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You are the 7th doctor Jane is consulting to find some relief from five years of merciless, burning and piercing eye pain that can spread to her head and face and sometimes jaws.  Exposure to the dimmest light increases her burning eye pain.  Jane’s list of past treatments fills 2 pages.  The side-effects of those that “took the edge off the pain” were too much to tolerate.  A copy of her medical records including x-rays and MRIs showed nothing unusual.  She whispers that before retiring each night she prays that she will never wake up.  On examination her eyes were normal except for photosensitivity and perhaps fewer tears.  Does she have dry eyes as was suggested by other doctors?  On the other hand, you have seen many people with fewer tears whose eyes felt fine.  Even her Meibomian glands look healthy.  You instill anesthetic drops prior to the routine glaucoma test expecting that her eye pain will be suppressed temporarily.  It was reduced but not eliminated.  Is Jane a drug-seeker?  Does she have a psychiatric problem?  In fact, her symptoms are real.  But how can such devastating pain be caused by healthy eyes?

Pain is the key component of our body’s alarm system; a warning of impending or actual tissue damage.  We could not live long without it.  However, pain alarm systems can break down and themselves become the source of unrelenting pain that can destroy the quality of life.  This type is described as neuropathic pain and is typically severe and long-lasting (if not permanent).  Neuropathic pain symptoms are false alarms.  It is a disease in its own right.

Oculofacial Pain (OFP)

OFP is the term I have adopted to describe neuropathic pain caused by faulty circuits in the brain that process pain signals which originate in the tissues above our neck (the trigeminal receptive field) on their way to the cortex of our brain where they are decoded into conscious sensations.  It is also classified as a type of centralized pain that defines it as originating in our central nervous system.  On the other hand, painful sensations initiated in the brain’s pain circuits are interpreted as originating from the body part it serves.  For example, if our right hand is damaged we feel the pain in our right hand because its pain nerves travel to the part of our brain that is represents that part of our body.  If these same pain nerves are activated in the brain the pain will still be interpreted as coming your right hand even though it is normal or had been amputated.  In other words it is a form of phantom pain.  I believe that OFP represents a type of phantom pain which explains why its perceived sources such as eyes, etc. are normal.  In other words, if these eyes were removed the pain would persist and feel as if it originates from the non-existing eyes.

Symptoms of OFP vary between patients and within the same patient.  Although some of these victims experience dry eye-like symptoms, I suggest that its mechanisms differ from those of the common type of so-called dry eye disease.  Instead of the hypersensitive response to tear evaporation taking place in the corneal nerve terminals (neuropathy), my theory is that when it occurs as a symptom of OFP it is caused by the amplification and distortion of normal incoming corneal evaporative signals in the dysfunctional pain wiring of the brain.  Moreover, it is my impression that centralized dry eye-like pain tend to be more intense and are often associated with corneal hypersensitivity to chemicals and cold.  On the other hand, pain associated with OFP is often spontaneous and appears to originate in the head (headaches) and/or ears, face, jaws and even teeth.  Moreover, their quality is typically described as aching/pressure/pounding, burning, sharp, scratchy, pins and needles, etc.

Oculofacial pain can sometimes be associated with reduced tears although it is usually insufficient to explain the intensity of dry eye-like symptoms.  This finding and the presence of unexplained photosensitivity in many OFP patients suggest involvement of a part of the brain (trigeminal brainstem) involved in controlling corneal surface wetness and monitoring the painful quality of exposure to light.  (I have labelled the type of photosensitivity experienced in the absence of a visible cause as neuropathic photophobia).  Although dry eye-like symptoms are intensified by tear deficiency, I argue that when reduced tears and dry eye-like symptoms coexist they are each a complication of the underlying neuropathic disease and that although inadequate tears worsens dry eye-like pain their relationship is one of association rather than causation.  On the other hand, while the contrast between the intensity of symptoms and the minimal (if any signs) is a key feature of centralized projected pain, this distinction may become less striking if these eyes become drier over time, presumably due to disrupted central mechanisms.

