Correct identification of a swollen optic nerve requires a combination of a thorough history & symptoms, coupled with a 3D stereoscopic ONH appearance. This lecture will cover the 3 most common ocular pathologies and go through a complete differential diagnosis table of what to look out for and how to tell them apart. The College of Optometrists referral guidelines and how they can be used to guide the practitioner on the correct referral urgency to preserve the vision in both the affected and unaffected eye will also be discussed.