Are you using wrap-around sunglasses? These stop harmful rays getting in through the side of the eyeball and should be worn both inside the aircraft and outside. Is the flightdeck warmer during daylight flights or do you feel warmer from the direct action of the sun? If so, you may be mildly dehydrated so try increasing your fluid intake. You have already said that you will mention it to your AME and that is the most sensible idea. An eye test wouldn't go amiss either.