Effects of light scattering on the multifocal electroretinogram (mfERG)

Abstract

Introduction The multifocal electroretinogram (mfERG) was developed by Suffer & Trans in 1992 and has been used for the objective examination of numerous retinal diseases such as age-related macular degeneration, diabetic retinopathy and retinitis pigmentosa. Patients who suffer from these eye diseases are normally elderly and they may have a certain degree of age-related change in the crystalline lens which would cause light scattering. Forward light scattering reduces the stimulus contrast and backward light scattering reduces the stimulus luminance. Both affect the mfERG. Therefore, the effect of light scattering on the mfERG is of interest. Objectives To study the effects of forward light scattering on mfERG topography. To study the effects of different degrees of nuclear cataract on mfERG topography. To compare mfERG topography before and after cataract surgery. To study the effects of aging on mfERG topography. Methods There are four experiments in this study. In Experiment 1, a liquid crystal diffuser (L-C-D) was used to produce different degrees of forward light scattering. The mfERG was recorded in thirty young subjects under different degrees of forward light scattering produced by the liquid crystal diffuser. In Experiment 2, the mfERG was recorded from thirty elderly subjects, ten with very mild, ten with mild, and ten with moderate nuclear cataract. Their mfERG topographies were compared. In Experiment 3, the mfERG was recorded from ten elderly subjects (10 eyes) with nuclear cataract of grade five (Lens Opacities Classification System III) before and after cataract surgery. In Experiment 4, the mfERG were recorded in three groups of subjects: 1) eighteen young subjects (age 18-24 years), 2) eighteen elderly subjects (aged 60-70 years) with intraocular lens (IOL), and 3) eighteen elderly subjects (aged 75-85 years) with IOL. Results In Experiment 1, we found that the amplitudes of P1 from the central retina decreased, but the amplitudes of P1 in the mid peripheral retina increased with the increase of forward light scattering. N1 latency, P1 latency, and N1 amplitude were not affected by forward light scattering. In Experiment 2 and 3, we found that cataract can significantly decrease the N1 and P1 amplitudes from the central retina, but N1and P1 amplitudes from the mid peripheral retina did not change significantly. In Experiment 3, we found that both N1 latency and P1 latency did not change significantly after cataract surgery. In Experiment 4, by comparing the mfERG responses in young subjects to elderly subjects with IOL, we found that N1 and P1 amplitudes from central to mid peripheral retina (0o to 43.8o diameter) did not change significantly with increasing age. However, N1 latency from central to peripheral retina increased significantly after the age of 70 years. Conclusions Forward light scattering can affect mfERG topography. As cataract can affect the topography of the mfERG, caution should be taken when interpreting the mfERG topography in subjects who have some degree of cataract. We suggest that each laboratory should establish a norm for different degrees of cataract for clinical diagnosis. Since our results showed that elderly subjects with IOL have similar response amplitude to young subjects, age-related decline of the mfERG response amplitude shown in previous studies are likely to be due to optical rather than neural factors.