Definitions
- ◾
Keratoconjunctivitis sicca (KCS) : eye with some degree of dryness.
- ◾
Xerophthalmia : dry eye associated with vitamin A deficiency.
- ◾
Xerosis : extreme dryness with keratinization occurring secondary to severe conjunctival cicatrization.
- ◾
Sjögren syndrome : autoimmune inflammatory disease of which KCS is a typical feature (see below).
Physiology
The tear film has three layers ( Fig. 5.1 ):
- ◾
Lipid layer : secreted by the meibomian glands. Functions: (a) to prevent evaporation and maintain tear film thickness, (b) to act as a surfactant allowing spread of the tear film.
- ◾
Aqueous layer : secreted by the lacrimal glands. Functions: (a) to provide oxygen to the corneal epithelium, (b) antibacterial activity, (c) to wash away debris, (d) to optically enhance the corneal surface.
- ◾
Mucous layer : secreted principally by the goblet cells. Functions: (a) lubrication, (b) permits wetting by converting the corneal surface from a hydrophobic to a hydrophilic state.
- ◾
Regulation of tear film components : (a) hormonal, especially androgens, oestrogens and progesterones, (b) neural.
Mechanism of disease
The four core inter-related mechanisms responsible for the manifestations of dry eye are: (a) tear instability, (b) tear hyperosmolarity, (c) inflammation, (d) ocular surface damage.
Classification of keratoconjunctivitis sicca
- ◾
Aqueous layer deficiency : (a) Sjögren syndrome, (b) non-Sjögren age-related hyposecretion, (c) absence or damage to lacrimal tissue, (d) conjunctival scarring with obstruction of lacrimal gland ductules, (e) neurological lesions with sensory or motor reflex loss, (f) vitamin A deficiency.
- ◾
Evaporative : (a) meibomian gland disease, (b) exposure keratopathy, (c) defective blinking, (d) contact lens-associated, (e) environmental factors.
Sjögren syndrome
Pathogenesis:
autoimmune inflammation and destruction of lacrimal and salivary glands occurring in isolation (primary), or in association with other diseases such as rheumatoid arthritis and systemic lupus erythematosus (secondary); affects females more commonly than males.
Diagnosis
- ◾
Presentation : adult life with grittiness of the eyes and dryness of the mouth (xerostomia).
- ◾
Signs : (a) enlarged salivary and occasionally lacrimal glands, (b) xerostomia with a fissured tongue, (c) dry nasal passages, (d) diminished vaginal secretions, (e) Raynaud phenomenon, (f) arthralgia, myalgia and fatigue.
- ◾
Complications : (a) dental caries, (b) reflux oesophagitis and gastritis, (c) malabsorption due to pancreatic failure, (d) pulmonary disease.
- ◾
Investigations : (a) serum autoantibodies, (b) Schirmer test, (c) biopsy of minor salivary glands.
Treatment:
symptomatic (see below), salivary stimulants and immunosuppression.
Diagnosis of dry eye syndrome
Symptoms
- ◾
Dryness, grittiness and burning, characteristically worse during the day.
- ◾
Stringy discharge, transient blurring of vision, redness and crusting of the lids are common.
Signs
- ◾
Marginal tear meniscus is thinned or absent (normal height 1 mm).
- ◾
Corneal punctate epithelial erosions ( Fig. 5.2A )
