A review of the developmental and reproductive toxicity of styrene

The reproductive and developmental toxicity of styrene has been studied in animals and humans. The animal studies on styrene have diverse study designs and conclusions. Developmental or reproductive toxicity studies have been conducted in rats, mice, rabbits, and hamsters. In most cases, high doses are required to elicit effects, and the effects are not unique to reproduction or development. In a number of the reports, either the experimental designs are limited or the descriptions of the designs and the endpoints measured are insufficient to draw conclusions about the toxicity of styrene. The more complete and better-reported studies show that styrene does not cause developmental toxicity at dose levels that are not maternally toxic. Some neurochemical or neurobehavioral effects have been reported at high exposures. Styrene does not affect fertility or reproductive function. Considerable animal toxicity data on styrene support the conclusion that styrene is neither an endocrine-active substance nor an endocrine disrupter. Human studies often suffer from either inadequate exposure data or exposure to a wide variety of materials, so that attribution of effects to styrene exposure is impossible. Furthermore, investigators often have failed to account for other exposures in the workplace or for other potentially confounding factors in their studies. Menstrual cycle irregularities and congenital abnormalities were initially reported; however, the better and more recent reports do not show that styrene causes developmental or reproductive effects in humans. Human studies also support the conclusion that styrene is not an endocrine disrupter. Although some study authors have concluded that styrene is either a human or an animal reproductive or developmental toxicant, careful review demonstrates that such conclusions are not justified.

Ocular effects of apraclonidine in Horner syndrome

OBJECTIVE

To determine the location of action of apraclonidine, an alpha-adrenergic receptor agonist that reduces aqueous production and lowers intraocular pressure (IOP).

METHODS

The study cohort consisted of 6 patients with Horner syndrome (decreased or absent sympathetic innervation of 1 eye). We instilled 1% apraclonidine into the affected eye, and the changes in IOP and pupil diameter (PD) of both eyes were measured over 4 hours. In a separate session, apraclonidine was instilled into the normal eye and the measurements were repeated.

RESULTS

The average baseline IOP was 16.3 mm Hg for affected eyes and 16.7 mm Hg for normal eyes. The average maximum ipsilateral reduction in IOP was 5.8 mm Hg in affected eyes and 5.2 mm Hg in normal eyes; this difference was not statistically significant. The average baseline PDs for affected and normal eyes were 3.2 mm and 4.2 mm, respectively. Instillation of apraclonidine into affected eyes produced mydriasis of 1.0 to 4.5 mm; baseline anisocoria reversed in all patients. There was no significant change in the PD of normal eyes after ipsilateral instillation of apraclonidine.

CONCLUSIONS

Apraclonidine's major site of pharmacologic action for reduction of aqueous production is on postjunctional alpha(2) receptors in the ciliary body. The up-regulation of alpha receptors that occurs with sympathetic denervation unmasks apraclonidine's alpha(1) effect, which clinically causes pupil dilation. Apraclonidine may be a useful medication for the diagnosis of Horner syndrome. Arch Ophthalmol. 2000;118:951-954

Chemical testing strategies for predicting health hazards to children

The United States Environmental Protection Agency has proposed the development of a Children's Health Test Program under the Toxic Substances Control Act. The Environmental Protection Agency's proposal for the children's health test battery has 12 different assays including general toxicity, genotoxicity, carcinogenicity, neurotoxicity, and developmental and reproductive toxicity. The current Environmental Protection Agency testing proposal is an "all or nothing" test battery. An alternative and preferable approach would be to use a science-based, tiered testing scheme. It is proposed that the Screening Information Dataset program, currently used by the Organization for Economic Co-operation and Development (OECD) for the Screening Information Dataset-High Production Volume test battery, or equivalent, be considered for the first step. Step 1 would include acute and repeat dose toxicity testing, developmental toxicity testing (first species OECD 414 or OECD 422), reproductive toxicity screening (OECD 415 or 422), and genetic toxicity testing. For this step, the rat would be the initial and only species tested unless the mouse was used for in vivo genetic toxicity. Step 2 of the proposed children's health test battery would include developmental testing (second species OECD 414) or special mode of action studies performed for those chemicals that proved to be developmental toxicants in Step 1. Those chemicals that tested positive as reproductive toxicants in Step 1 would be tested in a two-generation reproduction study (OECD 416) or a special mode of action study. Steps 1 and 2 provide information on whether oncogenicity or developmental neurotoxicity testing is useful. Step 3 would include chronic toxicity/oncogenicity testing for those chemicals that tested positive for genetic toxicity in Step 1, and positive for developmental concerns in Step 2. In this step, chemicals would also be tested for developmental neurotoxicity if they showed evidence of neuropathy, behavioral effects, or neurotoxic potential in earlier studies. This stepwise approach would conserve resources and answer scientific questions in a logical, orderly, timely, and cost-effective manner.

