What Do People in Comas See? A Scientific Explanation

People in a true coma almost certainly do not see anything in the way you or I experience vision. A coma involves a deep state of unconsciousness in which the eyes are closed, there is no voluntary response to stimulation, and the brain’s higher-order processing is profoundly suppressed. Yet the relationship between coma and visual experience is far more layered than a simple on-off switch, because “coma” is often used loosely to describe a range of states, some of which may harbor surprising flickers of awareness.

Why True Coma Likely Means No Visual Experience

In a deep coma, the eyes stay shut. Without any light reaching the retina and without the cortical machinery to interpret signals even if it did, the conditions for vision simply are not met. The brain’s arousal systems, which normally keep you alert and processing sensory input, are severely impaired. Neuroimaging studies show that while some baseline brain activity persists in unconscious states, this activity does not appear to reflect conscious experience. Research into blood-flow patterns in the brains of comatose, anesthetized, and sleeping individuals has found that the default-mode network, a set of brain regions active during wakeful rest, maintains some coherent low-level activity even in coma. But the researchers who discovered this emphasized that these slow, synchronized fluctuations likely reflect the brain’s structural wiring rather than any form of awareness, and that their functional meaning “remains largely in the dark.”¹

What these imaging studies consistently show is that the higher-order association areas of the brain, the frontoparietal and cingulate cortices that knit sensory information into coherent experience, are systematically impaired across coma, deep anesthesia, and other unconscious states. The visual cortex at the back of the brain might still receive rudimentary signals, but without the associative networks that turn raw signals into images, scenes, or anything recognizable as “seeing,” those signals go nowhere meaningful.

When “Coma” Is Not Quite Coma

Much of the confusion around what people in comas see comes from the fact that the word “coma” is used casually to describe several distinct conditions. A true coma rarely lasts more than a few weeks. After that, patients either recover, die, or transition into other states, most commonly the vegetative state (now often called unresponsive wakefulness syndrome) or the minimally conscious state. The differences between these conditions are crucial for the question of visual experience.

In the vegetative state, patients open their eyes and go through sleep-wake cycles, which can look startlingly like wakefulness to family members. But eye-opening alone does not mean seeing. Whether a patient can fix their gaze on an object and visually track it is one of the key clinical tests that separates the vegetative state from the minimally conscious state, in which some reproducible evidence of awareness exists.² A patient who consistently follows a mirror or a face with their eyes is considered to have crossed a threshold into at least minimal consciousness, and with it, the possibility of some visual experience, however fragmentary.

The trouble is that this threshold is maddeningly difficult to assess at the bedside. One well-documented case illustrates the problem: a 45-year-old man hit by a car suffered widespread brain damage and was classified as vegetative on nine of eleven assessment days over several years. On two days, he showed possible visual tracking in one eye and possible movement in response to commands, but these behaviors could not be reliably reproduced. Standard behavioral tests kept returning a vegetative-state diagnosis. Yet when the same patient was placed in a brain scanner and asked to imagine specific activities, his brain reliably produced distinct patterns of activity in response to different instructions, demonstrating a level of covert awareness that no bedside exam had been able to confirm.³

Cases like this suggest that some patients who appear entirely unresponsive may have richer inner lives than their outward behavior reveals. Whether that inner life includes anything resembling vision is unknown for most individuals, but the possibility cannot be dismissed.

Covert Awareness and What It Might Mean for Perception

The discovery that some behaviorally unresponsive patients can follow mental commands during brain scans has reshaped how researchers think about consciousness after severe brain injury. These patients are sometimes described as having “cognitive motor dissociation,” meaning their minds can respond even though their bodies cannot. Brain-computer interface research has tried to exploit this, using brain signals to detect awareness in people diagnosed with disorders of consciousness. In one study, several patients classified as vegetative or minimally conscious achieved above-chance accuracy on a hybrid brain-computer interface that combined visual and other stimuli, with some patients hitting accuracy rates of 70 percent or higher.⁴

That a patient diagnosed as vegetative could produce reliable brain responses to visual stimuli is remarkable and suggests that at least some visual processing pathways can remain intact even when all outward signs point to a complete absence of awareness. Brain-computer interfaces have been explored using several different signal types, including those evoked by visual stimuli, and researchers have noted that these tools hold potential for uncovering hidden awareness in patients who cannot move or speak.⁵

None of this proves that such patients experience subjective vision the way a healthy person does. But it does demonstrate that the visual brain can be more active than appearances suggest, and that the line between “no awareness” and “some awareness” is far blurrier than clinical labels imply.

The Eyes Still Matter, Even in Unconsciousness

Even when a comatose patient cannot see in any meaningful sense, the eyes provide clinicians with critical information. One of the most basic neurological exams performed on comatose patients is the pupillary light reflex, shining a light into the eye and watching whether the pupil constricts. This reflex operates through brainstem circuits and does not require consciousness, but its presence or absence says a great deal about which parts of the brain are still functioning. Quantitative pupillometry, which uses a device to precisely measure the pupil’s response, is now a guideline-recommended tool for predicting outcomes in patients who remain comatose after cardiac arrest.⁶

Separately, light may play a therapeutic role even for patients who are not aware of it. A study of patients with severe brain injuries found that simulating natural daylight patterns in their hospital rooms, gradually brightening and dimming the lights over the course of a day, brought their body-temperature rhythms significantly closer to a normal 24-hour cycle compared to standard hospital lighting. Under the dynamic daylight conditions, the patients’ body clocks deviated from 24 hours by only about half an hour on average, compared to more than three and a half hours under regular hospital lights.⁷ The eyes continued to transmit light signals that regulated biological rhythms, even when the patients showed no behavioral evidence of visual awareness. This is because circadian entrainment relies on specialized retinal cells that send signals directly to the brain’s internal clock, a pathway that operates below the level of conscious sight.

