EyeWorld Asia-Pacific June 2012 Issue

June 2012 14 EWAP FEATURE 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 A similar area in a normal subject Source: Pedram Hamrah, MD The subbasal nerve layer 1 year after LASIK in a patient with keratoneuralgia. There are very faint nerves and a large number of hyper-reflective immune cells. The same patient. Another area in the same plane with no immune cells, but with increased reflectivity of nerves and beading (signs of inflammatory nerve changes) Treating unexplainable pain by Faith A. Hayden EyeWorld Contributing Editor 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 excruciating. 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 function or reduced tear break-up time, but there’s nothing to warrant her extreme symptoms. “Patients go to their ophthalmologists, some of them suicidal because of the pain, and their eyes on the slit lamp look perfectly normal,” said Perry Rosenthal, MD , founder, Boston Foundation for Sight. “Doctors send them to a psychiatrist because they think the [patients 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, MD , cornea, external disease, and refractive surgery, Naval Medical Center, San Diego, Calif., USA, during the 6th Annual International Military Refractive Surgery Symposium held in San Antonio in early January. “Because of that, many of us think they’re just making it up. These patients have a true disease process, it’s just not well understood.” What causes corneal neural- gia? 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. “Obviously, LASIK and PRK are classic examples of this. It’s what happens next after the damage that determines 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 neuropathic. “In a simple way, acute pain can in certain vulnerable people damage their pain system. And the pain continues independently of initial trauma or insult,” Dr. Rosenthal explained. “So for example, corneas can heal perfectly fine and normal. But you can’t see the nerve circuitry. The ophthalmologist just assumes if you can’t see it, it isn’t there. This is wrong. If a patient has chronic pain and you can’t see it, it’s neuropathic pain unless proven otherwise.” Diagnosing the pain Patients with corneal neuralgia may complain of burning, stinging, scratchiness, or something as vague as pure pain. The first step toward a diagnosis is differentiating between discomfort from dry eye, blepharitis, and corneal pain. “There’s a continuum of disease that’s partially due to the dry eyes patients develop after refractive surgery and partially due to inflammation, which is leading to the corneal neuralgia,” explained Pedram Hamrah, MD , director, Ocular Surface Imaging Center, Henry Allen Cornea Scholar, Cornea & Refractive Surgery Service, Massachusetts Eye & Ear Infirmary, Boston, Mass., USA. “In dry eyes, you can obviously see the surface staining and other dry eye signs. In corneal neuralgia alone, you don’t see these signs. It’s just the symptoms of the patient.” A simple slit lamp examination is not enough to diagnosis this condition, Dr. Hamrah said. You must examine these patients on a cellular level with an in vivo confocal microscope. Using this, “you can see inflammation lingering,” he said. “You can see abnormalities of the nerves. There are things we can detect on a pathological level, but not at the slit lamp level necessarily.” Other telling symptoms include exaggerated pain response to touch, air, and drops; lowered Schirmer’s scores, but frequently borderline or within the normal range; and depressed cornea sensitivity by Cochet-Bonnet esthesiometry. “There’s a high likelihood we’ve all seen patients like this and attributed it to something else,” Dr. Cason said. If patients aren’t responding to dry eye treatments such as artificial tears and anti- inflammatories, he said, “our suspicion has to be high.” A multidisciplinary treatment plan Depending on the disease stage, patients with corneal neuralgia may need special, usually multifaceted, treatment. If caught and treated early, patients respond fairly well. “When I am referred [patients]