Examining retinal structure and visual function in patients with brain injury



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Purpose: To determine whether inner retinal structure and function are altered in civilian traumatic brain injury (TBI) patients and the extent to which inner retinal abnormalities are related to alterations in visual function. Methods: Macular ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (RNFL) thicknesses were quantified globally and sectorally using spectral domain optical coherence tomography in 20 mild TBI (mTBI) and 29 severe TBI (sTBI) eyes, 17 of which had homonymous hemianopia (HH). The photopic negative response (PhNR) was used to assess retinal ganglion (RGC) function via the full-field flash electroretinogram. Visual function was quantified via 30-2 standard automated perimetry. Structure-function relationships were assessed on global and sectoral scales using established correspondence maps. Rod-cone and intrinsically photosensitive RGC (ipRGC) driven pupil responses were also measured in 21 TBI and 51 control subjects using 2 protocols: (i) a 1-second red stimulus and 10, 1-second blue stimuli of increasing intensity, and (ii) two minutes each of 0.1 Hz red and 0.1 Hz blue stimuli. Results: Global GCIPL and RNFL thicknesses were reduced in sTBI (P< 0.001) eyes relative to normative values, but not in mTBI eyes (P> 0.2). PhNR amplitude was reduced in both sTBI and mTBI eyes (P< 0.001). Reduced GCIPL thickness was measured more often in sectors corresponding to the side of hemianopic field loss (78-83%) compared to the side of spared vision (22-39%) (P<0.02). Several structure-function relationships existed in HH TBI patients (r = 0.5-0.8, P<0.04), but not in non-HH eyes (P>0.08). No ipRGC-driven pupillary metrics were significantly different between TBI and control subjects for red or blue stimuli (P>0.05 for all). Conclusion: The PhNR may objectively detect functional abnormalities in the inner retina in mTBI patients without structural damage and potentially better classify TBI. Preferential damage of inner retinal structure in locations corresponding to the side of hemianopic field loss is suggestive of retrograde degeneration. The similar ipRGC-driven pupil responses between TBI and control subjects suggest that ipRGCs are not selectively damaged in civilian TBI. These findings provide improved understanding of structural and functional properties of the visual system in TBI patients.



Traumatic Brain Injury, Concussion, TBI, Retina, Retinal Ganglion Cell, Melanopsin, Neurodegeneration, Optical Coherence Tomography, Electroretinogram