blind spot
Summary
The blind spot is the optic disc, where the optic nerve leaves the retina. It has no rods or cones, so light falling on it is not detected. We usually do not notice it because the other eye covers the gap and the brain fills in the missing area.
Detail
Meaning: The blind spot is the optic disc, the patch of retina where retinal ganglion cell axons gather and leave the eye as the optic nerve and where blood vessels pass through. It has no rods or cones, so light striking it produces no signal. It lies on the nasal side of the fovea in each eye, so it corresponds to a point in the temporal visual field.
On the MCAT: A common setup is a demonstration in which you close one eye, fixate on a cross, and move a dot until it disappears. The usual question is why people do not notice the gap in everyday vision. Two accounts work together: the two eyes' blind spots fall on different parts of the visual field, so the other eye covers the gap in binocular viewing, and the brain fills in the missing region from the surrounding scene (perceptual filling-in).
Common confusion: Students mix it up with the fovea. The fovea is packed with cones and gives the sharpest acuity, while the blind spot has no photoreceptors at all. The blind spot is also a normal feature of a healthy retina, not damage or a sign of dead photoreceptors.
Sources
- Psychology (Myers)
- Sensation and Perception (Wolfe et al.)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.