The Arched Rainbow Brow in Thyroid Eye Disease

To morphologically describe and mathematically quantify a novel clinical feature of thyroid eye disease (TED).

A retrospective study was conducted of TED patients and age-sex-matched normal controls. The arched Rainbow Brow appearance in TED patients was determined by unanimous agreement of 3 oculoplastic surgeons. Eyebrow curvature was assessed by plotting 15 points along the eyebrow in ImageJ. The fourth-degree polynomial ( y = ax4 + bx3 + cx2 + dx + e ) was fitted to each eyebrow.

Two hundred seventy-one eyes were analyzed (200 TED and 71 age-sex-matched normal controls). A Rainbow Brow was identified in 42% of TED patients. A unilateral Rainbow Brow was seen in 15% of patients. The fourth-degree polynomial coefficients yielded significant differences between Rainbow Brow patients and age-sex-matched normal controls for the coefficients a, b, c , and d . Similar analysis of TED patients with and without a Rainbow Brow showed differences in coefficients a and b . Age >50 years ( p = 0.009) and the presence of brow fat expansion ( p < 0.001) were associated with the presence of a Rainbow Brow. Proptosis >24 mm showed a trend toward association with the presence of a Rainbow Brow ( p = 0.057). When considering the contribution of these features in a multivariable analysis, only brow fat expansion was a significant contributing factor ( p = 0.009).

The Rainbow Brow is a distinct entity in TED and is likely consequent to brow fat pad expansion. Patients with a Rainbow Brow have different eyebrow curvature as compared to both normal age-sex-matched controls and TED patients without a Rainbow Brow.