Seasonal affective disorder and your eyes

In a nutshell: Light exposure genuinely affects mood, and it happens through your eyes. Light hitting the retina helps set your body clock and influences serotonin and melatonin, two chemicals closely linked to mood and sleep. Less daylight in autumn and winter is one of the main triggers behind seasonal affective disorder (SAD), also known as ‘winter depression’. It’s not the only factor, and glasses alone cannot fix it, but understanding the eye-light-mood link can help you make small, sensible changes that support how you feel.

Seasonal affective disorder (SAD) is a type of depression that follows a seasonal pattern, usually starting in autumn and easing off by spring. Rethink Mental Illness estimates that about 1 in 15 people in the UK get winter SAD symptoms, and about 3 in 100 are severely affected.

Seasonal affective disorder symptoms vary from person to person, but the most common signs include:

• a low mood that lingers for weeks, not days
• less energy and motivation, even for everyday tasks
• sleeping more than usual but still feeling tired
• craving carbohydrates and gaining weight
• finding it harder to concentrate or feel sociable

SAD isn't the same as feeling a bit flat when the clocks go back. It's a recognised form of depression, and it's treatable.

It starts with the retina, the light-sensing layer at the back of the eye. As well as the cells that let you see, the retina has specialised light-sensitive cells that play very little part in forming the images you see. Their main job is to tell the brain how bright it is outside.

That signal travels to a part of the brain called the suprachiasmatic nucleus, which works as your internal body clock. It uses light levels to time when the pineal gland releases melatonin, the hormone that makes you feel sleepy. Melatonin rises when light drops and falls when light increases, which is why dark winter mornings can leave you feeling groggy long after you’re supposed to be awake.

Light exposure is also linked to serotonin, a neurotransmitter that affects mood, appetite and sleep. A study published in The Lancet found that the brain produced less serotonin in winter, and that production rose with hours of bright sunlight, which lines up with the low mood and fatigue reported in SAD.

So, in short: it's not a metaphor when people say winter light 'affects the mind'. There's a direct, physical pathway from the eyes to the brain systems that regulate mood and sleep.

Reduced daylight is one of the most established causes of seasonal affective disorder, but it’s rarely the only one. Genetics, existing mental health and how sensitive someone’s body clock is to light all play a part. Location matters too: SAD is more common further from the equator, where winter daylight hours are shorter.

Researchers are still investigating why some people's eyes and brains respond differently to the same light conditions. It's an active area of study, not a settled one, so treat any single explanation with a little caution.

It can work for some people. Light therapy involves sitting near a specially designed lightbox, typically for 20–30 minutes in the morning, at a brightness far higher than ordinary room lighting. A 2020 review of clinical trials concluded it's an effective treatment for SAD, though the studies were small and varied. The NHS notes it isn't usually available on the NHS because the evidence isn't strong enough yet, but many people find it helps.

A few practical points if you're considering it:

• Morning use tends to work better than evening use.
• Choose a lightbox made for SAD, not a standard desk lamp. The NHS recommends one that's 10,000 lux, UV-free and UKCA or CE marked.
• Speak to a GP first if you have an eye condition, migraines, or take medication that increases light sensitivity.

It's a support, not a replacement for other treatment your GP recommends.

Winter doesn’t just affect your mood; it puts extra demands on your eyes. Good winter eye care covers two things: getting enough light for your body clock and protecting your eyes from the season’s drier, harsher conditions.

1. Make the most of daylight

You don't need special equipment to start. Small, consistent habits make a real difference:

• Get outside earlier in the day. The NHS suggests getting as much natural daylight as you can, and even overcast daylight is far brighter than indoor lighting.
• Sit near a window when you're working or eating, rather than in the darkest corner of the room.
• Keep indoor lighting brighter through winter; dim, warm bulbs can work against you at this time of year.
• Take regular breaks from screens, especially during darker afternoons when eye strain and low light combine.

If glare or harsh artificial lighting bothers your eyes indoors, anti-glare lenses can make the darker months more comfortable when everyone spends more time indoors.

If you move between dim indoor rooms and bright outdoor light, light-adaptive lenses adjust automatically, so you're not squinting outside or straining indoors.

2. Avoid dry eyes in winter

Central heating, cold wind and low humidity all draw moisture from the surface of the eye, which is why dry eyes in winter are so common, even for people who don’t usually notice it. Typical signs include grittiness, redness and eyes that water more rather than less, as they try to compensate.

