Acute bilateral optic neuritis is common in Asia but presents differently from that seen in Caucasians. This study measures the corneo-fundal potential as shown by the EOG and expressed as the Arden Ratio in Sri Lankan patients.
Thirty-six patients (Age 18-85 years, Median 45 years, 18 Males and 18 Females) with bilateral optic neuritis were studied within 5-21 days of onset of acute bilateral optic neuritis and compared with 40 control subjects (Age 24-60 years, Median 34 years). Ethical approval from the University of Peradeniya was granted. Diagnosis was clinical aided by visual acuity, colour vision, pupillary reflexes, fundoscopy and oculomotor measurement. Neither scanning nor AQP4-IgG estimation was available. All patients had delayed P100 PR-VEPs but none had other neurological symptoms or signs.
The EOG was measured from electrodes placed at the outer canthi of the two eyes after dark adaptation, the dark trough (DT) followed by light adaptation, The light peak (LP). The Arden Ratio, LP/DT, is typically 1.7 – 4.3.
Our control value for the Arden Ratio was 1.84±0.3. The Arden Ratio of the patient group was significantly reduced at 1.60±0.4. Twenty of the 36 patients had an Arden Ratio of <1.7 which is taken as the lower limit of normal. In this group there were significantly more females and pain was more often a symptom.
The corneo-fundal potential is generated by the retinal pigment epithelium and is typically affected by retinal degenerative disease and would not be expected to be altered in disease of the optic pathway. These findings need confirmation using more tightly controlled methods, for instance we had no ganzfeld and no light meter available.