Ocular teratology

Early ophthalmic growth deficits in preterm-born children are not compensated for during later development

The renewed focus on eye growth in preterm-born children was primarily triggered by Danish cohort studies, including the Copenhagen Project, which focused on children born from 1959-1961. The retinotoxic effects of excessive oxygen on premature neonates had long been clarified and therapeutically adjusted for. Later, ultrasound oculometry and keratometry established that ocular size deficits, linked to development, also occurred in normally developing children, not just frail outliers. This indicated that general catch-up had not been achieved. This paper discusses whether one early segment of eye development does not occur in preterm, and here even in more robust neonates, without later compensation.

Ocular development after highly effective modulator treatment early in life

Highly effective cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapies (HEMT), including elexacaftor-tezacaftor-ivacaftor, correct the underlying molecular defect causing CF. HEMT decreases general symptom burden by improving clinical metrics and quality of life for most people with CF (PwCF) with eligible CFTR variants. This has resulted in more pregnancies in women living with CF. All HEMT are known to be able pass through the placenta and into breast milk in mothers who continue on this therapy while pregnant and breast feeding. Toxicity studies of HEMT in young rats demonstrated infant cataracts, and case reports have reported the presence of congenital cataracts in early life exposure to HEMT. This article reviews the evidence for how HEMT influences the dynamic and interdependent processes of healthy and abnormal lens development in the context of HEMT exposure during pregnancy and breastfeeding, and raises questions that remain unanswered.

EPHA2 Segregates with Microphthalmia and Congenital Cataracts in Two Unrelated Families

EPHA2 is a transmembrane tyrosine kinase receptor that, when disrupted, causes congenital and age-related cataracts. Cat-Map reports 22 pathogenic EPHA2 variants associated with congenital cataracts, variable microcornea, and lenticonus, but no previous association with microphthalmia (small, underdeveloped eye, ≥2 standard deviations below normal axial length). Microphthalmia arises from ocular maldevelopment with >90 monogenic causes, and can include a complex ocular phenotype. In this paper, we report two pathogenic EPHA2 variants in unrelated families presenting with bilateral microphthalmia and congenital cataracts. Whole genome sequencing through the 100,000 Genomes Project and cataract-related targeted gene panel testing identified autosomal dominant heterozygous mutations segregating with the disease: (i) missense c.1751C>T, p.(Pro584Leu) and (ii) splice site c.2826-9G>A. To functionally validate pathogenicity, morpholino knockdown of epha2a/epha2b in zebrafish resulted in significantly reduced eye size ± cataract formation. Misexpression of N-cadherin and retained fibre cell nuclei were observed in the developing lens of the epha2b knockdown morphant fish by 3 days post-fertilisation, which indicated a putative mechanism for microphthalmia pathogenesis through disruption of cadherin-mediated adherens junctions, preventing lens maturation and the critical signals stimulating eye growth. This study demonstrates a novel association of EPHA2 with microphthalmia, suggesting further analysis of pathogenic variants in unsolved microphthalmia cohorts may increase molecular diagnostic rates.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

Middle-aged individuals with thalidomide embryopathy have undergone few surgical limb procedures and demonstrate a high degree of physical independence

Background

Thalidomide is known to have induced thalidomide embryopathy (TE) in more than 10,000 live-born children worldwide between 1957–1962.

Aim

The aim of this study was to investigate the need for orthopaedic surgery and limb orthosis in relation to function and physical independence in middle-aged individuals with TE.

Methods

13 women/18 men with a mean age of 45.8 (SD 1.1) years were included. Information about limb surgery, the use of orthotic devices, jobs, accommodation, disability adjustments and personal assistants was collected. Physical function was measured by a modified general function score. The time needed for activities of daily living (ADL) was collected. Individuals with proximal focal femoral deficiency, PFFD, and participants in need of home or work adaptations were compared with the rest of the group.

Result

31 surgical procedures had been performed in the extremities. Three individuals were in need of personal assistance and seven had disability-adjusted homes. 28 individuals were working and 24 reported participation in exercises. Those with PFFD had significantly lower function score and needed a significantly longer time for ADL in the morning (p = 0.001 and p = 0.032). The group in need of home or work adjustments had significantly lower function score and needed longer time for morning ADL (p = 0.012 and p = 0.009).

