Changes in intraocular pressure and corneal and retinal nerve fiber layer thicknesses in hypothyroidism

PURPOSE. To evaluate the changes in intraocular pressure (IOP), corneal thickness (CT), and retinal nerve fiber layer thickness (RNFLT) in patients with hypothyroidism before and after treatment. METHODS. A complete ophthalmic examination including visual acuity, IOP, anterior segment, and fundus examination together with CT and RNFLT measurements were performed for each patient with newly diagnosed hypothyroidism, at the initial diagnosis and the third and ninth months of the L-thyroxine treatment. Wilcoxon signed rank test and Spearman's correlation test were used for statistical evaluation of the results. RESULTS. A total of 56 eyes of 28 patients were included in the study. The mean IOP and CT values were found to decrease with medical treatment (p = 0.000). There was no significant change in any of the RNFLT parameters measured with scanning laser polarimeter after L-thyroxine treatment (Wilcoxon, p > 0.05). The change in IOP levels was not correlated with the change in thyroid hormone levels (Spearman's correlation test, p > 0.05). The mean increase in serum free T₃ and serum free T₄ levels and the mean decrease in serum TSH levels at the ninth month of the therapy were found to be correlated with the decrease in CT in the left eyes (Spearman's correlation test, R > 0.4 and p < 0.05). CONCLUSIONS. Hypothyroidism seems to cause a reversible increase in CT and IOP. IOP changes may be secondary to CT changes. RNFLT parameters measured with scanning laser polarimeter do not seem to be affected by hypothyroidism. When the CT is taken into account and the IOPs corrected for CT, the prevalence of glaucoma in hypothyroidism may not be as high as previously reported. This issue should be taken into account while assessing glaucoma in patients with hypothyroidism.