Elevated dark adaptation thresholds in traumatic brain injury

Primary objective: To expand upon earlier findings of elevated dark adaptation ( scotopic) thresholds in photosensitive individuals with traumatic brain injury (TBI). Methods and procedures: To assess scotopic thresholds in individuals with TBI (n = 17) manifesting varying degrees of photosensitivity ( mild, moderate or marked), but without retinal dysfunction, to those of non-photosensitive, visually-normal individuals (n = 21) using a hand-held dark adaptometer. Main outcomes and results: The group mean scotopic threshold for the TBI group was significantly higher than that of the visually-normal group. Over 50% (nine out of 17) of the TBI group exhibited elevated thresholds. There was no correlation between the threshold value and degree of photosensitivity. Conclusion: The elevated scotopic thresholds suggest an abnormality in cortical gain control. An anomalous adaptive response may develop due to cortical damage, thereby attenuating subjective light sensation.