Dry Eye Explained
The two main types of Dry Eye Disease can occur independently or co-exist. The signs and symptoms of both affect the entire ocular surface, including the tear film, cornea, conjunctiva, eyelids, lacrimal and meibomian glands.
Tears have three layers:
An outer lipid layer produced by the meibomian glands to prevent the tear film from evaporating.
A middle aqueous layer produced by the lacrimal glands that helps hydrate the eye, repel bacteria, protect the cornea and bring important electrolytes to the surface of the eye. This watery layer also helps smooth the surface of the eye and allows it to refract light so you can see clearly.
An inner mucin layer that helps the tear film spread evenly across the surface of the eye. This layer is produced by conjunctival goblet cells, specialized epithelial cells that secrete mucus onto the surface of the eyes.
Evaporative Dry Eye
Evaporative Dry Eye or EDE is due to a deficient tear film lipid layer, which increases tear evaporation. It is caused by meibomian gland dysfunction, which occurs in over 85% of dry eye disease. Blepharitis, or lid margin inflammation, is both a cause and an effect of meibomian gland dysfunction. The differential diagnosis of blepharitis includes ocular rosacea and atopy, seborrhoeic dermatitis, staphylococcal infection and Demodex mite infestation. Tear deficiency is thought to alter resistance to infection, so dry eye disease is both a cause and an effect of blepharitis.
Aqueous Deficient Dry Eye
Aqueous tear-deficient dry eye or ADDE occurs when your body doesn't produce enough water for your tears, leading to dry eyes. ADDE is classified into two groups: Sjogren's and Non-Sjogren's. Sjogren's syndrome is an autoimmune disorder that predominantly affects women and may be due to an abnormal immune response to environmental or viral triggers in susceptible patients. It mainly targets the lacrimal and salivary glands and can cause gland destruction and signs and symptoms of dry eye and mouth. Aqueous Deficient Dry Eye that is Non-Sjogren's can involve congenital or acquired forms of Dry Eye Disease. Causes can include damage to the lacrimal gland, aging of the ocular surface, viral infection, or other systemic conditions. Another contributing factor includes decreased corneal sensation, which can be brought on post-refractive surgery or secondary to disease.
Blepharitis
Blepharitis is a common condition that causes inflammation of the eyelids. It may be associated with flakes on the eyelashes, loss of eyelashes, eye redness, dry eyes, light sensitivity, and irritation of the eyes. There are two main types of blepharitis, anterior blepharitis and posterior blepharitis, both characterized by inflammations of the glands on the eyelids. Anterior blepharitis causes inflammation of the glands along the base of the eyelashes and is most often associated with the presence of excessive bacteria at the lid margin, particularly Staphylococcus. Posterior blepharitis causes inflammation and obstruction of the oil glands along the waterline. It is often associated with systemic disease such as acne rosacea atopic dermatitis, and seborrheic dermatitis. Blepharitis can also be caused by an infestation of mites, called Demodex, at the lid margin. Blepharitis is a chronic condition with no cure and requiring maintenance but there are several ways to treat blepharitis and patients can manage it themselves with good eyelid hygiene at home. Click on the diagram to visit the CAO’s page on Blepharitis.
Meibomian Gland Dysfunction
The most common causes of Evaporative Dry Eye are miebomian gland obstruction or a decrease in the secretion of meibum. This means the glands aren't producing either the quantity or quality of oil needed to prevent the eyes from getting dry. MGD can be congenital or acquired and can be attributed to various risk factors such as hormonal factors, systemic and topical medications, dietary intake, contact lens wear and more. Click the diagram to view the clinical study for more information and other linked studies.
Lid Hygiene for Blepharitis and Demodex
The most common treatment for blepharitis is eyelid hygiene - cleaning the eyelid margin and lashes using a medical grade lid wipe. Previous treatment modalities used to recommend baby shampoo which has since been proven to cause damage to goblet cells which are needed to produce the proper tear film composition.
Blepharitis is commonly associated with dry eye disease, meibomian gland dysfunction and even rosacea. Demodex, which are mites that live in hair follicles, can attach to eyelashes and are commonly found alongside Blepharitis and can lead to inflamed, itchy lid margins. When Demodex are present, additional treatments such as a gentle Okra based product may be recommended. In office treatments using intense pulsed light (IPL) can also kill Demodex mites and help with blepharitis management.
