Ocular anterior segment changes and corneal biomechanics in pregnancy

Abstract

In their recent article, Goldich et al.1 reported the potential ocular anterior segment changes during pregnancy. They examined 60 pregnant and 60 nonpregnant women with the aid of a dynamic bidirectional applanation device (Ocular Response Analyzer, Reichert Ophthalmic Instruments) and Scheimpflug imaging (Pentacam HR, Oculus Optikgeräte GmbH) and showed that pregnant women had significantly steeper keratometry (K) values and significantly lower Goldmann-correlated intraocular pressure (IOP) and cornea-compensated IOP than the control group. They did not observe between-group differences in corneal hysteresis (CH), corneal resistance factor (CRF), corneal posterior curvature, central corneal thickness and volume, anterior chamber depth and volume, or iridocorneal angle. Their results suggest that hormonal changes during pregnancy may lead to decreased IOP and increased corneal curvature. The authors also conclude that current available technology cannot determine whether there are pregnancy-induced changes in corneal biomechanics. We would like to highlight some aspects of the study that merit further attention. First, the authors did not include data about the participants’ stage of pregnancy. Did they examine women in the first, second, or third trimester? Or did they enroll pregnant women at different gestational stages? It is well established that pregnancy is associated with decreased IOP, increased corneal thickness, and higher K values than normal subjects.2–5 However, these changes occur particularly during the second and third trimesters, with increasing intensity as the pregnancy progresses.2–4 Based on the fact that hormonal changes during pregnancy vary significantly between the trimesters and considering that unexpected biomechanical changes during pregnancy, such as post-laser in situ keratomileusis ectasia or exacerbation of keratoconus, are mainly attributed to these hormonal influences,6,7 we believe that biomechanical evaluation of the cornea should be trimester related and always correlated to analytical hormonal screening of the patients. Therefore, in our opinion, comparative study of the 3 trimesters of pregnancy is essential to be able to extrapolate valid conclusions about the impact of pregnancy on corneal parameters. On the other hand, the authors use CH and CRF to evaluate the corneal biomechanical properties in both groups. Again, the presumable enrollment of pregnant women at different gestational stages may have severely influenced the results, masking the true impact of late-stage pregnancy on corneal biomechanics. Moreover, it is well known that CH and CRF are descriptive metrics that reflect a rough estimation of high-magnitude biomechanical changes, but they cannot depict more subtle biomechanical variations.6 In our opinion, sophisticated dynamic bidirectional applanation device signal analysis by evaluating fundamental dynamic bidirectional applanation device–derived parameters, which are more sensitive to small-scale biomechanical changes,8,9 is the key to unraveling the complex corneal biomechanical alterations during pregnancy.