Dry Eye

 What is dry eye?

 

The eye is like a camera with the lens at the front and the photographic film or retina at the back of the eye. The main focusing lens is called the cornea which is the clear window at the front of the eye (where the contact lens is placed if you are a contact lens wearer).  

The front surface of the cornea is exposed to the air in the atmosphere and needs to remain smooth, clear and shiny if it is to function properly as a powerful lens that focuses light accurately to the back of the eye. The cornea is covered by a fluid layer called tears and the surface of the cornea is being continually wiped with tears (when awake) by the blinking of the lids.

The film of tears on the surface of the eye is in fact made up of 3 important layers. The first layer is a layer of mucous produced by special cells from the conjunctiva which is the skin that covers the white of the eye. This acts as a “wetting agent” to allow the next layer (the watery layer) to stick to it. The second layer is a watery layer produced by the lacrimal glands and lubricates the eyes and provides a good optical surface to the eye.  The third and final layer is an oily layer which floats on the surface of the watery layer (oil floats on water) and prevents the water from evaporating and so keeps the water there for longer. The oil is produced by a series of glands in the lids called meibomian glands and the gland opening or pores are all along the lid margin just behind where the lashes come out.

Dry eye can be due to a deficiency in all, some or just one of these layers and results in the eyes feeling gritty and sore and can also cause transient blurring of vision that improves with blinking.  In most cases of dry eye there is no underlying health problem but some patients with rheumatoid disease can have dry eye and also a dry mouth mainly due to a problem with the watery component due to poor function of the lacrimal (and salivary) glands. Patients with blepharitis (a sterile inflammatory change on the lid margins) can also suffer from dry eye as the oil layer may be deficient due to the meibomian glands producing oil that is too thick and blocks the pores of the glands as well as not providing a good oil layer to the tears and therefore allowing the water to evaporate quickly and the eye to dry.

What is the treatment for dry eye?

 

Treatment of dry eye is mainly replacing the poor tears with artificial tear drops.  There are numerous artificial tear drops on the market and to a certain extent it is a question of trial and error. There has however been a great deal of research into this area with many new types of artificial tear available in the last few years. The most important advance has been the development of preservative free drops that can be kept in a large bottle.  Preservative free drops are the best ones to obtain from the chemist. The drops can be instilled into the eyes as much as is needed to keep the eyes comfortable. The length of time drops remain effective depends on the type of drop but tear drops can be put in every hour during the day to start off with and then reduce the frequency of drops as the symptoms improve. If you are putting in other drops such as glaucoma drops make sure you leave at least 5 minutes between drops so that the artificial tear drop does not dilute the effect of the glaucoma drop.

It is also very important if you have blepharitis to treat this with lid hygiene on a regular (at least every morning) basis so that the oily component of the tear film is as healthy as possible.

If the eyes feel very stuck together and sore first thing in the morning on waking it would be advisable to put in a lubricating ointment (such as VitaPOS, lacrilube or simple eye ointment) before you go to bed at night to prevent the eyes drying out when you are asleep. Do not forget however to put the ointment in just before going to sleep as the ointment blurs the vision for a while and would make it difficult to read in bed.

 

In severe cases of dry eye special plugs called punctal plugs are inserted as an outpatient procedure with anaesthetic drops to block the begining of the tear passage from the inner aspect of the lids to the nose.  Any tears produced (or drops instilled) will therefore stay on the surface of the eye for longer as they will not be able to drain away.

In some patients there is a specific problem with the mucous layer of the tear film resulting in a condition called filimentary keratits where mucous "threads" develop on the cornea and cause discomfort.  A specific drop called Ilube (acetylcystine) is used as this drug acts to break up thick mucus.

Very severe cases of dry eye can have a drop called Ikervis (cyclosporine) prescribed.  This works over a period of weeks or months and acts in a different fashion to other lubricating drops as this drop helps increase the production of tears from the lacrimal gland rather than just replacing tears.