Maturation of electroretinograms and visual evoked potentials in preterm infants

Retinogenesis of the Human Fetal Retina: An Apical Polarity Perspective

The Crumbs complex has prominent roles in the control of apical cell polarity, in the coupling of cell density sensing to downstream cell signaling pathways, and in regulating junctional structures and cell adhesion. The Crumbs complex acts as a conductor orchestrating multiple downstream signaling pathways in epithelial and neuronal tissue development. These pathways lead to the regulation of cell size, cell fate, cell self-renewal, proliferation, differentiation, migration, mitosis, and apoptosis. In retinogenesis, these are all pivotal processes with important roles for the Crumbs complex to maintain proper spatiotemporal cell processes. Loss of Crumbs function in the retina results in loss of the stratified appearance resulting in retinal degeneration and loss of visual function. In this review, we begin by discussing the physiology of vision. We continue by outlining the processes of retinogenesis and how well this is recapitulated between the human fetal retina and human embryonic stem cell (ESC) or induced pluripotent stem cell (iPSC)-derived retinal organoids. Additionally, we discuss the functionality of in utero and preterm human fetal retina and the current level of functionality as detected in human stem cell-derived organoids. We discuss the roles of apical-basal cell polarity in retinogenesis with a focus on Leber congenital amaurosis which leads to blindness shortly after birth. Finally, we discuss Crumbs homolog (CRB)-based gene augmentation.

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.

Visual Development and Neuropsychological Profile in Preterm Children from 6 Months to School Age

The aim of this semilongitudinal study was to investigate the development of central visual pathways in children born preterm but without major neurologic impairments and to establish their cognitive and behavioral profile at school age. Ten children born preterm were assessed at 6 months and at school age, using visual evoked potentials at both time points and cognitive and behavioral tests at school age. We also tested 10 age-matched children born full-term. At 6 months' corrected age, we found no significant differences between preterm and full-term groups for either amplitude or latency of N1 and P1 components. At school age, the preterm group manifested significantly higher N1 amplitudes and tended to show higher P1 amplitudes than the full-term group. We found no significant differences in cognitive and behavioral measures at school age. These results suggest that preterm birth affects visual pathways development, yet the children born preterm did not manifest cognitive problems.

Comparison of spin-echo and gradient-echo T1-weighted and spin-echo T2-weighted images at 3T in evaluating term-neonatal myelination

SUMMARY

A prior clinical report of 3T MR imaging in subsequently healthy very premature neonates imaged at term-equivalent age found that both gradient recalled-echo-T1WI and spin-echo-T2WI showed higher rates of myelinated structures, compared with spin-echo-T1WI. The current study set out to assess those rates on the same sequences at 3T in term neonates and thus consisted of 16 term neonates with normal-appearing MR imaging findings who subsequently had normal findings at clinical follow-up. Two neuroradiologists independently assessed 19 structures in those infants on all 3 sequences. Gradient recalled-echo-T1WI showed a slightly higher rate of myelination (57.2%-72.4% of all structures) and interobserver agreement (κ = 0.546, P < .0001) than spin-echo-T2WI (58.2%-64.8%; κ = 0.468, P < .0001), while spin-echo-T1WI had the lowest myelination rate and agreement (25.0%-48.4%; κ = 0.384, P < .0001). Both observers noted that the following structures were myelinated in 88%-100% of patients on gradient recalled-echo-T1WI: the brachium of the inferior colliculus, decussation of the superior cerebellar peduncle, habenular commissure, medial lemniscus, pyramidal decussation, posterior limb of the internal capsule, and superior cerebellar peduncle; on spin-echo-T2WI, there was myelination in 88%-100% of the following structures: the brachium of the inferior colliculus, decussation of the superior cerebellar peduncle, inferior cerebellar peduncle, medial lemniscus, and posterior limb of the internal capsule. In conclusion, this study confirmed that similar to the findings in term-equivalent-age premature infants, myelination changes in term neonates may be best assessed on both gradient recalled-echo-T1WI and spin-echo-T2WI at 3T, and not on spin-echo-T1WI.

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.

