Some of the earlier studies reported that the amplitude of flash ERGs recorded with conventional systems were significantly reduced in eyes with a cataract but other studies reported that they were not reduced [8, 9]. Although a cataract can reduce the intensity of the stimulating light which would reduce the amplitude of the ERGs, it also scatters the light thus stimulating a larger area of the retina which would increase the amplitude of the ERGs . Previous studies had shown that a cataract will reduce the density of the multifocal ERGs (mfERGs) in the macular area but increase the peripheral mfERGs because of the light scattering [11, 12]. These differences in the stimulating conditions caused by cataracts may explain the differences in the amplitudes reported.
The flicker ERGs recorded with the RETeval™ system were done under mydriatic-free conditions, and the pupils would be constricted with the continuous stimulation. Thus, it was assumed that light scattering might be reduced which should then reduce the amplitude of the flicker ERGs. In addition, the contribution of the peripheral retina to the flicker ERGs should be minimal because the flicker ERGs originate mainly from the cone system.
Recently Kato et al. reported that as pupil size increased, the implicit times of the flicker ERGs recorded with RETeval™ system were significantly prolonged for larger pupil sizes. They assumed that the Stiles-Crawford effect is explainable reason for their results in that paper . However, they showed that there were no significant differences in implicit times under 6 mm pupil size in their report.
As best we know, there are no reports on the relationship between the implicit times of the flicker ERGs and media opacities. In our patients, the average implicit time of the Grade 3 cataract group was significantly longer than that of eyes in the Grade 2 cataract group and the pseudophakic group. Thus, we conclude that the implicit times of the flicker ERGs were significantly affected by cataracts as with the amplitudes.
It has been reported that the amplitudes of the conventional ERGs and the mfERGs were affected by the age [14, 15]. In general, the b-wave amplitudes of conventional flash ERGs and the density of the mfERGs decreased with increasing age. However, it is possible that these results might have been affected by cataracts.
In our study, we showed that the age of IOL group was not significantly correlated with both the amplitudes and the implicit times of flicker ERGs with the RETeval™ system.
These results indicated that flicker ERGs elicited by the stimulus described above with the RETeval™ system under mydriatic-free conditions are not affected by ages.
In addition, some limitations of the current study should be noted. One limitation was the setting of RETeval™ system. We used intensity of 8 Td-s, which is the recommended default setting for flicker ERGs for eyes without dilation in the RETeval™ system. However, this stimulus was much weaker than that for light-adopted 3.0 flicker ERG which is recommended by International Society for Clinical Electrophysiology of Vision . These settings of the light intensities might be the cause of the variations of the results. Therefore, it was assumed that the differences in the amplitudes and implicit times might decrease if the ERGs were elicited from stronger light stimuli in the three groups.
Another limitation of this study was that we compared eyes of different patients. Individual differences of the values of ERG might also affect the results. Further investigations with various pupil sizes, various light intensities, patients with more severe cataract than grade 3 cataract or the same individual eye before and after cataract surgery are needed.
RETeval™ system needs to measure the pupil size to keep a constant flash retinal illuminance. There were no failures to record flicker ERGs with RETeval™ system in all examination of this study period except few cases that corneal opacities prevented a proper detection of the pupil. This fact indicated that RETeval™ system is the simple and easy to examine unless the system could not detect pupil properly.