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The visual pathway consists of structures that carry visual information from the retina to the brain.Lesions in that pathway cause a variety of visual field defects. In the visual system of human eye, the visual information processed by retinal photoreceptor cells travel in the following way:
The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, [1] of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle frontal gyrus with the precentral gyrus , consisting of a frontal and parietal portion. [ 2 ]
The visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; [1] in ophthalmology and neurology the emphasis is mostly on the structure inside the visual field and it is then considered “the field of functional capacity obtained and recorded by means of perimetry”.
The function of the feedback from the visual cortex back to the LGN is unknown. The optic radiation is activated during working memory tasks. [3] The optic radiations are usually unilateral and commonly vascular in origin. Field defects, therefore, develop abruptly, in contrast to the slow progression of defects associated with tumors.
Figure 1 - Humphrey field analyser. Humphrey field analyser (HFA) is a tool for measuring the human visual field that is commonly used by optometrists, orthoptists and ophthalmologists, particularly for detecting monocular visual field. [1] The results of the analyser identify the type of vision defect.
It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration, Epiretinal membrane), as well as the optic nerve and the visual pathway to the brain. Amsler grid usually help detecting defects in central 20 degrees of the visual field. [2]
A scotoma is an area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that is surrounded by a field of normal – or relatively well-preserved – vision. Every normal mammalian eye has a scotoma in its field of vision, usually termed its blind spot.
A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits.