The Rainbow Brow in Thyroid Eye Disease

Abstract

Purpose : To describe a novel physical exam finding in thyroid eye disease (TED) – the “Rainbow Brow (RB)” – and quantify the finding mathematically

Methods : Eyebrows of subjects with TED and controls were analazyed, and the presence of RB appearance was determined by unanimous agreement of 3 oculoplastic surgeons. Eyebrow curvature was assessed by plotting 15 points along the eyebrow (figure 1A). The quadrinomial was fitted to each eyebrow in Excel.¹ Mann-Whitney U analysis was performed on the five coefficients (a, b, c, d, & e) of the quadrinomial in the form ax⁴+bx³+cx²+dx+e to evaluate for a difference in brow curvature. TED eyes with RB appearance were compared to age-sex-matched normal controls and other TED eyes without RB appearance. Univariable and multivariable logistic regression were performed to evaluate anatomical features that predicted RB appearance in TED eyes.

Results : A total of 271 eyes were analyzed (200 TED and 71 control). The majority of TED patients were female (82.5%) with a mean age of 53 ± 16 years. A Rainbow Brow was identified in 42% of TED patients, with 13% of TED patients having only unilateral RB appearance. Mann-Whitney U analysis of the quadrinomial coefficients yielded significant differences between RB eyes and controls for the coefficients a (p = 0.034), b (p = 0.003), c (p = 0.001), and d (p = 0.000). Similar analysis between TED eyes with and without RB appearance showed differences in coefficients a (p = 0.034) and b (p = 0.041). Features that were found to increase the odds of RB appearance included age greater than 50 (OR 2.307, p = 0.009, 95% CI 1.229 – 4.328) and the presence of brow fat expansion (OR 3.555, p = 0.000, 95% CI 1.935 – 6.529). When considering the contribution of these features in a multivariable analysis, only the brow fat expansion was a statistically significant contributing factor for RB appearance (p = 0.009).

Conclusions : The Rainbow Brow is a distinct entity in TED and is likely a consequence of the expansion of the brow fat pad. Eyes with RB have a statistically significant difference in eyebrow curvature compared to those of TED without RB and controls.

This is a 2021 ARVO Annual Meeting abstract.

 

(A) Right Rainbow Brow eye traced with fifteen points. (B) Fifteen-point brow curvature fitted with quadrinomial, y-2.96E-09x⁴ + 9.51E-09x³ + 1.08E-02x² + 5.88x + 814.65

 

Quadrinomial coefficients delineating eyebrow architecture in Rainbow Brow TED eyes, age-sex-matched controls, and non- Rainbow Brow TED eyes