Hi. I have seen similar questions but they do not seem to apply specifically to my case. I am 60 years old and I get pretty good exercise (bicycling on mostly paved trails and cardio workouts at a gym.) Whenever I push myself on the bicycle on especially hot days (as in a two-hour ride (mostly level) of about 15 miles in temps of 80-95 degrees) I experience a constant very bright vision for an hour or more after the exercise. I keep fairly hydrated (drink about 2 quarts of water during the ride - average speed of 9-14 mph when actually pedaling) and when the bright vision occurs, it is so severe that I will not drive because I do not see things well enough to feel safe. Sunglasses help but not enough. My vision starts to return to normal after about 30 minutes and after I drink another quart of water. It is usually back to normal after an hour. When this happens I am usually more fatigued than I am after a more sedate ride or a ride on a cooler day. I m just wondering if this is normal or dangerous - this will not happen after a gym workout except when I push myself a lot more than I normally do AND when it is hot. I happens about twice a month during the summer. THANK YOU for any info! Mike