[Changes of visual field and visual evoked potential in nasopharyngeal carcinoma patients after radiotherapy]

Radiotherapy is the main treatment for nasopharyngeal carcinoma (NPC). The incidence of radiation-induced complications, especially radiation optic neuropathy (RON), increases along with prolonging survival time of the patients. This study was to investigate RON in NPC patients after irradiation by visual field and visual evoked potential (VEP) tests.

A total of 28 NPC patients, who underwent conventional external-beam irradiation, received visual field and VEP tests before irradiation, at the end of irradiation, and 5 years after irradiation.

Thirty-four (60.7%) eyes in 21 patients developed pathological visual field; 15 (44.1%) of these 34 eyes occurred within 10-24 months after irradiation. Of the 34 eyes, 8 showed concentric visual field constriction; 6 showed bitemporal hemianopia; 8 showed local photosensitivity descend; 10 showed central or cecocentral scotoma; 2 showed scotoma enlargement. Forty-four (78.6%) eyes in 26 patients appeared VEP abnormity; 24 (54.5%) of these 44 eyes occurred within 14 months after irradiation. In small, medium, and large elements, VEP latencies were significantly longer within 1 year after irradiation than pre-irradiation (P < 0.001, P < 0.001, and P=0.001); VEP amplitudes were lower within 1 year after irradiation than pre-irradiation without significant difference (P=0.249, P=0.940, and P=0.450). One year after treatment, VEP latency delay maintained in each element (P=0.004, P < 0.001, P < 0.001); VEP amplitudes were decreased (P=0.002, P=0.189, P < 0.001). The incidence of pathologic visual field was significantly lower in patients received irradiation of < or =70 Gy than in patients received irradiation of > 70 Gy (50.0% vs. 77.3%, P=0.041).

RON correlates to total irradiation dose. Pathologic visual field may indicate the position of RON.