Dry eye has a tendency to become the catch-all diagnosis for any reported ocular surface irritation or unexplained observed damage to the ocular surface, even without symptoms.
In the hospital eye service, it is generally an irritation after cataract or laser refractive surgery or following the commencement of glaucoma treatment. So, how serious a problem is it and how difficult can diagnosis and management really be?
Most of us are used to going to a GP or hospital where the staff measure a biological variable such as blood sugar, white cell count or temperature and then provide a confident diagnosis. However, when it comes to dry eye, there is no one accepted marker. The ‘dry eye’ terminology is acknowledged as less than satisfactory as patients could have a watery eye for example, but attempts to rename it have lacked traction so the terminology remains.
I have heard it said on podiums that there is a type of dry eye with no symptoms, but this goes against the global dry eye disease consensus definition of TFOS DEWS and reiterated in TFOS DEWS II. If there are no symptoms, then the patient does not have dry eye. They may have sub-clinical disease that could become dry eye so we choose to monitor them more often, or they could have neurotrophic disease where dry eye has damaged the nerves badly enough to dull the sensation, in which case treating the ocular surface may initially increase symptomology so then they fall into the dry eye category.
"I have heard it said on podiums that there is a type of dry eye with no symptoms, but this goes against the global dry eye disease consensus definition of TFOS DEWS and reiterated in TFOS DEWS II"
So, what are the best clinical tests to confirm the ‘loss of homeostasis’ element of the new definition? Recalling our clinical training, we examine the sensitivity and specificity of the tests with a group of non-dry eye patients compared to a dry eye cohort to pick an appropriate cut-off value and then select the test with the highest numbers. However, the criteria for selecting normal and disease patients often leaves people who fit neither category, and the more severe the disease group and the similarity between the tested technique and those used to decide the disease group, the greater the sensitivity and specificity values will be. Hence, other aspects such as non-invasiveness and the ability to conduct a test in a clinical setting also play a role in test selection. The TFOS DEWS II report identified non-invasive breakup time, osmolarity and ocular surface damage as a diagnostic of dry eye in combination with symptoms.
Finally, treatment choice requires sub-classification on the spectrum between aqueous deficiency and evaporative dry eye. While there is good evidence that many treatments can be effective in dry eye, there is disappointingly little information to guide clinicians on what treatments work best at what severity and with which type of dry eye. Hence, we are trying now to better understand how clinicians currently manage the disease to inform future practice and research. So, the certainty of diagnosis of this chronic, debilitating disease has been improved for both patient and clinician, but our efforts continue to aid treatment decisions between the ever increasing over the counter and in-office options.
Professor James Wolffsohn is a lecturer at Aston University. He sat on the DEWS II steering committee and was nominated to chair the diagnostic methodology committee.