8.1 Brain is an extension of the eyes

(The visual pathway - looking from the base of the brain)

The visual pathway of course travels all the way from the eyes to the back of the brain (see above, in red). Anything untoward that occurs along the pathway will manifest as an ophthalmic problem. And in addition to the second cranial nerve, the extraocular muscles are innervated by the third, 4th and 6th cranial nerves. Plus, the pupillary responses are controlled by yet another set of nervous pathway. Neuro-ophthalmology is indeed a very interesting and challenging field. With very simple tools, such as a penlight, an occluder, a tangent screen and/or perimeter, definitive diagnosis often can be reached. With time, more tools become available. And brain imaging is now consisted of many modalities:

(From socialfiction.org)

These modalities include the old standby CT, the re-vamped PET, the anatomical MRI and the more powerful fMRI (f=functional), and a close relative of fMRI, the Optical Imaging of Intrinsic Signals (OIS). (Note: Cryo is imaging of frozen brain in slices, not for the living.)

Of these, we will go into more about MRI, in order to discuss important subjects such as "perivenous syndrome" and "brain plasticity". And to understand MRI, we will need to start from its humble beginning, NMR. Next post is therefore "8.2 NMR".