What the Dying Brain Might Experience

Perhaps the most provocative research related to this question comes from studies of what happens in the brain in the moments surrounding death. If a comatose patient’s heart stops, the brain does not simply go quiet. In experiments with rats, researchers found a transient surge of highly synchronized gamma oscillations within the first 30 seconds after cardiac arrest. These gamma waves, a type of brain activity associated with conscious perception in healthy brains, were global and coherent, and their strength actually exceeded levels found during normal wakefulness.⁸

In 2023, the same research group reported similar findings in dying humans. Among four comatose patients who had life support withdrawn, two showed a rapid and marked surge of gamma power along with increased connectivity between brain regions, particularly in the posterior cortical “hot zone,” a region that neuroscientists have long identified as critical for conscious visual experience. This surge was triggered by the loss of oxygen and intensified as heart function deteriorated.⁹ A review of the broader evidence for these dying-brain surges noted that this line of research may offer a neurobiological foundation for near-death experiences, which commonly include vivid visual phenomena like tunnels of light, panoramic life reviews, and encounters with deceased relatives.¹⁰

The critical caveat is that we cannot ask dying patients what, if anything, they experienced during these surges. The brain activity patterns look like what the brain produces during conscious perception, and they occur in the right regions for visual experience, but whether this translates into actual subjective vision remains an open and possibly unanswerable question. Not all dying patients showed these surges either; two of the four in the human study did, and two did not, suggesting this is not a universal phenomenon.

Near-Death Experiences in People Who Have Never Seen

One of the stranger findings in the near-death experience literature is that blind people, including those blind from birth, report visual experiences during NDEs. A study that specifically investigated NDEs and out-of-body experiences in blind individuals found that these experiences closely resembled those reported by sighted people, and that the great majority of blind participants claimed to see during these episodes. In some cases, the visual details they reported could be independently verified by others who were present.¹¹

A systematic review of visual and spatial imagery in blind individuals confirmed that visual impressions have been reported by blind subjects during near-death and out-of-body experiences, though the review also highlighted ongoing debate about whether these reports reflect genuine visual perception or some other form of mental representation that the person interprets as visual.¹² The implications are unsettling for any simple model of what the brain does in extreme states. If someone who has never had functional eyes reports seeing during a near-death crisis, whatever is happening does not rely on the normal visual pipeline. This either points to something genuinely mysterious about consciousness under extreme physiological stress, or it suggests that the brain can generate experiences coded as “visual” from non-visual neural activity, something researchers still lack a clear mechanism to explain.

What Happens to Vision After Waking Up

For patients who do emerge from coma, vision is not always waiting for them on the other side. Cortical blindness, a loss of vision caused by damage to the visual processing areas of the brain rather than to the eyes themselves, is a well-documented complication of the kind of oxygen deprivation that often causes coma in the first place. In these cases, the eyes work fine and the pupils respond normally to light, but the brain cannot turn the incoming signals into sight.

This condition can appear in different forms. In one documented case, a child who suffered a hypoxic brain injury showed extensive damage throughout the cortex on brain imaging, including in the occipital cortex and the calcarine fissures, the primary areas responsible for processing visual information.¹³ In another case, a patient developed delayed-onset cortical blindness twelve days after a hypoxic event, with vision reduced to detecting hand motion at close range. Testing confirmed that the eyes and retinas were functioning normally, but the visual signals were not reaching or being processed by the brain’s visual cortex, which showed characteristic damage on imaging.¹⁴

Recovery from cortical blindness varies enormously. Some patients regain functional vision over weeks or months as surviving neurons compensate and brain plasticity allows partial reorganization of visual processing. Others remain permanently impaired. The delayed onset in some cases can be particularly cruel and confusing: a patient wakes from a coma apparently able to see, only to lose vision days later as the full extent of the cortical damage declares itself.

Why Anecdotal Reports Are So Hard to Interpret

You may have encountered stories from people who say they could hear conversations, see the hospital room, or experience vivid dreamlike scenes while in a coma. These accounts are real in the sense that the people genuinely believe them, but interpreting them scientifically is a minefield. Memory is reconstructive. When a person emerges from a prolonged period of disordered consciousness, fragments of auditory input that seeped through during lighter phases of impaired awareness can be woven into coherent narratives after the fact. The brain is skilled at filling gaps and constructing plausible stories from incomplete data.

Additionally, many of these reports come from patients who were not in a true coma at the time but were in a minimally conscious state, under heavy sedation in an ICU, or in the confused twilight period of emergence. These are all states in which some degree of sensory processing can occur, but they are categorically different from deep coma. A patient who was sedated and intermittently rousing in an intensive care unit is not having the same experience as someone in a coma caused by catastrophic brain injury, even though both might be described by family members as having been “in a coma.”

The honest scientific answer is that for patients in a true, deep coma, we have no evidence that visual experience occurs, and good reason from neuroimaging to think it does not. For patients in the grey zones around coma, particularly the minimally conscious state, some degree of visual processing appears possible in at least a subset of individuals. And for the dying brain, there are tantalizing signs of neural activity in visual regions that resembles what we see during waking consciousness, though we cannot confirm these produce subjective experience. The question “what do people in comas see?” turns out to be less about vision and more about where the boundary of consciousness actually lies, a question neuroscience is still a long way from answering definitively.