11/04/2025
Schematic of The Visual Pathway displaying VF Loss at Different Stages:
◾Relative afferent pupillary defect (rAPD) will be evident in the most anterior part of the visual pathway in more severe retinal or optic nerve diseases with both ipsilateral and contralateral rAPD possible.
◾The VFs tend to be more congruous further back along the pathway, especially at the visual cortex.
◾The monocular crescent is reflected by the most temporal VF in each eye extending from around 60º to 90º.
◾The most anterior part of the primary visual cortex (Locations A&B) is the most likely anatomical location of the monocular crescent.
◾The macular representation of almost one half of the visual cortex is outlined by E&F with locations C&D reflecting the remainder of the VF.
➖Lesions in severe retinal conditions and ON have asymmetric visual dysfunction, thus a rAPD is often present and associated VF defects (Locations 1&2).
➖Chiasmal lesions typically produce bitemporal VF defects with a hallmark feature of respecting the vertical midline with various levels of rAPD depending upon the congruity of pupillary fiber involvement (Location 3).
➖Optic tract lesions (Locations 4&5) will have a subtle contralateral rAPD because there are more crossed than uncrossed pupillary fibers, and they may have a complete homonymous hemianopia in more severe cases.
➖VF defects caused by lesions at the LGN are rare: they display a characteristic bilateral “pie-shaped” VF defect without rAPD.
➖There is no rAPD found in lesions at or beyond the LGN.
➖Temporal lobe lesions are characterized by an incongruous superior “pie in the sky” VF defect, and parietal lobe lesions by an incongruous inferior “pie on the floor” VF defect (Locations 7&8).
➖Larger lesions in the temporal or parietal lobe regions may result in complete homonymous hemianopias. Such findings beyond the LGN may be discriminated by evaluating the associated clinical signs and symptoms associated with lesions in specific visual areas.
➖VF defects at the visual cortex are characterized by their congruous nature, and lesions at this location is where macular sparing of the VF can occur (Locations 9 to 12).
➖The visual cortex above the calcarine sulcus projects to the contralateral inferior VF, and vice-versa for the area below the calcarine sulcus.
➖The most anterior part of the visual cortex represents the monocular temporal crescent, and thus with this exception, all other cortical lesions cause bilateral VF loss beyond the optic chiasm.
Credit: www.reviewofoptometry.com