Intact sensory fusion in a child with divergence paresis caused by a pontine glioma

PURPOSE

To describe a child with divergence paresis esotropia caused by a brain tumor with intact sensory and motor fusion.

METHOD

Case report.

RESULTS

A 9-year-old boy who had one episode of double vision was initially seen with a small, variably present esophoria at near vision, an intermittent 10 prism diopter esotropia at distance, and stereopsis of 80 arc seconds. A magnetic resonance imaging examination disclosed a 4.0 x 4.5-cm pontine glioma.

CONCLUSIONS

Ophthalmologists should recognize that the presence of intact sensory and motor fusion in a child with acute, comitant esotropia of the divergence paresis type does not preclude intracranial abnormality. If immediate neuroimaging is deferred, repeated thorough ocular motility examinations are warranted to detect progression.

Cluster of diplopia cases after periocular anesthesia without hyaluronidase

PURPOSE

To describe a cluster of cases of iatrogenic diplopia after cataract surgery that occurred in 1998, when hyaluronidase was unavailable for use in periocular anesthetic regimens.

SETTING

The clinical practices of the authors.

METHODS

This study comprised a retrospective chart review.

RESULTS

Twenty-five cases of transient or permanent diplopia were reported. Of these, 13 eyes had retrobulbar and 10 had peribulbar injections; in 2 cases the injection technique was unknown. The inferior rectus was affected in 19 eyes; of these, 1 had a temporary palsy and 18 had permanent restriction. Temporary paresis developed in the lateral rectus in 5 cases and the superior rectus in 2. Eleven cases were submitted by 4 anterior segment surgeons, who collectively had a zero incidence of iatrogenic postoperative diplopia in the preceding 4 to 11 years of practice (approximately 6900 cases).

CONCLUSION

Hyaluronidase may be more important than previously suspected in preventing anesthetic-related damage to the extraocular muscles. The inferior rectus muscle is particularly vulnerable, presumably because of the injection technique.

Sleeping position in infants over 6 months of age: implications for theories of sudden infant death syndrome

The aim of this study was to determine the prevalence of prone and supine sleeping in infants aged 0-12 months and relate this to changes in the number of cases of sudden infant death syndrome (SIDS) since 1985. Seventy-two babies, 38 male and 34 female, were followed for the first 18 months of life with regular home visits and sleeping position was recorded. In addition, data on the number of cases of SIDS in England and Wales between 1985 and 1995 were analysed. All babies slept supine for the first 5 months of life, but once they could turn over in their cots (mean age 7.34 months, range 5-11 months) the majority slept prone. By 11 months of age, 53 regularly slept prone (73%), 95% CI +/- 19.8%), while 11 slept supine, three adopted the side position and five varied from night to night. The number of cases of SIDS in infants aged 7-11 months has fallen significantly (P<0.0001) in a period in which the prevalence of prone sleeping, in that age group, has not changed. The most plausible explanation for this paradoxical result is that supine sleeping in the first 5 months of life reduces the absolute risk of SIDS in the second 6 months of life even though most babies are then sleeping prone. It is suggested that reduced exposure to nasopharyngeal bacterial superantigens in babies sleeping prone might explain this effect.

The nasopharyngeal bacterial flora in infancy: effects of age, gender, season, viral upper respiratory tract infection and sleeping position

The aim of the investigation was to determine the effect of age, gender, viral upper respiratory tract infection (URTI), season and sleeping position on the composition of the nasopharyngeal bacterial flora in infancy. Seventy-two babies, 38 male and 34 female, whose birthdates were evenly spread throughout the year were followed from birth to 18 months of age. From 0 to 6 months nasopharyngeal swabs were obtained once a month in periods without URTI and daily for 3 days during episodes of URTI. From 12 to 18 months of age nasopharyngeal swabs were obtained in the early morning alter an overnight sleep and later in the day after the baby had been up for over 2 h. Swabs were obtained in prone and supine sleepers with and without infection. In infants aged 0-6 months URTI had little effect on the nasopharyngeal bacterial flora, but there was a marked effect of age and less marked effect of season and gender. In particular Staphylococcus aureus carriage decreased with age, was most common in the winter months and the density of colonisation was greater in males than females. In infants aged 12-18 months the combination of prone sleeping with URTI and an early morning swab led to increased carriage of staphylococci, streptococci. Haemophilus influenzae and Gram-negative bacilli which are not normally part of the nasopharyngeal flora. These results are relevant to sudden infant death syndrome (SIDS). The combination of prone sleeping and URTI reproduces the nasopharyngeal flora seen in SIDS. Gram-negative bacilli isolated from SIDS cases should not be dismissed as post-mortem contaminants. The features of S. aureus make it a prime candidate for a pathogenic role in SIDS.

