Gradual vision loss is like dusk coming on. Maybe you're sitting outside at the picnic table on a late summer afternoon, talking with a friend, sharing some laughs and a beer. Maybe you've been sitting and chatting for a couple of hours as the sun slowly crosses the sky. You're having a good time, enjoying each other's company, you're barely registering the passing of time or the diminishing of the light. Then one of you says, "Hey, it's getting dark," and suddenly it is.