A 70-year-old female developed a sudden onset of slurring of speech and dryness of mouth after snake bite. During presentation in local hospital after 2 h of the event, the patient was unconscious and needed intubation. Anti-snake venom (ASV) was given immediately according to the local protocol. She regained her consciousness the next day and was extubated. There was no limb weakness, blurring of vision, diplopia, or other neurological symptoms. The patient did not recall any specific character of the snake; however, the geographic region suggested the snake was most likely to be a cobra snake. She was discharged after 3 days of admission; slurring of speech completely improved during discharge. After 16 days of the episode, the patient presented to our center with a complaint of blurring of vision for 10 days followed by bilateral loss of vision. The detailed timeline of events is shown in Figure 1. Loss of vision was painless and progressive. The vision loss was diffuse, and no postural variation was present. There was no redness of the eye, photophobia, increased lacrimation, or pain in eye movement. There was no headache, vomiting, limb weakness, slurring of speech, nasal intonation of voice, or nasal regurgitation. She did not complain of any tingling sensation, numbness, paresthesia, abnormal body movement, and weakness of the limbs. She was a diabetic under regular oral antidiabetic drugs for 16 years. She was also diagnosed with hypertension 10 years back for which she has been under regular antihypertensive medication. There is no history of cigarette smoking or consumption of alcohol.
On examination, her vitals were stable with the pulse rate of 72 beats/min, 120/80 mm of Hg blood pressure, respiratory rate of 20 breaths/min, and temperature of 98 F. Visual acuity was assessed using the Snellen Chart, but as the patient could not read the largest letter, could not count finger or see hand movement, and only see the light shined in bilateral eyes, visual acuity of <<perception of light>> in both eyes was recorded. The cup to disc ratio was 0.1:1 in the right eye and 0.2:1 in the left eye, and the disc was hyperemic. On neurological examination, higher mental function was intact with normal cranial nerves except CN II where visual acuity was limited to perception of light. Pupils were regular and round while both direct and consensual light reflex were sluggish. Examination of the anterior and posterior segments, ocular motility, and intraocular pressures were normal. Motor and sensory system examinations were normal. There were no signs of cerebellar dysfunction and meningeal irritation. Routine blood investigations such as complete blood count and renal and hepatic function tests were normal. CSF examination for total protein, albumin, IgG, IgA, IgM, glucose, lactate, cell count, microbiological/virological analysis, and the oligoclonal band was normal. With this history and examination findings, a provisional diagnosis of ON was made. and visual-evoked potential (VEP) and MRI of the brain were planned but were not done due to patient uncooperativeness. On the basis of our provisional diagnosis, 1 g intravenous methylprednisolone (MP) was given for 5 days along with oral thiamine and methyl cyanocobalamin supplements. Chest X-ray was performed before administrating the steroid to rule out pulmonary tuberculosis, and it was normal. On the 2nd day of treatment, the patient was able to perceive hand movements. The patient's visual symptoms gradually improved to bilateral visual acuity of 6/60 on the fifth day of admission. Pinhole correction further did not show any visual acuity correction. There was abnormal color vision assessed by the Ishihara chart. MRI of the brain was also done which showed no abnormal findings (shown in Fig. 2). Intraocular pressure, VEP, and visual perimetry test were normal. Examination of the fundus showed a bilateral normal optic disc (shown in Fig. 3). The patient was given oral steroids at an initial dose of 1 mg/kg and tapering over 4 weeks after completion of intravenous MP. On the ninth day, the patient was discharged with improved visual acuity to 6/36 on left and 6/12 on right. On 2 months' follow-up, the patient's visual acuity improved to 6/9 on the left side and 6/6 on the right. Blood sugar monitoring was done throughout the course of treatment, and it did not rise to the level that warranted possible discontinuation of steroids or other treatments.