macula

Meaning: In vision, the macula is a small, yellowish area near the center of the retina. Its middle, the fovea, has the densest packing of cones and few or no rods, so light from whatever you look at directly lands here and is seen with high acuity and color. Rods are more numerous in the periphery, which suits dim light and detecting motion.

In the vestibular system, a macula is a patch of hair cells in the utricle or saccule. The hair cells project into a gelatinous layer weighted with otoliths (calcium carbonate crystals). When the head tilts or accelerates in a straight line, the layer shifts, bends the hair cells, and changes the signal sent to the brain.

On the MCAT: Expect questions on where acuity is highest (fovea, within the macula), which photoreceptor dominates there, or why damage to the central retina causes loss of central vision while peripheral vision is relatively spared. Vestibular questions ask which structure senses linear acceleration and which senses rotation.

Common confusion: The macula is not the blind spot. The blind spot is the optic disc, where the optic nerve leaves the eye and no photoreceptors are present. In the ear, the maculae detect linear acceleration and head position relative to gravity, while the semicircular canals detect rotation.