The optic chiasm is located directly above the sella turcica of the sphenoid bone. Left and right optic nerves then converge at the optic chiasm. Once inside the skull, the optic nerve travels along the floor of the middle cranial fossa, through the medial aspect of the cavernous sinus. The optic nerve travels through the bony orbit and enters the middle cranial fossa through the optic canal, a defect in the lesser wing of the sphenoid. It may be considered an extension of the forebrain as it is covered by the meninges of the central nervous system, rather than by epi/peri/endoneurium like other peripheral nerves. The optic nerve is the second cranial nerve, responsible for transmitting the special sensory information for vision.
The optic nerve then exits the eye, travelling through a defect in the lamina cribrosa of the sclera. The retinal ganglion cells converge at the optic disc, forming the optic nerve. The photoreceptors synapse with retinal bipolar cells, which in turn transmit these signals to retinal ganglion cells. rhodopsin) of these cells are stimulated to propagate second messenger responses which convert light energy into electrical signals. Light-sensitive surface membrane proteins (e.g. The photoreceptors (rods and cones) in the retina are stimulated by photons of light entering the eye. It can be more accurately assessed using perimetry studies. The image of an object in the visual field is inverted upside-down and flipped left-to-right on the retina, as illustrated in figure 1.Ĭonfrontational assessment of the visual field is an important part of the cranial nerve examination. The visual field is the entire area that can be seen by a patient without movement of their head and with their eyes fixed on one point. When discussing vision, it is important to understand the visual field and how it differs from the image presented to the retina. You might also be interested in our Anatomy Flashcard Collection which contains over 2000 anatomy flashcards in addition to advanced features such as spaced repetition.
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