Testing colour vision

What does a colour vision test involve?
20 February 2020

Interview with 

Sonam Ruparelia, Anglia Ruskin University




Optometrist and colour vision PhD student Sonam Ruparelia from Anglia Ruskin University’s eye clinic put Katie Haylor's cones under the metaphorical microscope with a colour vision test...

Sonam - We're in our colour vision lab actually in the eye clinic, so we carry out a range of colour vision tests in here. Particularly useful for those who want to get occupational colour vision screening checks done and if someone has been identified to have a colour vision deficiency, then we can test for the extent of it here as well.

Katie - Turns out not everyone actually has red, green and blue cones.

Sonam - And that's where we tend to have more severe colour vision deficiencies. So some people have two and others can only detect greyscale vision. For those who do have two cone cells, they can detect still a range of colours, but it tends to be varied compared to someone with normal colour vision. There is definitely a higher prevalence in male across the board from the studies that have been carried out. Colour vision deficiency is a recessive condition because males have an X chromosome and a Y chromosome. If that congenital deficiency is lying on the X chromosome, they are likely to have the condition. With females because they have two X chromosomes, there is the possibility that because it's a recessive condition, they may be able to get away with not having anything, if that chromosome doesn't fall on both Xs.

Katie - How are you going to test my vision?

Sonam - So if you went for an eye test at an opticians, chances are they may carry out an Ishihara test. So that's what we'll be using today. And what that test involves is looking at numbers of a specific colour on a different coloured background.

Katie - Okay. She says slightly nervously. Let's do it.

Sonam - Okay. So what we're going to use is an Ishihara book, and we're going to have good lighting, and we're going to take a look at the pages and see what we can see. If I show you the first page, take a look at that and just tell me what number you can see.

Katie - It looks like an orange 12 on a bluey greeny bubble background.

Sonam - Excellent. So this one is particularly good when we're testing children as well because this is what we call a demonstration plate. We expect everyone to be able to see this regardless of whether they have normal colour vision or not.

Katie - Okay. So you're just testing me.

Sonam - That's right. Yes. Particularly good for children. Um, especially if they want to be wearing spectacles. They like saying all sorts.

Katie - I see. Wow. So you're a fib detector as well as an optician!

Sonam - We try! What number can you see on there?

Katie - It looks like to me an eight, pink and orange on a bubbly green background.

Sonam - Perfect. And then we move on to the next page.

Katie - Same colours. Looks like a 29.

Sonam - Very good. So someone with abnormal colour vision may see a different number on this background compared to what someone with normal colour vision would see.

Sonam - Has that got anything to do with the more bluey bubbles I can see around the 2 and around the 9?

Sonam - That's right, yes. So they would be unable to see that red very well. They would detect that green a little bit more. So if you wanted to look at that one.

Katie - So this to me looks like a 5 in a bluey green hue on an orange bubble background and then the page next to it, I think a 3 in the same colour tones.

Sonam - Excellent. Yes, that's exactly what it is. And if we were to carry on through those, particularly for very young children who struggle with this kind of test, we do have similar combinations but with patterns for them to trace instead. And likewise, if I show you this one here: so if I told you that there was a squiggle on this background, this multitude background of colours, would you be able to agree with me?

Katie - Honestly, I'm finding it really difficult. I don't think there's a pattern there. I can't see anything.

Sonam - So someone with abnormal colour vision would be able to see something here. It's not just designed to catch you out with everything you find difficult. The idea is also to be able to see things as well because there's always a motivation factor in being able to see something. So these are slightly different again, so we have a sort of black gray background and we have two different numbers and different colours on them. Take a look at that plate there. What number would you be able to see?

Katie - To me it looks like a red 2. And then a pink 6. So 26 on a grey background.

Sonam - Absolutely. And for someone with a specific type of colour vision deficiency, whether it's red that they struggle with, whether it's green that they struggle with, they may only see one of those two digits on there rather than both digits.

Sonam - For us, we can see them equally. They're both just as easy to see. For someone with a deficiency, they may be able to only just see the 6 and not really see the 2 very well at all. So there'd be a distinctive struggle with being able to see it.

Katie - So what's going on there? I imagine there's quite a few different types of colour vision deficiency, but in this example, what would your diagnosis be? What is the problem?

Sonam - So this patient would have definitely a congenital colour vision deficiency, whether that's red or green. The idea is that they go through all four plates of this background that we have. And using that scaling, we would then be able to determine whether it's likely to be a red deficiency or likely to be a green deficiency.

