L'migraine is the third most common disease in the worldwith an overall prevalence of 14.7%. In one third of patients, migraine is preceded by focal neurological disorderstypically visual, which are defined "migraine aura".
Migraine is considered, visually, a risk factor for ischaemic complications that may affect the retina and optic nerve; and is indicated as a risk factor for the diagnosis and progression of normal pressure glaucoma. I ophthalmic disorders associated with migraine with aura (migrain aura - MA), and to a lesser extent migraine without aura (migrain without aura - MO), include retinal artery and central vein occlusions, and venous occlusions; as well as the optic neuropathy ischaemic anterior and posterior. The disorders listed above have been reported both during and between acute migraine attacks, which leads to the hypothesis that migraine patients experience ocular perfusion changes, both acute and chronic which would lead to the aforementioned ocular complications.
The pathophysiology of ocular migraines is not completely known, but it is conceivable that a complex interaction between neurological and vascular factors underlies them.
La ocular vascularisation of migraine patients has been little researched, but the recent development of angiographic optical coherence tomography (OCTA), which allows visualisation of the retinal circulation using the intrinsic motion of blood cells, has enabled further research in this field.
A study recently published in Investigative Ophthalmology & Visual Science analysed, through OCTA, the macula and optic nerve vascularisation in patients with migraine with and without auraand compared the results obtained with healthy controls. The work showed that in the eyes of individuals with AD there was an enlargement of the foveal avascular zone and one decreased vessel density in the superficial fovea and upper peripapillary region. These results could explain the increased risk of ocular complicationssuch as retinal vascular occlusion, ischaemic optic neuropathy and glaucoma at normal pressure in some patients with migraine. The authors conclude by emphasising the need for further studies to establish whether OCTA findings in patients with AD correlate with a possible increased risk of ocular and systemic vascular events.
An ocular manifestation common to many patients with severe ocular migraines and neuro-ophthalmic disorders is the photophobiadefined as an 'abnormal sensitivity to light'. The International Classification of Headache Disorders considers photophobia one of the Main symptoms associated with ocular migrainesand its association with migraine is believed to derive from by activation of the trigeminal nerve which innervates the dura, skull, face and eye and is also the afferent for the ocular disorder associated with dry eye.
In diseases such as dry eye and diabetic neuropathy, the subbasal corneal nerve plexus (SBNP) has been extensively studied and quantitatively analysed using in vivo confocal microscopy (IVCM). The nerves that make up the SBNP derive from the nasociliary branch of the ophthalmic division of the trigeminal nerve, and its axons synapse in the brainstem where they perform nociceptive, protective and trophic functions.
The study on ocular migraines and photophobia
A recent study published in Cornea hypothesised that alterations in the subbasal corneal nerve plexus could accelerate or contribute to photophobia and other ocular symptoms of migraine. To this end, the study determined and quantified the structural differences in the SBNP of chronic migraine patients with and without photophobiacompared to a healthy control group, and correlated changes in SBNP with ocular pain and photophobia. The study showed, in patients with migraine associated with photophobiaa significant reduction in corneal nerve fibre length (CNFL), corneal total nerve fibre area (CNFA), corneal total branch density (CTBD) and corneal nerve branch density (CNBD). The authors conclude that structural changes in nociceptive corneal axons of SBNP in patients with migraine and photophobia further support the hypothesis that the trigeminal system plays a key role in the pathogenesis of ocular symptoms in migraine.
Although there is still much to be clarified about the correlation between migraine and the visual system, visual and ophthalmological disorders are commonly reported by migraine patients. Structural, functional and metabolic abnormalities of the visual system can be at the root of a migraine attack, which is why the ophthalmologist plays a key role not only in the differential diagnosis but also in establishing the extent to which the visual apparatus is involved.
Bibliography
-Chang MY, Phasukkijwatana N, Garrity S, et al. Foveal and peripapillary vascular decrement in migraine with aura demonstrated by optical coherence tomography angiography. Invest Ophthalmol Vis Sci. 2017.
-Shetty R, Deshmukh R, Shroff R, Dedhiya C, Jayadev C. Subbasal Nerve Plexus Changes in Chronic Migraine. Cornea. 2017 Oct 5.
Dr. Carmelo Chines
Direttore responsabile
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