I am 37 and I too get blurry vision about 1 to 2 hours after I exercise.
I went to the doctor and he told me he thought it was either dehydration or a drop in sugar perhaps.
I too don't know the limit of when I should stop my exercise either to avoid getting the blurry vision because I do not get overly winded or short of breath. I do sweat excessively when I exercise.
I went to the cardiologist about 1 1/2 years ago and everything appeared to be fine.
I have let it slip though lately and it is happening more often. Next week I am going to an endochronologist (diabetes doctor) to see if its my sugar levels that is causing this.
I get extremely nervous after this happens and suffer from major anxiety from it. Usually I have some sugar (juice, candy, etc.) and it goes away but I don't know.
I will report back when I get results from doctor.