Locally, there are no official recommendatory guidelines for guarding against ETON in patients being treated for TB. Previous guidelines have been proposed by the Joint Tuberculosis Committee of the British Thoracic Society and the Tuberculosis and Chest Service of the Department of Health of Hong Kong Special Administrative Region.8,29,39-40 We summarize some of these guidelines below with some modifications suited for the local setting.28 We hope to improve on these recommendations once data from the registry start coming

  1. Ideally, all patients undergoing treatment for TB should have pre-treatment assessment of visual acuity (Snellen Chart) and color perception (Ishihara Color Plates and other color tests).A Although simple testing for these two parameters can be performed by the prescribing internist, a formal ophthalmologic exam is still warranted to determine any pre-existing eye pathology (and perhaps also for medico-legal purposes).
  2. Advise the patient about the potential of anti-TB drugs to cause ocular toxicity. Describe what symptoms to expect should this occur. To guard against non-compliance of TB medication intake, explain that there is only a small risk of ETON occurring and that the condition should be detected early with proper monitoring.
  3. Monthly eye examinations should be performed from onset of treatment. If it is impractical for the patient to visit the ophthalmologist monthly, the internist can become part of the monitoring process by checking BOTH visual acuity and color perception himself (if color tests are available in his clinic).B The internist can also do a monthly verbal query from the patient about possible evolution of visual disturbances.
  4. Advise the patient to discontinue EMB from the anti-TB regimen when visual disturbances are experienced. He should be seen by an ophthalmologist and assessed for ETON. Once established as a diagnosis, the patient and prescribing internist must be advised about the possibility of permanently discontinuing EMB from the regimen.
  5. If the toxic optic neuropathy is severe, it may be advisable to discontinue EMB together with the INH. In less severe toxicity, INH may be continued, unless the optic neuropathy fails to stabilize six weeks after discontinuing EMB. At this point, one must reconsider the diagnosis and a formal neuro-ophthalmic work-up may be warranted to look for other causes of the patient’s bilateral optic neuropathy.C
  6. Report Case. FILL out the REGISTRY!
  1. The Joint Tuberculosis Committee of the British Thoracic Society advised that routine testing of visual acuity alone may be inadequate in early detection of ETON.39 Other visual parameters like color perception may be affected earlier than visual acuity and should likewise be tested prior to treatment.
  2. Dyschromatopsia in the form of red-green color deficiency may be the earliest sign of toxicity.19 Other reports claim that the blue-yellow wavelength may be more sensitive.20 However, the latter is detected only by the Desaturated Panel of Lanthony which is not readily available. Ishihara Color Plates may be the only option available to the internist in monitoring color perception.29 For the ophthalmologist, other color tests (Farnsworth-Munsell 100-Hue test or Farnsworth D-15 Color Test) when available, may be utilized.
  3. Many conditions can mimic the clinical presentation of ETON---i.e., bilateral optic neuropathy that is progressive (secondary to inflammatory, ischemic, infiltrative, hereditary and compressive lesions). Please heed WARNINGS 1 and 2 under “Differential Diagnosis/PRECAUTIONS”.