Ophthalmologymiddle twist
A 58-year-old woman has twice walked into the left-hand door frame this month and has scraped the driver's side of her car. She has noticed nothing wrong with her sight and reads the newspaper without difficulty. Corrected acuity is 6/6 in each eye. Tested separately, each eye loses the whole left half of its field to a sharp vertical edge, although a small central island is preserved in both. The two defects are identical in extent. The pupils are equal and neither dilates when the torch is swung between them, and both optic discs look normal. Which one of the following is the most likely site of the responsible lesion?