The importance of sleep for the eye and brain

We spend a third of our lives asleep. Why?

Medical science is slowly unravelling this mystery and recognising that sleep plays a vital role in good health and well-being throughout life. To most people, sleep is merely an end of day dormant passive rest we take when tired, something perhaps which if busy can be rationed, or even be done without in the digital age. Sleep is so much more than generally realised: it is essential in maintaining normal physiology, by active cellular processes of chemical restoration and repair.

We all know how rough we feel after a single poor night sleep, or when jet-lagged. It’s something like being in a fog, with bags of sugar weighing down the eyelids. Some patients with chronic insomnia somehow survive feeling like this all the time: not good. Most of us also know how rejuvenated we feel after a good night’s sleep.

I am an ophthalmologist who has become keen to understand how sleep can interact with eye performance and diseases.

In my clinical experience, poor sleep quality can have several profound effects on the eye which are under recognised by the profession. A good night’s sleep pretty much enables us to function normally in all we do through the next day. But why should this be? What goes on whilst we quietly sleep where the eyes and brain are concerned?

When we are awake, the eye surface has the protection of tears and blinking, but this mucus membrane still experiences hostile strain in being exposed to the atmosphere all day. At night, although things dry up under the closed lids, there is an increase in desquamation of the epithelial layer which acts to renew surface integrity. Poor sleep very commonly causes the problem of worsening ocular surface health, precipitating or exacerbating dry eye disease. With devitalised dry spots everywhere it is no surprise bleary eyes result.

In the brain, where chemical processes work like lightening throughout the day, it is during sleep that these metabolically active cells bring in fresh new chemicals and dump toxic waste products via the recently described glymphatic clearance pathway. Neurons make new connections and trim old ones. Poor sleep makes us feel sluggish and also impairs sub-conscious processes. The binocular reflexes which control single vision can be fatigued, leading to eye strain and double vision problems.

The retinal photoreceptor cells are one of the most metabolically active parts of the brain. It is known that rods and cones shed their outer segment tips shortly after going to sleep - it's like racking-up a new photo lab each day. Cellular waste is processed by the underlying pigment epithelial cellular layer.

Though only hypotheses, it could be that over many years poor sleep is a factor in the cause of drusen accumulation in dry age-related maculopathy, and amyloid plaques and neurofibillary tangles in Alzheimer's dementia.

Eye and brain health can be affected by altered sleep mechanics too.

If blood pressure drops too low at night (nocturnal dipping), the watershed areas of the eye and brain may not receive sufficient oxygen. This has been implicated in causing the vascular-type of normal tension glaucoma, and may well also be similarly implicated in being one of the causes of cerebral microvascular disease (these conditions are associated in 50% of cases as observed on MRI brain scans).

In the disorder of obstructive sleep apnoea, a floppy pharynx intermittently cuts off the airway. This drops oxygen levels in the blood to the point the brain alarm systems recognise, forcing a partial wake-up to cough or splutter a new breath. Such regular interruptions cause a poor night’s sleep and excessive day-time sleepiness. It is also linked with floppy eyelid syndrome, where hyper elastic eyelids can sometimes flip over against pillows leading to open eye exposure problems.

So what does all this mean?

The main point here is that correctly recognising these issues and addressing the underlying sleep disorder can in large part resolve many problems, including those of the eye. I have personally observed quite amazing improvements in patients with the likes of -

a) dry eye disease

b) asthenopia (eye strain)

c) decompensating phorias (latent squints)

d) convergence insufficiency (reading target problems)

- all just from getting a good restorative night’s sleep! This is a targeted and yet conservative approach which obviates the need for more complicated interventions. And in the long-term may well protect from disabling eye and brain wear-and-tear diseases.

OK! What is to be done?

The first approach to a good night’s sleep is a case of back to basics and concentrating effort into making things better. Routine is important. Have a set time to wake, and aim to fulfil a busy day of duties with some exercise. Adopt a set time to wind down before retiring to bed. Don’t eat or drink alcohol or caffeine late. Have a hot bath then a Horlicks. Read or listen to the radio before lights out.

Don’t dwell on issues of the day if you have trouble nodding off. Just try to empty the mind (write a list if it helps). This of course needs both a comfortable, quiet and dark bedroom. Most people fall asleep within 7-10 minutes this way. Don’t worry ‘I can’t fall asleep’ - just ignore all negative thoughts is best.

Of course if you are suffering from major life trauma, stress, anxiety or depression this warrants a top down approach - deal with each of the causes one by one if you can, with help if needs be, then tackle any remaining effects holistically or with medical help.

A pharmacist or your general medical practitioner should be able to offer assistance. There are tablets which can be used in the short-term and long-term to try and restore normal sleep rhythm. Underlying disorders of stress and anxiety are common and may need their own treatment whether by drugs or counselling cognitive behavioural therapy.

Don’t give up or be fobbed off. If you are still no better why not request a referral to a sleep expert, or consider hypnotherapy.

The power of the mind can win.

It turns out we should all take an active interest in sleep.