People with RPON experience different severity of pain, duration of symptoms, and frequency of attacks, which are also dependent on the treatment they received. The attacks of RPON usually occur on the same side of the head in subsequent episodes. Headache
The most common type of headache is migraine-like, usually accompanied by symptoms such as nausea, vomiting, photophobia, or phonophobia. Less commonly, RPON can occur without migrainous headache nor accompanied by the classical migrainous symptoms. The frequency of headaches can range from several times per month to once in several years, while the duration varies from several days to a week, which lasts longer than that of a typical migraine. Ophthalmoplegia
Ophthalmoplegia usually occurs either concurrently or within 1 week after the onset of headache, and less commonly up to 2 weeks. The ocular manifestation of RPON depend on which ocular cranial nerve is being affected. CNIII is involved in the vast majority of cases, but the involvement of CNVI and CNIV is also reported in studies. Typical ocular signs involving CNIII include outwards and downwards drifting of eyes (strabismus), difficulty in controlling inward and upward eye movements, drooping of eyelid (ptosis) and double vision. Pupil dilation (mydriasis) and reduction in pupillary light reflexes can also be observed as pupillomotor fibers are also affected by CNIII paralysis. Rare cases involve abducens nerve paralysis affects lateral eye movement while trochlear nerve paralysis affects vertical eye movement. Similar to headache, ophthalmoplegia usually resolve gradually and completely over time, but recovery may be incomplete after several episodes.
Pathophysiology
The etiology of RPON is still unknown and remains controversial - some scientists believe that RPON is a subtype of migraine, while others believe that it is a neuropathic disorder. As such, different potential etiologic mechanisms have been proposed based on case reports, including migrainous and neuropathic mechanisms. Yet, the renaming of RPON from OM indicates that the neuropathic cause may play a more important role than the migrainous cause in the pathophysiology of RPON. Migrainous mechanism
RPON was previously thought to be having a migrainous origin since it shares some common characteristics with migraine, and their only differences are the intensity and duration of headaches. Therefore, it was postulated that migraine caused ophthalmoplegia in RPON. However, the major argument against a migrainous origin is the long latency period between the onset of headache and ophthalmoplegia (up to 14 days), which is not consistent with a typical migraine. Nevertheless, several migrainous mechanisms have been proposed. Nerve compression
Compression mechanism is the first theory postulated regarding the pathophysiology of RPON. It is proposed that headache is caused by direct pressure on CNIII (compression neuropathy) within the cavernous sinus due to edema of the walls of the internal carotid artery (ICA) or posterior cerebral artery (PCA) during migraine episodes. Ischemia
Cavernous section of the ICA and a perforating vessel from the proximal PCA are responsible for supplying CNIII, CNIV, and CNVI. During migraine attacks, vasoconstriction of the ICA and PCA may lead to a reversible and ischemic breakdown of the blood-brain barrier.