Chromatic and luminance contrast sensitivity in fullterm and preterm infants

In order to investigate the contributions of visual experience vs. preprogrammed mechanisms on visual development, the current study compared contrast sensitivity in preterm vs. fullterm infants. If development is tied to time since conception, preterm infants should match the developmental trajectories of fullterm infants when plotted in postterm age. By contrast, if development is influenced by visual experience, preterm and fullterm infants should match when plotted in postnatal age. Luminance (light/dark) and chromatic (red/green) contrast sensitivities (CS) were measured in 25 preterm (born, on average, 6.6 weeks early) and 77 fullterm infants, between 1 and 6 months postterm. In the first few months, luminance CS was found to be predicted by postterm age, suggesting that preprogrammed development is sufficient to account for luminance CS. By contrast, chromatic CS exceeded that predicted by postterm age, which suggests that time since birth confers a benefit on chromatic CS. The preterms' 6.6 weeks of additional time since birth is roughly equivalent to 3.7 weeks of development in chromatic CS. In sum, these results suggest that chromatic CS is more influenced by early postnatal visual experience than luminance CS, which may have implications for development of parvocellular and magnocellular pathways.

Vascular endothelial growth factor in eye disease

Collectively, angiogenic ocular conditions represent the leading cause of irreversible vision loss in developed countries. In the US, for example, retinopathy of prematurity, diabetic retinopathy and age-related macular degeneration are the principal causes of blindness in the infant, working age and elderly populations, respectively. Evidence suggests that vascular endothelial growth factor (VEGF), a 40kDa dimeric glycoprotein, promotes angiogenesis in each of these conditions, making it a highly significant therapeutic target. However, VEGF is pleiotropic, affecting a broad spectrum of endothelial, neuronal and glial behaviors, and confounding the validity of anti-VEGF strategies, particularly under chronic disease conditions. In fact, among other functions VEGF can influence cell proliferation, cell migration, proteolysis, cell survival and vessel permeability in a wide variety of biological contexts. This article will describe the roles played by VEGF in the pathogenesis of retinopathy of prematurity, diabetic retinopathy and age-related macular degeneration. The potential disadvantages of inhibiting VEGF will be discussed, as will the rationales for targeting other VEGF-related modulators of angiogenesis.

Development of the electroretinogram between 30 and 50 weeks after conception

Maturation of the electroretinogram (ERG) reflects retinal development. Serial ERGs recorded from a preterm infant between 30 and 50 weeks after conception showed rapid maturation. A transient loss of retinal sensitivity coincided with clinical signs of stage 2 retinopathy of prematurity (ROP).

Assessment of gestational age and neuromaturation

Neuromaturation is the functional development of the central nervous system (CNS). It is by its very nature a dynamic process, a continuous interaction between the genome and first the intrauterine environment, then the extrauterine environment. Understanding neuromaturation and being able to measure it is fundamental to infant neurodevelopmental assessment. Fetal and preterm neuromaturation has become easier to observe with the advent of prenatal ultrasonography and neonatal intensive care units. A number of measures of degree of fetal maturation have been developed and used to estimate gestational age (GA) at birth. The most reliable measures of GA are prenatal measures, especially from the first trimester. Postnatal GA measurements tend to be least accurate at the extremes of gestation, that is, in extremely preterm and post-term infants. Observations of measures of neuromaturation in infants born to mothers with pregnancy complications, including intrauterine growth restriction, multiple gestation, and chronic hypertension, have led to the discovery that stressed pregnancies may accelerate fetal pulmonary and CNS maturation. This acceleration of neuromaturation does not occur before 30 weeks' gestation and has a cost with respect to cognitive limitations manifested in childhood. The ability to measure fetal and preterm neuromaturation provides an assessment of neurodevelopmental progress that can be used to reassure parents or identify at risk infants who would benefit from limited comprehensive follow-up and early intervention services. In addition, measures of neuromaturation have the potential to provide insight into mechanisms of CNS injury and recovery, much-needed early feedback in intervention or treatment trials and a measure of early CNS function for research into the relationships between CNS structure and function.

[Compared progression of visual-evoked potentials in preterm and term newborns]

PURPOSE

To compare the development of the visual pathway in healthy preterm and full-term newborns using flash and patterned (both transient and steady-state) visual-evoked potentials (fVEP, pVEP-t, pVEP-ss).

PATIENTS AND METHODS

Twenty-nine preterm newborns (28-35 weeks gestational age) were evaluated at four different times: at 3 months postnatal and corrected age, at 8 months postnatal and corrected age. They were matched with 92 term newborns tested at 3 and 8 months of life.

