Scientists injected cells from woman’s leg into her eyes to help restore her vision: How 'world-first experiment' went & what doctors discovered

Could the body’s own cellular “powerhouses” help rescue damaged nerve cells in the eye? Scientists have taken a first step towards answering that question by extracting mitochondria from a woman’s leg and injecting them into both of her eyes.

The experimental procedure was carried out in a 26-year-old woman who had suffered severe vision loss following a brain haemorrhage. According to a preprint case report led by neuroscientist David Putrino of the Icahn School of Medicine at Mount Sinai, the treatment did not restore her vision, but it produced temporary changes in the way her pupils responded to light.

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The findings, posted on Research Square, have not yet been peer reviewed. As reported by Nature, the procedure appeared to be relatively safe, although its effectiveness remains unproven.

Why did doctors inject mitochondria into the eyes?

Mitochondria are structures inside cells that produce the energy needed for cells to function. They are sometimes described as the “powerhouses” of cells because they convert nutrients and oxygen into usable cellular energy.

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Retinal ganglion cells, which carry visual information from the retina towards the brain through the optic nerve, have particularly high energy requirements. As per the researchers, these cells depend heavily on mitochondrial energy production.

The idea behind mitochondrial transplantation is not to bring dead nerve cells back to life. Instead, scientists are investigating whether healthy mitochondria can provide an energy boost to damaged cells that are still viable and potentially capable of recovery.

Previous animal studies have suggested that mitochondria delivered into the eye can be taken up by retinal cells and may improve the survival of retinal ganglion cells following optic nerve injury.

How were the mitochondria taken from the woman’s leg?

The patient had suffered a severe brain haemorrhage in February 2026. She reportedly did not reach hospital until about 18 hours after the event, resulting in prolonged disruption of blood and oxygen supply to her optic nerves.

Despite emergency treatment, she was left with profound vision loss in both eyes.

According to the Research Square preprint, doctors later found significant damage to her optic nerves and severe thinning of the retinal nerve-fibre and ganglion-cell layers. However, some of these structures remained, suggesting that not all of the affected nerve cells had been lost.

The researchers therefore explored whether the remaining cells could potentially benefit from a new source of functioning mitochondria.

To reduce the risk of an immune reaction, the team used the woman’s own tissue. A biopsy was taken from her thigh muscle and processed to isolate tens of millions of mitochondria.

The freshly isolated mitochondria were then injected into the vitreous, the jelly-like fluid inside each eye. The two injections were carried out 24 hours apart under emergency expanded access authorised by the US Food and Drug Administration (FDA), according to a scientific summary of the case.

What happened after the mitochondrial injections?

The most notable changes involved the woman’s pupils and measurements of activity in the visual cortex.

In the 71 days before treatment, doctors conducted 45 automated measurements of her pupillary response to light. None reached the researchers’ threshold for a normal response.

Within days of the mitochondrial injections, both eyes began showing some normal-range responses to light.

As per the Research Square report, organised responses in the visual cortex were also detected during brain-recording sessions conducted three, 44 and 45 days after treatment.

However, these changes did not translate into a measurable restoration of vision.

Did the woman regain her eyesight?

No. The woman’s visual acuity remained essentially at the level of light perception, with no measurable improvement following the treatment.

The pupil responses were also temporary. According to the report, the left eye recorded its last normal response on day 11, while the right eye continued to show sporadic normal responses until day 39. Nature reported that the effect had largely disappeared after about four weeks.

Nature also reported that a later low-vision assessment noted that the woman could perceive shapes and shadows with her left eye, although this does not amount to restored normal vision.

Was the experimental eye treatment safe?

So far, the safety findings are one of the most important parts of the experiment.

According to the researchers, neither eye developed serious adverse effects or signs of significant inflammation after the injections. The procedure also did not trigger a dangerous systemic immune reaction.

Nature reported that tests found no evidence of inflammation or damage to either eye following the treatment.

This was particularly important because one of the major concerns with introducing biological material into the eye is the possibility of an inflammatory or immune reaction.

What are the limitations of the mitochondrial transplant study?

There are several major reasons why the findings should be treated cautiously.

First, this was a single-patient case. There was no control group against which the patient's changes could be compared.

Second, the researchers did not directly demonstrate that the transplanted mitochondria entered the patient's retinal ganglion cells.

Third, the temporary pupil and brain responses cannot establish that the mitochondria themselves caused those changes.

The authors therefore do not claim that the treatment restored vision or proved that mitochondrial transplantation works as a therapy.

The World Mitochondria Society also described the study as a preliminary first step, noting that the report cannot establish efficacy because it involved one patient, had no control group and showed only temporary functional changes.

Could repeated mitochondrial injections work better?

The temporary nature of the responses has raised an important question for future research, whether damaged cells might need repeated doses of healthy mitochondria.

David Putrino told Nature that the team is now working with the FDA on a protocol for repeated, serial mitochondrial injections.

The researchers will first need to establish whether the transplanted mitochondria actually reach the intended retinal cells and whether they can meaningfully improve their energy production.

Future studies will also need to determine the right dose, timing and frequency of treatment, as well as which patients are most likely to have enough surviving nerve cells for the approach to work.

What does the first human eye mitochondrial transplant mean?

The experiment does not represent a cure for blindness, but it marks a new direction in regenerative medicine.

As per the Research Square preprint, mitochondrial transplantation had previously been investigated in humans in other organs, including the heart and brain, but this was the first reported attempt to deliver mitochondria directly into the human eye.

The basic concept is strikingly simple: take healthy mitochondria from one part of a patient's body and introduce them into damaged cells elsewhere in the body.

For now, however, the evidence only shows that the procedure can be performed without serious immediate complications and that temporary physiological changes can occur afterwards.

Whether those changes can eventually become sustained, meaningful improvements in vision remains an open scientific question.

The findings are currently available as a Research Square preprint and have not undergone peer review.