Visual-evoked potential predicts the efficacy of the optical canal decompression for traumatic optic nerve neuropathy showing blindness: A case report

Abstract

Background: The indication for surgical optic canal decompression (OCD) for traumatic optic neuropathy (TON) remains controversial because there is no reliable predictor of a good outcome. We report the case of a blind patient with TON whose remaining visual-evoked potential (VEP) suggested recovery potential of the injured optic nerve after OCD.

Case description: A 48-year-old man had fallen from a height of 7 m, striking his head. He immediately complained of right-eye blindness. He had no light perception and the direct light reflex disappeared from the right pupil, although there was no fracture or traumatic lesion on computed tomography and magnetic resonance imaging. Because the amplitude of the VEP with the right eye stimulation remained unchanged, we performed the right OCD. During surgical OCD, the amplitude and latency of VEP began to improve. Finally, the visual field improved in almost all directions, and eyesight improved to 0.2.

Conclusion: The retained VEP activity in TON may suggest the recovery potential of the injured optic nerve, even in cases of blindness. It is possible that VEP is an indicator of aggressive treatment for TON such as OCD.

Keywords: Optic canal decompression; Traumatic optic neuropathy; Visual-evoked potential.

Figure 1:

Computed tomography (CT) scan and magnetic resonance imaging (MRI) pre- and postoperatively. Thin-slice CT showing no optic canal fracture (a); MRI showing no intracranial traumatic lesions (b and c).

Figure 2:

Visual-evoked potential at admission. The mid-occipital electrode (Mo) is placed above the external occipital protuberance (inion). Lateral occipital electrodes (Lo and Ro) are placed 4 cm to the left and right to the Mo.

Figure 3:

Pre- and post-operation three-dementional images of optic canal decompression (a and b). White arrow indicates the decompressed optic canal.

Figure 4:

Changes of visual-evoked potential during operation and follow-up time. After craniotomy and drilling out of the optic canal, the amplitude increased at all electrodes in the right-sided stimulation. The final measurement improved from 2.1 μV to 6.1 μV at L0 (Left occipital electrode), from 4.5 μV to 9.5 μV at M0 (Middle occipital electrode), and from 4.3 μV to 10.4 μV at R0 (Right occipital electrode).

Figure 5:

Change in the visual field of the right eye by Goldmann visual field meter. (a) Pre-operatively. (b) Post-operatively. (c) Thirty days after the operation, vision was restored in all directions, except for the central field of view.