Stereopsis and binocular vision after surgery for unilateral infantile cataract

PURPOSE

To assess the prevalence and level of binocular function in children with unilateral congenital or very early infantile cataract.

METHODS

We retrospectively reviewed the charts of all patients with unilateral congenital or very early infantile cataract who underwent operation before 4 months of age, at the W. K. Kellogg Eye Center/University of Michigan Hospitals, from 1985 to 1995. Amblyopia was treated with a reduced patching schedule consisting of 1 hour per day per month of age for the first 6 months of life, in an attempt to improve binocular function by allowing more hours of binocular interaction during the presumed critical period for development of binocular cortical pathways.

RESULTS

Thirteen patients met the inclusion criteria. Seven patients had persistent hyperplastic primary vitreous (PHPV) cataract and 6 had non-PHPV cataract. Overall, visual acuity of 20/80 or better developed in 69% of patients; 100% of eyes with non-PHPV cataract achieved visual acuity of 20/60 or better. Stereopsis of 400 arc seconds or better was detectable in 62% of patients, including 3 with PHPV cataract and 3 who required strabismus surgery in the first year of life. Three children had better than 150 arc seconds of stereopsis. The incidence of large-angle strabismus was 54%.

CONCLUSIONS

Binocular cooperation, including gross and fine stereopsis, can develop in children with unilateral aphakia as a result of early removal of infantile cataracts. A less-strenuous patching schedule than has been historically advocated may foster this process, while restoring and maintaining good central visual acuity in patients with excellent compliance with contact lens and occlusion regimens.

Fresnel prism treatment of sensory exotropia with restoration of sensory and motor fusion

Anterior segment surgeons may treat patients with long-standing media opacities or uncorrected aphakia who have developed sensory strabismus. These patients are at risk for diplopia after surgery to clear the visual axis and restore emmetropia. This report describes 2 patients who regained comfortable single binocular vision without strabismus surgery. Sensory fusion was restored with Fresnel prisms, which were weaned and ultimately discarded as the patients' motor fusion was re-engaged after decades of disuse. Surgeons who restore vision in an eye with manifest sensory strabismus should be aware of this noninvasive, well-tolerated treatment option. Collaboration with an orthoptist or strabismologist may be helpful.

BRCA1 mutations and other sequence variants in a population-based sample of Australian women with breast cancer

The frequency, in women with breast cancer, of mutations and other variants in the susceptibility gene, BRCA1, was investigated using a population-based case-control-family study. Cases were women living in Melbourne or Sydney, Australia, with histologically confirmed, first primary, invasive breast cancer, diagnosed before the age of 40 years, recorded on the state Cancer Registries. Controls were women without breast cancer, frequency-matched for age, randomly selected from electoral rolls. Full manual sequencing of the coding region of BRCA1 was conducted in a randomly stratified sample of 91 cases; 47 with, and 44 without, a family history of breast cancer in a first- or second-degree relative. All detected variants were tested in a random sample of 67 controls. Three cases with a (protein-truncating) mutation were detected. Only one case had a family history; her mother had breast cancer, but did not carry the mutation. The proportion of Australian women with breast cancer before age 40 who carry a germline mutation in BRCA1 was estimated to be 3.8% (95% CI 0.3-12.6%). Seven rare variants were also detected, but for none was there evidence of a strong effect on breast cancer susceptibility. Therefore, on a population basis, rare variants are likely to contribute little to breast cancer incidence.

A technique for repair of iridodialysis in children

Iridodialysis can occur with blunt or penetrating trauma or inadvertently during intraocular surgery. A small dialysis may not need treatment. A larger iridodialysis that causes polycoria and diplopia, or a grossly eccentric pupil, needs to be reapproximated. A number of surgical techniques for repair, using double-armed polypropylene suture, have been reported. The suture is either left external on the surface of the sclera with the knot buried, covered with a triangular scleral flap, or retrieved with special forceps and buried in a scleral "groove." These techniques have also been used to allow posterior fixation of intraocular lens implants in the absence of capsular support; a complication of this approach is suture erosion through sclera, conjunctiva, or both. The pediatric sclera is softer and more elastic than adult sclera, and surgical repairs must last for decades. Concern about late suture erosion, and a desire for minimal scleral manipulation, led me to develop a simple technique for iridodialysis repair using a scleral tunnel incision and double-armed 10-0 polypropylene suture.