The experience of “going blind” is diverse and complex, depending heavily on the underlying medical cause. The term “blindness” exists on a spectrum, often defined legally rather than functionally. In the United States, a person is legally blind if their central visual acuity is 20/200 or less in their better eye (even with corrective lenses), or if their visual field is restricted to 20 degrees or less. This legal definition captures a wide range of visual impairments, only a small percentage of which involve total light loss. Understanding the experience requires exploring the many ways sight can diminish, moving past the simple idea of total darkness.
The Spectrum of Visual Loss
For the majority of people classified as legally blind, vision is not completely absent; instead, it is compromised in specific ways, a condition often referred to as low vision. This can manifest as a loss of peripheral vision, creating a “tunnel vision” effect where only the direct line of sight remains. Conditions like glaucoma or retinitis pigmentosa often cause this gradual constriction, making it difficult to detect objects outside the central field.
Conversely, some people experience a loss of central vision, which is common with age-related macular degeneration. In this case, the peripheral sight remains intact, but a dense, blurry, or dark spot appears directly in the middle of the visual field. Other patterns include scotomas, which are isolated dark or blind spots that can appear anywhere in the field of vision. The overall feeling is one of blurriness, distortion, or the inability to discern fine details, rather than a sudden cessation of sight.
The Sensory Experience of Total Darkness
A common misconception is that total blindness is like looking into a void of blackness, but for those with no light perception (NLP), the experience is the absence of any visual sensation. Black is a visual color that requires the brain’s visual processing center to interpret the absence of light. When the eyes and the neural pathways leading to the brain cannot transmit any information, there is simply no input to process.
A helpful way to conceptualize this is to consider what you “see” with your elbow or the back of your head. Because no visual receptors exist in those areas, there is no image, color, or darkness—there is nothing to perceive. For a person who has been blind since birth, they lack the visual frame of reference to define “black” or “darkness” as a visual concept. The experience is a non-experience, a state of visual nothingness.
Phantom Sights: Understanding Charles Bonnet Syndrome
A surprising sensation that can accompany significant vision loss is Charles Bonnet Syndrome (CBS). This condition involves experiencing complex, vivid visual hallucinations that the person knows are not real. Individuals may see detailed, silent images of people, animals, patterns, or intricate landscapes that are not present in their environment.
CBS is a neurological response to the lack of visual data from the eyes; the brain’s visual cortex, starved of input, essentially generates its own images. This process is called sensory deafferentation, causing the neurons in the visual centers to become spontaneously active. This is not a sign of mental illness or cognitive decline, and people with CBS are aware that the sights they are seeing are phantoms.
Adapting to a Non-Visual World
Over time, the brain responds to the loss of sight through neuroplasticity, which allows it to reorganize its sensory processing. Areas of the brain once dedicated to visual information are gradually repurposed for other senses, specifically touch and hearing. This is known as cross-modal plasticity, allowing the remaining senses to become more efficient at gathering information.
The result is that individuals who are blind often exhibit superior performance in non-visual tasks, such as localizing the source of a sound or discerning fine tactile details. The visual cortex can become active when a person is performing auditory or tactile tasks, showing that those brain regions are now dedicated to a non-visual function. This neurological adjustment is a long-term process that allows the individual to construct a detailed, non-visual map of the world based on auditory and tactile cues.