Normative Computed Tomography Values Identified, May Help in Thyroid Eye Disease Treatment

Interzygomatic distance (IZD) is associated with anterior globe position, axial globe length, and axial globe width, according to research published in the Canadian Journal of Ophthalmology. Understanding the correlation between these computed tomography (CT) values may help to diagnose radiologic exophthalmos or enophthalmos or measure treatment response in patients with thyroid eye disease (TED).

Researchers included 201 patients (mean age 53±20 years, 45% men) with suspected unilateral orbital disease in the analysis. They performed a series of CT measurements and assessed them for reliability and reproducibility.  

The team determined normal CT values for interzygomatic distance (IZD) (97.4±4.1 mm), anterior globe position (18.8±2.8 mm), posterior globe position, (6.2±2.9), axial globe length (24.9±1.1 mm), and axial globe width (25.9±1.2 mm). 

Investigators noted associations between IZD and anterior globe position (r=0.15; P =.03), axial globe length (r=0.33; P <.01), and axial globe width (r=0.30; P <.01). They also noted a correlation between axial globe length and posterior globe position (r=0.20; P <.01). Men tended to have larger IZD, anterior globe position value, and axial globe length and width compared with women (P <.05 for all).

Inter- and intra-observer reliability for most CT measurements were excellent, according to the report (ICC>0.90) with good agreement for axial length (ICC=0.65) and width (ICC=0.70). 

The researchers report higher normal globe position values compared with those seen in prior CT studies and caution that clinicians should be aware that longer axial globe length may indicate myopia without indicating true proptosis.

“The degree of proptosis is an important clinical sign that is used to monitor treatment response in patients with TED,” according to the investigators. The team stresses the importance of CT in identifying disease progression and states that CT “is unaffected by overlying soft tissue swelling and allows for a more accurate assessment of the degree of proptosis from the bony margins.”

The study is limited by the disproportionate number of individuals self-reporting as White in the study sample.

Reference

Rana K, Juniat V, Yong W, et al. Normative globe position values on orbital computed tomography in Australians. Can J Ophthalmol. Published online May 28, 2022. doi:10.1016/j.jcjo.2022.05.004

This article originally appeared on Optometry Advisor