Pharmacy Technician’s Guide – Dry eye disease: pathophysiology and risk factors

Dry eye disease is one of the most common chronic conditions, and is estimated to affect between 1 in 3 and 1 in 20 people^[1]
. Symptoms of dry eye disease, which usually affect both eyes, include:

• Irritation;
• Grittiness or feeling of sand in the eye;
• Burning;
• Soreness;
• Watery eyes;
• Visual disturbance.

These symptoms can occur in other conditions so diagnosis of dry eye disease can be a challenge. Other conditions with similar symptoms include hayfever and conjunctivitis. Hayfever usually occurs in combination with other symptoms, such as sneezing and itching. Bacterial conjunctivitis can also cause a sensation of grittiness and watery eyes, but symptoms usually start in one eye. The eye can become red and a yellow, sticky mucus is often present.  

If a patient enters the pharmacy with eye symptoms, there are several questions pharmacy staff can ask to help find out whether their symptoms may be related to dry eye disease^[2]
. Patients struggle to self-diagnose dry eye, so technicians should listen out for these symptoms and terms. These questions include:

• Is the dryness/burning/watering in both eyes? If the symptoms are in only one eye, it may be an indication of another condition, such as having a foreign body in the eye or bacterial conjunctivitis.
• How long has it lasted? If symptoms are severe with a sudden onset, this may be an indication of a more serious condition.
• Do you have mouth dryness? This could be a symptom of Sjögren’s syndrome.
• Was it precipitated by an event? Again, if the symptoms are brought on after a specific event, such as a head injury, this could be an indication of a more serious condition.
• Are you in pain? Patients with dry eye disease may feel discomfort or soreness, but severe pain may be an indication of a more serious condition.
• Does your vision clear when you blink? Dry eye disease may cause some slight visual disturbances, but this should clear when the patient blinks. If visual disturbance or difficulties persist, it may be a sign of something more serious.
• Is there redness or swelling? Patients with dry eye disease, or related conditions such as blepharitis, may have redness or swelling in their eyelids, but their eyes are likely to be unaffected. Pinkness in the whites of the eyes can be a sign of bacterial conjunctivitis.

Using these questions, pharmacy technicians can find out whether symptoms are likely to be related to dry eye disease, or whether patients need to be referred for another condition. If symptoms are mild and likely to be related to dry eye disease, pharmacy technicians can provide treatments and lifestyle advice. However, for a diagnosis of dry eye disease, patients should visit their optician or eyecare specialist.

When can pharmacy staff help?

Eyecare specialists are best placed to make a dry eye diagnosis; however, community pharmacists and pharmacy technicians may be able to help patients who come into the pharmacy in the following circumstances:

• If a patient has already received a diagnosis of dry eye disease and is looking for advice and relief of symptoms;
• If a patient is experiencing the symptoms for the first time, they may require advice and temporary relief of symptoms;
• If a patient has experienced the symptoms before and has previously found that over-the-counter treatments are effective.

Different advice and recommendations are appropriate depending on the severity and type of dry eye disease. There are two main types of dry eye disease: aqueous deficiency and evaporative dry eye. Each is caused by a different mechanism affecting the tear film in the eye.

Structure of the tear film

The tear film is a complex structure which comprises three layers:

• An oily layer, which prevents evaporation;
• A watery layer containing nutrients and essential proteins, which protect the eye;
• A sticky mucous layer.

Each part is made by special glands, including:

• The lacrimal gland (the main gland that produces the watery layer);
• Mucous glands (distributed across the surface of the eye);
• Meibomian glands (glands that produce the oily layer, running vertically in the upper and lower eyelids, opening just behind the roots of the lashes)^[3]
  .

The tear film is spread across the surface of the eye by the eyelids when eyes blink, and drains into the tear ducts (in the corner of the upper and lower lids) and then into the nose.

Types of dry eye disease

Evaporative dry eye is associated with an insufficient oily layer in the tear film, which can occur when the meibomian glands are damaged. Around 80% of patients with dry eye disease are affected by this type.

