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Abstract  The purpose of the study is to characterise retinal function using light-adapted electroretinograms (ERGs) in a series of young children with ONH, congenital dysplasia of retinal ganglion cells. ERGs were recorded with chloral hydrate sedation in 27 children with ONH (18 with bilateral and 9 with unilateral ONH, age 4–35 months) and an adult reference population (n = 12). Stimuli included ISCEV standard flash, oscillatory potentials (OPs) and standard flicker as well as a light-adapted luminance–response series (photopic hill). The disc diameter to disc macula (DD:DM) ratio was measured from fundus photographs. The results are eyes with ONH, classified by DD:DM, were severe (≤0.15, n = 22), moderate (0.16–0.30, n = 22), mild (0.31–0.35, n = 1), and fellow eyes (>0.35, n = 9), all had prolonged ERG implicit times and smaller i-waves than those of adults. Eyes with moderate or severe ONH also had smaller amplitudes for OPs and flicker ERGs and required stronger flashes to obtain the peak b-wave amplitude. Abnormalities of the photopic hill were a common but inconsistent feature of ONH and were not indicative of ONH severity. Abnormalities of the photopic hill of the ERG suggest that some cases of ONH may have retinal dysfunction with specific deficits in the ON or OFF pathways of the retina. ONH is a complex and heterogeneous condition that may involve dysfunction distal to the retinal ganglion cells. [ABSTRACT FROM AUTHOR]