Optic pathways and visual fields

When light enters the eye, it hits a light sensitive neural layer of tissue near the back of the eye called the retina.

That’s where phototransduction occurs, which is the process by which light waves are converted into electrical signals.

Afterwards, these electrical signals are sent to the brain for visual processing.

So, let’s start by taking a look at the optic pathway and understanding visual fields.

You can think of a visual field as everything that can be seen with a single eye, so we have a left visual field for the left eye, and a right visual field for the right eye.

These visual fields overlap and produce a binocular visual field, but for now, let’s just look at the left visual field.

The left visual field can be divided into two halves.

The half that’s closer to your nose is the nasal visual field, and the half that’s closer to your ear is the temporal visual field.

Similarly, the retina in each eye has a nasal and temporal region as well.

When light enters the eye, the temporal field of vision is projected to the opposite side, onto the medial nasal retina, and the nasal field of vision gets projected to the opposite side, onto the lateral temporal retina.

The visual fields are further divided into the superior and inferior visual fields, so the visual fields are actually divided into quadrants.

The superior visual field projects to the inferior retina, and the inferior visual field projects to the superior retina.

So, the visual information that appears in the right upper quadrant is actually project to the left lower retina.

When light hits the retina it triggers visual receptor cells in the retina, called rods and cones, to send an electrical signal.

The rods and cones synapse with bipolar cells which in turn synapse with ganglion cells.

These ganglion cells have long axons that travel through the retina layer to the back of the eye where they come together to form a single optic nerve, or cranial nerve II, that exits the retina from the optic disc.

This area in the retina where the optic nerve exits doesn’t have any receptor cells, so it’s also called the blind spot.