Calibrate my eyes, perhaps?
In sunny climes, every aspect of my eyesight seems to improve; sharpness, clarity, colour, the sheer possibilities of seeing things clearly
...
However, then, whenever I return to the overcast, bleak, charcoal skies of the British Isles, I am convinced that my eyesight has deteriorated dramatically.
Once, standing outside the airport, having just arrived back from a Sunny Somewhere Else, I recall being surprised (when I checked) that my glasses were still on my nose, as my pervasive sense of light deprivation, and lack of visual clarity made it seem that the abrupt deterioration in my vision could only have been cause by my inadvertently having removed my spectacles.
And what is a 'GATF' indicator?