RESULTS

The maximal perceived spatial frequencies in the groups were: 2 C/d at 3 months postnatal age, >2 C/d at 3 months corrected age and at 3 months at term, between 3 and 5C/d, >=5C/d at 8 months corrected age and at 8 months of life, respectively. The latencies of the P1 and P100 waves for the flash and the transient stimulation were, respectively, 192 ms and 207.9 ms at 3 months postnatal age, 144 ms and 137.7 ms at 3 months corrected age, 126.3 ms and 124.1 ms at 8 months postnatal age, 112.7 ms and 112.5 ms at 8 months corrected age, 137.3 and 110.1 ms at 3 months of life; and 122.3 and 100.5 ms at 8 months of life.

DISCUSSION

In the preterm infants of 3 gestational months, the latencies of the fVEP are comparable to those of the 3-month-old full-term infants, although the pVEP-t latencies are still delayed at 8 months. In the fVEP; however, we noted a shorter latency in the preterm infants at 8 months corrected age compared to those of the full-term infants. This tendency inversion was also evidenced at the steady-state stimulation.

CONCLUSIONS

As evidenced by our results, at 8 months of corrected age the preterm infants recovered the fVEP and pVEP-ss, but not the pVEP-t. Different results obtained with different visual-evoked stimulations suggest that similar neural pools are developed in not completely equal amounts of time.

Standard full-field electroretinography in healthy preterm infants

The purpose of this study was to determine electroretinographic parameters according to the standard protocol from the International Society for Clinical Electrophysiology of Vision (ISCEV) in healthy preterm infants with normal fundus. Seventeen healthy preterm infants with normal fundus were recruited and divided in two age groups: 3-week group, nine infants with mean adjusted age at test = 2.67 +/- 0.92 weeks and 8-week group, eight infants with mean adjusted age at test = 7.92 +/- 1.72 weeks. Full-field ERGs were obtained with a Burian-Allen bipolar contact lens electrode from the anesthetized cornea in one eye, through a fully dilated pupil after 30 min of dark adaptation. The standard ISCEV protocol was used and the following responses were recorded: rod, maximal, oscillatory potentials, cone and 30 Hz flicker. Median values and 1st, 5th, 95th and 99th percentiles for amplitude and implicit time are described for both age groups. There was statistically larger amplitude for 30 Hz flicker (t = 2.191; p = 0.046) and for cone response (t = 2.307; p = 0.044) in the 8-week-old group. Statistically shorter implicit times were found in 8-week group for rod response (t = 3.219; p = 0.015), cone response (t = 2.839; p = 0.016) and flicker response (t = 3.326; p = 0.005). Shortening of implicit time was evident in the older group of preterms and this finding is consistent with other maturational studies confirming the anatomical and functional development of the photoreceptors. Medians and ranges between the 1st and 99th and the 5th and 95th percentiles can be used as a baseline for future comparisons with infants with ROP.

Contact lens electroretinography in preterm infants from 32 weeks after conception: a development in current methodology

AIM

To assess the feasibility of using a contact lens electrode to record the electroretinogram (ERG) in preterm infants less than 35 weeks after conception.

METHODS

The ERG was recorded from seven very low birthweight preterm infants on a total of 14 occasions using an infant monkey contact lens electrode. Age at recording the first ERG ranged from 23 to 51 days (gestational age 32-34 weeks), and weight ranged upwards from 1100 g.

RESULTS

No complications were observed. With advancing age and maturity the dark adapted rod threshold decreased, indicating increased retinal sensitivity.

CONCLUSIONS

Contact lens recording of the ERG from extremely small immature preterm infants is a practicable and well tolerated procedure. This method of recording the ERG will enable further evaluation of retinal development in this vulnerable population.

The discrepancy between maturation of visual-evoked potentials and cognitive outcome at five years in very preterm infants with and without hemodynamic signs of fetal brain-sparing

OBJECTIVE

After intrauterine growth restriction we found at the age of 6 months an acceleration of neurophysiologic maturation. However, at later ages impaired cognitive outcome has been reported. Therefore, we investigated in children with and without fetal hemodynamic adaptation to intrauterine growth restriction whether the accelerated neurophysiologic maturation in infancy might be associated with impaired cognitive outcome at preschool age.

