VISUAL CONTRAST SENSITIVITY DEFICITS IN BOHEMIAN CHILDREN

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 Re public. Study 1 compared children in standard schools and schools for the learning disabled. Studies 2 and 3 compared children in Teplice, a n area in which soft-brown coal combustion produced high levels of pol lutants (e.g. Hg, As, SO2, NOx, and aromatic hydrocarbons), with child ren in areas of low air pollution, Znojmo and/or Prachatice. It was hy pothesized that in utero exposure to the combustion products disrupted neurological development (Sram, 1991). The VCS test (Stereo Optical C o.) consisted of circular fields containing sinusoidal gratings at 5 s patial frequencies (1.5-18 cycles/degree) and various levels of contra st. Subjects indicated orientation of the gratings by pointing left, u p, or right. Visual acuity and VCS were measured in each eye of 74 chi ldren 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 a nd 3 and analyzed for Hg and As content. Children attending schools fo r the learning disabled scored significantly lower than controls on VC S, whereas visual acuity was normal. The deficit was greatest at mid- to high spatial frequency. In Study 2, significant VCS deficits were s een in exposed second-grade children at low to mid-spatial frequency e ven 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 we re not observed in the fourth-grade students of Teplice in Study 3. Th e results of Study 1 indicated that behavioral VCS testing in field st udies is practical in young, non-English speaking children, and sugges ted that vision may be compromised in learning-disabled children. Stud ies 2 and 3 indicated that at these levels, current Hg body-burdens ar e poor predictors of VCS. If the VCS deficits seen in Study 2 were rel ated to prenatal exposures, the results of Study 3 suggest that they r epresent a developmental delay. A longitudinal-study design is needed to address this issue. (C) 1996 Inter Press, Inc.