Type I intrinsically photosensitive retinal ganglion cells of early post-natal development correspond to the M4 subtype

Table 4 Electrophysiologic ipRGC subtypes

Age	Type I	Type II	Type III
P8	On-latency > 12-s at IR 12.0	On-latency > 12-s at IR 12.0	On-latency ≤ 12-s at IR 12.0
P8	Light response at IR 13.6 with response at 12.0 of > 10 % 13.6 response	Light response at IR 13.6 with response at 12.0 of ≤ 10 % 13.6 response
P15 and P30	Not present	On-latency > 12-s at IR 13	On-latency ≤ 12-s at IR 13

Method for categorizing ipRGC electrophysiologic subtypes. Irradiance (IR) is presented as the log₁₀ (photon cm⁻² s⁻¹). On-latency is the time from lights on until peak firing rate

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