The Visual System – Neuroanatomy
The Globe and Uveo-Retinal Tract
ciliary body: a ring of fibroglandular tissue toward the front of the eye that produces the aqueous humor but that also acts to anchor the ciliary muscle; the bulk of the ciliary body is formed by the smooth muscle fibres of the ciliary muscle, that alters the shape of the lens to change the focus (focal point).
ciliary process: the region of the uveo-retinal tract between the iris and choroid
choroid: pigmented vascular layer covered by sclera externally and lined by the retina internally
retina: orbital extension of the optic nerve (and hence brain) made of photoreceptors sensitive to light
The Optic Nerve (CN-I)
A bundle of a million nerve fibres connecting the globe’s retina to the brain. It forms a small invagination of the globe posteriorly that effectively creates an area devoid of photoreceptors and a “blind spot” in the corresponding visual field.
Posterior of cross-section of orbital globe through the optic nerve
The primary visual cortex is inversely representative of the visual field:
The left visual field projects to the right temporal hemiretina and the left nasal hemiretina.The right visual field projects to the left temporal hemiretina and the right nasal hemiretina.
- The LEFT visual field is projected onto the RIGHT occipital cortex.
- The RIGHT visual field is projected onto the LEFT occipital cortex.
- The SUPERIOR visual field projects to the INFERIOR visual cortex.
- The INFERIOR visual field projects to the SUPERIOR visual cortex.
| Locus of the visual pathway | Blood supply |
| Optic nerve | Ophthalmic artery |
| Optic chiasm | Branches from: Internal carotid Posterior communicating artery Anterior cerebral artery Anterior communicating artery |
| Optic tract | Middle cerebral artery (MCA) |
| Lateral geniculate nucleus | Anterior choroidal branches of the MCA Thalamogeniculate branches of the posterior cerebral artery (PCA) |
| Optic radiations | MCA |
| Calcarine sulcus | Mostly by the PCA. The MCA also helps supply the anterior portion, which corresponds to the macula. |
References
Arjuna & Lynn, Savannah. (2016). Alzheimer’s-Related Amyloid Beta Peptide Aggregates in the Ageing Retina: Implications for Sight Loss and Dementia. 10.5772/64790.
