Does macular sparing really exist in occipital lobe lesions?
Or is it just an artifact?
At least when you use computerized perimetry it is uncommon to observe it.
Yes, it really exists and it is explained by fibers from right hemisphere spreading into left one and opposite, which maintance central visual field reflected by macula
Dear Marianne, I know that you can find that theories in classic textbooks. A very good review was published in Brain in 2004: A historical review of the representation of the visual field in primary visual cortex with special reference to the neural mechanisms underlying macular sparing.
The thing is that in the last ten years I have seen several occipital lobe strokes, and I think that at least with 24-2 Humphrey visual fields, macular sparing is not evident. The two central points on the side of the hemianopia are not usually spared.
Maybe 10-2 visual fields should be used to demonstrate macular sparing. Or maybe macular sparing is just a myth (like junctional scotoma).
Best regards.
Julio.
I think that macular sparing was revealed by kinetic perimetry, but not by static computer one
Standard automated perimetry (SAP) with a fixed 6 × 6° grid testing the central 24° of the visual field (eg, 24-2 and 30-2 tests) is the commonly used reference standard to define the presence of glaucomatous functional loss.1 In clinical practice and randomized clinical trials, the results of this modality of testing have been used as main outcome measures to determine glaucoma onset2,3 and progression4-6 often aided by optic nerve imaging techniques.
There is growing evidence that 24-2 SAP results can miss damage within the central 10° of the visual field that would otherwise be detected if one used a denser grid (2 × 2°), such as that tested with 10-2 SAP.
You might find this case interesting when macular sparing developed after several days.
Shin HY, Kim SH, Lee MY, Kim SY, Lee YC. Late emergence of macular sparing in a stroke patient: Clinical Case Report. Medicine (Baltimore). 2017;96(29):e7567. doi:10.1097/MD.0000000000007567
The authors cite:
"However, the mechanism of macular sparing is controversial. One hypothesis is that the visual cortex has a dual blood supply, from the middle (MCA) and posterior (PCA) cerebral arteries or the posterior temporal and calcarine arteries. The occlusion of 1 artery might result in macular sparing if another artery still provides blood to the visual cortex that represents macular vision. However, Smith and Richardson reported a variety of patterns by which the 4 branches of the PCA supply the visual cortex. Therefore, another hypothesis, incomplete damage to the visual cortex, might explain this phenomenon."
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