What parts of the visual system could be responsible for a fixed, monocular scotoma? Light enters the cornea, crosses the lens, hits the retina. Electric sinal travels from retina through the optic nerve, reaches the chiasma, crosses and makes its way to the visual cortex. **My question is: given a fixed, absolute scotoma in one of the eyes, what parts of the vision could be at fault?** Initially, I believe the cornea/lens couldn't be, otherwise the scotoma wouldn't be absolute and fixed. Moreover, I suspect that, after the chiasma, signals from the same visual position are joined, so, the problem couldn't be after it, otherwise the scotoma would be binocular. As such, am I right to conclude that a fixed monocular scotoma could only be caused by issues on either the retina, or on the optic nerve?

Yes. You're right.

A scotoma only affecting one eye (i.e., one that is not perceived when one eye is closed) is diagnostic of a lesion upstream from the optic chiasm.

See Brust's Practice of Neural Science, Fig. 3-2. The figure demonstrates a full cut, with complete blindness in one eye, but the principle is the same for a scotoma.

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