Inferior homonymous quadrantanopia

Loss of the lower quarter of the visual field on the same side in both eyes, nicknamed ‘pie on the floor’.

After a complete lesion of the right parietal optic radiation: left inferior homonymous quadrantanopia. Fields as the patient sees them, central 30° with rings at 10° and 20°. Hatched areas are lost, and the dark ovals are the normal blind spots.

Lesion site: Optic radiation, parietal lobe
Left eye loses: Lower temporal quadrant, 25% of the plotted field
Right eye loses: Lower nasal quadrant, 25% of the plotted field
Pattern: Homonymous: the same half in both eyes, so the lesion is behind the chiasm
Lost to both eyes at once: 25% of the central 30°
Fibers cut: 2 of the 8 fiber groups the model draws

Try in: Visual Field Defects Explorer →

Put the lesion on the right parietal radiation to see the two upper-retina fibers cut.

Which lesion causes an inferior quadrantanopia?

A lesion of the optic radiation in the parietal lobe on the opposite side. Fibers from the upper half of each retina, which see the lower field, run back through the parietal lobe toward the occipital cortex, so cutting them takes the lower quarter of the opposite half of the field from both eyes.

Why the lower quarter

The lens turns the image over, so the upper retina sees the lower field. Its fibers leave the lateral geniculate nucleus and run back more directly than the lower retina’s, through the parietal lobe instead of looping forward into the temporal lobe, and they end on the upper bank of the calcarine sulcus, the cuneus, where the lower field is mapped.

The fiber groups cut by a complete lesion of the right parietal optic radiation
Fibers from	See	Cross at the chiasm	Then run in
Left eye, nasal retina, upper half	Lower temporal quarter	Yes	Right optic tract, then the parietal radiation
Right eye, temporal retina, upper half	Lower nasal quarter	No	Right optic tract, then the parietal radiation

2 of the 8 fiber groups the model draws are cut; the other 6 reach the cortex.

Usual causes

Strokes in the territory of the middle cerebral artery, and tumors. A larger parietal lesion that reaches the whole radiation gives a complete homonymous hemianopia.

Telling it apart

A lesion of Meyer’s loop in the temporal lobe takes the upper quarter instead, the superior quadrantanopia or ‘pie in the sky’. Both are named for the side of the field that is lost, so a right parietal lesion gives a left inferior quadrantanopia, and both leave the pupil reactions normal, since the pupil fibers have already left for the midbrain.

Left-sided and right-sided lesions

The same site on the other side gives the mirror image, named for the half of the field it takes.

The defect from a complete lesion at this site on each side
Lesion	Defect	Left eye loses	Right eye loses
Left parietal optic radiation	Right inferior homonymous quadrantanopia	lower nasal quadrant	lower temporal quadrant
Right parietal optic radiation	Left inferior homonymous quadrantanopia	lower temporal quadrant	lower nasal quadrant

Tools for the visual pathway

Visualiser · Biology Visual Field Defects Explorer Place a lesion anywhere from optic nerve to visual cortex and see each eye’s field loss, named and explained. Visualiser · Biology Blind Spot Mapper Watch a dot vanish, as Mariotte’s paper did in 1668, then map your own blind spot in degrees and see it as the optic disc on the retina. Visualiser · Biology Brain Explorer 101 brain structures, gyri to ventricles, separable.

Visual Field Defects Explorer puts a lesion anywhere on the pathway and draws every fiber it cuts.
Blind Spot Mapper maps your own blind spot, the dark oval in each chart, in degrees.
Brain Explorer has the optic nerves, chiasm, tracts and geniculate bodies as 3D models.

Sources: Kandel, Principles of Neural Science, 6th edition, chapter 22, for the pathway and its lesions; Purves, Neuroscience, 6th edition, chapter 12, for the pathway and its lesions; Kupfer, Chumbley and Downer, Journal of Anatomy 1967;101:393, for the 53 percent of optic nerve fibers that cross at the chiasm. A teaching diagram of complete lesions: real fields are read with the history, the other eye, the optic discs and imaging.