Someone above you draws the line. This is because they have more knowledge on the subject than you. You're right, small haloes may not impair vision, but the docs still want to know if you have them. This is all part of the study. Same with allergies, they're rarely a problem at all, and usually won't NPQ a person, but its still wrong to deny them. There are reasons that they ask every question, whether it may be a disqualifying condition or something to give them a better overall picture of your health. Bottom line- it's not your call to make. They ask, you answer honestly.