Abstract:
Aim: Many studies have described the functions of ipRGCs, but the interaction between ipRGCs and other retinal cells is not fully understood. However, an interaction between melanopsin, the light sensitive pigment of ipRGCs, and S-cones has been reported (Spitschan et al., 2014). S-cone activity can be recorded as a small positive peak (P) of the transient PERG, recorded with a blue/black checkerboard stimulus after adaptation to a yellow light (Niepel & Dodt, 1989). As S-cones and melanopsin have similar spectral sensitivities, it is possible that melanopsin participates in the S-cone peak of the PERG. Therefore, in this study we sought to correlate this P peak with the activity of melanopsin and to examine whether the PERG to blue stimulation also induces the activity of ipRGCs. For this purpose, we compared recordings of the PERG with those of pupillography parameters, as melanopsin is known to participate in the pupil response. We collected results from healthy volunteers, as well as from patients with glaucoma, who have been shown to have a reduced ipRGC activity (Kankipati et al., 2011). Methods: Ten healthy volunteers and 10 patients with open-angle glaucoma were examined. Only one eye from each participant was considered. The PERG was performed with a blue / black stimulus, 1 minute and 2 minutes after yellow light adaptation. Pupillography was performed with a blue and a red stimulus after light and dark adaptation. In addition, blood pressure, O2 and pulse were measured 3 times, i. e. before, between and at the end of the recordings, to ensure that changes in these parameters do not affect the results. Results: The majority of PERG recordings after yellow light adaptation showed a small peak (P) after the P50 peak with an implicit time between 90-110 msec. The amplitude of P was significantly different between healthy subjects and glaucoma patients in the first minute after light adaptation (p = 0.018). The redilation times from the pupillography recordings, significant differences were also found between healthy controls and glaucoma patients after a blue stimulus with light adaptation (p = 0.047), as well as after dark adaptation (p = 0.001). Moderately positive correlations were found in healthy volunteers between the amplitude of P and the redilation time with a blue stimulus 2 min after DA (CC = 0.620) and in glaucoma patients 2 min after adaptation with a red or blue stimulus (CC = 0.678 and 0.508, respectively). In the healthy group, there was a moderately negative correlation between P in the first minute after yellow light adaptation and the redilation time with blue stimulus and light adaptation (CC = -0.550). Discussion: The results corroborate the theory that healthy ipRGCs have an influence on the S-cone peak (P) amplitude in the PERG recordings. The results of the pupillography additionally show that the mean redilation time is higher in the healthy group than in the glaucoma group, except for the blue stimulus with light adaptation. This can be explained by the known influence of ipRGCs on the regulation of pupil function, which is reduced in glaucoma patients. The results suggest a possible indirect participation of ipRGCs in the P-amplitude of the S-cone, but due to several limitations in our study, further studies are necessary to confirm this involvement and to better understand the correlation between ipRGCs and the P amplitude of the S-cone.
ipRGCs
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