Pattern Electroretinogram as an Objective Measure of Contrast Sensitivity in Diffractive Multifocal Intraocular Lenses
Received Date: August 07, 2019; Published Date: August 14, 2019
Purpose: Traditionally, contrast sensitivity (CS) has been an important component of vision measured by subjective in-office testing that can be qualitatively, but not quantitatively analyzed without introduction of patient biases such as motivation, effort and capacity to focus. Alternatively, Pattern Electroretinogram (PERG) provides objective, quantifiable changes in waveform amplitudes that are generated as the final common pathway of visual processing. It is less influenced by subject bias. In this study, we have developed and validated methodology to use N95 waveform amplitudes generated by PERG as a tool to objectively measure CS. We then applied this methodology to a second experiment to quantify changes in CS in young healthy eyes induced by an ex-vivo lens system which incorporated different intraocular lenses (IOL). This allowed us to objectively measure CS changes induced by different IOLs.
Methods: Five young healthy subjects with best corrected visual acuities of at least 20/20 were recruited for this study. The pERGs were recorded using an ISCEV compliant protocol at 7 different spatial frequencies across 7 contrast intensities. The N95 amplitude and the contrast intensity at which the N95 amplitude was 50% on maximal was determined for each subject (termed contrast threshold (CT)). The effects of IOLs were determined using an ex-vivo lens system using four different experimental paradigms. The N95 was again measured and statistically analyzed was preformed using SATA.
Results: Pattern ERG as a measure of CS: There was a linear decrease in the N95 amplitude as contrast intensity decreased, and across all CPD/ spatial frequency trials. In all subjects CT increased between 0.125 and 0.25 CPD and subsequently decreased until 5 CPD. This CT curve mirrored classical contrast by logarithmic VA and normalized contrast sensitivity by CPD curves that mirror the increasing, followed by decreasing CSF at increasing spatial frequencies. CS and Intra-Ocular Lenses: As the percent contrast increased the N95 amplitude increased as well and the highest amplitude was recorded with no IOL or lens system in place (Paradigm 1). There was a significant decrease in the N95 progressing from no lens system to the custom trial lens system (Paradigm 1 v 2; p <0.0001) There was however no further reduction in the N95 amplitude by placing a neutralized monofocal lens in the lens system (Paradigm 2 v 3; p>0.05). Importantly there was a significant decrease in the N95 amplitude when the multifocal IOL was placed (Paradigm 4) when compared to the other three paradigms (Paradigm 1 v 4; p<0.0001, Paradigm 2 v 4; p<0.0001; Paradigm 3 v 4; p<0.0005).
Conclusion: Contrast sensitivity can be measured by pERG and this provides an objective way to measure the effects on contrast by optical devices.