Katie - Whilst informative, Sonam told me that the Ishihara test isn't really the gold standard. So if an optometrist suspects you might have less than perfect colour vision, they might send you for further tests. And speaking of tests...

Sonam - You have very normal colour vision!

Katie - Okay, that's a relief! Having said that, would I necessarily know if I had a problem with my colour vision?

Sonam - It may not be necessarily that you're aware of a deficiency unless you come across a particular scenario where you find yourself struggling. Um, a lot of times people can get through life and not be aware until they hit that point in life where suddenly they've realised, actually I'm really struggling with this task. And it can be simple things like being able to cook meat or looking at fresh fruit from raw fruit, not being able to take those colours. So it can be general daily life activities which we take for granted.

Katie - Can you not get colour vision problems throughout life? Do you have to be born with say two cones and not three?

Sonam - The type of deficiency you're likely to get that's acquired or obtained through life is generally a blue-yellow type of deficiency. There are some conditions where commonly known as the red-green deficiency can be obtained through ocular disease. So if something goes wrong at the back of the eye, but even then the blue-yellow type is more likely to occur: that one's the one that occurs if things are going wrong at the back of the eyes.

Katie - Does it tend to be associated with age?

Sonam - A lot of the time, yes. So things like macular degeneration are more commonly occurring when someone gets older. Likewise with things like cataracts, also an age related process, there can be other systemic conditions as well. So things like diabetes. If there's diabetic retinopathy, so bleeding at the back of the eyes, then that's likely to cause shifts in colour vision as well.

Katie - So in that situation you've got a chronic condition which may have a consequence for your vision. Is it ever the case that changes in colour vision could actually be symptomatic of a bigger problem further up in the visual system?

Sonam - Yes. At times it can indicate that there is something else going on. So earlier we mentioned that red-green colour vision deficiencies are congenital, that people are born with them. However, there are some conditions which can have an effect on the red-green deficiency, which are acquired and that's incredibly rare but it can be life threatening at the point where it can indicate high pressure in the brain for example, and that sort of condition would be a sudden difficulty in being able to discriminate the colour red compared to having never had that problem before.

Sonam - When someone does have a congenital colour vision deficiency, we can't do very much about that condition itself to get rid of it. The most we can do in terms of recommendations is having more of an awareness of the condition. Particularly for children. If a parent is advised that their child has a deficiency, then that parent can take responsibility in how they guide their child's education towards specific career goals. There are some occupations where a child would not be able to take part in once they reached that age simply because they have abnormal colour vision. Pilots, train conductors, firefighters: that field of work does require very specific colour vision because it can have an impact on that person's life and other people's lives as well.

Katie - Is there any evidence to suggest that having colour vision difficulty has an impact on your education?

Sonam - Well, this is what we're looking into at the moment. Accounts previously have suggested that people with a colour vision deficiency have struggled with tasks and activities, such as titrations when doing GCSE chemistry or looking at litmus paper for example. So those sorts of tasks which rely on the use of colour have been suggested as being a difficulty.

Katie - I notice you haven't used the phrase colour blindness.

Sonam - Colour blindness is actually a complete inability to see colours at all. Someone with a colour vision deficiency will have a shift in the colours that they can see. There'll be a restricted number of colours that they will be able to detect. Colour blindness would imply complete grey scale vision.

Katie - From what you said, there's actually not a lot that can be done for somebody who does have difficulties. What would someone like yourself suggest they do? Is it a case of lifestyle adaptation? Can you do anything to help?

Sonam - It can be more simple things like labelling. When we go to a grocery store, if we're choosing apples, we look at red apples, we look at green apples. There can be some confusion for someone with a colour vision deficiency, so whether it's having more of a description on just what it is that the person would like to purchase or if someone is using crayons or colouring pencils. Having the name of that colour written down as well can make things a little easier. Raising awareness and trying to improve accessibility is is the way forward.

Katie - Do you have any general tips for looking after our colour vision?

Sonam - With any eye related reasons, it's to have regular eye tests. A lot of the times some of the acquired deficiencies can occur because of medication that you have been advised to take. So it's always worth reading all, all the health and safety at the back of that instructions box or in the little leaflet inside. And likewise when you go in for your eye tests as well, let your optometrist know what medication you are taking. There are some medications that we almost have red flags for where we can double check colour vision a lot more and keep a closer eye on things. So whether that means more regular eye tests compared to just a routine two year checkup. That way if there is something that is cropping up, we can keep an eye on it. Or if we need to refer back to the general practitioner in regards to potentially discussing the medication. 


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