Ocular morphology development and function in children with congenital hypothyroidism diagnosed by neonatal screening

Background The ocular globe, as part of central nervous system, is vulnerable to the lack of appropriate thyroid hormones (TH) levels especially during a period of active and rapid growth named “brain growth spurt”, which carries on in early postnatal life. In animal models of congenital hypothyroidism (CH), TH have shown a crucial function in craniofacial and eye development. In particular, corneal maturation, in term of light transmission and epithelial development, as well as retinal thickness and layering, have been related to TH levels. The aim of this study was to evaluate whether ocular parameters are different in 32 screened CH children than in 20 age- and sex-matched healthy controls. Material and methods CH highly selected patients, with preliminarily excluded negative interference of both treatment variables and other underlying risk factors, at a median age of 15.4 years, underwent the ophthalmologic examination including visual acuity assessment, refraction, ocular motility and slit lamp evaluation. The instrumental analysis comprised Pentacam (Oculus, Germany) to investigate mean corneal and anterior segment parameters and IOL Master (Zeiss, Germany) to measure the axial length. The main outcome measures considered for evaluation were: the corneal curvature (diopters), diameter (mm), central thickness (mm), corneal volume, anterior chamber depth (mm), corneal transparency and lens density (unitless), axial length (mm). Results Dividing CH population in subgroups according defect of organogenesis, we found that anterior chamber depth and volume as well as corneal diameter in left eyes were lower in eutopic gland subgroup then in ectopic gland one (p=0.03, p=0.04 and p=0.004 respectively). Analogous difference was demonstrated in right eyes although without a statistical significance. The lower gestational age of eutopic subgroup (p=0.001) can explain these results. In addition, we divided the study population according sex and refractive errors, pointing out: no statistical differences in biometric ocular parameters between myopic, hypermetropic and emmetropic patients; whereas CH female showed a shorter axial length and a higher corneal curvature value than male (p =0.014 and p<0.001 respectively), as expected considering the physiological gender difference. Finally, the correlation analysis revealed no statistically significant influence of timing of therapy onset, Levothyroxine dose and serum TSH at CH diagnosis for ocular parameters. Moreover, there was no statistically significant difference between CH group and controls in any of considered ocular parameters and in refractive errors frequency (χ²= 2.49 p=0.1147) Conclusion Early and adequate hormonal replacement therapy, is sufficient to guarantee a normal morphology ocular development in all its components (retina, cornea, lens) and function (i.e visual acuity) in CH children.