Discussion

Few orthopaedic procedures had been performed. The TE individuals except the ones with PFFD and those in the need of disability adjustments, were mostly active workers, reported good physical function and participated in exercises, despite limb malformations.

Anomalous Vascular Patterns of the Optic Disc in Amblyopia

PURPOSE

To evaluate the presence of anomalies of the optic disc vascular patterns in subjects with amblyopia.

DESIGN

Case controlled study. The outcome measure is temporal deviation of central retinal vessels and / or vascular pattern asymmetry.

METHODS

A total of 342 hyperopic amblyopic patients were evaluated. An additional 88 subjects with equal visual acuity with strabismus, and 108 subjects with equal visual acuity and anisometropia were evaluated.

RESULTS

In this study, more than 50% of amblyopic patients had optic disc deformities. Sixty-five percent of subjects with amblyopia, orthophoria, and anisometropia exceeding 1.5 D had these anomalies compared with less than 7% of the groups without amblyopia or strabismus.

CONCLUSIONS

These disc anomalies may be associated with disorganization of optic nerve axons. This finding indicates the possibility of a peripheral cause for impaired vision and could provide an explanation for the variability in visual defects associated with amblyopia. Optic nerve imaging should be incorporated into clinical protocols for amblyopia research.

Myelination changes in the rat optic nerve after prenatal exposure to methamphetamine

The use of psychostimulants during adolescence and early adult life has increased in recent years. It is known that these substances affect the sensory systems, and the optic nerve has been shown to be a target tissue. This work was conducted to evaluate the effects of prenatal exposure to methamphetamine (MA) on the developmental pattern of the rat optic nerve. Pregnant female rats were given 5 mg/kg body weight/day MA, s.c., in 0.9% saline from gestational days 8 to 22. The control group was injected with an isovolumetric dose of 0.9% saline. Animal model parameters, such as gestational body weight evolution, food intake and pups parameters were registered. The offspring were sacrificed at postnatal days (PND) 7, 14 and 21. Morphometric analyses were performed at light and electron microscopic levels on optic nerve cross sections; parameters measured included optic nerve diameter and area, axonal density, total number of axons and myelin thickness. Myelin basic protein (MBP) was measured by western blotting in optic nerve samples at PND14 and PND21. The animal model parameters, such as maternal and pup weight, showed no significant differences between MA and control groups. Optic nerve diameter was smaller at PND7 in the male MA group and in both male and female MA groups at PND21. The mean cross-sectional area was smaller at PND14 in the male MA group and in both male and female groups at PND21. The total number of myelinated axons did not vary between groups at any of the studied ages. The myelin thickness of the axons in MA-treated females was thinner when compared with the respective control group at PND21. No other differences were found concerning myelin thickness. There was a reduction of MBP protein expression in MA-injected females at PND14 and PND21. The combined results suggest that prenatal exposure to MA affects the myelination process.

The epidemiology of anophthalmia and microphthalmia in Sweden

Infants with a clinical diagnosis of anophthalmia or microphthalmia were identified from four health registers in Sweden, covering different parts of the period 1965-2001. During the observation period, the rate of anophthalmia decreased from the early 1970s from 0.4 to 0.2 per 10,000 births. The registered rate of microphthalmia increased markedly during the observation period to reach a maximum in 1987 of about 1.5 per 10,000. About 10% of the 432 identified children had a chromosome anomaly. There was no geographical variation in prevalence and infants born in urban or rural districts had, if anything, a lower risk than infants born in cities (0.93 and 1.13 per 10,000, respectively). Non-eye malformations were more common at anophthalmia (63%) than at microphthalmia (30%). Sex ratio was normal and no statistically significant variation between sub-groups (anophthalmia, microphthalmia, isolated, associated with non-eye malformations) could be demonstrated. There was a marked risk increase with maternal age but no certain parity effect, no effect of maternal education, but a possible association with subfertility. Maternal smoking in early pregnancy seemed to increase the risk for anophthalmia or microphthalmia in the absence of a coloboma.

Corneal Endothelial Abnormalities Associated With Thalidomide Toxicity

PURPOSE

To describe bilateral corneal endothelial abnormalities associated with thalidomide toxicity.

METHODS

Observational case report.

RESULTS

A 30-year-old man, born with bilateral hypoplastic upper limb defects (phocomelia) caused by thalidomide toxicity, presented with bilateral symmetrical corneal endothelial changes resembling guttata without corneal edema. Pachymetry, specular microscopy, and confocal microscopy were performed. Biomicroscopy findings over a 10-year follow-up showed no changes.

CONCLUSIONS

Nonprogressive bilateral corneal endothelial changes resembling cornea guttata should possibly be included in the ocular manifestations of thalidomide toxicity. We postulate that thalidomide may have affected the migration and development of the mesenchymal neural crest cells, which are the developmental precursors of the corneal endothelium and stroma.

Teratogenicity of retinoic acid and its effects on TGF-β2 expression in the developing cerebral cortex of the rat

Vitamin A metabolites are potent teratogens in a wide variety of species, including man. Transforming growth factor betas (TGF-betas) are involved in several mammalian prenatal developmental processes. The aim of this study was to determine the effects of exogenous and excessive all-trans retinoic acid on TGFbeta2 expression in the developing cerebral cortex of the rat. Many of the malformations including exencephaly, exophtalmus, abdominal wall defects, extremity reduction defects observed in this study were dependent on the time of administration of retinoic acid. TGF-beta2 was diversely expressed, as revealed immunohistochemically, in the cerebral cortex and plexus choroideus. The diversity depended on the gestational day and the was affected by the administration of retinoic acid. In the 15-day-old fetus from mothers who had been fed by gavage a single dose of 60 mg/kg body weight of all-trans retinoic acid on the 8th day of gestation, TGF-beta2 immunoreactivity in the brain was decreased. However, by the 18th day of gestation, TGF-beta2 expression increased. The expression of TGF-beta2 in fetuses whose mothers had been given all-trans retinoic acid after the neurulation period (on day 12 of gestation) was generally similar to that in a control group. We conclude that all-trans retinoic acid leads to severe congenital malformations if administered before neurulation whereas if given after neurulation, it is not so teratogenic. Further, retinoic acid has a variable effect on the expression of TGF-beta2.

Optic nerve hypoplasia and small eyes in presumed amblyopia

PURPOSE

To assess the anatomy of eyes presumed to be amblyopic and their fellow eyes.

PARTICIPANTS

Two hundred seventy-five patients diagnosed with amblyopia and 88 healthy or glaucomatous subjects.

METHODS

All subjects underwent complete examinations, including cycloplegic refraction, slit lamp examination, ophthalmoscopy, and retinal imaging. Axial lengths were determined on 263 amblyopic and 88 healthy and glaucomatous subjects by ultrasonic biometry.

MAIN OUTCOME MEASURES

Optic disc areas were determined by magnification correction of disc images performed with formulas. Dysversion of the optic disc was determined by simultaneous viewing of disc photographs, digitized images of both eyes, or both.

RESULTS

The mean disc area of eyes presumed to be amblyopic was 1.72 mm(2) +/- 0. 73 SD and 1.95 mm(2) +/- 0.69 SD for nonamblyopic eyes (P =.0017). The mean disc area for 176 optic discs of glaucomatous and healthy eyes was 2.61 mm(2) +/- 0.95 SD. The mean axial length for eyes in the general population is 23.65 mm +/- 1.35 SD. The healthy and glaucomatous group in this study had a mean axial length of 23.89 mm +/- 1.29 SD. The eyes with poorer vision that were assumed to be amblyopic averaged 22.42 mm +/- 2.01 SD in length, whereas their nonamblyopic fellow eyes averaged 22.83 mm +/- 1.89 SD (P =.022). The differences between eyes in the healthy population and eyes that are presumably amblyopic, as well as the healthy and fellow eyes, are highly significant (P <.0001)(7.0 x 10(-16)).

CONCLUSION

Vision impairment in presumed amblyopia is associated with optic nerve hypoplasia with relative microphthalmos, which is more notable in those eyes with poorer vision.

Effects of irradiation and methyl-triazene on craniofacial development in mouse embryos: a semiautomated morphometric analysis

OBJECTIVE

The purpose of the present study was a 2D-semiautomated morphometric analysis of craniofacial growth in nuclear magnetic resonance imaged (NMRI) mouse embryos.

METHODS

The NMRI mouse embryos were exposed in utero to either a single dose of 2 Gy X-irradiation on day 9 of gestation (113 embryos) or to 1.5 mg methyl-triazene administered orally to their pregnant mothers on gestational day 10.5 (124 embryos). An additional group of 108 embryos was used as controls. Digitized pictures of embryos from gestational days 14 to 17 were taken in lateral right view using a video system. Landmarks were located and digitized for computerized analysis of growth changes in relation to developmental stages of the face.

RESULTS

The results revealed that the snout of control embryos lengthens during the developmental period considered. The snout of embryos previously submitted to methyl-triazene displayed micrognathia, and all treated fetuses exhibited macroscopic signs of microcephaly with a reduced mandible. The snouts of irradiated embryos appeared shortened at the 14-day stage and continued to shorten as development proceeded. A shortening of the midface was detected macroscopically in 83% of the cases.

CONCLUSION

The results of this morphometric analysis enabled us to trace the developmental progression of the induced dysmorphosis and to assess the differences compared with normal development.

Effects of prenatal alcohol exposure on the postnatal morphology of the rat oculomotor nucleus

Morphological development of the rat oculomotor nucleus was investigated on postnatal day 15 following a prenatal ethanol exposure. Analysis of toluidine blue stained plastic sections showed that the prenatal alcohol exposure caused a decrease in the density of neurons and an increase in the density of astrocytes in the center of the nucleus. There was an alcohol-induced reduction in the overall size of the cross-sectional region of the oculomotor nucleus, but no effect on the number of neurons per unit area of that total oculomotor region, indicating a delay or alteration of the migration of neurons to their normal clustered position in the center of the nucleus. The areas of the neuronal cell nucleus and nucleolus were not affected by the alcohol exposure. Analysis of Golgi-Cox-impregnated multipolar neurons showed that the alcohol exposure caused a reduction in area of the cell soma; a reduction in the number of dendritic branches; and a reduction in the complexity of the dendritic arbor relative to distance from the soma, based on concentric ring analysis. The results of this study demonstrate that gestational alcohol exposure can retard the maturation of the oculomotor nucleus.

Optic nerve hypoplasia: comparative effects in children and rats exposed to alcohol during pregnancy

Children with the fetal alcohol syndrome often have ocular anomalies. These include abnormalities of the eyes and adnexa (strabismus, blepharoptosis, epicanthus), as well as intraocular defects (cataract, glaucoma, persistent hyperplastic primary vitreous, retinal and optic nerve anomalies). Based on the clinical results in an ophthalmological study of a group of Swedish children with the fetal alcohol syndrome, in which optic nerve hypoplasia was found in up to one-half of the group, an experimental study was designed in rats pre- and perinatally exposed to alcohol by means of a liquid diet. The optic nerve was seriously affected. Macroglial cells and optic axons were ultrastructurally damaged. The diameter of the optic nerve cross section, glial cell nuclear area, axonal diameter, and the total number of optic axons showed significantly lower values in the alcohol-exposed group than in the controls. In addition, the retina from the alcohol-exposed animals displayed significantly lower values of the retinal thickness and ganglion cell nuclear volume, as compared to the controls. Thus, rats exposed to alcohol in utero developed hypoplasia of the optic nerve similar to the findings in children born to alcoholic mothers. This strongly supports the hypothesis that prenatal alcohol exposure may adversely affect the development of the optic nerve.

