What is dry eye?
Dry eye is a very common problem that can occur in any age group, but is a particular problem in the older adult. About 1 in 10 adults in Australia will experience significant dry eyes.
Dry eyes occur due to a problem with the production or retention of the tear film on the surface of the eye. The tear film is very important for maintaining a healthy and comfortable eye, and is also an important part of the optical system that allows us to see clearly.
What is the tear film?
The tear film is a complex structure that consists of 3 distinct layers, all with important functions:
1.Outer OILY LAYER
This layer is made by oil-producing glands within the eyelids. This layer coats the outer surface of the tear film, and acts as an oily “slick” to smooth the tear film and reduce the evaporation of the watery layer of the tear film.
2.Middle WATERY LAYER
This is the thickest layer and is produced by a gland (Lacrimal gland) located in the upper outer eyelid. This layer moistens and keeps the eye clean by washing out any foreign irritants and particles.
3.Inner MUCUS LAYER
This layer is made by the conjunctiva (transparent membrane covering the white of the eye), and helps the watery layer spread evenly and stick to the surface of the eye.
What causes dry eye?
Dry eye is due to abnormalities in one or more of the tear film layers, which results either in a sparse tear film, or an unstable tear film that evaporates quickly from the eye. The most common cause of dry eye is an inadequate production of the watery layer of the tear film
Common causes of dry eye include:
As we get older, production of the watery layer by the lacrimal gland naturally slows down.
Androgen hormones (eg testosterone) stimulate function of the glands that produce the watery and oily part of the tear film. Reduced androgen levels are seen after the menopause, during pregnancy, in women on the oral contraceptive pill or hormone replacement therapy (especially estrogen-only pills). Thus dry eyes may occur in these patients.
(see separate Blepharitis information sheet) or Meibomian gland dysfunctioninterferes with the production of the oily layer, and results in a tear film that evaporates quickly.
Dry, dusty, windy, smoky, polluted conditions will cause or exacerbate dry eye.
Certain medications decrease tear production, such as diuretics and beta blockers (for blood pressure), anti-histamines, sleeping pills and certain anti-depressants.
Contact lens wear may cause or exacerbate dry eyes.
6.Eyelid malposition or malfunction.
Any condition that results in eyelids that do not close completely or do not blink properly, will affect the stability of the tear film. Entropion or ectropion (see separate information sheet) of the eyelids, facial palsy, Parkinson’s disease and stroke may all lead to dry eyes.
Some patients also have a naturally slow blink rate. This may cause dry eyes as they get older.
7.Specific diseases affecting tear production.
These include Sjogren’s syndrome and vitamin A deficiency.
8.Trauma, inflammation or surgery to the surface of the eyes.
Any severe infection, burn, chronic inflammatory condition or surgery to the surface of the eyes may affect the tear film and lead to reduced tear production or an unstable tear film.
How do I know that I have dry eye?
Patients with dry eye will have one or more of the following symptoms:
- feel dry
- itchy, scratchy, burning, foreign-body sensation, stabbing pains
- tired eyes
- forced blinking
- intermittent misty vision, which clears on blinking
- “watery eyes”
It is important to recognise that dry eyes can cause watery eyes. This is because the eyes will increase production of the watery layer of the tear film in response to any sensation of dryness or irritation. This reflex watering will often occur when outdoors or in windy, dry and dusty conditions, and may result in tears running down the cheeks.
Dry eye symptoms are often worse at the end of the day, and after any concentration-type activity such as reading or computer work. This is because you do not blink as much whilst performing these activities, which accelerates tear evaporation.
Your ophthalmologist will perform a comprehensive examination of your eyelids and eyes to diagnose dry eyes, look for any treatable causes, and assess for any complications of dry eyes. Sometimes they will assess your tear production (Schirmer’s test) with paper strips placed in the lower eyelid. If a specific disease that affects tear production is suspected, other investigations may be performed.
Can dry eye affect my vision?
Dry eye is not usually sight-threatening.
However, a smooth and uninterrupted tear film is very important for clear vision. The tears also nourish and oxygenate the cornea of the eye, which is a vital structure in vision.