Aqueous deficient dry eye, on the other hand, occurs when the lacrimal glands do not produce enough of the watery component of tears to maintain a healthy eye surface.

These can occur individually or in combination.

Diagnosis of dry eye disease^[4]

There are several tests that can be used to help eyecare specialists diagnose dry eye disease. These include:

• Non-invasive tear film break-up time. This is defined as the time taken to observe the first complete disruption in a light reflection off the tear film surface after a blink.
• Fluorescein dye test. Eye drops containing a yellow-orange dye are used to see the tears more clearly. This helps to assess how long it takes for the eye to start drying out. Advise patients who are concerned about the dye that it is only temporary. The colour of the dye will fade — it simply helps to show damaged areas of the eye.
• Schirmer’s test. Small strips of blotting paper are hooked over the lower eyelid. After five minutes, the strips are removed and studied to determine how wet the paper is. If the paper has wetted less than 10mm in five minutes, this indicates dry eye disease.
• Phenol red test. This is similar to Schirmer’s test, but uses a pH indicator hooked over the lower lids instead of paper, and is required to sit on the lower lid for only 15 seconds.
• Lissamine green test. Lissamine green is a dye in a paper strip. The strip is diluted with a salt solution (saline) and dropped on to the surface of the eye. The green dye allows the specialist to see early damage to the surface of the eye.
• Blink test. The blink test and non-invasive tear break-up time test require an individual to report how long they can prevent their eyes from blinking while staring at a screen, with ≤10 seconds leading to a suggestion that they may have dry eye this test can easily be performed by technicians in the pharmacy, however, the results of both the blink test and non-invasive tear break-up time test should not be considered a diagnosis, but may prompt further conversation.
• Slit lamp biomicroscopy. This involves observing the eye at high magnification with specific lighting techniques to examine the redness of the eye, the meibomian glands and the tear film in greater detail.

Some questionnaires can be used to help with diagnosis of dry eye disease or to assess how severe it is. Examples of these include the Dry Eye Questionnaire, Ocular Surface Disease Index, McMonnies test, SPEED test and Salisbury Eye Evaluation.

Risk factors for dry eye disease

There are several factors that can increase a person’s risk for dry eye disease or that can trigger an underlying condition. These can include being in a hot or windy climate and getting older — up to a third of people aged 65 or older may have dry eye syndrome^[3]
. Women are also more likely to be affected by dry eye disease than men, and hormonal changes such as pregnancy or menopause can be a trigger for the condition.

Having certain diseases is also associated with dry eye disease^[3]
. These diseases include:

• Allergic conjunctivitis;
• Contact dermatitis;
• Sjörgen’s syndrome;
• Rheumatoid arthritis;
• Lupus;
• Scleroderma;
• Bell’s palsy;
• HIV;
• Diabetes, especially if patients have high blood sugar.

Recent laser eye surgery (LASIK surgery) temporarily disrupts the normal activity of the tear film mechanism. Also, during laser surgery, the majority of the superficial nerve fibres in the cornea are cut, which increases the sensation of dryness and reduces the production of aqueous tears. This can lead to several months of dry eye symptoms, which usually resolve themselves.

Patients who take certain medicines may also be more susceptible to dry eye disease. These medicines include antihistamines, antidepressants (tricyclic antidepressants and selective serotonin inhibitors), beta-blockers and diuretics. Patients who wear contact lenses are also more likely to experience dry eye disease.

Evaporative dry eye can be caused by related eye and skin conditions, such as blepharitis or rosacea. Blepharitis is a condition where the edges of the eyelids become inflamed, causing itchy, sore and red eyelids that stick together, crusty or greasy eyelashes, a burning, gritty sensation in the eyes and increased sensitivity to light. One type of blepharitis, posterior blepharitis, can cause the meibomian glands to become blocked and dysfunctional, which affects the oily layer of the eye and leads to dry eye. Rosacea, a condition in which the skin on the face becomes red and blotchy, can also lead to blockage of the meibomian glands and, therefore, evaporative dry eye disease.