Clinical condition of the visual center
Damage to the visual path can be caused by numerous processes: Such damage can result in relatively specific vision failures, depending on the location of the visual path or visual system. For example, a unilateral lesion of the optic nerve leads to unilateral blindness. This can occur, for example, as a result of an optic nerve rupture in a traffic accident.
A lesion in the area of the middle part of the optic chiasm leads to a so-called bitemporal hemianopsy, i.e. the affected person can no longer see anything in the external visual field on either side, since the fibers for this purpose cross the middle of the opposite side in the chiasm. Such a failure can be caused by a tumor in the area of the pituitary gland, for example. In the area of the brain, a lesion often leads to even more serious failures, as many important processing steps take place in a small space.
If the primary visual cortex is damaged on one side, this leads – depending on the extent – to smaller visual field failures or to a homonymous hemianopsy. This means that in one eye the lateral visual field is lost in one eye and the medial visual field in the other. This is due to the fact that the fibers crossing in the chiasm, for example, cause the left side of the brain to receive fibers from the medial side of the left visual field and the lateral side of the right visual field.
In processes in the area of the primary visual cortex, it is because the visual cortices of both sides are very close to each other, but more often the primary visual cortex of both sides is affected, for example by a tumor in this area. This can then lead to complete blindness. Lesions in the area of the secondary visual cortex, however, do not lead to visual field loss or blindness.
In this case the patient can no longer process and recognize what he has seen. This is called visual agnosia. If it is a failure of only a small area of the secondary visual cortex, selective recognition processes may be disturbed, for example, only the recognition of faces (prosopagnosia) may be affected. The visual system thus consists of a complex network and switching of fibers on the way from the eye to the brain, where the seen is processed only to the extent that it can be consciously perceived and interpreted.
- Traumas
- Inflammations
- Tumors and others.
