Axial Length in Patients with Myopia and Interpretation of Pattern Electroretinogram Recordings

PURPOSE: To assess pattern electroretinogram (PERG) recordings in patients with axial myopia with a special focus on the correct interpretation of findings. PATIENTS AND METHODS: Sixty patients divided into three groups according to the spherical equivalent of refractive error (group 1, error −3 D to −6 D; group 2, error > −6 D; and controls, error −1 D to +1 D) were examined. Data for the right eye of every patient were considered in the statistical analysis. All patients had a full ophthalmic examination including the measurement of visual acuity, intraocular pressure, degree of refractive error, axial length, biomicroscopic evaluation of the anterior segment, fundoscopy and PERG. The differences of basic parameters and P50 and N95 amplitudes as well as P50 implicit time between groups were studied. Correlations between P50 and N95 amplitudes and P50 implicit time were axial length and refractive error was established. RESULTS: The P50 amplitude, N95 amplitude and P50 peak time differed significantly between the groups (P<0.01). No significant differences were found for the N95/P50 ratio. Significantly lower P50 and N95 amplitudes (r=−0.42, P<0.01; r=−0.42, P<0.01) and increased P50 peak time (r=0.64, P<0.01) correlated with elongated axial length. A 1-mm increase in axial length corresponded with a 0.41 µV decrease in the P50 amplitude and 0.55 µV reduction of the N95 amplitude. There was also 1.11 ms increase of P50 wave peak time per 1 mm increase of axial length. Significantly lower amplitudes and longer peak times are associated with increased axial length and increased refractive error. CONCLUSION: According to results observed in this study, the correct interpretation of PERG recordings requires the consideration of axial length.