Got an email from Oliver Sacks’ office this week about the BBC Documentary, Imagine, that will be playing in the UK this weekend. I cited it when it was broadcast originally last summer, though it appears they’ve disabled video links to the program. Here’s a photo of Sue Barry watching a 3D film together with Imagine’s producer, Alan Yentob. The series is based on Sacks’s book The Mind’s Eye, which included the story of Stereo Sue, but its title – The Man Who Forgot How to Read – is a story that belongs to Howard Engel. I’ve covered Engel’s story before in a three-part series on The Visuality of Reading. In short, Sacks relates how Engel lost his ability to read when he suffered an occipital lobe lesion, though leaving his ability to write intact – a condition termed alexia sine agraphia. That’s alexia [inability to read] sine [without] agraphia [inability to write].
Your occipital lobe, in the back of the brain, is the hub for much visual information. Here’s a nice MRI photo taken from a neuro-ophthalmology textbook showing classic localization of a left occipital lobe lesion in a patient who has alexia sine agraphia. Because the disturbance occurs in the left region of the occipital lobe, it classically results in loss of visual field on the patient’s right side. Loss of this nature is referred to as homonymous, and the “anopia” or absence of seeing is classified according to whether it involves half of the field (hemianopia) or a sector (quadrantanopia).
Ruth, a 68 year-old retired reading teacher, came to see me earlier this year. She was referred by a friend who swore by (not at) our practice, and her initial impression was that she needed a change in her glasses because she was having trouble reading. We conduct an automated visual field screening on every patient above age 17, and occasionally you’ll see diagnostic fields that alert you to the possibility that something is deeply wrong, well beyond the need for a change in glasses. Ruth came in to my exam room and when I asked her to read the Snellen Chart she was stymied in identifying the letters verbally. The “blur” that she thought was related to her eyes was clearly occurring somewhere deeper in her brain.
We referred Ruth for a neurology work-up and an MRI, but in the interim conducted a 24-2 SITA Standard Threshold Visual Field Test. As you can see from the above, Ruth essentially had a right homonymous field loss, the top photo being the plot of the R eye and the bottom of the L eye. Though there appears to be some sparing of field on the right side, her Pattern Deviation graph makes the functional effect more obvious, again the top is the R eye and bottom is the L eye.
We probed further. Sure enough, Ruth could write but she had no idea what letters she had written. She had Alexia Sine Agraphia. Now what?