Abstract
Dry eye disease aetiologies can be classified dichotomously into aqueous deficient and evaporative types although many cases involve combinations of both. Differential diagnosis can be confounded by some features of dry eye disease being common to both aetiologies. For example, short tear break-up times are prime diagnostic findings of tear instability due to lipid and/or mucin deficiencies, but thin tear layers in aqueous deficient eyes also shorten tear break-up times, even at normal range rates of evaporation in eyes without lipid and/or mucin deficiencies. Because tear instability and short tear film break-up times due to thin tear layers can be independent of lipid and/or mucin deficiency, aqueous deficiency can be another form of evaporation-related dry eye. Conversely, tear layers which are thickened by punctal occlusion can be less susceptible to tear break-up. An inflamed lacrimal gland producing reduced quantities of warmer tears can be a basis for thin tear layers and tear instability demonstrated by shorter tear break-up times. Commonly used clinical tests for aqueous deficiency can be unreliable and less sensitive. Consequently, failure to detect or confirm aqueous deficiency as a contributor to short tear break-up times could result in too much weight being given to a diagnosis of meibomian gland deficiency. Less successful treatment outcomes may be a consequence of failing to detect aqueous deficiency. Refining disease classification by considering aqueous deficiency as a contributor to, or even a form of evaporation-related dry eye, could be the basis for more comprehensive and appropriate treatment strategies. For example, some treatment methods for evaporation-related dry eye might be appropriate for aqueous and mucin-deficient as well as lipid-deficient dry eyes. Anti-inflammatory treatment for the lacrimal gland as well as the conjunctiva, may result in increased aqueous production, reduced tear temperature, tear instability and evaporation rates as well as lower osmolarity.
Highlights
BackgroundAccurate diagnosis and classification of dry eye disease is challenging but is necessary as the basis for the provision of the most appropriate therapy [1]
The aqueous layer is secreted by the main and accessory lacrimal glands
The predominance of an evaporative form of dry eye disease [3] which is due to lipid and/or mucin deficiencies may disregard the contributions from aqueous deficient dry eye (ADDE) to shorter tear break-up times which are the subject of this review
Summary
Accurate diagnosis and classification of dry eye disease is challenging but is necessary as the basis for the provision of the most appropriate therapy [1]. The predominant aetiologies of dry eye disease are aqueous deficient dry eye (ADDE) and evaporative dry eye (EDE) or a combination of them, with or without other etiological factors for dry eye disease [2]. Meibomian gland dysfunction as a contributor to EDE is considered the leading cause of dry eye disease in clinic and populationbased studies [2]. Of 224 subjects diagnosed with dry eye disease using an objective composite disease severity scale, 49.7% were further classified as having
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