Maturation of rod function in preterm infants with and without retinopathy of prematurity

Flicker electroretinogram in preterm infants

BACKGROUND

Infants born prematurely are at risk of developing retinopathy of prematurity, which is associated with abnormalities in retinal function as measured using electroretinography. The aim of this study was to record non-invasive flicker electroretinograms (ERGs) in preterm infants and compare function of moderate and very or extremely preterm infants.

METHODS

In this non-randomized, cross-sectional study, 40 moderate preterm (gestational age (GA) 34 0/7 to 36 6/7 weeks, Group A) and 40 very or extremely preterm infants (GA ≤ 31 weeks, Group B) were recruited for flicker ERG recording through closed eyelids using the RETeval® device and skin electrodes. Group A was tested within the first week of life and Group B between 34th and 37th week postmenstrual age. Flicker stimuli were presented at 28.3 Hz with stimulus levels of 3, 6, 12, 30 and 50 cd•s/m2. Primary endpoints were peak time (ms) and amplitude (µV).

RESULTS

Flicker ERGs were recordable in most infants with the highest proportion of reproducible ERGs at 30 cd•s/m2. Amplitudes increased with stronger flicker stimulation, while peak times did not differ significantly between stimulus levels nor groups. Amplitudes were significantly greater in Group B at the strongest stimulus level (Mann-Whitney-U-Test=198.00, Z = 4.097, p = <0.001).

CONCLUSIONS

Feasibility of collecting flicker ERG data in most preterm infants was confirmed. We found no evidence of reduced retinal responses to flicker stimuli associated with extreme prematurity. Higher amplitudes in very and extremely preterm infants could indicate acceleration of retinal development following birth, triggered by visual stimulation.

The Use of the RETeval Portable Electroretinography Device for Low-Cost Screening: A Mini-Review

Electroretinography (ERG) provides crucial insights into retinal function and the integrity of the visual pathways. However, ERG assessments classically require a complicated technical background with costly equipment. In addition, the placement of corneal or conjunctival electrodes is not always tolerated by the patients, which restricts the measurement for pediatric evaluations. In this short review, we give an overview of the use of the RETeval portable ERG device (LKC Technologies, Inc., Gaithersburg, MD, USA), a modern portable ERG device that can facilitate screening for diseases involving the retina and the optic nerve. We also review its potential to provide ocular biomarkers in systemic pathologies, such as Alzheimer's disease and central nervous system alterations, within the framework of oculomics.

Flicker electroretinogram in newborn infants

PURPOSE

To develop and validate a flicker electroretinogram (ERG) protocol in term-born neonates as a potential tool for assessing preterm infants at risk of developing retinopathy of prematurity.

METHODS

A custom flicker ERG protocol was developed for use with the hand-held RETeval® electrophysiology device. Feasibility of measuring flicker ERG through closed eyelids and without mydriasis was established in a pilot study enabling optimisation of the test protocol. Following this, healthy term-born neonates (gestational age 37-42 weeks) were recruited at the Neonatology clinic of the University Hospital Zurich. Flicker ERG recordings were performed using proprietary disposable skin electrodes during the first four days of life when the infants were sleeping. Flicker stimuli were presented at 28.3 Hz for a stimulus series at 3, 6, 12, 30, and 50 cd·s/m², with two measurements at each stimulus level. Results were analysed offline. Flicker ERG peak times and amplitudes were derived from the averaged measurements per stimulus level for each subject.

RESULTS

28 term-born neonates were included in the analysis. All infants tolerated the testing procedure well. Flicker ERG recording was achieved in all subjects with reproducible flicker ERG waveforms for 30 and 50 cd·s/m² stimuli. Reproducible ERGs were recorded in the majority of infants for the weaker stimuli (with detectable ERGs in 20/28, 25/28, and 27/28 at 3, 6, and 12 cd·s/m², respectively). Flicker ERG amplitudes increased with increasing stimulus strength, with peak times concurrently decreasing slightly.

