Corneal Topographic Characteristics in TED Show Similarity to Keratoconus

Corneal topographic characteristics between patients with thyroid eye disease (TED) and keratoconus have some similarities, according to research published in Contact Lens and Anterior Eye. TED-associated changes, which include increased anterior corneal astigmatism in the oblique axis, may allow clinicians to diagnose the disease early, the report suggests. 

Researchers included patients with TED (n=26; mean age, 52.06 years; 22 women) and age- and sex-matched control group individuals (n=20; mean age, 54.86 years; 16 women) in a cross-sectional investigation performed between January and December 2021. Study participants underwent ophthalmic examinations, corneal topography using a dual Scheimpflug camera, and thyroid function assessments. The investigators compared corneal topographic characteristics and examined differences in the cross-sectional area of the inferior and medial rectus muscles between the 2 cohorts. 

The research team noted significant variations in corneal topographic characteristics between participants with TED and individuals in the control group, including differences in central corneal thickness (537.85 vs 559.77 µm; P =.002), irregular astigmatism index (0.49 vs 0.46 diopters [D]; P  =.005), inferior-superior index (1.62 vs 0.99 D; P =.006), keratoconus prediction index (12.66% vs 5.37%; P =.003), keratoconus probability (21.54% vs 7.41%; P =.002), opposite sector index (1.69 vs 1.24 D; P =.015), surface asymmetry index (1.08 vs 0.79 D; P =.002), surface regularity index (0.96 vs 0.83 D; P =.003), and simulated keratometry astigmatism (1.11 vs 1.48 D; P =.04). 

Eyes with TED also demonstrated more variations in anterior instantaneous astigmatism axis compared with eyes in the control group (80.06° vs 94.38°; P =.03) and distribution was more scattered among participants with TED. This reveals more astigmatism outside of the regular axis in participants with TED.

These corneal topographic characteristic changes may identify early TED, according to the report. 

A subgroup analysis of patients with TED who had hyperthyroidism (eyes, 25), hypothyroidism (eyes, 10), and euthyroidism (eyes, 17), revealed no significant difference in corneal topographic characteristics between TED subtypes.

“According to the findings of this study, TED shares some corneal topographic changes with keratoconus …” according to the researchers. “Therefore, clinically differentiating TED from keratoconus is crucial as the treatments and etiology are completely different.”

Study limitations include a small sample size, single center design, and potential confounding due to the inclusion of patients with dry eye symptoms.