The numerous co-morbidities that present with similar symptoms make diagnosis and, consequently, treatment difficult. Furthermore, sometimes patients have signs of disease and symtpoms that match and at other times they don’t match (see Symptoms). One study reported that patients may have signs of disease but few symptoms and patients with mild signs of disease may have severe symptoms. The incongruence makes diagnosis based on symptoms alone problematic.
The 2014 article in Eye and Contact Lens notes “the incongruence when comparing subjective symptoms with objective signs, thereby highlighting the urgent need for the development of reliable metrics to better quantify dry eye symptoms and also the development of a more sensitive and specific test that can be used as the gold standard to diagnose dry eye.”
From: Perceptions of Dry Eye Disease management in current clinical practice
A 2014 article in the British Journal of Ophthalmology states that there is a “disconnect between signs, symptoms and severity makes symptomatology alone a relatively poor indicator of severity in some patients, and also a confounding variable in clinical trials.”
From: Diagnosing the severity of dry eye: a clear and practical algorithm
Perhaps most important is understanding that tear film is a complex structure that is produced and maintained by physical, mechanical and biochemical agents all of which have to be healthy and functioning properly at the right time and in the right quantities: meibomian glands, lacrimal glands, lid margins, goblet cells, epithelial cells, mucin layer, aqueous layer, lipid layer, accessory glands, hormones, immune system, blinking, eyelids, conjunctiva, cornea, and the list goes on an on. If anything goes wrong with one or more of these, the whole system can be affected leading to potentially debilitating and life-altering symptoms that may be difficult to differentiate from one another.