CONCLUSION

Flicker ERG recording is feasible and reliably recorded in sleeping neonates through closed eyelids using skin electrodes and without mydriasis. Flicker ERG amplitude decreases for lower luminance flicker but remains detectable for 3 cd·s/m² flicker in the majority of healthy term-born neonates. These data provide a basis to study retinal function in premature infants using this protocol.

Risk Factors Associated with Retinopathy of Prematurity in Very and Extremely Preterm Infants

Background and Objectives: Retinopathy of prematurity (ROP) is the leading cause of blindness in preterm infants. We studied the relationship between different perinatal characteristics, i.e., sex; gestational age (GA); birth weight (BW); C-reactive protein (CRP) and lactate dehydrogenase (LDH) concentrations; ventilation, continuous positive airway pressure (CPAP), and surfactant administration; and the incidence of Stage 1–3 ROP. Materials and Methods: This study included 247 preterm infants with gestational age (GA) < 32 weeks that were successfully screened for ROP. Univariate and multivariate binary analyses were performed to find the most significant risk factors for ROP (Stage 1–3), while multivariate multinomial analysis was used to find the most significant risk factors for specific ROP stages, i.e., Stage 1, 2, and 3. Results: The incidence of ROP (Stage 1–3) was 66.40% (164 infants), while that of Stage 1, 2, and 3 ROP was 15.38% (38 infants), 27.53% (68 infants), and 23.48% (58 infants), respectively. Following univariate analysis, multiple perinatal characteristics, i.e., GA; BW; and ventilation, CPAP, and surfactant administration, were found to be statistically significant risk factors for ROP (p < 0.001). However, in a multivariate model using the same characteristics, only BW and ventilation were significant ROP predictors (p < 0.001 and p < 0.05, respectively). Multivariate multinomial analysis revealed that BW was only significantly correlated with Stage 2 and 3 ROP (p < 0.05 and p < 0.001, respectively), while ventilation was only significantly correlated with Stage 2 ROP (p < 0.05). Conclusions: The results indicate that GA; BW; and the use of ventilation, CPAP, and surfactant were all significant risk factors for ROP (Stage 1–3), but only BW and ventilation were significantly correlated with ROP and specific stages of the disease, namely Stage 2 and 3 ROP and Stage 2 ROP, respectively, in multivariate models.

The Inability of the Choroid to Revascularize in Oxygen-Induced Retinopathy Results from Increased p53/miR-Let-7b Activity

Retinopathy of prematurity (ROP) is characterized by an initial retinal avascularization, followed by pathologic neovascularization. Recently, choroidal thinning has also been detected in children formerly diagnosed with ROP; a similar sustained choroidal thinning is observed in ROP models. But the mechanism underlying the lack of choroidal revascularization remains unclear and was investigated in an oxygen-induced retinopathy (OIR) model. In OIR, evidence of senescence was detected, preceded by oxidative stress in the choroid and the retinal pigment epithelium. This was associated with a global reduction of proangiogenic factors, including insulin-like growth factor 1 receptor (Igf1R). Coincidentally, tumor suppressor p53 was highly expressed in the OIR retinae. Curtailing p53 activity resulted in reversal of senescence, normalization of Igf1r expression, and preservation of choroidal integrity. OIR-induced down-regulation of Igf1r was mediated at least partly by miR-let-7b as i) let-7b expression was augmented throughout and beyond the period of oxygen exposure, ii) let-7b directly targeted Igf1r mRNA, and iii) p53 knock-down blunted let-7b expression, restored Igf1r expression, and elicited choroidal revascularization. Finally, restoration of Igf1r expression rescued choroid thickness. Altogether, this study uncovers a significant mechanism for defective choroidal revascularization in OIR, revealing a new role for p53/let-7b/IGF-1R axis in the retina. Future investigations on this (and connected) pathway could further our understanding of other degenerative choroidopathies, such as geographic atrophy.

