Strokes
Strokes can affect vision in a number of ways, including decreased vision and double vision:
Decreased vision is caused by damage to the fibers that transmit visual information from the eyes to the brain. This can occur in a variety of locations, since the nerve fibers that transmit vision have a long course from the eyes to the rearmost part of the brain, called the occipital lobe.
Double vision is caused by damage to nerves responsible for moving the eyes and ensuring that both eyes are aligned (i.e. looking at the same place).
After the optic nerve exits the eyeball from the back of each eye, it travels a short distance before the nasal fibers (the optic nerve fibers on the side of the eye closer to the nose) from each eye cross over to the opposite side (make an "X") as they continue traveling toward the brain. Here is what happens in the eye and brain when we look at an object:
In the right eye, the nasal fibers (shown in orange in the diagram above), which see the far right part of the visual field, cross over to the left side of the brain, while the temporal fibers (those on the side of the eye closer to the temple) which see the far left part of the visual field, do not cross over (in purple).
In the left eye, the nasal fibers (in purple), which see the far left part of the visual field, cross over to the right side of the brain, while the temporal fibers (those on the side of the eye closer to the temple) which see the far right part of the visual field, do not cross over (in orange). Therefore a stroke, lesion, or injury at the point where the nasal fibers from each eye cross (where the fibers make an "X", called the optic chiasm), would cause loss of the right visual field in the right eye and loss of the left visual field in the left eye.
Scleritis is Scleral inflammation may occur in one or both eyes.
Pain is the hallmark symptom and signs of scleritis include focal or diffuse redness or violaceous discoloration, initial scleral thickening, late scleral thinning, nodules, and necrosis. It may be associated with keratitis, iritis, glaucoma, and exudative retinal detachment.
Scleritis commonly has an underlying cause, usually an autoimmune disease (rheumatoid arthritis, granulomatosis with polyangiitis, other vasculitic/connective tissue diseases).
Treatment include corticosteroids, nonsteroidal anti-inflammatory drugs (NSAIDs),immunosuppressives, and biologics.
Sudden loss of vision
Some patients describe their symptoms as a gradually descending gray-black curtain or as blurring, fogging, or dimming of vision. Symptoms usually last a few minutes but can persist for hours. Variation in frequency ranges from a single episode to many episodes per day; recurrences may continue for years but more frequently occur over seconds to hours.
Many different causes of sudden visual loss are recognized; however, the most common reason for painless sudden visual loss is ischemia. Vision loss with positive scotoma may be seen with migraine. Vision loss with a negative scotoma may be seen with amaurosisfugax.
Other etiologies of sudden visual loss include infection/inflammation, vasculitis, trauma, mechanical dysfunction, and idiopathic causes