Visual hallucinations in peripheral vision happen primarily because of how the brain processes visual information and reacts to reduced or altered input from the eyes. The peripheral vision—the area outside the direct line of sight—is more sensitive to motion and less detailed than central vision, and when the brain receives less or distorted information from this area, it can create false images or hallucinations.
One major reason for these hallucinations is a condition called Charles Bonnet Syndrome (CBS), which often occurs in people who have lost part of their vision, especially in the peripheral fields. When the eyes or the visual pathways to the brain are damaged or impaired, the brain receives less sensory input from those areas. Instead of going quiet, the visual parts of the brain become hyperactive or disinhibited, essentially “firing” spontaneously. This neural activity can produce vivid images or patterns that seem real but are actually generated internally by the brain. These hallucinations often appear in the regions corresponding to the lost or impaired vision, which can include peripheral vision[1][2].
The peripheral vision is particularly prone to this because it normally provides less detailed but continuous background information. When this input is missing or reduced, the brain tries to “fill in the gaps” using stored memories, imagination, or random neural noise. This filling-in process can lead to seeing shapes, colors, or even complex scenes that aren’t actually there. Since peripheral vision is less precise, the hallucinations may be more abstract or fleeting compared to central vision hallucinations, which tend to be more detailed.
Another factor is the way the visual system is organized. The retina sends signals to the brain through different pathways, including the parvocellular and magnocellular layers of the lateral geniculate nucleus (LGN). The parvocellular pathway, which carries color and fine detail information, is more concentrated in the central vision, while the magnocellular pathway, which detects motion and broad shapes, dominates peripheral vision. Damage to these pathways or the retina itself, such as in macular degeneration or other eye diseases, disrupts normal signaling. This disruption can cause the brain’s visual cortex to become spontaneously active, especially in areas responsible for peripheral vision, leading to hallucinations in that visual field[1][3].
Age is another important factor. As people age, the likelihood of eye diseases that reduce peripheral vision increases, and the brain’s ability to process visual information changes. Older adults are more prone to CBS and related hallucinations because of these combined effects of sensory loss and brain changes. Social isolation and spending long periods in low-light environments can also increase the risk, as the brain has less external stimulation and may generate more internal images to compensate[2].
The hallucinations themselves can vary widely. Some people see simple patterns, flashes of light, or geometric shapes in their peripheral vision. Others might see more complex images like faces, animals, or scenes. These hallucinations are usually recognized by the person as not real, which distinguishes them from hallucinations caused by psychiatric conditions. They do not involve other senses like hearing or touch and typically do not have emotional content or voices associated with them[2][4].
In summary, visual hallucinations in peripheral vision happen because when the brain loses normal input from the eyes—due to damage, disease, or aging—it tries to compensate by generating its own images. The peripheral visual system’s unique sensitivity to motion and broad shapes, combined with reduced sensory input, makes it a common area for these hallucinations to appear. This phenomenon reflects the brain’s remarkable but sometimes imperfect ability to maintain a continuous visual experience even when the actual sensory data is incomplete or missing.
