My diagnosis was shortly before I turned three years old, which was a long time ago. I have prosopagnosia and there's just no way I can see a face all at once. If I try to see it in its entirety, the individual features sort of pop in and out. My mind lacks the ability to hold more than a couple of features at one time. There have been times when I've run into trouble at work because I mis-read a coworker's facial expression. However I score approximately average on facial recognition tests. I've put in lots of effort in being able to recognize individual features, like shape of eyebrows, cheekbones, shape of head, shape of hair, distance between eyes, shape of mouth, etc. There is a percentage of people who have very average features, and those folks I have a very hard time recognizing and remembering. In fact I often feel a bit of panic when approached by such a person because I don't know how to respond. I don't think a facial recognition test is valuable for diagnosing autism in adults because many of us learn to compensate for that agnosia.