Thyroid Eye Disease Structural Changes Precede Functional Changes

Patients with thyroid eye disease (TED) and dysthyroid optic neuropathy (DON) may experience retinal nerve fiber layer (RNFL) and ganglion cell layer/ inner plexiform layer (GCL/IPL) thinning before and after orbital decompression surgery, according to research published in Eye. These finding indicate that structural damage might occur before functional impairment in patients with TED.

Researchers enrolled 60 patients with TED (eyes, 105; 38 women) and stratified them according to severity. Among the cohort, 9 patients had mild TED (18 eyes), 24 had moderate to severe TED (43 eyes), and 27 had DON (44 eyes). All patients underwent optical coherence tomography (OCT) imaging, visual field analysis, and best corrected visual acuity measurement. A subset of eyes underwent deep lateral wall decompression surgical intervention.

Among patients with moderate to severe TED and participants with DON, 29 and 34 eyes underwent decompression surgery, respectively. In participants with moderate to severe TED, significant reductions in GCL/IPL thickness and superior nasal, inferior, inferior temporal GCL/IPL thicknesses and proptosis thickness were observed (all P ≤.03) at postoperative follow-up (mean, 3.9 months). 

Individuals with DON experienced significant GCL/IPL thickness reductions (all regions P ≤.019) except in the inferior temporal region at post surgical follow-up (mean, 2.6 months). They also experienced RNFL thinning (all regions P ≤.048), proptosis thinning (21.7±2.3 to 17.3±2.2 mm; P <.001), visual acuity improvement (0.44±0.38 to 0.26±0.3 logarithm of the minimum angle of resolution [logMAR]; P <.001), intraocular pressure (IOP) decrease (18.9±5.1 to 17.6±4.3 mmHg; P =.012), and increased mean deviation (-11.1±8.3 to -5.9±6.5 dB; P <.001).

In eyes with DON, 17 had optic disc swelling, 6 had optic disc atrophy, and 11 had normal appearing optic discs. All of these eyes experienced significant reductions in mean GCL/IPL thickness (all P ≤.03) and both eyes with swelling and normal optic discs had significant reductions in mean RNFL thickness (both P ≤.02).

Among eyes that did not undergo decompression surgery, no significant changes were observed in the mild (n=18) or moderate to severe (n=14) cohorts at follow-up (3.3-4.9 months). Eyes with DON (n=10) experienced significant reductions in mean GCL/IPL thickness (P =.04), particularly in the superior (P =.027), superior temporal (P =.022), and inferior temporal (P =.029) GCL/IPL regions. RNFL thickness tended to increase in eyes with DON that did not undergo surgical intervention, but this value failed to achieve statistical significance.

“[F]or eyes with DON, [retinal ganglion cell] damage may be progressive before surgery, although changes in visual function are not obvious,” according to the researchers. “In addition, the decreased swelling and persistent degeneration in [retinal ganglion cells] may continue for a relatively long period of time after orbital decompression surgery.”

Study limitations include a small sample size and short follow-up duration.

Reference

Guo J, Ma R, Gan L, et al. Changes in retinal nerve fibre layer, ganglion cell layer and visual function in eyes with thyroid eye disease of different severities with and without orbital decompression. Eye. Published online July 28, 2022. doi:10.1038/s41433-022-02142-y