Comparison of electroretinogram between healthy preterm and term infants

To investigate the retinal development in healthy preterm infants through standard ganzfeld electroretinograms (ERG) and compare the difference of ERG between the healthy preterm and term infants. Forty-nine 49 healthy infants were recruited to this study, including 20 preterm and 29 term infants. All the infants were grouped as follows: term 40 W group (ERG recorded at birth), term 44 W group (ERG recorded at 4 weeks after birth), preterm 35 W group (ERG recorded at birth) and preterm 40 W group (ERG recorded at due date). Standard ganzfeld flash ERG was performed according to the ISCEV standard for the clinical electroretinogram (2008). The ERG amplitudes in the term 44 W group were notably larger than those of the term 40 W group, but there was no significant difference between the two groups for combined-b and cone-b responses. The implicit time of cone-b, combined-a and 30 Hz in term 44 W group was significantly shorter than that in term 40 W group, and there was no significant difference in other ERG responses between the two groups. Amplitude of ERG waves in preterm 35 W group was only 48.7-78.0% of that in term 40 W group, and the difference of all ERG waves between the two groups was statistically significant, but there was no significant difference between the two groups for implicit time of all responses except rod-b. There was no significant difference between the amplitude of ERG waves in term 40 W and preterm 40 W groups; however, implicit time of cone-a and cone-b in term 40 W is significantly longer than that in preterm 40 W group. The ERG amplitudes in the preterm 35 W group were notably smaller than those of the preterm 40 W group, and except cone-a response, the difference between the two groups was statistically significant, while the difference of the implicit time between the two groups was not significant. OPs could not be recorded in some infants. OPs were seen significantly less frequently in the preterm 35 W group than in either the term 40 W group (Fisher exact test, P = 0.006) or the term 44 W group (Fisher exact test, P = 0.02). No other significant inter-group frequency differences were found. The mean amplitude ratio b/a was not significantly different between the four groups (P > 0.05) (analysis of variance). The retina is not fully developed at birth in healthy preterm infants. The preterm ISCEV ERG matures rapidly after birth and by term reaches the degree of maturation found in term born neonates.