The term “blindness” is often used broadly, yet the actual visual experience of a person with severe vision loss exists along a wide spectrum. Many people who are clinically considered blind still possess some degree of functional sight, such as the ability to perceive light or vague shapes. To understand what complete blindness looks like, it is necessary to focus on the most severe classification, which involves a total absence of any visual input. This experience is far more complex than the common assumption of living in perpetual darkness.
Differentiating Levels of Vision Loss
Vision loss is categorized into several distinct levels, only one of which represents a complete lack of sight. The most common designation is “legal blindness,” a classification used for governmental and legal purposes, not a description of visual function. A person is generally considered legally blind in the United States if their corrected visual acuity is 20/200 or worse in the better eye, or if their visual field is restricted to 20 degrees or less. This definition means that a person with legal blindness can often still see light, color, and shapes, though their vision is severely limited.
Approximately 85% of individuals with significant visual impairment retain some residual sight. This residual vision may allow them to differentiate between bright and dark or detect the source of a light. The ability to detect light is called “light perception” and is an important distinction in functional vision.
Complete blindness, by contrast, is a definitive clinical state known as “No Light Perception” or NLP. This designation means the individual is unable to perceive any light whatsoever. Only about 15% of people with eye disorders are considered to have total blindness.
The Sensory Perception of Total Blindness
For an individual with No Light Perception (NLP), the experience is not typically described as seeing the color black. Black is a visual color that requires the brain to process light information. Since complete blindness means the visual system is no longer receiving or processing any external light signals, there is no color, including black, to perceive.
When asked to describe what they see, many people with congenital total blindness or long-term NLP often state that they see “nothing.” This absence of vision is often compared to what a sighted person “sees” with their elbow or the back of their head. The brain does not register a visual image or color in the absence of input.
The experience can differ slightly for people who lost their sight later in life, particularly those who were suddenly blinded. They may initially experience a sensation of blackness or retain visual memories that fade over time. However, as the brain adapts to the lack of input from the retina, this perception of darkness generally gives way to the absence of sight characteristic of true NLP. The disruption of the circadian rhythm is an indirect effect of this total lack of light perception, as the body’s internal clock relies on light signals to regulate the sleep-wake cycle.
Visual Phenomena Experienced Without Sight
Even in the absence of external light perception, the visual cortex in the brain can still generate internal visual experiences. These phenomena show that the brain’s visual processing centers remain active even when the eyes are not sending signals.
One common internal visual experience is the perception of phosphenes, which are brief flashes, sparks, or geometric shapes of light. These are not caused by external light entering the eye, but by mechanical or spontaneous neural stimulation of the retina or the visual cortex. Simply rubbing the eyes can trigger these pressure phosphenes, showing that the visual pathway is capable of generating light sensations on its own.
A more complex phenomenon is Charles Bonnet Syndrome (CBS), which involves intricate visual hallucinations. These are often detailed, vivid images such as geometric patterns, miniature people, or landscapes. The syndrome is believed to occur when the visual cortex, deprived of real-world input, begins to fire spontaneously, filling the void with stored or generated images.
People experiencing CBS maintain complete intellectual clarity and know that the images they see are not real, distinguishing the condition from psychiatric issues. The hallucinations are purely visual and do not involve other senses. This neurological response highlights the brain’s need for constant stimulation.