( CNN ) -- Tod Purvis and his brother Justin knew that they were going blind . Both had been diagnosed with choroideremia , a rare genetic disorder that causes progressive vision loss and eventually leads to complete blindness . So six years ago , the brothers went on a road trip across the United States . A documentary about their journey , `` Driving Blind , '' was released this year after winning awards at independent film festivals in 2013 . On the documentary 's website , the filmmakers had this to say : . `` We started filming under the impression that Tod and Justin had at least half of their eyesight left . It is revealed at the end that their eyesight was much much worse , and in truth the trip or film would have never happened had we knew they would in fact be driving blind . Justin was declared legally blind at the conclusion of the trip . '' Child goes on 'bucket list ' trip before he goes blind . Tod Purvis took to the Internet community Reddit on Sunday to conduct an AMA ( Ask Me Anything ) about their trip , the documentary and choroideremia . The most beautiful place they visited ? Devil 's Tower in Wyoming , Purvis said . The second ? Glacier Park in Montana . `` We took the trip to put the memories in our brain where we could always call them up even if we completely lost our sight , '' Purvis posted . Choroideremia affects approximately 1 in every 50,000 people , according to the Choroideremia Research Foundation . It primarily occurs in males and starts in early childhood . It is caused by a gene mutation and is passed on to children via the X chromosome , according to the National Institutes of Health . `` Without the protein produced by the CHM gene , pigment cells in the retina of the eye slowly stop working , then die off , '' according to NLO , a center for eye research at the University of Oxford . `` As the disease progresses , the surviving retina gradually shrinks in size , reducing vision . '' Purvis said that his sight is down to about 50 % but had difficulty describing what losing it was like to Reddit users . `` It 's hard to describe nothing . It 's not black , it 's like if you were looking through a tunnel , and the walls of the tunnel were made of mirrors and it reflected what was at the end of the tunnel . '' Purvis wrapped up the AMA after more than 600 comments , never wavering from the documentary 's main message : . `` No matter what your situation ... live your life to the fullest . ''
Brothers diagnosed with choroideremia knew they were going blind . Comment: Their documentary , `` Driving Blind , '' was released this year .