Evaluation of the effects of radiotherapy to the chiasm and optic nerve by visual psychophysical and electrophysiologic tests in nasopharyngeal carcinoma.

Purpose: To evaluate the effects of high-dose radiotherapy (RT) to the chiasm and optic nerves in locally advanced nasopharyngeal carcinoma patients by visual psychophysical and electrophysiologic tests.

Methods And Materials: A series of visual tests, including visual evoked potentials (VEPs), contrast sensitivity, and visual field and visual acuity tests, were administered to 27 patients with locally advanced (T4) nasopharyngeal carcinoma who had undergone RT to high doses 6 to 74 months previously. As a control group, the same tests were administered to 40 unirradiated patients who had been referred to the ophthalmology department for any reason.

Results: The median values of VEP latency, VEP amplitude, and contrast sensitivity and the rate of visual field defect were significantly worse in the RT group (p = 0.06, p <0.001, p <0.001, and p = 0.005, respectively). No dose-response relationship was found in any tests when 50 Gy was the cutoff value. However, a positive correlation between the interval after RT and VEP latency (r = 0.406, p = 0.003) and a negative correlation between the interval and contrast sensitivity (r = -0.499, p <0.001) was noted; no correlation could be established regarding VEP amplitude and the interval after RT.

Conclusion: Radiation-induced injury to the anterior visual pathways could result in an increase in VEP latency and a decrease in VEP amplitude and contrast sensitivity. This injury seems to be a continuous process developing with time.