The early ‘flashing light’ warning sign in your eyesight that could be the first symptom of multiple sclerosis, as cases mysteriously rise

Sasha Clark was getting ready for work one January morning in 2018 when she suddenly realised she couldn’t see clearly.

Assuming it was the beginning of a migraine, she took two ibuprofen and hoped it would pass.

She found that if she closed one eye she had some vision, but when both eyes were open the world became a blur.

‘If I was watching TV or scrolling on my phone, I would always have to keep one eye shut to see properly,’ says Sasha, 28, a charity worker from Essex.

But within two weeks her health began to nosedive. ‘My co-ordination was completely off and eating became difficult. I was picking up food with a fork and going to put it into my mouth, but my mouth wasn’t where I thought it was.’

Her balance was also affected, leaving her unable to walk without clinging to the walls.

‘I was getting headaches and was taking painkillers, thinking it would go away, but nothing would touch it,’ she says. ‘I was sleeping for 18 hours a day but was still exhausted. I couldn’t leave the house, go to the toilet on my own or bathe myself.

‘I was 19 and should have been having fun at university – not bedbound with my mum washing my hair and getting me dressed.

‘That’s when I thought something more serious was happening – because it all happened over such a short period of time.’

Just two months later, in March, Sasha was diagnosed with multiple sclerosis (MS), an incurable autoimmune disease.

MS damages myelin, the protective coating surrounding nerves, particularly in the brain and spinal cord, but it also damages the optic nerves, disrupting signals between the eyes and brain and leading to vision problems.

A 2025 study from researchers in Canada found that neurology and ophthalmology visits begin to increase eight to nine years before an MS diagnosis.

‘There is a lot more awareness of the early symptoms of MS now,’ says Dr Aravinthan Varatharaj, clinical academic neurologist and associate professor at the University of Southampton.

‘But while many people are familiar with MS symptoms caused by damage to the brain and spinal cord, such as walking problems, balance issues and bladder or bowel difficulties, far fewer know how MS can affect the optic nerves and vision.

‘The optic nerves are heavily coated in myelin, making them particularly vulnerable to damage from MS.’

Damage to the optic nerves causes optic neuritis. Symptoms typically develop over several days and can include eye pain, blurred vision, blind spots, washed-out colours and flashing lights.

While optic neuritis often improves on its own over a few weeks, it is important to visit an optician who can check for damage to the nerve fibres at the back of the eye.

Besides MS, inflammation of the optic nerve can occur with other conditions, including infections or immune diseases such as lupus.

‘It is really important to recognise that sometimes, even though it gets better on its own, optic neuritis can be the first episode of what may later turn out to be MS,’ says Dr Varatharaj.

Dr Catherine Godbold, senior research communications manager at the MS Society UK, says: ‘The latest research shows that if we can understand this period before a diagnosis or clinical onset of typical symptoms, we could combine it with other data and identify people at higher risk of developing MS. We’re currently funding a new study at King’s College London that aims to do just that.’

While optic neuritis is the most common eye problem linked to MS, it isn’t the only one.

The condition can also disrupt nerve pathways that control eye movements, causing double vision, difficulty reading, distorted straight lines or overlapping images. 

Because the parts of the brain that control eye movements sit close to areas involved in balance, co-ordination and nausea, double vision caused by MS is often accompanied by other symptoms, such as being unsteady on your feet or feeling sick.

Another, less common, symptom is oscillopsia, which can make surroundings appear to bounce while walking because the brain can no longer stabilise visual information.

As with other MS-related visual symptoms, these problems usually evolve over days, last for a while and then begin to improve, especially when MS is treated promptly.

Sasha’s advice for others is to trust their instincts and push for answers. ‘Be quite firm with your GP – if you feel like something’s not right, listen to your body and keep investigating,’ she says.

‘MS doesn’t always start with obvious mobility problems. For some people, vision changes or problems with fine motor skills can be among the first signs.’