| The purposes of the study were to determine whether the pattern electroretinogram (PERG) could detect the presence of selective functional impairment in early glaucoma and to what extent this impairment correlated with functional and anatomical measures from the macula and optic nerve. Participants had a complete eye examination and performed standard automated perimetry, frequency-doubling perimetry, stereoscopic photography of the optic nerve, measurements of macular and retinal nerve fiber layer thickness with the optical coherence tomograph and, finally, achromatic PERG. 35 participants were classified as normal, 36 were patients with early glaucoma, and 41 were glaucoma suspect. Data from one eye per participant was included in the analysis. Transient and steady-state PERG were recorded with visual stimulus of high contrast checkerboard patterns of four spatial frequencies (0.04, 0.625, 1.25 and 2.5 cycles/degree), reversed at two temporal frequencies, 2.5 Hertz (Hz) and 9.5 Hz, respectively. Amplitudes for the transient response were measured with the peak-to-peak method and at the second harmonic of Fourier transformation. Amplitudes for the steady-state were measured at the second harmonic only. In normal eyes, amplitudes presented a tuning curve that peaked at intermediate spatial frequencies tested for 2.5 and 9.5 Hz. Glaucomatous and suspect eyes showed a flattening of this curve, with a prominent amplitude reduction at 0.625 and 1.25 cpd for 2.5 and 9.5 Hz. Furthermore, the proportion of amplitude reduction was similar for a stimulus biased to parvocellular and magnocellular function. These findings suggest the presence of a generalized impairment in early glaucoma.; Amplitudes from transient and steady-state responses correlated significantly with standard automated perimetry results. Meanwhile, only the steady state response correlated with frequency-doubling perimetry results. Based on the magnitude of R2, however, greater correlations were observed between PERG amplitudes and nerve fiber layer and macular thickness. Additionally, among all four functional and structural measurements, retinal nerve fiber layer thickness was the only significant independent predictor of the PERG amplitude. These findings suggested that PERG amplitudes were better explained by structural rather than functional measurements. In summary, PERG detected early glaucomatous impairment and correlated better with the degree of ganglion cell loss. |
