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Kenneth J. Ciuffreda, Naveen K. Yadav, Esther Han, Diana P. Ludlam, Angela Peddle, Paul Hulse, Suzzane Walter, Jennifer Han; Distance Perception in Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4696.
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© ARVO (1962-2015); The Authors (2016-present)
Mild traumatic brain injury (mTBI) patients frequently report difficulty judging distances. Thus, the purpose of this study was to assess egocentric distance perception in individuals with mTBI having the symptom of "poor depth perception". Currently, there are no such data in the mTBI population.
Ten individuals with mTBI and the symptom of "poor depth perception" were tested, and they were compared with ten asymptomatic visually-normal individuals with respect to (1) egocentric distance perception, and (2) Randot stereoacuity at distance and near. Distance perception was assessed in both a clustered (n = 6 objects presented simultaneously; 6 distances: 0.77, 1.52, 3.86, 7.41, 8.37 and 12.87 m) and isolated (n = 1 object at a time; 3 distances: 1.52, 3.86 and 12.87 m) static hallway environment. Magnitude estimation was used to obtain the distance perception response function slope comparing physical versus perceived distance. Testing was performed under monocular (dominant eye) and binocular viewing conditions. Stereoacuity was assessed binocularly at 40 cm and 3 m.
Mean egocentric distance perception response function slope values were not significantly different (p > 0.05) in the two groups (normals and mTBI) under any of the test conditions. Overestimation of near distances, and underestimation of far distances, was found as predicted by earlier studies in normals. However, 2 of the 10 mTBI subjects exhibited abnormal overestimation of perceived distances for all six objects in the clustered environment. Mean stereoacuity (sec arc) was 36 and 84 in the mTBI, and 20 and 51 in the normals, at near and distance, respectively. The stereoacuity difference between the two groups was significant at near (p = 0.02), but not at distance (p = 0.09).
Similarity of the group mTBI egocentric distance response slope functions under both the monocular and binocular viewing conditions suggested absence of a "binocular vergence" contribution (e.g., abnormal vergence innervation) to their symptom. Similarly, the slightly reduced stereoacuity in the mTBI group was likely insufficient to explain their symptom of "poor depth perception". Since in only 2 of the 10 mTBI individuals could their abnormal distance slope function and/or stereoacuity account for the symptom, it is speculated that in most, an injury to higher-level cortical perceptual centers computing distance perception, such as the posterior parietal cortex, are involved. Testing under dynamic conditions may elucidate more fully the underlying mechanisms.
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