Visual impairment and ocular abnormalities in children with fetal alcohol syndrome

Persistance et hyperplasie du vitré primitif

The persistence of the fetal vascular system is a rare ocular malformation whose origin remains unknown. It comprises a group of complex ocular malformations from which the various clinical forms have a heterogeneous functional prognosis. The diagnosis depends on a precise and complete examination of the child's eye, often under general anesthesia. Various clinical forms can be found together, ranging from the tiny form with no visual repercussion or ocular or systemic anomaly associated with the major forms involving the totality of the ocular structures and systemic syndromes. A systematic general pediatric examination is therefore recommended. The treatment is adapted individually for early and specific surgical and medical treatment. In the event of intervention, the induced aphakia will be corrected in one procedure with an implantation, generally sutured with the sclera, or at the time of a second intervention after the wearing of glasses or a contact lens. However, the complications can sometimes lead to rapid phthisis bulbi. Whatever solution is chosen, the final functional result has progressed thanks to early diagnosis, the surgical techniques suggested, even if implantation continues to be debated. Amblyopia must be treated for the entire sensitive period. However, despite good rehabilitation, the average functional prognosis remains disappointing, probably because of the overall ocular malformation.

Long-term effects of prenatal alcohol exposure on the size of the whisker representation in juvenile and adult rat barrel cortex

Children of mothers who abused alcohol during pregnancy are often reported to suffer from growth retardation and central nervous system (CNS) abnormalities. The use of prenatal alcohol exposed (PAE) animal models has revealed reductions in body and brain weights as well as regional specific brain deficits in neonatal pups. Recently, we and others reported reductions in the size of the posteromedial barrel subfield (PMBSF) in first somatosensory cortex (SI) associated with the representation of the large mystacial vibrissae in neonatal rats and mice that were exposed to alcohol at various times during gestation. While these reductions in barrel field size were reported in neonates, it was unclear whether similar reductions persisted later in life or whether some catch-up might take place in older animals. In the present study, we examined the effect of PAE on measures of barrel field size in juvenile (6 weeks of age) and adult (7 months of age) rats; body and brain weights were also measured. Pregnant rats (Sprague-Dawley) were intragastrically gavaged during gestational days 1-20 with alcohol (6 g/kg) to simulate a binge-like pattern of alcohol consumption (Alc); 6 g/kg alcohol produced blood alcohol levels ranging between 207.4 and 478.6 mg/dl. Chow-fed (CF), pair-fed (PF), and cross-foster (XF) groups served as normal, nutritional/stress, and maternal controls, respectively, for juvenile rats; an XF group was not included for adult rats. The major findings in the present study are (i) PAE significantly reduced the size of the total barrel field in Alc juvenile rats (13%) and adult rats (9%) compared to CF controls, (ii) PAE significantly reduced the total averaged sizes of individual PMBSF barrels in juvenile (14%) and adult (13%) rats, (iii) PAE did not significantly alter the septal area between barrels or the barrel pattern, (iv) PAE significantly reduced body weight of juvenile rats but only in comparison to PF controls (18%), (v) PAE significantly reduced whole brain (8%) and forebrain (7%) weights of juvenile rats but not adult rats, (vi) no differences were observed in forebrain/PMBSF body ratios nor was forebrain weight correlated with PMBSF area, and (vii) PAE resulted in a greater reduction in anterior barrels compared to posterior barrels. These results suggest that the effects of PAE previously reported in neonate PMBSF areas persist into adulthood.

Effects of ethanol on photoreceptors and visual function in developing zebrafish

PURPOSE

Children born to mothers who have consumed alcohol during pregnancy have an array of retinal abnormalities and visual dysfunctions. In the past, rodent systems have been used to study the teratogenic effects of ethanol on vertebrate embryonic development. The exact developmental windows in which ethanol causes specific developmental defects have been difficult to determine because rodents and other mammals develop in utero. In this study, we characterized how ethanol affects the function and development of the visual system in an ex utero embryonic system, the zebrafish.

METHODS

Zebrafish embryos were raised in fish water containing various concentrations of ethanol from 2 to 5 days after fertilization. The effects of ethanol on retinal morphology were assessed by histologic and immunohistochemical analyses and those on retinal function were analyzed by optokinetic response (OKR) and electroretinography (ERG).

RESULTS

Zebrafish embryos exposed to moderate and high levels of ethanol during early embryonic development had morphological abnormalities of the eye characterized by hypoplasia of the optic nerve and inhibition of photoreceptor outer segment growth. Ethanol treatment also caused an increased visual threshold as measured by the OKR. Analysis with the ERG indicated that there was a severe reduction of both the a- and b-waves, suggesting that ethanol affects the function of the photoreceptors. Indeed, low levels of ethanol that did not cause obvious morphologic changes in either the body or retina did affect both the OKR visual threshold and the a- and b-wave amplitudes.

CONCLUSIONS

Ethanol affects photoreceptor function at low concentrations that do not disturb retinal morphology. Higher levels of ethanol inhibit photoreceptor development and cause hypoplasia of the optic nerve.