Even in our era of modern health care, it is often challenging to identify and manage dry eye disease (DED)—at least in part because it is often difficult to diagnose.1 This disparity may be due to the fact that in many instances, the signs, symptoms, and severity of the condition correlate poorly or not at all.2 For the patient, perhaps the most significant symptom of DED is fluctuating or reduced vision.
Dry eye and osmolarity
According to the Dry Eye WorkShop (DEWS) definition, 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.”3
Related: Combating dry eye with punctal plugs
Stern et al identified the disparate components that function together to protect and nourish the ocular surface:4
• Accessory lacrimal glands
• Meibomian glands
• Main lacrimal gland
• Interconnecting innervation system
This cumulative system eventually came to be known as the lacrimal functional unit (LFU).4 The concept of a multi-component unit that protects the ocular surface is vital; it reinforces the theory that failure of one or more segments of the unit can lead to DED. We must consider dry eye as a chronic, bilateral, asymmetric, progressive disease.
In 2014, Bron and colleagues sought to dispel several misconceptions that hamper clinical diagnosis and management of DED. They concluded that “osmolarity appears to be the best marker across all levels of disease severity as well as in different subtypes of DED.”5
Related: How to know when it’s not dry eye
The concept of an association between increased tear osmolarity (TO) and DED is not new. In 1981, Farris published the first report showing a positive correlation among female gender, increasing age, contact lens wear, and elevated TO. Large-scale studies have reinforced the value of TO as a consistent marker in DED.6
In 2006, Tomlinson’s meta-analysis of TO in normal eyes and diverse subtypes of dry eye showed a predictive accuracy of 89 percent for the diagnosis of DED.7