What is the effect of lesion of the visual pathway at different levels?
When the lesion is in the visual cortex, it results in loss of part or one half of the contralateral visual field (visual half field on the opposite side). Diffuse metabolic changes may cause loss of certain type of information without permanent field defects.
What happens if there is a lesion at the optic tract?
A lesion in one optic tract, interrupting all fibers carrying information from the contralateral visual fields, may cause homonymous hemianopia. When an injury to the left optic tract occurs, the patient will have visual difficulties (visual field cuts) in the right eye’s inner field, but in the left eye’s outer field.
What type of visual field defect would result from a lesion in the right optic tract?
A lesion of the right optic tract causes a complete loss of vision in the left hemifield: contralateral “homonymous” hemianopsia. A lesion of the right optic radiation just after the LGN also causes a loss of vision in the left hemifield: contralateral “homonymous” hemianopsia.
What would be the result of a lesion in the optic chiasm?
A pattern where the lesion at the optic chiasm disrupts the axons from the nasal field of both eyes resulting in the loss of vision of the right half of the right visual field and the left half of the left visual field. This visual defect is called non-homonymous bitemporal hemianopia.
What happens if the left LGN is damaged?
Damage at site #1: this would be like losing sight in the left eye. The entire left optic nerve would be cut and there would be a total loss of vision from the left eye. Damage at site #2: partial damage to the left optic nerve.
What is a lesion on the optic nerve?
Optic nerve lesions. Unilateral visual loss, commencing with a central or paracentral (off-centre) scotoma, is the hallmark of an optic nerve lesion. Because most fibres in the optic nerve subserve macular vision, lesions within the nerve disproportionately affect central vision and colour vision.
What are visual pathway disorders?
Hemianopia: vision loss in one half of the visual field separated by the vertical midline. Bitemporal heteronymous hemianopia: vision loss at the outer (temporal) half of the visual field of both eyes. Binasal hemianopia: vision loss at the inner (nasal) half of the visual field of both eyes.
What are the 3 visual pathways?
Structure and Function
- Optic Pathway. The optic pathway begins in the retina, which is a complex structure made up of ten different layers.
- Pupillary Light Reflex Pathway (parasympathetic innervation pathway)
- The sympathetic Visual System.
- Conjugate Gaze.
What are the steps of the visual pathway?
For children with normal vision, the following things happen in this order:
- Light enters the eye through the cornea.
- From the cornea, the light passes through the pupil.
- From there, it then hits the lens.
- Next, light passes through the vitreous humor.
- Finally, the light reaches the retina.
What is the pathway and where pathway?
In the currently prevailing view, the different maps are organised hierarchically into two major pathways, one involved in recognition and memory (the ventral stream or ‘what’ pathway) and the other in the programming of action (the dorsal stream or ‘where’ pathway).
What causes a lesion in the optic tract?
Common etiologies. Optic tract lesions are most commonly caused by infarction (40%), tumors (32%), and trauma (17%) (Zhang et al., 2006b). Rarely, demyelinating disease may involve the optic tract in isolation (Savino et al., 1978; Rosenblatt et al., 1987).
What lesion means?
Listen to pronunciation. (LEE-zhun) An area of abnormal tissue. A lesion may be benign (not cancer) or malignant (cancer).
What is the pathophysiology of visual processing?
Cortical visual processing is commonly thought to proceed along two distinct pathways, a dorsal pathway projecting into parietal cortex, and a ventral pathway, projecting into temporal cortex.
What happens when the ventral visual pathway is impaired?
Lesion studies: When the ventral visual pathway is impaired, orientation as well as complex shape discrimination being compromised, and perceptial invariance affected. Lesions to the ventral stream however do not disrupt any functions of the dorsal stream. Impaired ventral pathway can be demonstrated in agnostic patients.
What is the medial pathway to the visual field?
This medial pathway has only weak connections with the ventral portions of either TEO or TE, making it a somewhat distinct channel for object quality information biased toward peripheral portions of the visual field (see for a further review of the connectivity of these regions).
What is the ventral visual pathway in primates?
Primate neuroanatomy of the ventral visual pathway In primates, the ventral stream also consists of extrastriate cortical areas in the temporal cortex downstream of the V4 visual area.