Understanding ocular surface disease and glaucoma

We’re delighted to bring you this article on the topic of ocular surface disease and its relationship with glaucoma, a subject requested by one of our valued members. This article is a collaborative effort between Robyn Asprey, Glaucoma UK’s Development Manager (Outreach Services), and Dan Calladine, Consultant Ophthalmologist and founder of OcuPlan. 

OcuPlan’s partnership with Glaucoma UK aims to enhance patient awareness of glaucoma and the different eye care choices available to them. This article focuses on ocular surface disease and its significance for individuals managing glaucoma. 

We know that many people with glaucoma might also experience ocular surface disease. When talking about ocular surface disease, we are talking about the front, outside surface of the eye. This includes the white of the eye, the clear window at the front of the eye (the cornea), and the underneath and edges of the eyelids. This part of the eye is very sensitive as you may have felt if you have ever had an eyelash go into your eye! Because of this sensitivity, if the surface of the eye becomes dry, it can feel very uncomfortable. 

The front of the eye is also incredibly important for vision. The shape of the eye determines what we can see. About 90% of our ability to focus comes from the shape of the cornea. A key part of the ability to focus is the tear film on the surface of the cornea. The tear film is the first thing that light hits when it comes into the eye. So if the tear film is distorted because of ocular surface disease, the vision is likely to be blurred. 

The surface of the eye is constantly moist. Because of this, it is very sensitive to the environment. If an irritant enters the eye, it moves across the surface of the eye quickly through the tears. So, it is not surprising that glaucoma drops have a huge impact on the surface of the eye, in terms of vision and discomfort. 

There are two types of tears – natural tears and crying tears. Natural tears are produced constantly, because they’re full of important components including water, electrolytes, oils, mucus and lots of different proteins. Crying tears are much saltier. Crying tears can wash away natural tears – that is why if you have been crying for a long time, your eyes can become really sore. If you don’t have enough natural tears, the eyes can become irritated. This irritation can cause the eyes to water. Therefore, one of the first signs of ocular surface disease is that your eyes start to water lots, which can seem confusing. This is because the irritation that is caused by not having enough natural tears means that you produce more crying tears. 

Natural tears are made in three places: in the lacrimal glands just above the eye, the meibomian glands in the eyelids and the goblet cells in the white of the eye. Each area produces a different part of the tears. The lacrimal glands produce the water, the meibomian glands produce oil and the goblet cells produce mucus. These three parts of the tears are formed roughly in layers, with the mucus layer sticking the tear to the eye, the watery layer sitting in the middle, and the oily layer floating on top. The purpose of these tears is to lubricate the eye, protect the surface of the eye and maintain clarity of vision. When a person experiences ocular surface disease, it is often because there isn’t the right balance of the three layers of the tear film. 

Different people will experience ocular surface disease differently, depending on which layer of the film is most affected. Eye specialists can tell which layers of the tear film are most affected by using dyes. There is a green dye that sticks to the mucus layer, and there is a yellow dye that dissolves in the watery layer. These show what type of ocular surface disease a person has. 

Symptoms for ocular surface disease, can vary depending on how severe the disease is. They can include: 

• Very watery eyes, especially if it is windy. 
• Fluctuating vision that you may need to blink to clear. 
• Mucus build-up. 
• Difficulty opening your eyes in the morning. 
• Tiredness in your eyes as the day goes on. 
• Pain in your eyes. 
• Stinging when you put your eye drops in. 
• Difficulty getting the right prescription for your glasses. 

A person may develop ocular surface disease for many reasons. These include not producing enough natural tears. There may be a number of reasons why not enough natural tears are being produced. Examples include: 

• Age 
• Medication – including beta blockers and previous chemotherapy 
• Hormones – especially during menopause 
• Medical conditions – including rheumatoid arthritis and thyroid issues 

Ocular surface disease may also be caused by inflammation, especially if you are allergic to something that makes its way into the eye. Some people may experience this if they have an allergy to glaucoma drops or during hay fever season. There may also be an issue with how the oil glands in the eyelids are working. If the glands get blocked, as the oil gets thicker with age, this can make it harder to come out onto the surface of the eye. This can lead to a lack of oil in the tears, which can be red, sore and itchy. The environment can also play a big part in ocular surface disease. Central heating, air conditioning, wind and sun can all cause ocular surface disease to feel worse. 

One reason why many people with glaucoma may be more prone to ocular surface disease is due to the chemicals in the eye drops. Glaucoma drops are designed to reduce the pressure inside the eye, not necessarily to protect the front of the eye. In fact, the drop needs to be able to get into the eye in order to work effectively, so it may actively be breaking down the surface of the eye in order to do that most effectively. The chemicals eye in many glaucoma drops are preservatives. These are added to reduce the risk of infection within the bottle. Many glaucoma drops are now available as preservative-free options and may be preferable for people with ocular surface disease. If you are using a single dose unit, or an eye drop bottle that is almost flat on the top with a little blister in the middle, it is likely to be preservative free. If the bottle is a more traditional shape with the more pointed top, it is likely to contain preservatives. If you are not sure if your glaucoma drop contains preservatives, please give our helpline a call and they will be glad to help. 

People often ask us what they can do to help manage their ocular surface disease. Here are a few suggestions: 

• Avoid things that are likely to aggravate it such as air conditioning. 
• Use some artificial tears to help lubricate the eye where the natural tear is not effectively able to. Check the label to make sure these are preservative free. 
• Clean the edges of your eyelids thoroughly morning and evening. This can help to reduce some of the blockages in the meibomian glands. Place a warm flannel or heated eye mask on the eyes for 1-2 minutes, and then wipe the edges of the eyelids thoroughly. More information can be found in our ‘blepharitis’ leaflet which you can order here.
• Lower the amount of Omega 6 being eaten and increase the amount of Omega 3. Omega 6 is found in sunflower and vegetable oils, so swapping them for oils found in fish or walnut oils may help. This can help with meibomian gland function. 
• Ask your eye specialist if your glaucoma drops are preservative free. If they are not, ask to swap to some that are. 
  

Here are some tips for using artificial tears: 

• Choose the right type: There are many different types of artificial tears available over the counter, it can be hard to know which to choose. Always opt for preservative-free options to minimise irritation.
• Consult professionals: If you’re unsure which product to choose, consult a pharmacist or optometrist for recommendations. 
• Testing and adjustment: Use the drops regularly for a week, applying them every 1-2 hours and monitor your symptoms. 
• Evaluate effectiveness: If your symptoms improve, continue using the same type. If not, try a different product. 
• Expect trial and error: Finding the right artificial tears can be a process of trial and error, so be patient as you determine which works best for you. 

Most people with ocular surface disease can manage their symptoms at home. Sometimes, though, the disease may progress and additional medical help may be needed. For example, if a person has very inflammatory dry eye (a type of ocular surface disease), they may need a course of steroid drops to help manage it. Alternatively, they may need to have small devices put into their tear ducts (where the tears drain out of the eye) called punctal plugs. These keep the natural tears, and the artificial tear drops in the eye for longer. 

There is help that can be provided for ocular surface disease, you don’t need to just live with it. If you have tried the suggestions in this article, please speak to your eye specialist. Alternatively, you can email the Glaucoma UK helpline at helpline@glaucoma.uk or call them on 01233 64 81 70 for more support.