What Awaits Surgeons In The Evaluation Of Hypothyroid Refractive Surgery Candidates?

Hypothyroidism is a common worldwide health problem and its incidence has increased over the last few decades. As the effect of hypothyroidism on the cornea is controversial, the aim of this study was to investigate the effects of hypothyroid and euthyroid states of the same participants on corneal topographic, topometric, and tomographic features.

Ulucanlar Eye Training and Research Hospital

Fifty eyes of newly diagnosed 25 hypothyroid patients (19 female, 6 male) with clinically clear corneas were enrolled in this study. Participants who had no ocular disorder and no systemic disease, except for hypothyroidism, were included. Topographic, topometric, and tomographic analyses via Scheimpflug corneal topography (Pentacam®HR, Wetzlar, Germany) were performed at the time of hypothyroidism diagnosis and after appropriate thyroid replacement therapy which provides the euthyroid phase. Three consecutive measurements were performed in each visit, and the mean values of measurements were used for statistical analysis. Wilcoxon signed-rank test was used to detect differences between hypothyroid and euthyroid states.

Flat (K1) and mean (Kmean) keratometry readings of the anterior surface of the cornea were significantly higher in the euthyroid state than in the hypothyroid state (p < 0.001 and p = 0.013). After euthyroidism was provided, mean central corneal thickness (CCT) and thinnest pachymetry (CTmin) values significantly decreased by 5.5 and 5.3 µm, respectively (p < 0.001, for all). Lower corneal volume, total corneal densitometry, and spherical aberration measurements were detected in the euthyroid state (p < 0.05, for all). The average (PPIavg) and maximal progression index (PPImax) increased in the euthyroidism phase compared to the hypothyroidism phase, while maximum Ambrόsio relational thickness (ARTmax) decreased (p < 0.001, for all).

The results of this study, including increased CCT, CTmin, and corneal volume and densitometry in the hypothyroid state, indicate that subtle corneal edema may occur in patients with hypothyroidism. Moreover, the evaluation of a hypothyroid patient with corneal imaging devices may cause to underestimate the risk of keratoconus and overestimate optic aberrations. Hence, thyroid function tests should be performed before corneal refractive surgery to detect actual ectasia risk and precise residual corneal thickness.