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The headaches associated with typical scintillating scotomas,flashes of light
is due to migraine
and you need to take analgesics for the headache and tab.flunarizine 10 mg at night for one month for its prophylaxis.
About the grey shadow behind the retina, first the lesion has to be identified by retina examination , ultrasound
of the eye and if required CT scan of the orbit
to know if there is any retro-orbital lesion. Once the lesion is identified then only a diagnosis can be made and treatment is started. Cancer of the retina is seen in early childhood and never at your age , hence you need not worry in that aspect.
Your symptoms are more likely due to migraine and will respond to treatment. Since there are aggravating and relieving factors you need to identify them and avoid aggravating factors such as certain food items like sweets, chocalates, certain sounds or visual factors .
To summarize you need to get your eyes tested by an ophthalmologist
to identify the lesion maybe after the required tests and continue treatment of migraine and its prophylaxis.
Thanks and best wishes
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