EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/78716
88 EW FEATURE February 2011 Refractive March 2012 Treating unexplainable pain by Faith A. Hayden EyeWorld Staff Writer AT A GLANCE • If a patient has chronic pain and you can't see it, it's neuropathic pain unless proven otherwise • Patients with corneal neuralgia may complain of burning, stinging, scratchiness, or something as vague as pure pain • Autoimmune disease is a significant risk factor What can be done for patients with post-LASIK corneal neuralgia? A 30-something female with a history of bilateral, uncomplicated LASIK 2 years prior comes into your office complaining of persistent burning pain, almost a foreign-body sensation in both eyes. A simple breeze across her face is ex- cruciating. The pain is so severe it prevents her from living a normal life, and she has thoughts of suicide. The slit lamp examination, though, is overwhelmingly unremarkable and free of corneal staining. Maybe she has slightly variable tear func- tion or reduced tear break-up time, but there's nothing to warrant her extreme symptoms. "Patients go to their ophthal- mologists, some of them suicidal because of the pain, and their eyes on the slit lamp look perfectly nor- mal," said Perry Rosenthal, M.D., founder, Boston Foundation for Sight. "Doctors send them to a psy- chiatrist because they think the [pa- tients are] exaggerating. It just adds to the patients' burden." Before you dismiss this patient as a crazy hypochondriac and send her on her way, consider corneal neuropathic disease, an extremely rare condition that causes intense pain along corneal nerves. "The hallmark of this disease is how uncomfortable patients are. These patients are very difficult to treat and keep coming back to your clinic, failing all the therapies you give them," said LCDR John B. Cason, M.D., cornea, external disease, and refractive surgery, Naval Medical Center, San Diego, during the 6th Annual Interna- tional Military Refractive Surgery Symposium held in San Antonio in early January. "Because of that, many of us think they're just mak- ing it up. These patients have a true disease process, it's just not well un- derstood." What causes corneal neuralgia? No one knows exactly what causes this neuropathic pain to develop after photorefractive keratectomy (PRK) and LASIK, but there are some theories. First, it's important to note that the cornea is the most powerful pain generator in the human body, 200 times more powerful than skin. "The most common cause of neuropathic pain anywhere in the body is damage to the sensory nerves," Dr. Rosenthal said. "Obvi- ously, LASIK and PRK are classic ex- amples of this. It's what happens next after the damage that deter- mines if the post-op pain resolves as the corneal tissue heals or whether it triggers the development of that chronic disease called neuropathic pain." The pain becomes chronic when it's centralized and in the brain, which is called central sensitization. It's when the central sensitization is no longer reversible that it's neuro- pathic. "In a simple way, acute pain can in certain vulnerable people damage their pain system. And the pain con- tinues independently of initial trauma or insult," Dr. Rosenthal ex-