Classification and Diagnosis of Dry Eye
Classification of Keratoconjunctivitis Sicca
The condition of keratoconjunctivitis sicca (KCS) is synonymous with that of dry eye. According to the International Dry Eye Workshop (DEWS) the dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface. It comprises two subgroups: tear- or aque-ous-deficient dry eye (aqueous tear deficiency) is due to a failure of lacrimal func-tion while evaporative dry eye is due, predominantly but not entirely, to lipid tear deficiency . Either form may cause damage to the interpalpebral ocular sur-face and is associated with symptoms of ocular discomfort. A unifying mechanism
is tear hyperosmolarity, which can directly cause damage to surface epithelial cells. However, an additional factor is the release of pro-inflammatory cytokines in the lacrimal gland and tears, which can both initiate autoimmune lacrimal damage, as in Sjogren's syndrome, or perpetuate chronic conjunctival inflammation.
The commonest form of tear-deficient KCS is non-Sjogren's dry eye, whose age-related form has a prevalence of about 15% in the older population. It is due to a T-cell infiltration of the lacrimal gland which reduces secretory function. Non-Sjogren's dry eye can be caused by other lacrimal diseases such as graft-ver- sus-host disease and sarcoidosis, by lacrimal obstruction in cicatricial conjuncti¬val diseases (e.g. ocular pemphigoid, Stevens-Johnson syndrome and trachoma) and also by reduced sensation at the ocular surface, leading to a loss of afferent reflex drive to the lacrimal gland. Sjogren's syndrome is a less common disorder, with a prevalence of about 0.2-0.5%. It is an autoimmune exocrinopathy giving rise to dry eye and dry mouth and affects other mucous membranes and even the central nervous system. Primary Sjogren's syndrome occurs in the absence of a defined connective tissue disorder, whereas secondary Sjogren's syndrome is accompanied by such a condition, such as rheumatoid arthritis, systemic lupus or Wegener's disease. In general, the onset of Sjogren's syndrome dry eye is earlier than that of non-Sjogren's dry eye and it evolves with greater severity.
The commonest form of evaporative dry eye is due to meibomian gland obstruction and this in turn has a strong association with skin disorders such as acne rosacea, atopic dermatitis (affecting the face) and seborrhoeic dermatitis. Evaporative dry eye can also result from lid-globe malposition (e.g. proptosis), contact-lens wear and occupational and environmental stresses. Thus it may be associated with low humidity due to air conditioning, with a reduction in blink rate while performing microscopy or with increased width of the palpebral aperture which occurs when working at a video display terminal. Such events may contribute to the office eye syndrome.
Classification of Keratoconjunctivitis Sicca
The condition of keratoconjunctivitis sicca (KCS) is synonymous with that of dry eye. According to the International Dry Eye Workshop (DEWS) the dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface. It comprises two subgroups: tear- or aque-ous-deficient dry eye (aqueous tear deficiency) is due to a failure of lacrimal func-tion while evaporative dry eye is due, predominantly but not entirely, to lipid tear deficiency . Either form may cause damage to the interpalpebral ocular sur-face and is associated with symptoms of ocular discomfort. A unifying mechanism
is tear hyperosmolarity, which can directly cause damage to surface epithelial cells. However, an additional factor is the release of pro-inflammatory cytokines in the lacrimal gland and tears, which can both initiate autoimmune lacrimal damage, as in Sjogren's syndrome, or perpetuate chronic conjunctival inflammation.
The commonest form of tear-deficient KCS is non-Sjogren's dry eye, whose age-related form has a prevalence of about 15% in the older population. It is due to a T-cell infiltration of the lacrimal gland which reduces secretory function. Non-Sjogren's dry eye can be caused by other lacrimal diseases such as graft-ver- sus-host disease and sarcoidosis, by lacrimal obstruction in cicatricial conjuncti¬val diseases (e.g. ocular pemphigoid, Stevens-Johnson syndrome and trachoma) and also by reduced sensation at the ocular surface, leading to a loss of afferent reflex drive to the lacrimal gland. Sjogren's syndrome is a less common disorder, with a prevalence of about 0.2-0.5%. It is an autoimmune exocrinopathy giving rise to dry eye and dry mouth and affects other mucous membranes and even the central nervous system. Primary Sjogren's syndrome occurs in the absence of a defined connective tissue disorder, whereas secondary Sjogren's syndrome is accompanied by such a condition, such as rheumatoid arthritis, systemic lupus or Wegener's disease. In general, the onset of Sjogren's syndrome dry eye is earlier than that of non-Sjogren's dry eye and it evolves with greater severity.
The commonest form of evaporative dry eye is due to meibomian gland obstruction and this in turn has a strong association with skin disorders such as acne rosacea, atopic dermatitis (affecting the face) and seborrhoeic dermatitis. Evaporative dry eye can also result from lid-globe malposition (e.g. proptosis), contact-lens wear and occupational and environmental stresses. Thus it may be associated with low humidity due to air conditioning, with a reduction in blink rate while performing microscopy or with increased width of the palpebral aperture which occurs when working at a video display terminal. Such events may contribute to the office eye syndrome.
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