‘Pain without stain’ patients provide us with a model to understand the process of neuropathic dry eye. Because they do not have significant meibomian gland dysfunction or aqueous deficiency, we are able to isolate the neuropathic disease and hopefully identify new therapies to relieve their symptoms.
While these patients represent what is probably a very rare subtype of dry eye, it is likely that many more dry eye patients who do have clinical signs also have neuropathic pain as a component of their dry eye. In fact, I believe that most of the patients who fail, even partially, to respond to stepwise, appropriate dry eye therapy or for whom resolution of signs does not lead to significant improvement in symptoms, might also have an additional neuropathic disorder.
What we learn from treating the extreme form, therefore, has the potential to benefit a much broader range of patients whose pain is inadequately addressed with current therapy.
It has become clear to me that there is a strong unmet need for treatments that specifically address ocular surface pain. Although much research remains to be undertaken, I am optimistic about the potential for cannabinoid therapies, particularly if we are able to confirm that use of an SFA drug delivery technology is effective in reaching the target tissues without systemic side effects.