In pregnancy, very large changes in hormone concentrations take place, with the two most important being oestrogen and thyroid hormone.
The female sex hormone estrogen is produced in pregnancy in much higher concentrations – and also leads to changes in the cornea, in particular, in the seventh and eighth month of pregnancy, when the concentration of this hormone in the blood increases 40,000-fold.
Estrogen prepares the female body for childbirth by softening connective tissue. Of course, this is very important for the birth process… but it also results in a softer cornea and this can massively increase a pre-existing keratoconus.
This research area is new and there are not yet many scientific publications on the subject. Some of the key publications come from our research group.
One of the first scientific descriptions ever was by our group in 2013, published in the Journal of Cataract and Refractive Surgery. In one woman with a keratoconus in her first pregnancy, we observed in one eye, temporary, and in the other eye, lasting changes – that even increased during the woman’s second pregnancy.
Thyroid hormone also seems to play an important role in the mechanics of the cornea. It has been known for years that the risk of corneal disease increases when, for example, the thyroid gland has to be removed for a disease such as Hashimoto’s thyroiditis. But it has only been in recent years, that the evidence that thyroid hormone clearly affects the biomechanics of the cornea have truly become apparent.
Thyroid hormone is naturally reduced during pregnancy. At the University of Geneva from 2012 to 2014, Professor Hafezi a large-scale study where pregnant women were regularly examined throughout the pregnancy and in the first six months after birth. The researchers examined the hormone concentrations of oestrogen and thyroid hormone and compared and correlated these hormone levels with measurements made of the cornea during this time. The results appeared in the American Journal of Ophthalmology at the end of 2017 and clearly showed a clear link between hyperthyroidism and the cornea.