ISCEV extended protocol for the stimulus-response series for the dark-adapted full-field ERG b-wave

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum protocol for clinical testing but encourages more extensive testing where appropriate. This ISCEV extended protocol describes an extension of the ISCEV full-field ERG standard, in which methods to record and evaluate the growth of the dark-adapted (DA) ERG b-wave with increasing stimulus energy are described. The flashes span a range that includes the weakest flash required to generate a reliable DA ERG b-wave and that required to generate a maximal b-wave amplitude. The DA ERG b-wave stimulus-response series (also known historically as the "intensity-response" or "luminance-response" series) can more comprehensively characterize generalized rod system function than the ISCEV standard ERG protocol and may be of diagnostic or prognostic value in disorders that cause generalized rod system dysfunction.

Reduction of Rod and Cone Function in 6.5-Year-Old Children Born Extremely Preterm

Importance

The function of rods and cones in children born extremely preterm has not yet been fully investigated.

Objective

To compare retinal function via full-field electroretinographic (ffERG) recordings in 6.5-year-old children born extremely preterm with children born at term.

Design, Setting, and Participants

A subcohort study was conducted from July 1, 2010, to January 15, 2014, of the national Extremely Preterm Infants in Sweden Study, including preterm children (<27 weeks' gestational age) and children born at term, at 6.5 years of age and living in the Uppsala health care region in Sweden. Full-field electroretinography was performed binocularly, using DTL electrodes and electroretinographic (ERG) protocols with flash strengths of 0.009, 0.17, 3.0, and 12.0 candelas (cd)/s/m2, together with 30-Hz flicker and 3.0 cd/s/m2 single-cone flash.

Main Outcomes and Measures

The ffERG recordings were analyzed, and their associations with gestational age and retinopathy of prematurity were examined.

Results

Adequate ffERG recordings were obtained from 52 preterm children (19 girls and 33 boys; mean [SD] age at examination, 6.6 [0.1] years) and 45 children born at term (22 girls and 23 boys; mean [SD] age at examination, 6.6 [0.1] years). Lower amplitudes of the combined rod and cone responses (the a-wave of the dark-adapted ERG protocol of 3.0 cd/s/m2: mean difference, -48.9 μV [95% CI, -80.0 to -17.9 μV]; P=.003; the a-wave of the dark-adapted ERG protocol of 12.0 cd/s/m2: mean difference, -55.7 μV [95% CI, -92.5 to -18.8 μV]; P = .004), as well as of the isolated cone response (30-Hz flicker ERG: mean difference, -12.1 μV [95% CI, -22.5 to -1.6 μV]; P = .03), were found in the preterm group in comparison with the group born at term. The implicit time of the combined rod and cone responses (the a-wave of the dark-adapted ERG protocol of 12.0 cd/s/m2) was longer (mean difference, 1.2 milliseconds [95% CI, 0.3-2.0 milliseconds]; P = .01) in the preterm group, as were the isolated cone responses (30-Hz flicker ERG: mean difference, 1.2 milliseconds [95% CI, 0.5-1.8 milliseconds]; P < .001), than in the group born at term. No association was found between the ffERG recordings and gestational age or retinopathy of prematurity in the preterm group.

Conclusions and Relevance

Both rod function and cone function were reduced in children born extremely preterm when compared with children born at term. There was no association with retinopathy of prematurity in the preterm group, which suggests that being born extremely preterm may be one of the main reasons for a general retinal dysfunction.

The neural retina in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.

Long-term effect of high-dose supplementation with DHA on visual function at school age in children born at <33 wk gestational age: results from a follow-up of a randomized controlled trial

BACKGROUND

Children born preterm are at risk of visual-processing impairments. Several lines of evidence have contributed to the rationale that docosahexaenoic acid (DHA) supplementation of preterm infants may improve outcomes in visual processing.

OBJECTIVE

The aim was to determine whether at 7 y of age children who were born very preterm and who received a high-DHA diet have better visual-processing outcomes than do infants fed a standard-DHA diet.

