Sir,
Your father seems to be having Migraine headache. Visibility issues like seeing multiple images, sparks, flashes is very common in Migraine.
I suggest him to take Homeopathic treatment.
To start Homeopathic treatment we need complete history of him.
You can consult a nearby homeopath or me online here in Jayanagar Bangalore.
Next Steps
Hope he recovers soon.
Health Tips
He can take Homeopathic along with existing medication. Safe and non-addictive.