Objective Assessment of Visual Field Defects Caused by Optic Chiasm and Its Posterior Visual Pathway Injury

Abstract

Objective To investigate the characteristics and objective assessment method of visual field defects caused by optic chiasm and its posterior visual pathway injury. Methods Typical cases of visual field defects caused by injuries to the optic chiasm, optic tracts, optic radiations, and visual cortex were selected. Visual field examinations, visual evoked potential （VEP） and multifocal visual evolved potential （mfVEP） measurements, craniocerebral CT/MRI, and retinal optical coherence tomography （OCT） were performed, respectively, and the aforementioned visual electrophysiological and neuroimaging indicators were analyzed comprehensively. Results The electrophysiological manifestations of visual field defects caused by optic chiasm injuries were bitemporal hemianopsia mfVEP abnormalities. The visual field defects caused by optic tract, optic radiation, and visual cortex injuries were all manifested homonymous hemianopsia mfVEP abnormalities contralateral to the lesion. Mild relative afferent pupil disorder （RAPD） and characteristic optic nerve atrophy were observed in hemianopsia patients with optic tract injuries, but not in patients with optic radiation or visual cortex injuries. Neuroimaging could provide morphological evidence of damages to the optic chiasm and its posterior visual pathway. Conclusion Visual field defects caused by optic chiasm, optic tract, optic radiation, and visual cortex injuries have their respective characteristics. The combined application of mfVEP and static visual field measurements, in combination with neuroimaging, can maximize the assessment of the location and degree of visual pathway damage, providing an effective scheme for the identification of such injuries.

Keywords

• |forensic medicine|wounds and injuries|visual electrophysiology|visual pathway|field of view|optic chiasma|multifocal visual evoked potential （mfvep）|optic nerve injury