Jerry Jackson and his family
08/31/2014 AT 04:00 PM EDT
Jerry Jackson will never forget the last time he glimpsed his granddaughter.
She was not yet 2 when a ray of sunlight came through Jackson's farmhouse kitchen and hit the little girl's face, illuminating it for several seconds before blackness descended on him once again.
Jackson holds this and other recollections in his mind like an endlessly repeating home-movie loop.
"I remember what sunflowers look like, the rolling hills, the color of the sky and the trees," says the 68-year-old, blind for nearly four decades.
"I feel lucky for that. But I miss not seeing my kids and grandkids."
Those grandchildren are the youthful faces of an Iowa clan that has faced bad genetic luck with astonishing grit and resilience.
As a result of a rare disorder only recently identified
, 84 living and deceased members of the Jackson family have gone or are going blind.