Developmental changes in the optic nerve related to ethanol consumption in pregnant rats: analysis of the ethanol-exposed optic nerve

Visual impairment is one of the most common ophthalmic abnormalities in fetal alcohol syndrome. Pathologic changes in optic nerve development related to alcohol consumption could be involved in this dysfunction. In order to assess the consequences of pre- and postnatal exposure to alcohol on the developing optic nerve, we administered an ethanol-containing liquid diet (5% w/v) before and during gestation and throughout lactation to rats and their offspring. A group of control animals were kept on a pair-fed isocaloric diet. The optic nerves were obtained at key stages from fetuses (21 days of gestation) and pups (4, 7, 14, 21 and 28 postnatal days). Samples of the optic nerve cross-section, behind the eyeball, were processed for analysis of gliogenesis, myelinogenesis, axonal growth, and remodelling events, using light and electron microscopy. Qualitative, morphometric, and immunocytochemical analyses, alternatively using anti-GFAP and anti-MBP antibodies, were carried out. Optic nerve cross-sections from prenatal and postnatal alcohol-exposed rats showed a decrease in size. Ultrastructural alterations and retarded development in macroglial cells, optic axons, and myelin sheath were also observed. The most prominent abnormalities were: damage of cytoplasmic organelles and disorganization of cytoskeleton in astrocytes; a decrease in free ribosome density and nuclear membrane inclusions in oligodendrocytes; and fragmentation of lamellae, aberrant myelin sheaths and intralamellar inclusions in myelin. These findings suggest that alcohol abuse during pregnancy is teratogenic to the optic nerve and closely related to the altered visual function.

Classification of microphthalmos and coloboma

A new classification of microphthalmos and coloboma is proposed to bring order to the complexity of clinical and aetiological heterogeneity of these conditions. A phenotypic classification is presented which may help the clinician to give a systematic description of the anomalies. The phenotype does not predict the aetiology but a systematic description of ocular and systemic anomalies improves syndrome identification. There are two major classes, total and partial microphthalmos, and a subclassification which follows the embryology of the anomalies. The aetiological classification consists of three classes: (1) genetic (monogenic and chromosomal), (2) prenatally acquired (teratological agents and intrauterine deformations), and (3) associations. Genetic disorders give rise to malformations; prenatally acquired anomalies are disruptions or deformations. The aetiological classification can be applied to other congenital birth defects and improves counselling of families. Recurrence risks vary considerably between the classes.

Radiation and chemotherapy injury: pathophysiology, diagnosis, and treatment

The text in general is not meant to represent the participants' entire presentations. The lecture presenters in general are not responsible for the summaries, and cannot necessarily be assumed to agree with all that is stated, but they deserve credit for providing the lecture and handout material on which the summaries are based, and in most cases have contributed far more to the summaries than I have.

Recognition of thalidomide defects

Images

Update of sporadic microphthalmos and coloboma. Non-inherited anomalies

The majority of patients with microphthalmos and colobomas have genetic disorders. This is a survey of non-inherited, sporadic microphthalmos. Such cases may occur in the Goldenhar, CHARGE and VATER associations; it may also be due to teratological agents, for instance maternal ingestion of drugs, maternal infection, fever or irradiation. In these cases it is possible that neural crest cell development is abnormal. Some drugs, for instance retinoic acid are regulators of Hox genes which control an ordered sequence of differentiation; coloboma or microphthalmos may appear if deregulation occurs. Large choristomas of the anterior segment of the eye may be associated with microphthalmos or anophthalmos. Encephaloceles or orbital tumours may deform the growing eye and are another cause of non-inherited microphthalmos.

Ocular teratology. Observations, speculations, questions, principles reaffirmed

Teratology is most simply defined as "the study of environmental agents which disturb development". A more comprehensive definition is "the study of causes, mechanisms, and manifestations of developmental deviation, structural or functional." Teratology has several important purposes. Obviously, the most important is to protect future generations by identifying environmental agents that cause malformations. In this sphere, ophthalmologists are generally not the primary detectors. One notable exception is when Gregg, in 1941, recognised that an increase in congenital cataracts was due to a viral agent and brought rubella embryopathy to the attention of the medical community. Another pertinent reason for teratology is that it gives us insights into normal development. As Harvey said with such flair, "nature is nowhere accustomed more openly to display her secret mysteries than in cases where she shows tracings of her workings apart from the beaten path".