Until Today I Have Spent The Past 61 Years Blissfully Unaware I Suffered From a condition known as the Troxler Effect,

then I received an e-mail from Jeff in sunny Phuket,

and learnt that I have it, in lay terms Troxler's fading or Troxler's effect is a phenomenon of visual perception, when one fixates a particular point, after about 20 seconds or so, a stimulus away from the fixation point, in peripheral vision, will fade away and disappear, although the example above is not an active one if you want to see if it affects you here is the site to try the test, yet another thing to worry about in my frail dotage!