Steven Heller, 70, has lived with Parkinson’s for more than 10 years. Véronique Vienne, 79, only recently learned that she had the disease. Both have had long careers as art directors, and the two have been friends for more than three decades. Back in March, the pair exchanged a flurry of emails over a 10-day period, where they explored the “before” and “after” of a Parkinson’s diagnosis.