This is kind of interesting. I can't get much from this abstract, but it looks to be an alternative to intraepidermal testing? (Albeit a bit more daunting since it concerns the eye). Are they saying that SFN affects the cornea? If so that is interesting since my left blink reflex is pretty feeble....well, ok, gone.

http://jnnp.bmj.com/content/81/7/731.short?rss=1

http://jnnp.bmj.com/content/81/7/731.short?rss=1