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The occipital pole is an anatomical landmark that corresponds to the posterior portion of the occipital lobe. It is formed by the convergence of the superior and inferior occipital gyri in the majority of individuals; the middle occipital gyrus also contributes when it is present 1.
It contains the part of the primary visual cortex (Brodmann area 17) representing the macular (central) vision. This posterior segment accounts for the majority of the primary visual cortex because of the disproportionate macular representation within the cortex 2; axons coming from the fovea and a 1 mm 3 area around it (representing the central 10 degrees and corresponding to ~2% of the total visual field) innervate ~60% of the primary visual cortex 2.
The vasculature of the occipital pole is unique in that it receives a dual blood supply, with anastomoses from the posterior cerebral artery (PCA) as well as the deep branch of the middle cerebral artery 4.
Lesions of the occipital pole result in a contralateral homonymous defect of macular vision (HMV) 4.
The dual blood supply explains the phenomenon of a macula-sparing hemianopia that occurs with occlusion of the PCA in which the anterior portions of the primary visual cortex representing peripheral vision are affected while the occipital pole is spared. However, HMV is not as uncommon in PCA infarct as may be expected; a retrospective case-series of 54 patients with PCA infarcts found that of the 43 with visual field defects, 6 had HMV while 4 had macula-sparing hemianopia 4.
- 1. Alves RV, Ribas GC, Párraga RG et-al. The occipital lobe convexity sulci and gyri. J. Neurosurg. 2012;116 (5): 1014-23. doi:10.3171/2012.1.JNS11978 - Pubmed citation
- 2. Rajakumar R. Barr's The Human Nervous System: An Anatomical Viewpoint. LWW. ISBN:145117327X. Read it at Google Books - Find it at Amazon
- 3. De Moraes CG. Anatomy of the visual pathways. J. Glaucoma. 2013;22 Suppl 5: S2-7. doi:10.1097/IJG.0b013e3182934978 - Pubmed citation
- 4. Isa K, Miyashita K, Yanagimoto S et-al. Homonymous defect of macular vision in ischemic stroke. Eur. Neurol. 2001;46 (3): 126-30. Pubmed citation