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G. Mirabella, C. Lafoyiannis, C.A. Westall, J. Rovet; Infants of Hypothyroid Mothers Show Contrast Sensitivity Deficits With High Temporal Frequency Gratings . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3159.
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Thyroid hormone (TH) is essential for the normal development of the visual system. Mirabella et al. (2005) first demonstrated these deficits in humans by measuring contrast sensitivity functions using sweep visual evoked potentials (VEPs) in infants with prenatal thyroid hormone insufficiencies. Results showed that offspring of hypothyroid mothers, who represent thyroid insufficiency during early gestation, showed significant reductions in contrast sensitivity but a sparing of grating acuity. These results corroborated animal studies showing that TH was critical for the development of the primary visual pathway. Further, deficits in contrast sensitivity suggest that TH may be particularly critical for the development of the magnocellular pathway, since these are the neurons that respond to low spatial frequency, high temporal frequency stimuli (Kaplan & Shapley, 1982, Livingstone & Hubel, 1988).
We tested this hypothesis by measuring contrast sensitivity in 6 month old offspring of hypothyroid mothers (n=23), comparing them to a group of normal, full term infants (n=16). Contrast sensitivity was assessed using the sweep visual evoked potential. Infants were presented with a 1 cpd sinusoidal grating alternating in counterphase at 6, 10 and 15 Hz. We tested contrast sensitivity at higher temporal frequencies in order to isolate the response from the magnocellular pathway. All children had standard eye exams to insure that optical aberrations did not affect the results.
Both the hypothyroid and control groups showed an expected drop in contrast sensitivity with increasing temporal frequency. However, infants in the hypothyroid group showed an additional 0.2 log–unit drop in contrast sensitivity at 6 and 10 Hz compared to controls. There were no significant differences in sensitivity for the 15 Hz grating. Also, there were no significant eye exam differences between groups. The eye exams showed no ocular differences or abnormalities between groups.
Contrast sensitivity deficits in offspring of hypothyroid mothers persist when the temporal frequency of the grating is increased. This finding replicates Mirabella et al. (2000) and lends further support to the role of thyroid hormone in the development of the magnocellular pathway.
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