Selective deficits of S-cone in thyroid-associated ophthalmopathy patients without clinical signs of dysthyroid optic neuropathy

Abstract

Purpose: We explored whether thyroid-associated ophthalmopathy (TAO) patients without clinical signs of dysthyroid optic neuropathy (DON) would have a selective deficit mediated by S-cone.

Methods: Thirty-two TAO patients without clinical signs of DON (non-DON, 42.03 ± 9.59 years old) and 27 healthy controls (41.46 ± 6.72 years old) participated in this prospective, cross-sectional study. All observers were tested psychophysically after passing color screening tests and a comprehensive ocular examination. Isolated L-, M-, and S-cone contrast thresholds were measured at 0.5 cyc/deg using Gabor patches. We calculated the area under the receiver operating characteristic (ROC) curve to quantify the ability of chromatic contrast sensitivity to detect the early visual function changes in non-DON patients.

Results: S-cone contrast sensitivity in non-DON patients was found to be lower than that of healthy controls (P < 0.001), whereas the sensitivities to L- and M-cone Gabor patches were similar between these two groups (P = 0.297, 0.666, respectively). Our analysis of the ROC curve revealed that the sensitivity to S-cone had the highest index to discriminate non-DON patients from healthy controls (AUC = 0.846, P < 0.001). The deficit of S-cone was significantly correlated with muscle index in non-DON patients (R = 0.576, P = 0.001).

Conclusion: There is a selective S-cone deficit in the early stage of TAO. S-cone contrast sensitivity could serve as a sensitive measure of visual impairments associated with early DON in patients with TAO.

Keywords: S-cone; color vision; dysthyroid optic neuropathy; thyroid-associated ophthalmopathy; visual impairments.

FIGURE 1

Measurements were taken at the coronal CT scan halfway between the posterior globe and orbital apex. (A) Medial rectus muscle. (B) Lateral rectus muscle. (C) Orbital width. (D) Superior rectus/levator complex. (E) Inferior rectus muscle. (F) Orbital height. The horizontal muscle index = (A+B)/C. The vertical muscle index = (D+E)/F. The larger one of these two indexes was taken as final muscle index.

FIGURE 2

The fixation and L-, M-, and S-cone Gabors.

FIGURE 3

Contrast sensitivities to L- (A), M- (B), and S-cone (C) Gabors of the control and non-DON group.

FIGURE 4

Receiver operating characteristic analysis of the chromatic sensitivity in the TAO patients without clinical signs of DON.

FIGURE 5

Correlations between S-cone contrast sensitivity and clinical parameters in non-DON patients. Correlations between S-cone contrast sensitivity and muscle index (A), intraocular pressure (B), exophthalmometry (C), clinical activity score (D), free triiodothyronine (E) and free thyroxine (F).