2 separate scenarios arise for me. At least from what is available in this story.
1) Her exam may have been correct and his problem actually occurred after the visit.
2) His situation had to have worsened between that visit and his death and yet he was never taken to an optometrist by his parents to be reexamined.
The real problem here, at least to me, is socialized medicine, as it promotes eliminating what is so often referred to as "unnecessary" additional exams. Because cost and savings are more important than actual medical care. On top of it the option to sue is eliminated. So not only may you die due to a missed, or even botched, diagnosis, getting compensated monetarily is not an option either. You and your family are just SOL.
The old adage, be careful what you wish for because you just may get your wish, comes to mind.
Socialized Medicine will surely be a disaster for this country. People here really think they will get all the health care they need. But rationing health care is the only current way to lower health care costs. A rude awakening is awaiting all those Americans who think their health care problems will be solved, if we just have single payer.