Assessment of corneal topographical and endothelial cell parameters in hypothyroidism before and after thyroid replacement therapy.

Clinical relevance: Hypothyroidism is a common endocrine disorder that can influence various physiological processes throughout the human body.

Background: Despite its clinical significance, there is a notable gap in directly comparing corneal characteristics between hypothyroid and euthyroid individuals within the same study cohort. This study aimed to explore the impact of hypothyroid and euthyroid states in the same participants on corneal topometry, tomography, densitometry, and aberrometry parameters.

Methods: Thirty eyes from 30 newly diagnosed hypothyroid patients with clinically clear corneas were enrolled in this study. Corneal parameter analyses using Scheimpflug corneal topography (Pentacam®HR, Wetzlar, Germany) and specular microscopy (EM-4000; Tomey Corp. Nagoya, Japan) were performed at the time of hypothyroidism diagnosis and after thyroid replacement therapy.

Results: The flat and mean keratometric 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 = 0.002). After euthyroidism was provided, mean central corneal thickness and thinnest pachymetry values significantly decreased by 4.5 µm and 5.2 µm, respectively (p = 0.003 and p = 0.001). Significantly lower corneal densitometry values were detected in the euthyroid state (p < 0.05). Although there was no difference in pupil diameter, spherical aberration measurements were significantly higher at the time of diagnosis than during the euthyroidism period (p = 0.001). Average and maximal progression index significantly increased in the euthyroidism phase compared to the hypothyroidism phase, while maximum Ambrόsio relational thickness decreased (p < 0.05). The endothelial characteristics were statistically similar (p > 0.05).

Conclusion: The study suggests that patients with hypothyroidism may experience subtle corneal changes. The evaluation of a hypothyroid patient with corneal imaging devices may underestimate the risk of keratoconus and overestimate optic aberrations.