Since Gregg is wearing an eye patch, the ability for depth perception is reduced or even absent significantly. Since Gregg suffered an eye injury, most probably a blowout fracture leading to entrapment of the extraocular muscles as well as enophthalmos with increased intraocular pressure, the optic disc (or the part of the optic nerve bulging to the vitreous) will be pushed more posteriorly leading to an increased cup-disc ratio, making his blind spot more accentuated. Similar symptoms with glaucoma albeit milder.