DESIGN

At 5 years of age cognitive function was assessed using the Revision of the Amsterdam Children's Intelligence Test in 73 preterm infants (26-33 weeks) who were prospectively followed from the antenatal period up to the age of 5 years. Maternal educational level was used as a background variable to estimate the confounding effects of socioeconomic status on cognitive function. Fetal Doppler studies were performed and the umbilical artery pulsatility index (PI) divided by the middle cerebral artery PI ratio (U/C ratio) was calculated. A U/C ratio >0.725 was considered as an indication of fetal cerebral hemodynamic adaptation to a compromised placental perfusion, ie, fetal brain-sparing. Visual-evoked potentials (VEPs) were recorded at 6 months and 1 year of age. In addition, data on neurologic status at 3 years were available.

RESULTS

Mean IQ score was significantly lower for children born with a raised U/C ratio (87 +/- 16) compared with children with a normal U/C ratio (96 +/- 17). VEP latencies decreased significantly in infants with a normal U/C ratio, whereas no decrease was found in infants with a raised U/C ratio. Variables contributing significantly to the variance of cognitive function were: U/C group, VEP latency maturation, level of maternal education, and neurodevelopmental outcome at 3 years. The linear regression model explained 33% of the variance in cognitive function.

CONCLUSIONS

Both being born with a raised U/C ratio and an acceleration of VEP latencies are negatively associated with cognitive outcome at 5 years of age. Fetal brain-sparing, although a seemingly beneficial adaptive mechanism for intact neurologic survival, is, however, later associated with a poorer cognitive outcome.

Early neurological and neuropsychological development of the preterm infant and polyunsaturated fatty acids supply

OBJECTIVES

To compare the early neurological maturation of premature newborns (PT) fed breast milk (BM) or a formula containing only 18-carbon polyunsaturated fatty acids (PUFA) (A) or enriched with long chain (LC) PUFA (B).

METHODS

PT enrolled the 2nd day of enteral feeding (D0) were fed BM (n = 15; 4 dropped out) or randomly assigned to A (n = 11; 2) or B (n = 14; 1) for at least 30 days (D30). Auditory and visual evoked potentials (EPs) and nerve conduction velocity (NCV) and plasma and red blood cell (RBC) phospholipid composition were determined at D0 and D30. No difference was found between groups for the D0-D30 changes in EP parameters. The maturation of motor NCV was slower in the B group than in the two other groups. In plasma, the changes were higher in B than in the BM and A groups for linoleic acid (P < 0.05), in BM versus B group for arachidonic acid (P < 0.02). In RBC, formula groups displayed higher linoleic acid level than the BM group (P < 0.05). No difference was found between groups for the changes in arachidonic and docosahexaenoic acids.

CONCLUSIONS

A balanced supply of n-6 and n-3 PUFA without addition of LC-PUFA allowed an adequate early maturation of the central nerve system. The effects of LC-PUFA on the maturation of NCV remain to be confirmed.

Light reduction and the electroretinogram of preterm infants

AIMS

To examine the effects of light on retinal development and function in preterm infants as measured by the electroretinogram (ERG). Secondary outcomes included visual acuity testing, the incidence of retinopathy of prematurity, and general wellbeing, reflected in feeding tolerance, rate of weight gain, and length of hospital stay.

METHODS

Eligibility criteria for enrollment were birthweight < or = 1250 g and gestational age < or = 31 weeks. Sixty one infants were randomly allocated by 6 hours after birth to a control or treatment group which wore 97% light filtering goggles for a minimum of four weeks or until the infant reached 31 weeks postmenstrual age.

RESULTS

There were no significant differences between the two groups in the numbers of electroretinograms performed at 36 weeks of postmenstrual age. Although the sample size was not large enough to exclude clinically important differences in secondary outcomes, no significant differences were observed between the groups in visual acuity testing at 4-6 months corrected age, incidence of retinopathy of prematurity, weight gain, or length of stay.

CONCLUSION

These data support the safety and feasibility of this intervention. A much larger study will be needed to determine whether light reduction to the eyes of very low birthweight infants will reduce the incidence of retinopathy of prematurity or enhance general well-being.

Neurological assessment of the preterm infant

Coinciding with improved overall management of the very preterm infant, more techniques have become available to assess the neurological well-being of these high-risk infants. An overview is given of the different techniques which are now used in many neonatal intensive care units, and their value in predicting neurodevelopmental outcome is discussed. Attention is mainly focused on cranial ultrasound, electroencephalography and the different evoked potential modalities.