Purpose: To evaluate the early changes in retinal function after photodynamic therapy (PDT) by multifocal electroretinogram (mfERG).
Design: Prospective interventional case series.
Methods: Seventeen eyes from 17 patients scheduled for standard PDT with verteporfin were prospectively recruited. Patients' diagnoses included choroidal neovascularization (CNV) secondary to age-related macular degeneration, idiopathic CNV, myopic CNV, polypoidal choroidal vasculopathy, and central serous chorioretinopathy. Serial mfERG recordings were performed before PDT, and at 4 days, 2 weeks, and 1 month after PDT. The first-order kernel N1 and P1 mfERG response from the central 0 to 7 degrees and peripheral 7 to 25 degrees were grouped and analyzed. The mean response amplitudes and peak latencies of the mfERG recordings were compared longitudinally.
Results: There were statistically significant reductions in the mean N1 response amplitude for the central group at 4 days (P =.007) and 2 weeks after PDT (P =.024), in the mean P1 response amplitude for both the central (P =.006) and peripheral (P =.013) groups at 4 days, and for the central group at 2 weeks after PDT (P =.017). There were also statistically significant increases in the mean P1 response latencies at 4 days (P =.004) and at 2 weeks (P =.018) after PDT for the central group and at 4 days after PDT (P =.026) for the peripheral group. At 1 month after PDT, no significant differences in the N1 and P1 mean response amplitudes and peak latencies were observed compared with pre-PDT mfERG.
Conclusions: Transient impairments in retinal function for as long as 2 weeks after PDT were noticed by reduction in response amplitudes and a delay in peak latencies of mfERG. These findings may explain the common adverse event of subjective visual disturbance early after PDT with normal findings in visual acuity and ophthalmoscopy.