DESIGN

This was a follow-up study in a subgroup of children from a randomized controlled trial. Infants were randomly assigned to milk containing a higher concentration of DHA (1% of total fatty acids; high-DHA group) or a standard amount of DHA (0.2-0.3% of total fatty acids as DHA; control group). The randomization schedule was stratified by sex and birth weights of <1250 or ≥1250 g. A total of 104 (49 in the high-DHA group and 55 in the standard-DHA group) children aged 7 y were assessed on a range of visual-processing measures, including visual acuity, contrast sensitivity, vernier acuity, binocular stereopsis, and visual perception.

RESULTS

There was no evidence of differences between the high-DHA and standard-DHA groups in any of the visual-processing measures. In the majority (12 of 13) of variables assessed, the direction of effect favored the control group. The study was large enough to detect a moderate treatment effect, if one truly existed.

CONCLUSION

Supplementing human milk with DHA at a dose of ∼1% of total fatty acids given in the first months of life to very preterm infants does not appear to confer any long-term benefit for visual processing at school age. This trial was registered at anzctr.org/au as ACTRN12606000327583.

17β-estradiol ameliorates oxygen-induced retinopathy in the early hyperoxic phase

Retinopathy of prematurity (ROP) is a major and leading cause of blindness in premature infants. It has been realized that early treatment for ROP is important. However, all the early treatments of ROP are focusing on peripheral retinal ablation which does not surmount the limit of extinguishing retinal neovascularization and protecting the retinas of children with ROP from the injury of ablation. In this study, we investigated the morphological changes of retina and oxidative stress alterations in the early phase of oxygen-induced retinopathy (OIR) and tested the effects of 17β-estradiol (17β-E2), a nonselective estrogen receptor (ER) agonist, on early phase OIR development. We found that large central capillary-free areas were induced in the retinas of pups exposed to hyperoxia on postnatal day 9 (P9), whereas vascularization was almost complete in the retinas of pups exposed to normoxia at the same age. The concentrations of malondiadehyde (MDA), an end-product of oxidative stress, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a major enzyme producing free radicals, as well as the activity of NADPH oxidase were significantly elevated in the retinas of pups exposed to hyperoxia on P9 and postnatal day 13 (P13) compared to those in age matched pups exposed to normoxia. Treatment with 17β-E2 decreased not only the percentage of the central capillary-free area to total retina area but also the concentrations of MDA and NADPH oxidase as well as the activity of NADPH oxidase in a dose-dependent manner in pups exposed to hyperoxia on p9 and P13. The concentration of VEGF was significantly decreased on P9 but increased on P14 in the retinas of pups exposed to hyperoxia, whereas it was significantly elevated on P9 but decreased on P14 in the retinas of pups treated with 17β-E2. The effect of 17β-E2 could be reversed by the co-treatment with ICI182780, a high affinity estrogen receptor antagonist, which suggested that 17β-E2 might exert its effect on early hyperoxic phase of OIR through estrogen receptor. Our results suggest that treatment with antioxidant drugs at early hyperoxic phase of ROP even before the appearance of retinal neovascularization may be more effective than their application to ROP at late phase, which may abolish the deleterious factors that contribute to retinal neovascularization and promote retinal blood vessels to develop healthily.

Photoreceptor Function in School-Aged Children is Affected by Preterm Birth

PURPOSE

Prematurely born children have affected visual functions at school age. Optical coherent tomography (OCT) has shown morphological changes in the retina, suggesting a disturbance in normal retinal development in these children. The aim of this study was to examine retinal function with fullfield electroretinogram (ffERG) in school-aged children born prematurely and compare with children born at term. A second aim was to correlate retinal function with visual acuity (VA), gestational age (GA), birth weight, and retinopathy of prematurity (ROP).

METHODS

The study group consisted of 35 former preterm children born before GA of 32 weeks. A group of 42 children born at term acted as controls. All children were between 5- and 18-years old. FfERG was performed in both eyes. Best-corrected VA and refraction in cycloplegia was determined.

