1. Mucus layer
• Innermost and thinnest layer (0.02-0.05 µm)
• Consists of mucin secreted by goblet cells and glands of Manz
• Converts hydrophobic corneal surface into hydrophilic
2. Aqueous layer
• Thickest layer (6.5 to 7.5 pm) and consists of tears secreted by main and accessory lacrimal glands
• Alkaline and saltish in taste
• Contains antibacterial substances – lysozyme, betalysin. lactoferrin, immunoglobulin-A.
3. Lipid or oily layer
• Outermost layer, about 0.1 pm thick
• Consists of secretions of Meibomian, Zeis and Moll glands
• Prevents the overflow of tears, retards their evaporation and lubricates the eyelids as they slide over the surface of the globe
• Keeps conjunctiva and cornea moist
• Provides oxygen to corneal epithelium
• Washes away debris and noxious irritants
• Antibacterial activity
• Facilitates movements of the lids over the globe
1. Aqueous tear deficiency — Kerato-conjunctivitis sicca (KCS)
• Congenital alacrimia (rare)
• Pure KCS: In it only lacrimal gland is damaged by infiltration with mononuclear cells
• Primary Sjogren’s syndrome (sicca complex) consists of KCS and a dry mouth (xerostomia)
• Secondary Sjogren’s syndrome consists of sicca complcx and a connective tissue disease (usually rheumatoid arthritis)
• Riley-Day Syndrome
• Idiopathic hyposecretion.
2. Mucin deficiency dry eye
• Hypovitaminosis – A
• Severe conjunctival scarring(trachoma, Stevens- Johnson syndrome, chemical bums, radiations and ocular pemphigoid).
3. Lipid deficiency and abnormalities
• Congenital absence of meibomian glands along with anhydrotic ectodermal dysplasia (rare)
• Chronic blepharitis and meibomitis (common)
4. Impaired eyelid functions
• Bell’s palsy
5. Corneal epitheliopathies
Tear film tests
1. Tear film break-up-time (BUT)
• It is the interval between a complete blink and appearance of first randomly distributed dry spot on the cornea
• Normal values: 15-35 seconds
• Value less than 10 seconds imply an unstable tear film
• Low values indicate mucin deficiency/disturbance.
• It measures total tear secretion (production)
• It is performed with 5 x 35 mm strip of Whatman – 41 filter paper
• Normal value: 15 mm or above/5 minutes
• Values between 5 and 10 mm: mild to moderate dry eye
• Value less than 5 mm: Severe dry eye
• Low values are suggestive of aqueous deficiency dry eye (kerato-conjunctivitis sicca)
3. Rose Bengal staining
• Stains devitalized cells
• Irritating – so use xylocaine
• Three staining patterns are described:
– C-pattem: fine punctate stain in interpalpebral area (suggests mild dry eye).
– B-pattem: extensive staining (moderate dry eye)
– A pattern: confluent staining of conjunctiva and cornea (severe dry eye).
THE WATERING EYE
• Primary hyperlacrimation occurs due to direct stimulation of the lacrimal gland as in early stages of lacrimal gland tumours and cysts and due to the effect of strong parasympathomimetic drugs.
• Reflex hyperlacrimation results from stimulation of sensory branches of fifth nerve due to irritation of cornea or conjunctiva.
(a) Physiological cause of epiphora is lacrimal pump failure due to lower lid laxity or weakness of orbicularis muscle.
(b) Mechanical obstruction in lacrimal passages.
Causes of epiphora
• The commonest cause of epiphora in a newborn is membrane at the lower end of NLD
• The commonest site of obstruction in epiphora occurring in an adult is junction of the sac and the NLD.
Causes of false negative regurgitation tests
• Internal fistula
• Wrong technique of performing regurgitation test
• Encysted mucocele
As many as 30 percent of newborn infants are believed to have closure of nasolacrimal duct at birth; mostly due to membraneous occlusion at its lower end, near the valve of Hastier.
• Massage over the lacrimal sac area and topical antibiotics constitute the treatment of congenital NLD block, up to 6-8 weeks of age. This conservative treatment cures obstruction in about 90 percent of the infants.
• Probing of NLD with Bowman’s probe should be performed, in case the condition is not cured by the age of 3-4 months (some surgeon wait up to 6 months). In most instances a single probing will relieve the obstruction. In case of failure, it may be repeated after an interval of 3-4 weeks.
• Dacryocystorhinostomy (DCR) operation Optimum age is 4 years.
• It is more common than the acute dacryocystitis.
• The disease is predominantly seen in females
SWELLINGS OF THE LACRIMAL GLAND
• Mickulicz’s syndrome. It is characterised by bilaterally symmetrical enlargement of the lacrimal and salivary glands associated with a variety of systemic diseases. These include: leukaemias, lymphosarcomas, benign lymphoid hyperplasia, Hodgkin’s disease, sarcoidosis and tuberculosis.
• Dacryops. It is a cystic swelling, which occurs due to retention of lacrimal secretions following blockage of the lacrimal ducts.
• Lymphoid tumours and inflammatory pseudotumours constitute approximately 50 percent of cases.
• Benign epithelial tumours include benign mixed tumours which account for 25 percent cases.
• Malignant epithelial tumours constitute 25 per cent of cases and include: malignant mixed tumour, adenoid cystic carcinoma, mucoepidermoid carcinoma and adenocarcinoma.
Benign mixed tumour
It is also known as pleomporphic adenoma and occurs predominantly in young adult males. It is the commonest tumour of the lacrimal gland. Clinically it presents as a slowly progressive painless swelling in the upper-outer quadrant of the orbit. The eyeball may be proptosed with a down and in displacement. It is locally invasive and may infiltrate its own pseudocapsule to involve the adjacent periosteum. Histologically, it is characterised by presence of pleomorphic myxomatous tissue, just like benign mixed tumour of salivary gland. Its treatment consists of complete surgical removal with the capsule. Recurrences are very common following incomplete removal.