Research has proposed many mechanisms, including decreased corneal sensitivity to mechanical and chemical stimuli with age and lacrimal gland damage from oxidative stress. 6 With this form, the accumulated changes in the ocular structures and function over time may contribute to the development of dry eye. Age-related ADDE is the most common form of non-SS dry eye, and its incidence increases around age 50. 6 Apart from the glandular destruction or dysfunction, reduction in lacrimal tear secretion may be attributed to a decreased corneal sensitivity to all sensory modalities. The clinical features of non-SS dry eye, although similar to SS dry eye, occur later in life and are usually less severe. 6 This destruction and additional inflammatory changes lead to a loss of aqueous tear flow. 6 In SS dry eye, immune cell infiltration of lacrimal and salivary glands leads to glandular destruction and sicca symptoms. SS is an autoimmune disorder consisting of immune cell infiltration of exocrine glands (i.e., salivary and lacrimal) and systemic complications secondary to events such as autoantibody production and lymphocytic infiltration of organs.
This is composed of two subcategories: Sjögren’s syndrome (SS) dry eye and non-SS dry eye. To understand mixed dry eye, clinicians must first understand the many physiological changes at play.ĪDDE. If the patient’s DED progresses to a more severe form, it may become associated with a slow tear film lipid layer spreading, resulting in an increase in tear evaporation-a hybrid of ADDE and EDE. 3,5 Thus, a patient with mild ADDE may present with low aqueous tear secretion secondary to lacrimal dysfunction and a normal evaporative rate in the absence of an eyelid or ocular surface-related cause. 5 DED may initially present as purely ADDE or EDE, but as it progresses, the characteristics of both will likely become more pronounced, presenting as a mixed form of DED. For one, researchers hypothesize that the early and late stages of DED may differ in their clinical features. Unfortunately, because the two are closely related, each able to affect the other, getting to the bottom of the problem isn’t as easy as it sounds. When diagnosing the primary etiology of a patient’s dry eye, an important first step is determining if it’s due to a lipid or an aqueous deficiency.
Ocular surface staining, as seen here, can help to reveal dry eye. The DEWS II report recognizes that these two subtypes, ADDE and EDE, can often coexist as a hybrid or mixed dry eye. 2 The tear film lipid deficiency from meibomian gland dysfunction (MGD) is a common example of the excessive evaporation seen in EDE. In EDE, however, the hyperosmolarity is created by an excessive evaporation from the tear film. Reduced tear secretion caused by lacrimal gland dysfunction in age-related DED is just one example of ADDE. 4 In ADDE, hyperosmolarity is created by a reduction of lacrimal secretion. Tear hyperosmolarity-the increased osmolarity of the tears compared with the epithelial cells-leads to reduced epithelial cell volume and increased solute concentrations. 2,3 According to DEWS II, tear hyperosmolarity and instability are the two major players of DED. 2 Considering epidemiological and clinical studies suggest that most DED is evaporative in nature, the report shows the majority of this continuum is EDE. 2Īdditionally, the revised classification system now indicates that ADDE and EDE are no longer two separate entities rather, they are coexistent on a continuum.
Tear film instability and hyperosmolarity, ocular surface inflammation and damage and neurosensory abnormalities are all included as possible etiologies. The TFOS DEWS II revised definition characterizes DED as a loss of tear film homeostasis accompanied by ocular symptoms. This lower lid shows signs of obstructed meibomian glands, and digital pressure releases thickened and cloudy meibum.
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1 This article explores the new understanding of mixed dry eye presented by the Tear Film and Ocular Surface Society’s (TFOS) Dry Eye Workshop (DEWS) II, and how to manage it in your clinic. Research now suggests 30% to 70% of dry eye patients may have a hybrid of both forms. Whether a patient has aqueous-deficient dry eye (ADDE) or evaporative dry eye (EDE) is a crucial distinction for management purposes, yet they are not mutually exclusive. Caring for patients with dry eye disease (DED) has always been a complex process that begins with a search for the underlying etiologies at play.
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