Association Between Keratoconus and Thyroid Gland Dysfunction: A Cross-Sectional Case–Control Study

Abstract

K eratoconus is a corneal ectatic disorder that starts at puberty and decreases the radius of curvature of the central cornea. 1 Kennedy et al. 2 reported that the incidence rate is 1 per 50,000 among the population. Moreover, the pathophysiological processes underlying keratoconus have not been fully explained and proposed mechanisms including oxidative dam-age, proteolytic degradation in the corneal stroma, epithelial mechanical injury, immunological factors, and genetic factors have been suggested. [1][2][3][4] reported an incidence of keratoconus in 3.5% to 8% of patients with Down syndrome. Furthermore, hormonal imbalances affect the corneal metabolism and may be associated with keratoconus. Likewise, thyroid gland ABSTRACT PURPOSE: To examine the clinical association between thyroid gland dysfunction and keratoconus. METHODS:This was a cross-sectional case-control study conducted between May 2018 and July 2019. After performing Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) examination, flat, steep, and maximum simulated keratometric readings were recorded for each patient. Serum concentrations of free triiodothyronine, free thyroxine, and thyroidstimulating hormone were measured. Further examinations by an endocrinologist were indicated for patients with positive laboratory results to confirm thyroid gland dysfunction. RESULTS:One hundred eighty-seven patients with bilateral keratoconus and 187 sex-and age-matched healthy controls without keratoconus were analyzed. Mean age was 26.4 ± 8.2 years for the patients with keratoconus and 27.1 ± 9.4 years for the control patients, with no significant difference. The results showed that thyroid gland dysfunction prevalence was 10 of 187 patients with keratoconus (5.3%) and 2 of 187 control patients (1.1%), and the difference was statistically significant (P = .036). For the patients with keratoconus and thyroid gland dysfunction, 8 were women and 2 were men. Additionally, 6 patients (2 men and 4 women) had hyperthyrosis and 4 women had hypothyrosis. For controls, the two patients had hypothyrosis. CONCLUSIONS:This study showed that there is a possible association between keratoconus and thyroid gland dysfunction, but more studies are needed to build upon these results.[J Refract Surg. 2020;36(4):253-257.] (AT). © 2020 El-Massry, Doheim, Iqbal, et al.; licensee SLACK Incorporated. This is an Open Access article distributed under the terms of the Creative Commons . This license allows users to copy and distribute, to remix, transform, and build upon the article non-commercially, provided the author is attributed and the new work is non-commercial.

Is keratoconus associated to thyroid diseases? Assessment of the corneal parameters in patients with congenital hypothyroidism

“…Some authors reported that hypothyroidism might be associated with corneal ectasia and could be one of the casual factors, but the recent studies on the association between thyroid gland dysfunction and KC reported conflicting results. 15–20,26,27…”

“…Likewise, Alhawari et al 19 did not find statistically significant association between autoimmune thyroiditis and keratoconus. Recently El-Massry et al 20 conducted a cross-sectional case-control study including 187 patients with keratoconus without previously diagnosed thyroid gland dysfunction and 187 healthy controls. The authors showed significant difference between prevalence of thyroid gland dysfunction in the KC group (5.35%) as compared to the control (1.1%) and hypothized a possible association between KC and thyroid disease.…”

“…9,10 Only few reports focused on the possible role of the thyroid gland dysfunction in the pathogenesis of keratoconus and the actual knowledge about the association between keratoconus and thyroid diseases remains poor and controversial. 15–20…”

Nutritional and Metabolic Imbalance in Keratoconus

“…The contribution of thyroid hormones is still under scrutiny. Some studies have reported a higher thyroid gland dysfunction prevalence among KC patients [72,73], but others failed to prove an association between them [74][75][76]. Nevertheless, increased levels of thyroxine hormone (T4) were found in tears [72,77] and aqueous humor [78].…”

The Role of Biomarkers in Keratoconus Pathogenesis and Diagnosis

“…Hormonal changes in the body are known to influence KC pathogenesis and progression. Thyroid related disease and other hormonal disorders can be associated with KC [47]. Hormonal changes during pregnancy can lead to biomechanical changes in the cornea and progression of keratoconus [48].…”