The common assumption is that being blind means seeing an absolute, uniform blackness, yet the reality is far more complex and varied. The visual experience of a person with vision loss is a spectrum defined by the underlying cause of the impairment and the degree of light processing ability that remains. For many, the experience is not an absence of light but a field of residual, distorted, or patchy visual information. What a person sees depends entirely on where they fall along this continuum of visual capability.
The Spectrum of Sight Loss
Blindness is a broad term encompassing a wide range of visual impairments. The most common designation is “low vision,” where sight is significantly impaired but some residual function remains, often uncorrectable with standard lenses. Many individuals are classified as “legally blind,” which is a definition based on specific measurements rather than a total lack of sight. This status is met if the best-corrected visual acuity is 20/200 or less, or if the field of vision is restricted to 20 degrees or less.
Total blindness is defined as having no light perception (NLP), meaning the person cannot detect any form of light, color, or shape. This extreme is rare, estimated to affect less than 2% of the population with visual impairment. The majority of people labeled as blind retain some level of light perception, which allows them to distinguish between light and dark, even if it is insufficient to form usable images.
Subjective Visual Experiences
For those who retain some residual vision, the subjective experience is often described not as black, but as a field of indistinct color or haze. Individuals with certain retinal diseases may describe their vision as a dense, milky fog or shifting gray and brown shades. This occurs because the damaged retina sends patchy and incomplete signals to the brain, resulting in ambiguous and low-contrast perceptions.
The ability to perceive light is common, allowing a person to tell if a light is on or off, or if they are facing a window. This light perception is often limited to a vague, shapeless glow or a flash, without the detail necessary to discern objects. In cases of complete achromatopsia, some individuals report seeing only black, white, and shades of gray, lacking all color vision.
The Brain’s Response: Visual Hallucinations
When the eyes fail to provide the brain with visual input, the brain sometimes compensates by generating its own images, a phenomenon known as phantom vision. This is associated with Charles Bonnet Syndrome (CBS), which affects many people who experience severe vision loss. CBS is a neurological response to sensory deprivation, analogous to the phantom limb sensation experienced by amputees.
The hallucinations can range from simple, repetitive geometric patterns, such as grids or flickering lights, to complex, vivid, and detailed scenes. These complex images may involve landscapes, people in costumes, or fantastical creatures, which the person knows are not real. The visual cortex, deprived of external stimulation, spontaneously activates, creating these images. A simpler form of visual input is phosphenes, which are brief flashes or spots of light caused by non-light stimulation of the retina or visual cortex, such as rubbing the eyes or a sudden movement.
Congenital Versus Acquired Blindness
The timing of vision loss fundamentally alters the subjective experience. People with acquired blindness, who lost their sight later in life, retain a library of visual memories. They know what colors, light, and objects look like, and their internal mental imagery draws upon these past experiences. Their adjustment involves grieving the loss of a known sensory experience.
For someone with congenital blindness, meaning they were blind from birth or very early childhood, the experience is entirely different. They have no concept of “light” or “darkness” as visual sensations, and the idea of “black” is meaningless since they lack a visual baseline for comparison. Their brain’s visual cortex often repurposes itself to process other sensory information, such as sound and touch, leading to a different kind of spatial awareness. Their mental imagery is based on spatial relationships and touch rather than visual appearance.