Effect of Axial Length on Full-Field and Multifocal Electroretinogram

Abstract

Abstract Background The Electroretinogram is a mass potential, which reflects the summed electrical activity of the retina. Full-field ERG measures the electrical signals from the whole retina in response to a light stimulus. The weakness of the full-field ERG is that it cannot provide topographical information regarding the functional integrity of the retina and cannot detect subtle functional defects. The response is dominated by the peripheral retina due to its predominance of retinal cells. Aim of the Work to investigate the effect of axial length on fullfield (ffERG)and multifocal ERG (mfERG). Subjects and Methods Forty-four eyes of 44 healthy subjects were included in this case series study which has been conducted at Ain shams university hospitals after the approval of the research ethical committee in the faculty of medicine, Ain Shams University between July 2018 and September 2019. Full ophthalmologic examination was performed for all participants, including visual acuity assessment (Best corrected visual acuity) using Snellen chart, calculation of spherical equivalent (SE), slit Lamp biomicroscopy examination with IOP measurement via Goldmann applanation tonometry (GAT), and fundus examination by indirect ophthalmoscope or via 90 D VOLK lens to assess macular area. Axial length measurement, ffERG & mf-ERG. Results; We found that in the absence of fundus changes, mfERG parameters showed decreased amplitudes with increase in axial length. The Six- Rings Response Densities showed negative correlation with AL while there is no significant correlation between Six- Rings Response Densities and SE. The Six- Rings P1 Amplitude showed negative correlation with AL while there is no significant correlation between P1 Amplitude and SE. The Six- Rings N1 Amplitude showed negative correlation with AL while there is no significant correlation between P1 Amplitude and SE. The four- quadrant Response Densities showed negative correlation with AL while there is no significant correlation between four- quadrant Response Densities and SE. The four- quadrant P1 Amplitude showed negative correlation with AL while there is no significant correlation between P1 Amplitude and SE. The four- quadrant N1 Amplitude showed negative correlation with AL while there is no significant correlation between P1 Amplitude and SE. There is no significant correlation between full-field clinical ERG parameters and both AL and SE. Conclusion In the absence of fundus changes, mfERG parameters showed decreased amplitudes with increase in axial length. For correct interpretation of ERG responses in clinical practice, we recommend consideration of axial length measurement when evaluating mfERG responses.