Purpose To determine the sensitivit y of the blue cone sys-tem by static perimetry in patients w ith unilateral acute idiopathic blind spot enlargement (AIBSE)syndrome.Design Observational case series.Methods Four patients with AIBSE syndrome,aged 16to 30yea rs,were studied.Diagnosis of the AIBSE syndrome was b ased on clinical findings including an enlarged blin d spot without corre-sponding ophthalmoscopic changes o f the ocular fundus and with depressed multifocal electoretinograms.The vi-sual sensitivity and mean deviation s(MD)were measured by white-on-white(W/W)and blue-on-yellow(B /Y)automated perimetry.Results The av erage difference in the MD between the affected and unaffected eyes was 4.87±1.51dB and 13.65±4.19dB for W/W and B /Y perimetries,respectively.The dif ference between the two groups of eyes was significantly gre ater for B /Y perimetry than that for W/Wperimetry(P =.01).Conclusions Our results suggest that the decrease of blue cone sensitivity is diffusely present over the retina in eyes with AIBSE syn-drome.We recommend B /Y perimetry as a sensitive measure to detect retinal dysfuncti on that is not detected byW/Wperimetry. Purpose To determine the sensitivit y of the blue cone sys-tem by static perimetry in patients w ith unilateral acute idiopathic blind spot enlargement (AIBSE) syndrome. Design Observational case series. Methods Four patients with AIBSE syndrome, aged 16 to 30yea rs, were studied . Diagnostic of the AIBSE syndrome was b ased on clinical findings including an enlarged blin d spot without corre-sponding ophthalmoscopic changes of the ocular fundus and with depressed multifocal electoretinograms. Vi-sual sensitivity and mean deviation s (MD) were measured by white -on-white (W / W) and blue-on-yellow (B / Y) automated perimetry. Results The Av erage difference in the MD between the affected and unaffected eyes was 4.87 ± 1.51 dB and 13.65 ± 4.19 dB for W / W and B / Y perimetries, respectively. Dif ference between the two groups of eyes was significantly gre ater for B / Y perimetry than that for W / Wperimetry (P = .01) .Conclusions Our results suggest that the decrease of blue cone sensitivity is diffusely presen t over the retina in eyes with AIBSE syn-drome.We recommend B / Y perimetry as a sensitive measure to detect retinal dysfuncti on that is not detected by W / Wperimetry.