A moist, healthy eye surface is essential for normal vision and this requires a sufficient quantity and quality of tears as well as regular blinking. The production and drainage of tears is a continuous biological process, but if this is compromised for any reason, dry eye symptoms may occur.
Dry eyes can occur at any time of life, but in general the problem is more often seen in older people. Estimates vary as to how many people suffer with dry eyes, but it is believed to affect around 13 per cent of people in their 50s and as many as one in three people in their 70s1. Women are more likely than men to experience the symptoms of dry eyes1.
The problem occurs when the tear film – the thin liquid layer that normally lubricates the eyes – fails to do its job effectively, so the eyes may become dry, feeling gritty and uncomfortable. They may also become red or watery.
Eye drops can help relieve symptoms, but it is important to choose drops which are formulated to mimic as closely as possible both the composition and the effectiveness of the natural tear film. This means that the drops stay on the surface of the eye as long as possible and behave as much like natural tears as possible when blinking. Some people may find that they need to try more than one type of eye drop before they find the right one for them.
What is tear film?
As well as acting as a lubricant for the eyes, the tear film also protects them against infection and helps stabilise vision. It is made up of three layers, each of which is produced by a separate set of glands in the eye. The film comprises a thin lipid outer layer, a middle watery layer and a thin inner mucus layer and is spread over the surface of the eye each time we blink.
- The watery layer is produced by the lachrymal glands which are just above and towards the outer side of each eye.
- The lipid layer is produced by the meibomian glands – a special type of sebaceous gland – in the eyelids. This oily layer helps reduce evaporation and keep the surface layer smooth.
- Cells in the conjunctiva produce the mucus layer which allows the watery tears to cover the surface of the eye evenly.
The tears drain away into the nose through the tear ducts at the inner corner of each eye.
What causes dry eyes?
If any of the tear film-producing glands are not functioning normally the quality or quantity of tears may be affected, so either the tears evaporate before more can be produced or not enough tears are produced to keep the eye lubricated. When eyes are insufficiently protected, the immune system sends infection-fighting cells to protect the eyes and these cause inflammation, making the eyes red.
A number of different factors may trigger dry eye problems, including:
- Medical conditions – dry eyes may occur in people suffering from various conditions, from dermatitis and rosacea to rheumatoid arthritis, lupus and shingles
- Side-effects of medication – diuretics, antihistamines, antidepressants and betablockers are thought to cause dry eyes in some people
- Environmental factors – these can cause tears to dry up, making eyes feel dry and they range from spending a long time using computers, which may lead to the operator blinking less frequently, to climatic conditions such as sun, wind or high altitude or central heating or air conditioning which lead to low humidity.
- Wearing contact lenses
- Hormonal changes – women may experience dry eye symptoms at the menopause and this may be one reason why women are more prone to dry eyes than men
- Injury or surgery
- Ageing – the problem affects more people as they get older.
Dry eyes are generally not considered a serious problem, but if left untreated, severe cases may lead to the surface of the eye becoming scarred and sight being affected. In very rare cases, surgery may be an option.
Symptoms of dry eyes
The condition usually affects both eyes and sufferers may experience feelings of dryness, grittiness or soreness which becomes worse as the day progresses. They may also find that their eyes are red, their eyes water – especially when exposed to the wind – or that when they wake up, their eyelids stick together. Hot, windy or smoky conditions may make the problem worse.
If someone experiences pain in their eyes, if eyes are red or if vision is affected they should be referred to their GP as these symptoms may indicate another medical condition or complication.
How to treat dry eyes
There is no cure for dry eye problems, but the symptoms can be controlled and there is a great deal which can be done to help keep eyes feeling healthier. Mild to moderate dry eye problems may be treated with eye drops formulated to imitate the properties of the natural tear film. Eye drops may be prescribed or bought over the counter.
Some eye drops contain a preservative to protect them from bacteria and these are not suitable for people who need to use eye drops repeatedly during the day as the preservative may damage the eye if the drops are used for a long period. For these patients, preservative-free drops should be recommended. Contact lens wearers also need to be very careful as many types of eye drops should not be used with contact lenses, so it is important to check this before making a recommendation.
Two ingredients which may be found in drops to relieve the symptoms of dry eyes are hyaluronic acid and Tamarind Seed Polysaccharide (TSP). Hyaluronic acid is a naturally occurring polymer which has the capacity to bind up to 3,000 times its own weight in water. It is found in many parts of the body including the joints and the eyes, where it mimics the natural tear film. It greatly reduces evaporation and, hence, fluid loss from the eyes.
TSP is a naturally-occurring muco-adhesive polymer which produces a visco-elastic solution. Its chemical structure is similar to mucins – important proteins on the eye’s surface.
When the two ingredients are combined, they mimic the behaviour of natural tears, becoming less viscous during blinking and more viscous between blinks. Their ability to retain fluid means water loss is minimised so they stay on the surface of the eye for longer.
Dry eye sufferers can do a great deal to help prevent problems arising or to relieve symptoms when they experience them. The following may be recommended:
- Clean eyes – keep the eyes clean by dipping a clean cloth dipped in warm water and holding it to closed eyes for several minutes and keep the tear ducts clear by gently removing any crustiness at the inner corner of the eye
- Protect eyes – if heat, smoke or wind affect your eyes, protect them with wraparound glasses. Smokers should make every effort to quit.
- Computer eyes – computer users should make an effort to blink regularly and to move away from the screen at least once an hour to give eyes a break. The monitor should be at or just below eye level.
- Moisten eyes – try to keep the air moist, by using a humidifier, keeping a bowl of fresh water in the room and opening the windows every day.
- Feed eyes – omega-3 fatty acids are believed to help prevent dry eyes, so recommend at least two portions of oily fish, such as mackerel, fresh tuna, herring or salmon each week. People who cannot or will not eat this amount may wish to consider an omega-3 supplement.
The Mentholatum Company Ltd