Dry Eye Disease is the diagnosis given to eyes that feel unusually dry, whether or not they are dry.
Dry eye symptoms are a unique type of pain that originates in the nerves of the highly sensitive cornea, the dome-shaped, transparent front surface of our eyes behind which our colored iris and black pupil are visible. Pain is our body’s alarm system warning us of impending or actual tissue damage. However, the priority of dry eye pain is to protect the tear film that covers our corneas. If this film is allowed to breakup through evaporation, vision will be suddenly reduced to seeing shadows until the tear film is restored.
To protect the critical tear film, an alarm system evolved to monitor its thickness in real time. As it becomes thinner through evaporation and approaches the danger point, the dry eye alarm triggers an unconscious call for more tears. If that response is insufficient, the alarm intensifies to conscious sensations of dry eye while sending messages to our brain to release all the tears it can mobilize. The conventional theory of dry eye disease is that the primary cause is the lack of tears.
Lack of tears does not explain why some eyes that feel dry are not dry.
The theory of insufficient tears has a fatal flaw. It does not explain why many eyes that feel dry are not dry. Nor does it explain why some people with meager tear films and non-functional Meibomian glands, a combination typically associated with dry eye symptoms, do not complain of having dry eyes.
Invisible diseased nerves of the corneal pain system can increase the sensitivity of the dry eye alarm and trigger false symptoms of dry eye when, in fact, the amount of tears is normal. However, as the nerve disease progresses it interferes with the production of tears and these eyes become dry. This explains the confusion of the findings that eyes that feel dry can be wet, while, as a whole group, these eyes are drier than those that don’t feel dry. In Dr. Rosenthal’s view, symptoms and reduced tear production are caused by the disease and are not causes of the disease.
There are two principal categories of invisible chronic eye pain.
Dr. Rosenthal proposes that there are two principal categories of invisible chronic eye pain, which can occur together:
- Diseased corneal nerves. In this situation, the terminals of corneal nerves are hypersensitive to tear evaporation, causing the dry eye alarm to be triggered even though tear films are may be normal in the early stages.
- Centralized corneal pain. Unlike the common type of dry eye disease, centralized corneal pain originates in the pain pathways of the brain, though patients feel as though the source of the pain is in and around their eyes. Similar to electrical short circuits, malfunctions in these pain ‘booster’ brain centers can trigger and sustain an extreme form of pain known as centralized pain, a devastating disease that, although it is well known in the pain field is not recognized by eye doctors.
- A combination of 1&2. Each category of neuropathic (nerve disease) pain can occur separately. However, the pain disease can start with damaged corneal nerves such as caused by LASIK surgery, which then can trigger devastating centralized pain.