Flicker ERG at high frequency of Isl1 ^CRE conditional Fat3 mice (Isl1 ^cKO ). (A) Schematic representation of cell classes, i.e., starburst ACs, RGCs, and ON-CBCs, that lose Fat3 expression in an Isl1^cKO shown in black outlines compared to magenta cells seen in WT controls. (B) VGAT immunostaining for control (exact genotype throughout this figure: Isl1^CRE/+;Fat3^fl/+) mice. (C) VGAT immunostaining for Isl1^cKO (exact genotype throughout this figure: Isl1^CRE/+;Fat3^fl/∆TM). (B′ and C′) TdTomato reporter of Cre expression is seen in B′ and C′. (D) Quantification of the OMPL score for Isl1^cKO. Controls: 0.095 ± 0.065 (n = 3 animals, 14 retinal regions); Isl1^cKO: 0.825 ± 0.074 (n = 3 animals, 19 retinal regions). Each data point corresponds to a retinal region, color-coded by animal, nested two-tailed test. Error bar: SEM. (E) DAPI and Bhlhb5 immunostaining of control retinas. (F) DAPI and Bhlhb5 immunostaining of Isl1^cKO retinas. (G) Quantification of the number of nuclei per field in the IPL. Controls: 1.25 ± 0.35 (n = 3 animals, 12 retinal regions); Isl1^cKO: 5.11 ± 0.39 (n = 3 animals, 18 retinal regions). Each data point corresponds to a retinal region, color-coded by animal, nested two-tailed test. Error bar: SEM. (H) Quantification of the number of Bhlhb5⁺ nuclei per field in the IPL and GCL. Controls: 3.67 ± 0.43 (n = 3 animals, 12 retinal regions); Isl1^cKO: 9.33 ± 0.67 (n = 3 animals, 18 retinal regions). Each data point corresponds to a retinal region, color-coded by animal, nested two-tailed test. Error bar: SEM. (I) Representative flicker ERG raw traces for control and Isl1^cKO. (J) Flicker ERG amplitude at 0.5, 10, 20, 30, 40, and 50 Hz for control (n = 6 eyes) and Isl1^cKO (n = 6 eyes). Unpaired two-tailed Student’s t test. Error bar: SEM. (K) Flicker ERG implicit time at 20 Hz for control (38.1 ± 0.8 ms, n = 6 eyes) and Isl1^cKO (38.5 ± 0.5 ms, n = 6 eyes). Unpaired two-tailed Student’s t test. Error bar: SEM. Scale bars: 20 µm.