Department of Ophthalmology, Semmelweis University, Budapest, Hungary.
Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary.
Invest Ophthalmol Vis Sci. 2021 May 3;62(6):20. doi: 10.1167/iovs.62.6.20.
In diabetic subjects, early visual functional alterations such as color vision deficiencies (CVDs) are known to precede clinically apparent diabetic retinopathy. Prominent photoreceptor outer segment degeneration and an increase in the number of retinal dual cones (co-expressing S- and M-opsins simultaneously) have been described in diabetic rat models, suggesting a connection with the development of CVDs. As cone opsin expression is controlled by thyroid hormones, we investigated the diabetic retina in association with thyroid hormone alterations.
In rat models of type 1 and 2 diabetes, dual cones were labeled by immunohistochemistry, and their numbers were analyzed in relation to free triiodothyronine (fT3) and free thyroxine (fT4) levels. Quantification of dual cones was also performed in human postmortem retinas. Additionally, a cross-sectional case-control study was performed where thyroid hormone levels were measured and color vision was assessed with Lanthony desaturated D15 discs.
A higher number of dual cones was detectable in diabetic rats, correlating with fT4 levels. Dual cones were also present in postmortem human retinas, with higher numbers in the three diabetic retinas. As expected, age was strongly associated with CVDs in human patients, and the presence of diabetes also increased the risk. However, the current study failed to detect any effect of thyroid hormones on the development of CVDs.
Our results point toward the involvement of thyroid homeostasis in the opsin expression changes in diabetic rats and human samples. The evaluation of the possible clinical consequences warrants further research.
在糖尿病患者中，众所周知，早期视觉功能改变，如色觉缺陷（CVDs），先于临床明显的糖尿病视网膜病变。在糖尿病大鼠模型中，已经描述了明显的光感受器外节变性和视网膜双锥体（同时表达 S 和 M 视蛋白）数量增加，这表明与 CVDs 的发展有关。由于锥体视蛋白的表达受甲状腺激素控制，我们研究了与甲状腺激素改变相关的糖尿病视网膜。
在 1 型和 2 型糖尿病大鼠模型中，通过免疫组织化学标记双锥体，并分析其数量与游离三碘甲状腺原氨酸（fT3）和游离甲状腺素（fT4）水平的关系。还在人死后视网膜中进行了双锥体的定量分析。此外，进行了一项横断面病例对照研究，测量甲状腺激素水平，并使用 Lanthony 去饱和 D15 圆盘评估色觉。
在糖尿病大鼠中可以检测到更多的双锥体，与 fT4 水平相关。在人死后的视网膜中也存在双锥体，在三个糖尿病视网膜中数量更高。正如预期的那样，年龄与人患者的 CVDs 强烈相关，而糖尿病的存在也增加了风险。然而，本研究未能检测到甲状腺激素对 CVDs 发展的任何影响。
我们的结果表明，甲状腺动态平衡参与了糖尿病大鼠和人样本中视蛋白表达变化。评估可能的临床后果需要进一步研究。
