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C. Lafoyiannis, C. Westall, C. Till, J. Rovet; Maternal Thyroid Disease and Offspring Color Vision . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3697.
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Research with animals has shown that thyroid hormone (TH) is essential for structural and functional development of the visual system. While comparable structural data is not available on humans, Mirabella et al (2005) found contrast sensitivity deficits in infants with TH insufficiencies in utero. In light of this and animal studies implicating TH in cone development, we sought to evaluate color vision in infants who experienced TH insufficiencies at different times of fetal development. Offspring of hypothyroid (HYPO) and treated hyperthyroid women (HYPER) were chosen to represent different periods of TH insufficiency. Until full development of the fetal thyroid in the third trimester, the fetus is heavily dependent on maternal TH. Thus, HYPO experience insufficient TH in the first half of pregnancy while HYPER have third trimester deficiencies due to the due to the blocking action of mothers’ antithyroid medications on fetal thyroid function.
To determine whether TH insufficiencies at different stages of pregnancy affect infant color vision.
Color vision was assessed in 74 infants between 6 and 8 months (HYPO= 32; HYPER=11; Control=31) using transient VEPs (temporal frequency=2Hz; spatial frequency=1cpd; grating contrast=80%; pattern onset=100msec; offset= 400msec). Chromatic sinusoidal stimuli were presented along the tritanopic confusion axis (blue–yellow) modulating short (S) wavelength cones and the orthogonal axis (red–green) modulating long (L) and medium (M) wavelength cones. Average peak latencies were measured from pattern onset to the first major negative peak. Responses producing uncharacteristic waveforms were labeled abnormal. Infants were given ocular exams to rule out optical problems.
No group differences were seen on ocular exam. Compared to controls, HYPO demonstrated a higher proportion of abnormal responses to blue–yellow stimuli (50% vs. 9.4%, p<.001), while both HYPO and HYPER had a greater proportion of abnormal responses to red–green stimuli (25% and 33% vs. 0%; p< 0.001). Among infants with normal waveforms, a significant group difference was observed in mean response latency to blue–yellow (P144 msec; P157 msec; P133 msec, p=.004) but not red–green stimuli. Effects were stronger for HYPER than HYPO (2= 0.186, p=.008; 2=.090, p=.036) suggesting a third–trimester effect.
Present findings support the view that TH is implicated in the developing human color vision system, particularly during the third trimester.
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