Keratoconjunctivitis Sicca (KCS) or Dry eye syndrome is mainly caused due to aqueous tear deficiency.
As per Dry Eye Workshop (DEWS) 2007, KCS is defined as ‘a multifactorial disease of the tear film and ocular surface that results in symptoms of discomfort, visual disturbance, and tears film instability with potential damage to the ocular surface. It is accompanied by increased osmolality of tear film and inflammation of the ocular surface’.
Tear film has three components:-
A defect in any component of tear film may lead to dry eye syndrome but primarily it is from aqueous tear deficiency.
Tears have smaller basic (resting) and larger reflex component. Reflex secretion occurs due to corneal sensory stimulation.
Effective spread and resurfacing, in addition to normal tear film, requires:-
Many patients do not have any symptoms. Some may have noticed deficient or reduced tears on peeling onions or even being emotional.
Common symptoms are:
Less common symptoms may include:
A. Aqueous layer deficiency :- It can be :
B. Dry eye due to evaporation of tears :- It can be :
Dry eye should be distinguished from other diseases affecting anterior surface of the eye e.g. conjunctivitis, infectious diseases, corneal abnormalities or keratopathies. Diagnosis depends upon clinical examination of eyes and conduct of certain specialised tests.
Tear film may show :
1. Increase in mucous strands due to accumulation of lipid contaminated mucin in the tear film. Mucous debris move with blinking.
2. Normally marginal tear meniscus is about 1mm high and convex. In dry eye, it is concave or absent altogether.
3. Froth in the tear film or along the lid margin.
Corneal examination may show :
1. Punctate lesions on cornea.
2. Mucous plaque formation. These are slightly elevated lesions on cornea.
3. Corneal filaments with one end attached to cornea and are very painful.
Tear film break-up time (BUT) :
This is the interval between last blink and the appearance of first dry spot.
Fluorescein dye is instilled in the eye and patient blinks to spread it and then stops blinking. Eye is examined under cobalt blue filter. After an interval, appearance of black spots or lines indicate formation of dry areas. Formation of dry area at same spot shows local corneal abnormality and is ignored. A BUT of less than 10 seconds suggests dry eye.
Rose Bengal test :
Rose Bengal dye stains mucus, dead and devitalised cells on cornea, being produced by dry eye. Use a small drop only since it causes ocular irritation, but local anaesthesia should not be instilled to avoid false positive results.
Lissamine green test :
Lissamine green dye stains both, healthy cells not covered by mucin as well as devitalised or dead cells. It does not cause irritation and stinging sensation like Rose Bengal dye but staining is more transient.
Schirmer’s test :
This test measures wetting of special filter paper ( Whatmann No.41) ,which is 35 mm long and 5 mm wide, when placed at the junction of middle and outer third of the lower eye lid. Eye is dried gently and patient keep eyes open and blinks as necessary. It measures basic and reflex secretion(Schirmer’s test 1). But when this test is done under topical anaesthesia(Schirmer’s test 2), it measures basic secretion mainly, since it reduces reflex secretion but does not abolish it completely.
Wetting is measured after 5 minutes. Less than 10 mm of wetting without anaesthesia and less than 6 mm of wetting after anaesthesia is considered abnormal.
InflammaDry test (Rapid Pathogen Screening Inc), 2013 :
InflammaDry test is a recent, FDA approved, rapid in-office test taking less than 2 minutes. It measures inflammatory marker matrix metalloproteinase-9 levels in tears. Matrix metalloproteinase-9 level is elevated in the tears of patients with dry eye disease.
Impression cytology :
Impression cytology determines population of mucin secreting goblet cells. It helps to monitor progression of ocular surface changes leading to dry eye.
Quantitative measurement of tear components :
Measurement of tear film osmolarity or analysis of tear proteins aids in diagnosis of dry eye.
Other tests that may be used are :
a. Tear stability analysis system.
b. Tear ferning test.
c. Tear function index.
Sjögren syndrome as a cause of KCS may be excluded by appropriate immunological blood tests and biopsy of labial salivary glands.
Aim is to provide symptomatic relief to patient. A smooth corneal surface prevents its further damage and aggravation of symptoms.
Various modalities may be :
Complications are usually not there or are minimal in mild to moderate KCS.
Severe cases may show :
b. Breakdown of epithelial layer covering front of eye.
c. Superficial peripheral vascularisation of cornea.
d. Secondary bacterial infection of cornea.
e. Descemetocele formation.
f. Melting of cornea.
g. Corneal perforation and its sequlae.