Sasha Clark was getting ready for work one January morning in 2018 when she suddenly realised she could not see clearly. Assuming it was the start of a migraine, she took two ibuprofen and hoped it would pass.
Clark, now 28 and a charity worker from Essex, found that closing one eye restored some of her vision, but with both eyes 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," she said.
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," she said.
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 said. "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," she said. "That's when I thought something more serious was happening, because it all happened over such a short period of time."
Two months later, in March, Clark was diagnosed with multiple sclerosis (MS), an incurable autoimmune disease.
How MS damages the optic nerve
MS damages myelin, the protective coating surrounding nerves, particularly in the brain and spinal cord. The disease also damages the optic nerves, disrupting signals between the eyes and brain and leading to vision problems.
A 2025 study by 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," said Dr Aravinthan Varatharaj, a 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," he said.
Optic neuritis and its symptoms
Damage to the optic nerves causes a condition called 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 within a few weeks, it is important to see 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 also 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," said Dr Varatharaj.
Research into early warning signs
Dr Catherine Godbold, senior research communications manager at the MS Society UK, said the latest research shows that if the period before a diagnosis or clinical onset of typical symptoms can be better understood, it could be combined with other data to 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," she said.
Other visual problems linked to MS
While optic neuritis is the most common eye problem linked to MS, it is not the only one. The condition can also disrupt the 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, coordination and nausea, double vision caused by MS is often accompanied by other symptoms, such as unsteadiness or feeling sick.
A 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 develop over days, last for a while and then begin to improve, especially when MS is treated promptly.
Sasha Clark's advice to others
Clark'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 said.
"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," she said.
