CLINICAL CHALLENGES
By the Book
Following a strict treatment protocol led to a happy ending for this case of RON.
by Eric Schmidt, O.D.

In eye care, the treatment of a certain condition is not always cut and dried. The way one doctor treats a case may be totally different than the treatment prescribed by another practitioner. There are some disease entities, though, for which the treatment regimen is very rigid. This article describes one such case where strict adherence to a therapeutic protocol yielded a great visual recovery.

A blurry presentation

It was the Monday after Thanksgiving and, as is typical of the day following a holiday weekend, my office was particularly busy. I rushed to the door of another exam room, picked up the chart, and read the history for my next patient. My technician had written that this 36-year-old female had blurry vision OS for the past two weeks. The patient stated that the vision suddenly became blurred one day at work and that it had progressively worsened over the past two weeks. The patient told my technician that the vision loss was exclusively in the left eye and that the vision in the right eye remained clear.

It was also noted that neither eye was painful, except for when the patient was suffering from a migraine headache, which she said occurred about once a week. The patient told us that she had been suffering with migraine headaches since she was 16 years of age and that she occasionally took Imitrex for them but usually just used Ibuprofen or extra-strength acetaminophen to combat the pain. She mentioned that the headaches had never before bothered her vision but that they did usually cause her eyes to hurt. My technician again asked her if either of her eyes were painful now and again the patient said that her eyes felt fine; the vision was just extremely blurry in the OS only.

The rest of the history was non-contributory. The patient denied any trauma, was in good health, had no overwhelming family history of disease and had never even worn spectacles in the past.

Meet the patient

On the chart it was noted that her visual acuity was 20/25 OD and hand motion at 10 feet OS without any correction. The OS did not improve with a pinhole occluder. As I opened the door to the exam room I was expecting to meet a woman who was either panicked or upset about her vision. Rather, I was met by a smiling, extremely pleasant lady who seemed to me to be very calm about her situation.

I introduced myself to V.A. and asked her some more questions. Once again she denied any pain in the eyes and couldn't identify any precipitating factors to her vision loss. She did say that she was under a lot of stress at work and wondered whether this might be the cause. She said that she had not had a migraine headache for about two weeks. When I asked her, she noted that she had never had any visual episodes with her migraines in the past. She also said that she felt fine and that she had no paresthesia or weakness along with her vision loss.

I remeasured her visual acuity. She couldn't see the 20/400 "E" and told me that she could only see part of the projected light. I tested her extraocular muscles and found no restriction or pain on movement. Confrontation fields showed a full field OD, but with the OS she saw my fingers only when they were held to her right side. The finger disappeared as I moved it towards the vertical mid line. I had her once again stare at my nose with her OS. She said that my entire face was distorted and that she could really only see my left eye and left ear.

To further quantify this defect, I had V.A. look at an Amsler grid. The result was normal OD with the exception of the lower left corner missing. The result with the OD showed a dense scotoma. V.A. was unable to see any lines on the left side of the grid and she stated that side of the grid was very gray. She was able to see the lines on the right half of the grid but they appeared "out of focus."

To help differentiate between a retinal or an optic nerve problem I performed a red cap test. I asked V.A. to cover her OS and to stare at the red top of a tropicamide bottle. I then told her that any red she sees is "worth" one dollar. Then V.A. covered her OD and fixated on the bottle top with her OS. When I asked her how much the red is worth in comparison to the other eye she said that she was unable to see the bottle top but that everything she could see appeared gray. I assessed her pupils next and found that they both measured 6mm in size and were equally reactive to light. There was no afferent pupil defect noted, which seemed curious to me.

The plot thickens

I was able to improve her vision to 20/20 with a mild cylinder correction, but I was unable to gain any improvement OS. My slit lamp examination revealed healthy anterior segments and her IOP was 18mm Hg OD, 17mm Hg OS. After dilation I thoroughly examined her posterior segment looking closely for optic nerve or retinal disorders. But the retinas and optic nerves of both eyes showed no abnormalities. Particularly, her optic nerve heads (ONH) showed no edema or hemorrhages and no pallor.

Fuzzy vision, fuzzy clues

I couldn't venture a diagnosis based on the examination, but it seemed to me that she had an optic nerve dysfunction OS. Given V.A.'s age, the lack of any retinal pathology, no observable

disk edema and her profound vision loss, the most likely diagnosis was retrobulbar optic neuritis. I could not however, rule out a psychological or neurological disorder. I asked V.A. to return to my office in 48 hours for a visual field analysis after which I would likely order a magnetic resonance imaging (MRI) scan.

V.A. returned as scheduled and performed the VF test extremely well. The results showed a very mild enlarged blind spot (or Seidel's scotoma) superiorly OD. The result for her left eye revealed a very dense almost absolute scotoma that was denser above than below and incorporated fixation. There was less of a defect in the right inferior quadrant. I examined V.A. one more time: nothing had changed with the exception a slight APD OS. Again, there was no disk edema or pallor and no retinal pathology. I ordered an MRI, which was performed that day. The result was normal. There was no tumor, bleeding or mass and no white matter lesions were noted.

The 90% solution

The presence of the APD OS and the altitudinal type VF defect led me to strongly believe that the diagnosis was retrobulbar optic neuritis (RON). I

quickly referred V.A. to a neuro-ophthalmologist who agreed with the RON diagnosis and immediately admitted her to a hospital for treatment.

Her treatment strictly followed the protocol set up by the Optic Neuritis Treatment Trial (ONTT), the first part of which is 250mg of intravenous methylprednisone Q6H for three days. This is followed by outpatient treatment with high dose oral prednisone for 11 days and then a rapid taper (see sidebar). The ONTT clearly showed that initiating treatment with IV steroid and following it with oral steroids greatly improved the chance of visual recovery in patients with optic neuritis or RON.

In this case, after one month V.A.'s vision had improved to 20/25 OS and the central scotma had cleared. There did remain a slight temporal defect OS. After six months the vision remained 20/25 and the VF, for all intents and purposes, was normal. A workup was also undertaken to try to elicit an etiology for the RON. As of this writing, none has been found, although the neurologist and I will both continue to watch for recurrences and for any evidence of multiple sclerosis.

Contributing Editor Dr. Schmidt is director of the Bladen Eye Center in Elizabethtown, N.C. E-mail him at schmidtyvision@bellsouth.net.