The question, "Which came first: the chicken or the egg?" is particularly fitting for the long-standing blepharospasm and dry eye disease (DED) conundrum. It is true that both conditions often occur together, nonetheless, mystery still surrounds the mechanism by which this happens. 

It is important to note that although both conditions commonly occur together, this is not always the case. Blepharospasm, especially in its early stages, is often misdiagnosed as DED because its symptoms mimic those of DED - at first glance. DED patients typically report eye irritation in the form of itching, stinging, burning, excessive watering, tired eyes or a foreign body sensation that persists despite blinking. Blepharospasm patients also reported tired eyes and excessive blinking, and this can easily be attributed to DED. However, if the symptomatic histories of these patients are recorded carefully, it often becomes apparent that the blinking is actually involuntary and exacerbated by triggers, including sunlight and watching television. These features are specific to blepharospasm and do not occur in simple DED. It is only by delving deeper to this level of detail that the true cause of a patient's symptoms can be identified. 

I have been treating patients with DED for over 20 years and in that time I have noticed just how important it is to make a correct diagnosis before initiating treatment. In theory, the practice of administering tear replacement eye drops to every patient that presents with DED symptoms may appear satisfactory. By giving everyone the same treatment, those who do have DED are treated and those who fail to respond to this therapy can be investigated for alternative causes of their symptoms. However, the reality is vastly different, and such therapy is rarely effective in DED patients if blepharospasm is also present. Irrespective of the method by which this dual pathology arises, I have found that treatment is only successful when it is targeted at correcting both conditions.  

Before commencing treatment, the first thing to do is to clarify the suspected diagnosis. The measurement of tear osmolarity is a highly accurate method of identifying the presence of DED. The precise measurement of osmolarity requires the use of a specific approach. For example, eye drops cannot be instilled into the eyes during the 6 hours before a measurement is taken. By adhering to this rule, a true picture of a patient's tear quality can be obtained, his or her DED type can be correctly classified, and the most effective treatment plan can be developed. I have been using the TearLab Osmolarity System (TearLab Corporation) for over a year and have noticed the difference it makes to the patient management process. This handheld device works by simply mounting a thin test card onto its tip. This card is then lightly dabbed onto the lower lid margin to provide a highly accurate tear osmolarity reading in less than one minute. As an objective test for DED, a positive diagnosis is made based on the detection of hyperosmolar tears - defnied as a tear osmolarity of greater than 308 mOsms/L. Furthermore, this test allows DED severity to be identified, with a tear osmolarity of 308–316 mOsms/L representing mild DED and an osmolarity of above 316 mOsms/L representing moderate to severe DED. 

In contrast, current diagnosis of blepharospasm is less objective. However, a thorough history record, accompanied with a comprehensive physical and ophthalmological examination, is usually sufficient for identifying blepharospasm, when present.  

Dr Dirard discusses why blepharospasm is regularly mistaken for DED