CASE REPORT

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ETHAMBUTOL OCULAR TOXICITY IN A PATIENT WITH PULMONARY TUBERCULOSIS
– A CASE REPORT

AK Tan MD^1,2 , PS Mallika MS², S Aziz MS¹, T Asok MMed¹, G Intan MS¹

¹Department of Ophthalmology, Hospital Umum Sarawak, Sarawak, Malaysia (Tan Aik Kah, Mohamad Aziz Salowi, Asokumaran Thanaraj, Intan Gudom)
²Department of Ophthalmology, Faculty of Medicine and Allied Health Science, Universiti Malaysia Sarawak (UNIMAS), Sarawak, Malaysia (Tan Aik Kah, Mallika Premsenthil)

Address for correspondence: Dr. Tan Aik Kah, Lecturer, Ophthalmology unit, Faculty of Medicine and Health Sciences, University Malaysia Sarawak, Lot 77, Sekysen 22 Kuching Town Land District, Jalan Tun Ahmad Zaidi Adruce, 93150 Kuching, Sarawak, Malaysia. Tel +6082 416550, Fax + 6082 422564, Email: portwinestain@hotmail.com, aktan@fmhs.unimas.my

INTRODUCTION

Internists routinely prescribe drugs that can potentially cause ocular toxicity. Many non-ophthalmologists use Ishihara Pseudoisochromatic Plates (ISP) to screen for acquired colour defects. Such use of ISP is not appropriate. The Farnsworth Panel D-15 Hue test is rarely available outside the ophthalmology department. In this case report, we highlight the value of the Farnsworth Panel D-15 Hue test in the detection of acquired blue-yellow colour defect and advocate its use by non-ophthalmologists.

CASE REPORT

A 70-year-old lady, diagnosed of having pulmonary tuberculosis (PTB), was started on EHRZ regime (ethambutol 15 mg/kg/day, isoniazid 5 mg/kg/day, rifampicin 10mg/kg/day and pyrazinamide 20 mg/kg/day). She was referred to our ophthalmology department 2 weeks after the treatment commenced. Her renal function was normal.
 
On presentation, she had mild blurring of vision for the past 10 years. Otherwise there were no acute visual symptoms. Her best corrected visual acuity (BCVA) was 6/12 in both eyes. Colour vision test with Ishihara Pseudoisochromatic Plates (ISP) revealed no abnormality. However, Farnsworth Panel D-15 hue test (Figure 1) revealed asymmetrical tritanomaly (blue-yellow colour deficiency) (Figure 2).

The Farnsworth Panel D-15 hue test was performed in day light in front of a wide window. The caps are numbered from 1 to 15. A reference cap is fixed in the box on the patient’s left side. The patient was first shown the normal order of the caps in the box. Then the caps were arranged in random order by the examiner. The test was performed first with the right eye. The patient was asked to rearrange the caps in normal order, step by step, starting from the reference cap. At the end of the test, the examiner closed the lid on the caps, turned the case up-side-down and opened it. The numbers of the caps will then appear. The numbers were reported on the score sheets in the order given by the patient. The test was repeated for the left eye. The result of the test can either be a “success” or a “failure”. For this patient, her diagram formed criss-crossed lines according to tritan axis.

She also had mild posterior subcapsular cataract in both eyes. Dilated pupil fundus examination showed no abnormality in both eyes.

She was diagnosed to have bilateral acquired blue-yellow colour deficiency secondary to ethambutol-induced optic neuropathy. She was immediately referred back to her chest physician in order to discontinue the offending anti-tuberculous medication. Two months after ethambutol discontinuation, a repeat Farnsworth Panel D-15 hue test showed that her colour vision returned to normal (Figure 3).

Figure 1. Farnsworth Panel D-15 hue test equipment. Different colour caps put in the black square socket; reverse side of the socket with the discs showing the serial number from 1-15.