RESULTS

The a-wave of the combined rod/cone responses was significantly reduced in the prematurely-born children compared with children born at term. There was a correlation between reduced a-wave amplitude in the combined rod/cone response and ROP and GA at birth.

CONCLUSION

Function of photoreceptors was affected in prematurely born children, possibly also in children without previous ROP. Whether immaturity per se affects the retinal function remains to be elucidated.

TRANSLATIONAL RELEVANCE

The present study illustrates that electrophysiological studies of the retinal function can help us understand visual dysfunctions in prematurely born children.

A frequency-tagging electrophysiological method to identify central and peripheral visual field deficits

BACKGROUND

The aim of this study was to develop a fast and efficient electrophysiological protocol to examine the visual field's integrity, which would be useful in pediatric testing.

METHODS

Steady-state visual-evoked potentials (ssVEPs) to field-specific radial checkerboards flickering at two cycle frequencies (7.5 and 6 Hz for central and peripheral stimulations, respectively) recorded at Oz were collected from 22 participants from 5 to 34 years old and from 5 visually impaired adolescents (12-16 years old). Responses from additional leads (POz, O1, O2), and the impact of gaze deviation on the signals, were also investigated in a subgroup of participants.

RESULTS

Steady-state visual-evoked potentials responses were similar at all electrode sites, although the signal from the central stimulation was significantly higher at Oz and was highly sensitive in detecting gaze deviation. No effect of age or sex was found, indicating similar ssVEP responses between adults and healthy children. Visual acuity was related to the central signal when comparing healthy participants with four central visual impaired adolescents. Clinical validation of our electrophysiological protocol was also achieved in a 15-year-old adolescent with a severe peripheral visual deficit, as assessed with Goldmann perimetry.

CONCLUSIONS

A single electrode over Oz is sufficient to gather both central and peripheral visual signals and also to control for gaze deviation. Our method presents several advantages in evaluating visual fields integrity, as it is fast, reliable, and efficient, and applicable in children as young as 5 years old. However, a larger sample of healthy children should be tested to establish clinical norms.

Vitamin A for preterm infants; where are we now?

In the 35 years since low plasma vitamin A levels were first described in premature infants, much effort has gone into attempting to describe the functional consequences of vitamin A deficiency in this population. Supplementation of extremely low birth weight infants with intramuscular (i.m.) vitamin A has a significant but modest beneficial effect upon the development of chronic lung disease (NNT 13), most likely due to reduced production of pro-inflammatory cytokines. Early high dose i.m. vitamin A also improves retinal development and there are limited clinical and laboratory data suggesting a role for vitamin A in prevention of retinopathy of prematurity. Despite evidence of benefit, there is reluctance to give routine i.m. vitamin A in the neonatal intensive care unit, but current intravenous supplementation is almost certainly inadequate. Further work is required to identify the optimal dose and most appropriate route of administration of vitamin A for preterm infants.

Dark-adapted oscillatory potentials in preterm infants with and without retinopathy of prematurity

PURPOSE

To describe the appearance and maturation of dark-adapted oscillatory potentials (OPs) in electroretinograms (ERGs) recorded from preterm infants, and to determine any effect of retinopathy of prematurity (ROP).

METHODS

Dark-adapted ERGs were recorded in conjunction with screening for ROP and at outpatient follow-up, using a flash luminance of 11.3 scot cd s m(-2) (4.06 phot cd s m(-2)). Eligible infants were born before 31 weeks' gestation and/or weighed ≤1,250 grams at birth.

RESULTS

Presence or absence of OPs was established for 68 ERG recordings from 38 infants at maturities ranging from 30 weeks' postmenstrual age (PMA) to 28 weeks' post-term corrected age. 20 infants did not develop ROP, eight developed stage 1, one stage 2 and one stage 3 disease which regressed spontaneously. Eight infants received treatment for threshold ROP. OPs were present in 50 % of infants at 36 weeks' PMA and in all by 50 weeks' PMA. The earliest appearance of OPs was at 30+5 weeks' PMA. Individual OP amplitudes increased and peak time of individual OPs decreased with increasing maturity. For infants with threshold ROP summed OP amplitudes tended to be smaller prior to treatment (6.5 vs 9.9μV, P = 0.09) and were significantly smaller by 50 weeks' PMA (14 vs 30μV, P = 0.007). OP1 was less likely to be present in infants who developed stage 3 or worse ROP (P = 0.000).

