Afferent Visual Manifestations of Traumatic Brain Injury

Abstract

Traumatic brain injury (TBI) causes structural and functional damage to the central nervous system including the visual pathway. Defects in the afferent visual pathways affect visual function and in severe cases causes complete visual loss. Visual dysfunction is detectable by structural and functional ophthalmic examinations that are routine in the eye clinic, including examination of the pupillary light reflex and optical coherence tomography (OCT). Assessment of pupillary light reflex is a non-invasive assessment combining afferent and efferent visual function. While a flashlight assessment is relatively insensitive, automated pupillometry marked 95% specificity and 78.1% sensitivity in detecting TBIrelated visual and cerebral dysfunction with an area under the curve (AUC) of 0.69-0.78. OCT may also serve as a non-invasive biomarker of TBI severity, demonstrating changes in the retinal ganglion cell layer and nerve fiber layer throughout the range of TBI severity even in the absence of visual symptoms. This review discusses the impact of TBI on visual structure and function.

Review: Emerging Eye-Based Diagnostic Technologies for Traumatic Brain Injury

“…Many of the areas of the brain most vulnerable to mild TBI are related to vision [56] , including the long axonal fibres connecting the retina to the lateral geniculate body (LGN) and the LGN to the visual cortex, that get distorted by trauma causing diffuse axonal injury (DAI) [47] . There is a further potential for TBI indicators to be found in the retina, which is as an extension of brain tissue with biochemical changes in the retina occurring after various neuronal disturbances [114] , and there is potential for ocular manifestations of TBI to be detected by ophthalmic imaging techniques [30] , despite the lack of prospective data [115] , for example, oculomotor deficits may be, demonstrated by eye tracking in paediatric patients [113] , [116] . Fifty four percent of blast induced TBI patients had global visual field loss and visual field dysfunctions were present in all TBI severities [117] .…”

“…Triaging can also prevent unnecessary time and costs spent on healthcare services used for scanning and monitoring. While there are numerous extensive reviews of ocular manifestations of common neurodegenerative (ND) diseases [20][21][22][23][24][25][26][27][28] , changes in the visual system after TBI, a common neurological condition with huge and growing socioeconomic implications is significantly less well reviewed [29][30][31][32] . TBI increases rates of ND disorders 33,34 , as trauma triggers neurodegeneration accompanied by an increase in ND biomarkers, such as amyloid-Beta and tau protein 29,[35][36][37] .…”

Mild-to-Moderate Traumatic Brain Injury: A Review with Focus on the Visual System

“…The mechanism of traumatic optic neuropathy is not fully understood, but may result from tension on the nerve or nerve compression and involve damage to the axons and/or reduction of the blood supply to the nerve [76][77][78]. The visual impairment from optic nerve damage in TBI generally occurs at the time of injury and may vary from a deficit in color vision to loss of visual acuity to sudden, complete visual loss [79,80]. Treatment is difficult and may be medical, with high dose systemic corticosteroids or surgical, with decompression of the optic canal, or a combination of surgery and corticosteroids.…”

A differential of the left eye and right eye neurological pupil index is associated with discharge modified Rankin scores in neurologically injured patients

“…The "swinging flashlight test" for example is a well-known procedure in neuro-ophthalmology in which the examiner, by swinging a penlight back and forth between the two eyes, tries to detect a difference in the amount of the dilation between the two pupils. The swinging flashlight test is a tool for measuring relative afferent pupillary defect, a condition of many retinal or optical nerve diseases [7][8][9][10]. Anisocoria which is the difference of the two diameters of the pupils at rest, is another expression of asymmetry often associated to intracranial pathologies [11].…”