A new cross-sectional study published in Translational Vision Science & Technology suggests that patients with inactive thyroid eye disease (TED) show diffuse stromal thinning across most corneal sectors—while epithelial thickness remains unchanged.
Let’s start with the basics: Why look at the cornea in TED?
TED is usually discussed in terms of its orbital signs, including proptosis, eyelid retraction and restricted eye movements.
However, these structural changes do not occur in isolation. As extraocular muscles enlarge and orbital tissues expand, the position of the globe can shift, blink mechanics may change and the ocular surface environment can become less stable.
Over time, those alterations raise an important question about whether the cornea itself undergoes measurable structural changes.
Now to some background on this …
Previous research examining central corneal thickness (CCT) in patients with thyroid dysfunction or TED has produced mixed results—with some studies suggesting temporary thickening, particularly in hypothyroid states, and others finding no meaningful differences compared with controls. A few reports have also indicated thinning.
But what has remained unclear is whether any change primarily affects the epithelium or the stroma and whether it occurs in a focal area or follows a broader sectoral pattern.
Which brings us to the study in question?
Indeed. This study sought to address those uncertainties by evaluating both layer-specific and sector-specific corneal thickness in patients with inactive TED.
What did the researchers evaluate?
The investigators conducted a retrospective cross-sectional study at a tertiary medical center in Taiwan, analyzing 75 eyes from 38 participants. The cohort included 29 patients with inactive TED and nine healthy controls.
- All TED participants had a clinical activity score (CAS) of 2 or less at the time of imaging, indicating stable disease.
Talk about the evaluations.
Each participant underwent a comprehensive ophthalmic examination in addition to corneal imaging with topography and spectral-domain optical coherence tomography (SD-OCT).
The researchers measured total corneal thickness (CT), epithelial thickness (ET), and stromal thickness (ST) across a 9 mm corneal map divided into 25 sectors.
- This approach allowed them to examine not only central thickness but also regional variations across the cornea.
To ensure that any differences were attributable to disease status rather than demographic variation, the analysis incorporated a mixed-effects statistical model and adjusted for age and sex.
Who was included?
The study population consisted of 25 women and 13 men, with 57 eyes in the TED group and 18 eyes in the control group. Age and sex were comparable between groups, and there were no statistically significant demographic differences.
The investigators applied strict inclusion and exclusion criteria to limit confounding variables. Patients with active inflammation, prior ocular surgery, trauma, contact lens wear or corneal abnormalities suggestive of keratoconus were excluded.
- To note: Although many patients with TED had dry eye disease, they were only included if their condition was managed with artificial tears.
By focusing on inactive disease and high-quality imaging, the authors aimed to isolate structural corneal differences associated specifically with TED.
So what did they find?
The most consistent and clinically relevant finding was diffuse stromal thinning in the TED group.
Across nearly all evaluated sectors, total CT and corneal ST were significantly lower in patients with inactive TED compared with controls.
- For example, central ST averaged 480.33 µm in the TED group compared with 498.94 µm in controls.
Similar reductions were observed in the superior, nasal, inferior and inferotemporal sectors. The temporal region did not reach statistical significance, although a thinning trend was still present.
And how did this compare to epithelial thickness?
In contrast, ET remained comparable between groups in all sectors.
- Because the reduction in total thickness closely paralleled the reduction in ST, the data support the conclusion that the structural change primarily involved the stromal layer rather than the epithelium.
What else to consider?
Corneal topographic indices related to irregularity were numerically higher in the TED group but remained within normal limits and did not reach statistical significance.
What this means: The cornea appeared thinner without demonstrating overt ectatic changes or abnormal surface patterns.
- Importantly, the differences in ST and total thickness persisted even after adjusting for age and sex—reinforcing that the association appears disease-specific.
How was the thinning distributed?
The pattern of thinning was diffuse rather than focal and followed the normal sectoral distribution pattern seen in healthy corneas.
In both groups, thickness gradually decreased from the superior sectors toward the inferotemporal and temporal regions, with a relative increase in the superotemporal sector.
While this overall distribution pattern was similar between groups, the absolute thickness values were consistently lower in the TED eyes across most sectors.
Go on …
ET followed its own distribution profile and did not significantly differ between groups.
In both cohorts, the superior epithelium tended to be thinner than inferior regions—a finding that has been attributed in previous literature to eyelid-induced mechanical forces during blinking rather than disease-related remodeling.
Any limitations to consider when interpreting the data?
Several …
- The control group was relatively small, consisting of only nine individuals, which may limit generalizability despite strict matching and quality control measures
- Because only patients with inactive TED were included, the findings may not reflect corneal changes during active inflammatory phases
- The cross-sectional design also prevented conclusions about progression over time
Additionally, many patients with TED had coexisting DED, which could influence CT measurements (even though it was managed with artificial tears).
And lastly: Two different imaging platforms were used for pachymetry and topography, although the authors reported consistent trends across modalities.
So why does this matter clinically?
These findings suggest that inactive TED may be associated with subtle but measurable stromal remodeling, even when the anterior corneal surface appears topographically normal.
For clinicians: This has potential implications when interpreting pachymetry values, assessing corneal biomechanics, or evaluating candidacy for anterior segment procedures.
- A thinner stroma in the absence of obvious surface irregularity may influence risk assessment in certain surgical contexts and underscores the value of layer-specific imaging rather than relying solely on total thickness or topographic appearance.
Take home.
In patients with inactive TED, corneal thinning appears to be diffuse and primarily confined to the stromal layer, while epithelial thickness remains stable and surface indices remain within normal limits.
Layer-specific corneal assessment may therefore offer additional insight when managing and monitoring individuals with TED.