Abstract
Purpose To analyze the association between hypothyroidism and keratoconus, we examined blood thyroid hormone levels and corneal tomographic parameters in healthy subjects and patients with keratoconus. Methods We included 626 subjects (304 left eyes, 49%; 431 males, 69%; age 38.4 ± 14.3 y). Patients with keratoconus were from our Homburg Keratoconus Center (HKC) (n = 463); patients with hypothyroidism were from the Department of Internal Medicine of Saarland Medical University, Homburg/Saar, Germany (n = 75); and healthy subjects were from the Department of Ophthalmology of Saarland University Medical Center (n = 88). We included only one randomly selected eye of each subject and the first examination data. Exclusion criteria Previous thyroid medication, previous ocular surgery, and patients with suspected keratoconus (topographic keratoconus classification, [TKC]: 0 < 1). Patient eyes were classified (TKC) with dedicated, instrument-based, keratoconus detection software provided with the Pentacam. TKC = 0 was considered “normal,” and TKCs ≥ 1 were considered keratoconus. Subjects were also classified as euthyroid or hypothyroid, based on blood thyroid hormone status (i.e., TSH, FT3, and FT4). A multiple logistic linear regression model was constructed to determine the effects of age (covariate), gender, and hypothyroidism (effect sizes) on “TKC-positive” disease. Results The significance levels for a constant parameter, sex, thyroid condition, and age were p < 0.0001, p < 0.0001, p < 0.0001, and p=0.003, respectively. The odds ratios for age, sex, and hypothyroidism were 0.98, 3.05, and 3.34, respectively. Male sex and a euthyroid condition had significantly positive, clinically relevant effects, and age had a significantly negative, but clinically irrelevant effect on the estimated TKC index. Conclusions Keratoconus appeared to occur more often in patients classified as euthyroid than in patients with hypothyroidism. Thus, hypothyroidism alone could not support the development of keratoconus. Based on these results, it should not be mandatory to screen patients with hypothyroidism for keratoconus or patients with keratoconus for hypothyroidism.
Highlights
Keratoconus is a bilateral, “noninflammatory” condition of the corneal tissue that causes progressive stromal thinning.is condition leads to a cone-shaped, central/paracentral, ectatic cornea
A multiple logistic linear regression model was constructed to determine the effects of age, gender, and hypothyroidism on TKCpositive disease. is model was tested with a receiver-operating characteristics (ROC) analysis, and the area under curve (AUC) was extracted as a general descriptor. e maximum Youden index value was used as the threshold for separating keratoconus from nonkeratoconus
Subjects classified as euthyroid or hypothyroid without keratoconus showed significant differences in the surface regularity index (SRI), measured with the TMS-5, the index of surface variance (ISV), the IVA, and the index of height decentration (IHD), measured with the Pentacam, and the keratoconus match index (KMI), measured with the ORA (p < 0.05 for all; Tables 2–4). e endothelial cell density was significantly different between subjects classified as euthyroid, without or with keratoconus (p < 0.05; Table 5)
Summary
Keratoconus is a bilateral, “noninflammatory” condition of the corneal tissue that causes progressive stromal thinning. E purpose of the present study was to analyze the association between hypothyroidism and keratoconus, by examining blood thyroid hormone levels, corneal topographic/tomographic parameters, and biomechanical parameters. Patients were considered euthyroid or hypothyroid, based on blood thyroid hormone levels. Subjects were examined with the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Buffalo, NY) to measure the biomechanical properties of the cornea, including the following parameters: keratoconus match index (KMI), corneal hysteresis (CH), and corneal resistance factor (CRF). Subjects were classified as euthyroid (n 458, 73%) or hypothyroid (n 168, 27%), based on blood thyroid hormone status (TSH, FT3, FT4). Of the total study population of 626 subjects, 465 (74%) had keratoconus, according to the TKC (Pentacam), and of these, 90 (19%) had hypothyroidism.
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