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Visual contrast sensitivity deficits in Bohemian children
H K Hudnell1, I Skalik, D Otto
1National Health and Environmental Effects Research Laboratory, U.S. EPA, RTP, NC 27711, USA.
Insights
Visual contrast sensitivity (VCS) testing revealed deficits in learning-disabled children and those exposed to air pollution. While mercury levels correlated with VCS deficits, results suggest developmental delays rather than current toxicity in children.
Area of Science:
- Environmental Health
- Neuroscience
- Ophthalmology
Background:
- Visual contrast sensitivity (VCS) testing is a validated tool for medical diagnosis and detecting subclinical neurotoxicity.
- Previous research hypothesized that in utero exposure to combustion pollutants disrupts neurological development.
- Air pollution from soft-brown coal combustion contains pollutants such as mercury (Hg), arsenic (As), sulfur dioxide (SO2), nitrogen oxides (NOx), and aromatic hydrocarbons.
Purpose of the Study:
- To investigate visual contrast sensitivity (VCS) in children exposed to different environmental conditions.
- To compare VCS in children attending standard schools versus those in schools for the learning disabled.
- To assess the relationship between environmental pollutant exposure (Hg, As) and VCS in children.
Main Methods:
- Three studies were conducted in the Czech Republic involving 74 to 426 children.
- Visual contrast sensitivity (VCS) was measured using sinusoidal gratings at five spatial frequencies.
- Hair samples were analyzed for mercury (Hg) and arsenic (As) content in Studies 2 and 3.
Main Results:
- Children in schools for the learning disabled showed significantly lower VCS compared to controls, with normal visual acuity.
- Children in a high air pollution area (Teplice) exhibited VCS deficits at low to mid-spatial frequencies, with no correlation to arsenic levels.
- A significant negative correlation was found between hair mercury levels and VCS in the exposed district, though higher mercury levels were found in a less polluted area (Prachatice).
Conclusions:
- Behavioral VCS testing is practical for field studies involving young children, including non-English speakers.
- VCS deficits may indicate compromised vision in learning-disabled children and potential developmental delays related to prenatal pollutant exposure.
- Current mercury body burden may not be a reliable predictor of VCS deficits, necessitating longitudinal studies to clarify developmental impacts.
Abstract:
Visual contrast sensitivity (VCS) tests have been used successfully in medical diagnosis and subclinical neurotoxicity detection. This paper reports VCS measurements in three studies of children in the Czech Republic. Study 1 compared children in standard schools and schools for the learning disabled. Studies 2 and 3 compared children in Teplice, an area in which soft-brown coal combustion produced high levels of pollutants (e.g. Hg, As, SO2, NOx, and aromatic hydrocarbons), with children in areas of low air pollution, Znojmo and/or Prachatice. It was hypothesized that in utero exposure to the combustion products disrupted neurological development (Sram, 1991). The VCS test (Stereo Optical Co.) consisted of circular fields containing sinusoidal gratings at 5 spatial frequencies (1.5-18 cycles/degree) and various levels of contrast. Subjects indicated orientation of the gratings by pointing left, up, or right. Visual acuity and VCS were measured in each eye of 74 children in Study 1,327 second-grade children in Study 2, and 426 fourth-grade children in Study 3. Hair samples were collected in Studies 2 and 3 analyzed for Hg and As content. Children attending schools for the learning disabled scored significantly lower than controls on VCS, whereas visual acuity was normal. The deficit was greatest at mid- to high spatial frequency. In Study 2, significant VCS deficits were seen in exposed second-grade children at low to mid-spatial frequency, even though visual acuity was slightly above control level. Regression analyses showed that VCS had no relationship to As, but a significant negative correlation with hair Hg was observed in the exposed district. However, current Hg levels were higher in Prachatice. VCS deficits were not observed in the fourth-grade students of Teplice in Study 3. The results of Study 1 indicated that behavioral VCS testing in field studies is practical in young, non-English speaking children, and suggested that vision may be compromised in learning-disabled children. Studies 2 and 3 indicated that at these levels, current Hg body-burdens are poor predictors of VCS. If the VCS deficits seen in Study 2 were related to prenatal exposures, the results of Study 3 suggest that they represent a developmental delay. A longitudinal-study design is needed to address this issue.