Thyroid hormones and vitamin A in the retina shape foetal vision

The development of vision begins long before a baby opens its eyes. During pregnancy, a complex series of biological processes carefully shapes the formation of the retina—the light-sensitive tissue at the back of the eye. Recent scientific findings suggest that Vitamin A and thyroid hormones play a critical and coordinated role in guiding this early visual development, influencing how fetal vision is formed even before birth.

The retina contains specialised cells called photoreceptors, which detect light and send signals to the brain. These photoreceptors are divided into rods, responsible for vision in low light, and cones, which enable colour perception and sharp central vision. The proper formation and differentiation of these cells are essential for healthy eyesight later in life.

Vitamin A is fundamental to eye development. In the body, it is converted into a molecule called retinoic acid, which acts as a signalling compound. Retinoic acid regulates gene expression, instructing developing retinal cells on how and when to mature. Without adequate Vitamin A, photoreceptors may not form correctly, potentially leading to long-term visual impairments. Severe deficiency during pregnancy has been linked to developmental abnormalities affecting the eyes and other organs.

At the same time, thyroid hormones—particularly thyroxine (T4) and triiodothyronine (T3)—are crucial regulators of growth and neurological development. These hormones influence the timing of retinal cell differentiation and the balance between rods and cones. Research suggests that thyroid hormones help determine which type of cone photoreceptor develops, thereby influencing colour vision capacity.

Scientists have discovered that Vitamin A and thyroid hormones interact within the retina in a finely tuned process. Retinoic acid helps establish early retinal structure, while thyroid hormones guide later stages of photoreceptor specialisation. If thyroid hormone levels are too high or too low during pregnancy, this delicate balance may be disrupted, potentially affecting the organisation and function of the retina.

The fetal thyroid gland begins functioning during the second trimester, but in early pregnancy, the fetus relies entirely on maternal thyroid hormones supplied through the placenta. This makes maternal health and nutrition especially important. Thyroid disorders in pregnancy, if untreated, can impact not only brain development but also the visual system.

These findings underscore the importance of adequate maternal nutrition and hormonal balance during pregnancy. Vitamin A is found in foods such as carrots, sweet potatoes, spinach, eggs, and dairy products. However, excessive Vitamin A intake—particularly from supplements—can be harmful during pregnancy, highlighting the need for careful medical guidance. Similarly, thyroid hormone levels should be monitored in expectant mothers, especially those with a history of thyroid disease.

Understanding how these biological factors shape fetal vision offers valuable insight into congenital eye disorders and may open new avenues for early intervention. Researchers hope that further studies will clarify how disruptions in Vitamin A metabolism or thyroid hormone signalling could be linked to vision problems later in life.

In conclusion, the development of sight begins in the womb, guided by an intricate interplay between Vitamin A and thyroid hormones in the retina. Their coordinated action ensures that photoreceptors form correctly, laying the foundation for healthy vision. Supporting maternal health remains a key factor in safeguarding a child’s visual future.