Why can’t I see in the dark?BMJ 2021; 373 doi: https://doi.org/10.1136/bmj.n1573 (Published 30 June 2021) Cite this as: BMJ 2021;373:n1573
- Selina Khan, specialist trainee registrar in ophthalmology1,
- Sophie Beavers, consultant histopathologist2,
- Claire Rice, consultant neurologist3,
- Denize Atan, consultant neuro-ophthalmologist3
- 1Bristol Eye Hospital, Bristol, UK
- 2Southmead Hospital, Bristol, UK
- 3Bristol Medical School, University of Bristol, UK
- Correspondence to: D Atan Denize.Atan@bristol.ac.uk
A man in his 70s presented with an eight month history of bilateral progressive visual loss. Initially, he could see well in bright daylight but was unable to see in the dark. He described his peripheral vision as becoming darker over time, until eventually he was unable to see in bright or dim light conditions.
He was congenitally deaf and communicated with sign language. He had no previous visual problems. Both parents and two siblings were also congenitally deaf; no family members were visually impaired.
Over the previous year the patient had lost about 13 kg in weight, despite consuming a healthy balanced diet, had chronic abdominal discomfort, and passed frequent loose, pale stools. Previous investigations showed microcytic anaemia with low ferritin levels (14 μg/L, normal range 33-490 μg/L). The results of computed tomography colonoscopy and chest radiography were normal and the patient was waiting for upper gastrointestinal endoscopy as an outpatient. His only medication was vitamin B12 injections for macrocytic anaemia diagnosed five years earlier.
On examination, the patient’s visual acuity of both eyes was reduced to …