There is an overview post which gives background and overview information, including my experiences with the NHS while trying to get my condition diagnosed. It can be found here.
About 6 months ago, I went to bed feeling perfectly normal, but woke up the following morning with my vision about 10-15% dimmer. This was a permanent change, and I did not see any improvement back to previous brightness levels.
There was some tiredness associated with this, but no other mental incapacity took place.
About every 1-2 weeks my brightness drops by probably 1-2% or so, from which there is no recovery, and over 6 months these drops have really started to add up.
I went through a milder version of this a few years ago, and in that case it just burnt itself out after a few months, resulting in my brightness levels stabilising even though they never recovered back to pre-illness levels. The cause was never diagnosed then either, and after the consultants refused to escalate it, I let it drop because it wasn't impacting my life at that time.
This time however, the intensity of this illness is much more severe and this stabilisation has not yet occurred.
My visual acuity has not really changed during this time, a fact which has been confirmed with a couple of optician eye tests.
This is a painless illness and in particular, there is no pain along the optic nerve.
I have noticed however when looking at, for example, faces on a LCD monitor or CRT television, that they appear somewhat washed out with fine detail lost in a uniform white, a problem which has got worse as the illness has progressed. However, I do not see this when looking at faces in the real world.
I am generally in excellent health apart from this vision problem.
Tests carried out
The following tests have been carried out:
Standard blood tests are fully normal, apart from a lower than normal, but stable, platelet count.
A brain MRI was normal.
Visual evoked potentials and a ERG were both normal.
Eye pressures are normal.
Unchanged visual acuity has been confirmed by standard optician eye tests.
Some auto-antibodies have been tested for as part of the low platelet condition and so far the results have been negative.
A dilated examination of the eyes did not reveal anything.
I score perfectly on colour blindness tests.
 I suspect what is tested for in a standard blood test may vary by country, so I am talking about the tests which the NHS carry out as part of it's standard blood tests.