Severe dry eyes may affect vision by intermittently interfering with the tear film, or by increasing the risk of infection or problems of the cornea.
How is dry eye treated?
There is no cure for dry eye. However, there are many treatments available that can minimise or eliminate the symptoms of dry eye. The effectiveness of these treatments depends on how well they are used, and usually need to be used for life.
Every patient with dry eye will be prescribed artificial tear replacements, either as eye drops, gels or ointments. There are many products on the market, with no product shown to be superior to any other. The success of treatment depends on the frequency at which the drops are used. Using drops once or twice a day is generally regarded as useless. For most patients with dry eye, a minimum of 4 times a day is required. In severe dry eye, you may be started on an intensive regime of 1-2 hourly drops, and then weaned down to a more manageable maintenance dose.
Artificial tears may come in preserved or non-preserved forms. If you are using tears more than 4 times per day, a non-preserved lubricant should be prescribed to avoid any toxicity or irritation from frequent use of preservatives. Your ophthalmologist will advise you on this.
Drops are easier to use than gels or ointments, but do not last as long. Gels and ointments are messier to use, and may temporarily blur the vision, but last longer in the eye. Each patient needs to find the combination of lubricants that suits their lifestyle best. Most patients will use drops/gels during the day, and an ointment at night before bed.
2.General measures to improve the tear film
As well as artificial tears, patients with dry eye should also:
- Drink plenty of water during the day
- Consider fish oil or flaxseed oil supplements (if not contraindicated), which have been shown to improve the oily layer of the tear film
- Remember to blink frequently, especially whilst performing concentration-type activities
- Optimise your environment. Avoid dry, dusty, windy conditions. Wear wrap-around sunglasses when outdoors. Avoid air-conditioned or over-heated rooms. Use a humidifier.
3.Specific measures to improve the tear film
Many patients with dry eye also have blepharitis (see separate information sheet on Blepharitis). Treatment of blepharitis with warm compresses and eyelid scrubs can greatly improve the oily part of your tear film and reduce tear film evaporation
If you are a contact lens wearer, minimise the time of lens wear. In some cases, a different type of lens be better tolerated if you develop dry eye.
If you are on any medications that exacerbate dry eye, consult your general practitioner to see if they can be ceased or changed to an alternative medication.
The tears normally drain into 2 small openings in the inner eyelids (one in the upper eyelid, and one in the lower eyelid), known as the puncta. These are the entry points into the tear drainage system, which continues into a tear sac (lacrimal sac) and a tear duct (nasolacrimal duct) located in the nose. That is why our nose runs when we cry.
In severe dry eyes, where artificial tears are not sufficient, occlusion of the puncta may be performed by your ophthalmologist. By blocking the puncta, the rate of tear drainage is reduced and tears can moisten the eye for longer. Punctal occlusion can be performed with:
These tiny plugs are made of collagen or silicone, are may be temporary or permanent. They are quickly, easily and painlessly inserted in the office, under the slit lamp microscope. There is no need for any anaesthetic. Tears can still drain around the plugs, but at a much slower rate. If they cause any irritation or over-watering of the eye, they can be just as easily removed.
b) Cautery or suture
Sometimes, in severe cases, your ophthalmologist may choose to entirely and permanently close the puncta with cautery (heat) or a suture. This is performed under local anaesthetic in the operating theatre.
5.Procedures to improve eyelid closure or blinking
In conditions where the eyelids do not close completely, are in an abnormal position or do not function/blink properly, surgery may be undertaken:
- Ectropion or entropion surgery (see separate information sheet)
- Tarsorrhaphy (sutures are used to temporarily or permanently close the outer or inner corners of the eyelids) to improve eyelid closure
- Gold weight insertion into the upper eyelid to improve eyelid closure or blinking
In certain cases, specific medications are used to treat severe dry eye, and include:
- Cyclosporine (0.05%) eye drops
- Autologous serum eye drops
These are usually reserved for cases where there is also severe disease of the surface of the eye.