The UK has always operated a system where you get tested only at your initial medical, and that test, if passed, is valid for life.
You get a choice of several methods. Initially the Isihara plates (which is a bad test and many CV-good people fail it), and then the Lantern test which comes in several versions. Then some others… and this can get very expensive.
You are permitted to fail each of these tests only once per life, so if you fail Isihara, you cannot ever re-take Isihara, anywhere in the world. You have to pass one of the others. In the JAA days, Hungary used to offer a concession whereby a fail was not recorded so you could have another go. Accordingly, large numbers of pilots went down that route. Most people are not “colourblind”; most just fail to distinguish a couple of colours, and a second go usually works 
However, some countries in Europe reportedly CV test at each medical. For those who fail Isihara, this could cost quite a lot.
I was originally told the “once per life” process was ICAO but now cannot find a reference to it. Since then I’ve been told it was an agreement between the CAA and airline pilot unions…
Does anyone know where this comes from?
The FAA also tests CV only once.
Very obviously there is no ICAO regulation on medical fitness that even comes close to the level of granularity to describe how often a CV test has to be performed.
AMC of part MED are quite clear on validity of the tests: Generally CV tests are only required for initial issue of medical, but “At revalidation, colour vision should be tested on clinical indication.”
So generally there is no need to do a CV test at every revalidation, but if there is a medical reason to believe that your color vision might have changed, it has to be done.
AFAIK the test only test red/blue colorblindness. My family always teases me about blue/green. Next to each other I can see the difference, no problems, but a surface of blue or green all by itself in normal room light, I have no clue if it’s blue or green It’s very weird these colors, and highly dependent on the light source.
I’ve found recurring colour vision tests for FAA medicals to be dependent on the AME…some do, most don’t. My last one (which was with a new AME, in England) didn’t. The ones I had in the US (each time with a new AME) did.
Can you even lose CV after you had it for the first part of your life? I mean in a way that doesn’t require consultation with an AME anyway, like when you smack really hard?
I’ve found recurring colour vision tests for FAA medicals to be dependent on the AME…some do, most don’t. My last one (which was with a new AME, in England) didn’t. The ones I had in the US (each time with a new AME) did.
That’s prob99 because you already have a UK PPL and the pass letter from that.
Can you even lose CV after you had it for the first part of your life?
Apparently it is very rare to see a decline, at least until you get into your 70s.
Peter wrote:
I was originally told the “once per life” process was ICAO but now cannot find a reference to it. Since then I’ve been told it was an agreement between the CAA and airline pilot unions…Does anyone know where this comes from?
There is no mention of such a restriction in part-MED. Also not in ICAO Annex 1, nor in ICAO Doc. 8984, “Manual of Civil Aviation Medicine”. For the Ishihara plates the wording could possibly be taken to imply that only one test is ever permitted, but it is not explicitly stated.
It might either have been an old rule, now abandoned, or just something that “everyone knows” even though it is incorrect.
I recently had to go to a new AME in the US and – to my surprise – he did the Ishihara. Let’s see if he does it again next time.
PS: to add, this was my first new AME in almost 20 years.
LeSving wrote:
My family always teases me about blue/green. Next to each other I can see the difference, no problems, but a surface of blue or green all by itself in normal room light, I have no clue if it’s blue or green
This has nothing to do with colorblindness. If you can differentiate two colors that are next to each other everything is fine.
The similarity between green and blue is more a cultural and a psychological one – different people have different mental models of the colors blue and green and therefor refer to the same color with a different verbal identification.
This goes as far as the Ancient Greek not even having a word in their language to differentiate between blue and green. Same with many ancient languages with the notable exception of the ancient Egypt who were some of the few early cultures who had synthetic blue colors. I’ve heard that in Japanese as of today there is no verbal differentiation between blue and green.
That doesn’t mean that all of these people do not see a difference, but they simply have other names (like “dark green” or “sea green”) that describe shades of green.
In English the blue spruce (also known as green spruce) is a good example that people have different perceptions of green and blue
