Increase in electroretinogram rod-driven peak frequency of oscillatory potentials and dark-adapted responses in a cohort of myopia patients

Purpose To study whether rod- and cone-driven electroretinogram (ERG) responses are altered in myopia patients. Methods Dark- and light-adapted ERGs were recorded from 57 myopic eyes of 32 patients aged 22-30 and 19 emmetropic eyes of 10 age-matched normal subjects. The myopic eyes were divided into 3 groups according to spherical equivalent (SE) of manifest refraction: 18 low myopia eyes (<= - 3.00 diopter (D), 23 moderate myopia eyes (- 3.25 to - 6.00 D), and 16 high myopia eyes (> - 6.25 D). The amplitudes of the dark- and light-adapted ERG a- and b-waves, as well as the frequency spectra of the cone-driven and rod-driven oscillatory potentials (OPs), were analyzed by fast Fourier transform. The peak frequency, implicit time, and total power of the OPs were determined. The axial length was measured with an IOL Master. The ERG parameters including those of the cone- and rod-driven OPs were compared among three groups. Results The amplitudes of the a-wave and b-wave of the dark-adapted ERGs were increased with refractive power (P < 0.05). Interestingly, the average peak frequency of the rod-driven OPs showed a significant positive correlation with refractive power (P < 0.001): 123.41 +/- 9.13 Hz in emmetropic controls, 129.12 +/- 10.28 Hz in low myopia, 133.90 +/- 9.13 Hz in moderate myopia, and 139.51 +/- 5.78 Hz in high myopia. However, the parameters of the light-adapted ERGs and the cone-driven OPs in myopic eyes were within normal ranges. Conclusion We found significant positive correlation between the peak frequency of rod-driven OPs, as well as the amplitudes of rod-driven ERG a- and b-waves, and the refractive power. The results suggest that the rod system function was changing during the progress of myopia, while the cone system function appeared unaffected. The peak frequency of OPs appeared as a novel ERG parameter for myopia, a common ocular condition.