Dry Eye and Ocular Surface Disease
What does the Tear Film do?
The tear film has many functions and responsibilities including:
- providing the smooth optical surface required for clear vision,
- providing oxygen and metabolic needs to the ocular surface (corneal epithelium and conjunctiva),
- ocular surface hydration and lubrication,
- ocular surface protection (e.g., rinse away irritants),
- and antibacterial protection via substances such as lysozyme, lactoferrin, betalysin, and immunoglobulin.
How is the Tear Film Structured?
The tear film is comprised of three layers:
- The superficial lipid layer: prevents the evaporation of the aqueous layer. It is secreted primarily by the meibomian glands.
- The middle aqueous layer: provides most of the functions of the tear film. It accounts for 99% of the tear volume and is secreted by the lacrimal and accessory lacrimal glands.
- The inner mucin layer: is responsible for enabling the tear film to spread evenly on the corneal epithelium which is usually hydrophobic ("water-hating") by making it hydrophilic ("water-loving"). It is secreted primarily from the goblet cells of the conjunctiva.
What are the Causes of Dry Eye and Ocular Surface Disease?
Dry eye is due to a decrease in the quantity or quality of the tear film. This results in a number of adverse changes to the ocular surface associated with the decreased function of the tear film (from very mild to severe changes). Ocular surface disease refers to not only "true" dry eye (unknown cause, any age or sex but often in older postmenopausal women) but also a spectrum of conditions which include the following:
- Blepharitis/Meibomianitis
- Contact Lens Associated
- Medication Induced (e.g., certain over-the-counter eye drops, certain antihistamines)
- Environmental/Toxic (e.g., wind, dust, air-conditioning, low humidity)
- Decreased Blink Rate (e.g., with computer use, with reading, nerve palsy)
- Exposure/Anatomical (e.g., incomplete eyelid closure, incomplete blinking)
- Scarring of ocular tissues (loss of gland function)
- Autoimmune conditions such as Keratoconjunctivitis Sicca (KCS) (alone or with Sjörgen's syndrome)
(Note: These conditions in themselves can also be the cause of dry eye)
What are the Signs and Symptoms of Dry Eye and Ocular Surface Disease?
The signs and symptoms of dry eye and ocular surface disease include:
- Burning
- Tiredness
- Redness
- Grittiness/Sensation of "Sandpaper"/Foreign Body Sensation
- Tearing (due to reflex tearing)
- Light Sensitivity (Photophobia)
These symptoms usually present themselves in both eyes. However, sometimes the symptom is reported in only one eye. The patient's symptoms are sometimes fairly severe and out of proportion to the clinical findings. Dry eye is sometimes difficult to differentiate from allergic conjunctivitis because of the similarity of symptoms. In addition, because of the poor tear film function associated with dry eye, it is often the cause of worsened symptoms of any associated allergy (i.e., tear film is not able to "rinse away" any allergens). Treatment of a dry eye will often reduce the signs and symptoms associated with mild allergies.
How do you Treat/Manage Dry Eye and Ocular Surface Disease?
The examination of dry eye and ocular surface disease should start with a thorough case history. A physical exam of the eye and associated structures should then be conducted. Special test procedures may be required to determine the cause of the dry eye and ocular surface disease. Multiple and simultaneous causes of dry eye and ocular surface disease are often present. Upon the determination of the cause(s), the necessary treatment, management, or appropriate referral can then be arranged.
Treatment and management of dry eye and ocular surface disease includes:
- Use of artificial tears (most common treatment, preservative or preservative-free, frequency of instillatio can vary from as needed to hourly)
- Use of gel lubricants (daytime or before bed)
- Use of lubricating ointments (daytime or before bed)
- Punctal occlusion (intentionally block the tear drainage system)
- Omega-3 fatty acid supplementation (may improve tear film quantity/quality after ongoing use)
- Use of medicated eyedrops for short or long term e.g., topical steroid or cyclosporin
- Patient education and counselling (e.g., understanding chronic nature of condition and ongoing management required, understanding environmental factors)
- Management of associated conditions (e.g., daily eyelid hygiene procedures for blepharitis, consider discontinuation of contact lenses)
Dry eye and ocular surface disease is usually a chronic (ongoing) condition. Treatment and management will vary depending on the severity of the signs and symptoms. Fortunately, although not curable, appropriate treatment can usually adequately manage the signs and symptoms associated with this condition. In addition, ongoing research in this area may produce new methods/medications to help improve the treatment of this condition.