What is the underlying cause of Oculofacial Pain?

My examinations of 200 of these patients that included laser scanning corneal confocal microscopy and subsequent interviews of 149 additional victims of OFP through detailed questionnaires have provided interesting information that could be useful in designing future studies.

Of the 149 OCP patients who visited this website and filled out the questionnaire, the sex ratio was 2:1 in favor of females.  Laser keratorefractive procedures were triggering events in 45 patients (30%).  Although symptoms of OFP typically began in the immediate post-operative period, a few patients reported a delayed onset of up to several months following surgery.  A few reported that the disease was initiated by fumes and chemicals that would ordinarily have produced only a transient noxious effect.  The disease appeared spontaneously in the remaining cases.  The question posed by these observations is why certain individuals are vulnerable to developing this neuropathic pain syndrome while most are not?  While a few of these patients suffered from certain rare pain nerve diseases such as small fiber neuropathy and complex regional pain syndrome, the most commonly associated disorders were fibromyalgia (FM) and/or its commonly related diseases such as irritable bowel, chronic fatigue, chronic pelvic pain, multichemical sensitivities, hypersensitivity to sounds, carpal tunnel and restless legs syndrome.  Symptoms of OFP preceded those of FM and related diseases by years in some patients.  Since FM is now believed to represent a pathological hypersensitive sensory state in the central nervous system these observations suggest a possible relationship between FM and OFP in many patients.

Personal reflections

Practical, objective methods of measuring the existence and intensity of pain do not exist.  In the case of OFP, even its presence cannot confirmed or excluded and the numbers of these patients are insfficient to be noticed as a specific disease.  Therefore, it is not surprising that many physicians prefer to avoid dealing with the uncertainty of chronic pain that has no established cause or visible presence.  Moreover, since ophthalmologists are unfamiliar with the concept of projected, invisible eye pain our instinctive reaction when faced with such a patient is to move as quickly as possible to the next one whose cataracts and treatment are obvious.  Since few have heard of intense unrelenting pain originating from healthy eyes Our mission is to give them a loud enough voice to validate this disease and their suffering, investigate its mechanisms and find effective treatments while keeping in mind that the complexity of these diseases probably precludes a one size fits all approach.  Although traditional pain treatments are generally ineffective, there are novel therapeutic interventions that seem to hold promise and I believe that it is reasonable to offer these patients realistic hope for a better future.

Suggested reading:

  1. Woolf CJ: Central sensitization: implications for the diagnosis and treatment of pain. Pain 2011, 152(3 Suppl):S2-15.
  2. Schott GD: Delayed onset and resolution of pain: some observations and implications. Brain : a journal of neurology 2001, 124(Pt 6):1067-1076.
  3. Rosenthal P, Borsook D: The corneal pain system. Part I: the missing piece of the dry eye puzzle. Ocul Surf 2012, 10(1):2-14.
  4. Lopez-Sola M, Pujol J, Wager TD, Garcia-Fontanals A, Blanco-Hinojo L, Garcia-Blanco S, Poca-Dias V, Harrison BJ, Contreras-Rodriguez O, Monfort J et al: Altered functional magnetic resonance imaging responses to nonpainful sensory stimulation in fibromyalgia patients. Arthritis & rheumatology 2014, 66(11):3200-3209.
  5. Hirata H, Okamoto K, Tashiro A, Bereiter DA: A novel class of neurons at the trigeminal subnucleus interpolaris/caudalis transition region monitors ocular surface fluid status and modulates tear production. The Journal of neuroscience : the official journal of the Society for Neuroscience 2004, 24(17):4224-4232.
  6. Rahman M, Okamoto K, Thompson R, Bereiter DA: Trigeminal pathways for hypertonic saline- and light-evoked corneal reflexes. Neuroscience 2014, 277:716-723.


Source: Peer Review

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