research could be conducted to develop and evaluate both sweets in a paediatric sorting task to screen for colour vision problems involving Skittles or M&Ms.
Figure 2: M&Ms seen in (a) normal colour, (b) as through deuteranope filter and (c) through a protanope filter
Further testing is required to determine the specific wavelength of the sweets to plot them on a confusion line on the CIE chromaticity diagram and verify their batch to batch consistancy.2
Figure 3: Skittles (fruit variety) seen in (a) normal colour, (b) as through deuteranope filter and (c) through a protanope filter
Figure 4: Skittles (fruit variety) seen in (a) normal colour, (b) as through deuteranope filter and (c) through a protanope filter
Also, this test needs to be tested in ophthalmic practice and evaluated against common screening tests such as the Ishihara to determine its sensitivity (in first detecting possible defectives) and specificity (in allowing normal to easily pass). Future data will need to be collected and published.
Michael Mandel and Joshua Mandel are pre-registration optometrists currently based in Canada.
Acknowledgements
Thanks to Dr Sarah Waugh, Dr Monika Formankiewicz and Maryam Mousavi for your help and guidance, and to Anglia Ruskin Universities’ Optometry Class of 2017.
References
1. Simunovic, M. (2009). Colour vision deficiency. Eye, 24(5), pp.747-755
2. Birch, J., 2001. Diagnosis of defective colour vision. 2nd ed. Boston: Butterworth-Heinemann.
3. Lillo, J., Alvaro, L. and Moreira, H. (2014). An experimental method for the assessment of color simulation tools. Journal of Vision, 14(8), pp.1-19.
4. Maule, L. and Featonby, D. (2016). Colour vision deficiency and physics teaching. Physics Education, 51(3), p.035005.
5. Mollon, J. and Cavonius, L. (2012). The Lagerlunda Collision and the Introduction of Color Vision Testing. Survey of Ophthalmology, 57(2), pp.178-194.
6. Association of Optometrists. 2017. Testing Colour Vision. [ONLINE] Available at:
https://www.aop.org.uk/advice-and-support/clinical... [Accessed 29 August 2017].
7. Vischeck.com. (2002). Vischeck: VischeckImage. [online] Available at: http://www.vischeck.com/vischeck/vischeckImage.php [Accessed 1 May 2017].
8. College of Optometrists. 2017-2018. Scheme for Registration Handbook. pp. 76-77