CONCLUSIONS

Dark-adapted OPs are recordable in some preterm infants from 30 weeks' PMA. Relative suppression of early OPs is a potential marker for developing ROP.

Vitamin A supplementation improves retinal function in infants at risk of retinopathy of prematurity

OBJECTIVE

Preterm infants show reduced retinal sensitivity at term corrected age compared with newborn term infants. We tested the hypothesis that retinal sensitivity in preterm infants is improved by early, high-dose vitamin A.

STUDY DESIGN

We report a double-blind, randomized controlled trial of infants <32 weeks' gestation and/or <1501 g birth weight. Supplemented infants received additional intramuscular vitamin A 10 000 IU 3 times weekly from day 2 for a minimum of 2 weeks or until establishment of oral feeding. Hepatic stores were assessed by relative dose response (RDR). The primary outcome measure was cone-corrected dark-adapted retinal rod sensitivity measured by electroretinogram at 36 weeks' postmenstrual age (PMA).

RESULTS

Eighty-nine infants (42 supplemented and 47 controls) were recruited. Plasma retinol was higher in supplemented infants at 7 and 28 days (median, 1.0 vs 0.5 μmol/L and 0.7 vs 0.6 μmol/L; P < .001 and .03, respectively). Neither plasma retinol nor RDR differed between groups at 36 weeks' PMA. Retinal sensitivity was greater in supplemented infants (-0.81 vs -0.61 log cd • s • m(-2); P < .03) and was not related to RDR.

CONCLUSIONS

Early high-dose intramuscular vitamin A supplementation for infants at risk of retinopathy of prematurity improves retinal function at 36 weeks' PMA.

Effect of carotenoid supplementation on plasma carotenoids, inflammation and visual development in preterm infants

OBJECTIVE

Dietary carotenoids (lutein, lycopene and β-carotene) may be important in preventing or ameliorating prematurity complications. Little is known about carotenoid status or effects of supplementation.

STUDY DESIGN

This randomized controlled multicenter trial compared plasma carotenoid levels among preterm infants (n=203, <33 weeks gestational age) fed diets with and without added lutein, lycopene and β-carotene with human milk (HM)-fed term infants. We assessed safety and health.

RESULT

Plasma carotenoid levels were higher in the supplemented group at all time points (P<0.0001) and were similar to those of term HM-fed infants. Supplemented infants had lower plasma C-reactive protein (P<0.001). Plasma lutein levels correlated with the full field electroretinogram-saturated response amplitude in rod photoreceptors (r=0.361, P=0.05). The supplemented group also showed greater rod photoreceptor sensitivity (least squares means 6.1 vs 4.1; P<0.05).

CONCLUSION

Carotenoid supplementation for preterm infants raises plasma concentrations to those observed in HM-fed term infants. Carotenoid supplementation may decrease inflammation. Our results point to protective effects of lutein on preterm retina health and maturation.

Update on retinopathy of prematurity: treatment options and outcomes

PURPOSE OF REVIEW

To evaluate and review the recent scientific literature on retinopathy of prematurity (ROP). Recent studies have shown advancement in treatment options in ROP as well as improved functional and structural outcomes. This review compiles some of these recent findings.

RECENT FINDINGS

New guidelines on ROP screening and treatment criteria have recently been developed and are now the standard of care for practitioners taking care of children having ROP. Recent advances in antiangiogenic therapies offer possible primary or adjunct treatment to the well established and effective laser treatment options. Follow-up of treated ROP patients informs us of the short-term and long-term complications requiring lifetime ophthalmology care.

SUMMARY

This review offers an update on the screening and treatment guidelines, new treatment options, and short-term and long-term complications in ROP.

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.