A few ways to protect your eyes in winter and keep dryness at bay:

• Blink deliberately and more often during long screen sessions, and take regular breaks.
• Run a humidifier in rooms with central heating, especially bedrooms.
• Clean your eyelids daily, as the NHS recommends, and drink enough fluids throughout the day.
• Wear glasses or wraparound styles outdoors to reduce wind exposure during your commute or dog walk.
• Don’t skip UV protection. Low winter sun and glare off wet pavements can be harsh, and fresh snow can reflect up to 80% of UV.

Some medicines, including some antidepressants, can also cause dry eyes. If you've started a new medicine and your eyes feel drier, tell your GP or optician, but don't stop taking it without medical advice.

If dryness sticks around, an optician can recommend drops or, in some cases, a different lens type or coating that suits your eyes better through winter. It’s also worth booking regular eye tests. They won’t diagnose SAD, but they can rule out other reasons your eyes might feel tired, dry or strained over winter, and make sure your prescription still suits the low-light conditions you're dealing with.

If low mood, low energy or disrupted sleep is sticking around for weeks, turning up most winters or making everyday life feel harder, it's worth speaking to a GP rather than waiting it out. SAD is a recognised, treatable condition, and a GP can discuss options including talking therapies, medication and light therapy.

If you're struggling right now, Mind and your GP practice are good places to start. If you need to talk to someone now, call Samaritans free on 116 123, any time. For urgent mental health help, call NHS 111 and choose the mental health option, or call 999 in an emergency.

FAQs: seasonal affective disorder and eye health

Is seasonal affective disorder (SAD) just 'winter blues', or is it more serious?

It's more than a passing low mood. SAD is a form of depression with a seasonal pattern, and it can be just as disruptive as depression that isn't seasonal. Some people have mild symptoms; others find it significantly affects their day-to-day life, including work, sleep and relationships.

Can sunglasses or blue light glasses cause or worsen seasonal affective disorder (SAD)?

There's no evidence that everyday sunglasses or blue light glasses cause SAD. Wearing very dark tints indoors during the darkest months isn't ideal, though. It reduces the light reaching your eyes when you need more of it, not less. Save darker tints for genuinely bright conditions.

Does seasonal affective disorder (SAD) only happen in winter?

No. Most people experience it in autumn and winter, but a smaller minority have a summer pattern instead, with low mood easing as the days shorten.

Do lightboxes for SAD need to be prescribed?

No, lightboxes for SAD are available to buy without a prescription in the UK, and the NHS doesn't usually provide them. It's sensible to check with a GP or optician first if you have an existing eye condition or take light-sensitising medication.

Will taking vitamin D help with seasonal affective disorder (SAD)?

It's not a treatment for SAD, but it's still worth taking in winter. Government advice is that everyone should consider a daily 10 microgram vitamin D supplement in autumn and winter, when the sun isn't strong enough for your body to make enough. It works differently from light therapy and isn't a substitute for treatment if you have SAD. Speak to a GP or pharmacist if you're unsure, take other medicines or have a health condition.

How long does seasonal affective disorder (SAD) usually last?

Symptoms typically build through autumn, peak in December and January, and ease as daylight hours increase in spring. Treatment can ease symptoms sooner, and many people need it every winter to stop symptoms from returning.

Sources & further reading

Support and advice

• Seasonal affective disorder (SAD) – NHS
• Understanding seasonal affective disorder – Mind
• Seasonal affective disorder: symptoms, causes and treatments – Rethink Mental Illness
• Samaritans – call 116 123, free, any time
• Dry eyes – NHS
• Vitamin D – NHS
• Ultraviolet radiation and health – World Health Organization

Research

• Pjrek E, et al. The efficacy of light therapy in the treatment of seasonal affective disorder: a meta-analysis of randomized controlled trials. Psychotherapy and Psychosomatics, 2020.
• Terman M, et al. Light therapy for seasonal affective disorder: a review of efficacy. Neuropsychopharmacology, 1989.
• Lambert GW, et al. Effect of sunlight and season on serotonin turnover in the brain. The Lancet, 2002.
• Schmidt TM, Chen SK, Hattar S. Intrinsically photosensitive retinal ganglion cells: many subtypes, diverse functions. Trends in Neurosciences, 2011.
• Singh S, et al. Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews, 2023.