Elsevier

Ophthalmology

Volume 119, Issue 10, October 2012, Pages 2174-2178
Ophthalmology

Original article
Quantitative Computed Tomographic Predictors of Compressive Optic Neuropathy in Patients with Thyroid Orbitopathy: A Volumetric Analysis

https://doi.org/10.1016/j.ophtha.2012.04.021Get rights and content

Purpose

To evaluate the relationship between orbital bony geometry and the volume of the intraorbital structures in predicting compressive dysthyroid optic neuropathy (DON).

Design

Retrospective, consecutive case series.

Participants

Images of 198 orbits from 99 patients suffering from thyroid-related orbitopathy were reviewed.

Methods

Clinical examination and computed tomography of the orbits, including volumetric analysis, were performed on all patients.

Main Outcome Measures

Clinical and radiologic predictors of DON.

Results

Significant volumetric univariate predictors of compressive optic neuropathy included medial rectus volume (P = 0.005), lateral rectus volume (P = 0.011), superior muscle group volume (P = 0.04), and total rectus muscle volume (P = 0.015). Inferior rectus muscle volume, orbital volume, bony orbital apex angle, globe diameter, and bony medial wall contour were not associated with optic neuropathy. Multivariate modeling found medial rectus volume the only independently significant predictor. Univariate modeling of simple rectus diameter measurements found medial rectus axial diameter (P = 0.003) and total recti diameter (P = 0.016) predictive of optic neuropathy. Lateral rectus, superior rectus, and inferior rectus diameters were not predictive. Multivariate modeling found only medial rectus diameter to be a significant independent predictor of optic neuropathy. The area under the receiver operating characteristic curve was not different between the volumetric and rectus diameter curves.

Conclusions

Medial rectus size was found to be the most important quantifiable predictor of compressive optic neuropathy in patients with optic neuropathy. In this study, simple maximum medial rectus diameter, as measured on axial scans, was equally predictive of compressive optic neuropathy as the more involved volumetric calculation. Assessment of orbital geometry, including bowing of the medial wall, orbital apex angle, globe diameter, and orbital volume, were not found to be predictive of DON.

Financial Disclosure(s)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Section snippets

Methods

A detailed description of the methodology and analysis has previously been published.6 Institutional ethics approval was obtained. In short, a consecutive series of patients evaluated at the University of British Columbia orbit clinic by 1 surgeon (J.R.) were enrolled. Subjects were evaluated using the VISA8 system and required an orbital CT with true axial and either true or coronal reconstructs. The VISA clinical examination scheme evaluates 4 categories: (1) visual function, (2)

Results

Images of 198 orbits from 99 patients were evaluated. Basic demographics are presented in Table 1. The mean exophthalmometry measurement was 20.3 (standard deviation [SD], 4.2) and inflammatory score was 2.1 out of 8 (SD, 1.8), with 15% having “active” disease (VISA inflammatory score ≥3). Nine percent were diagnosed with DON. The mean VISA inflammatory score for orbits with DON was 3.43 (SD, 1.81) and 1.75 (SD, 1.90) for those without DON.

Significant volumetric univariate predictors of DON

Discussion

Because patients can develop DON after their clinical evaluation, and certain patients present with an equivocal diagnosis of DON, a constellation of findings have been developed to aid the physician in defining the “at-risk” patient. Our prior research has shown that careful evaluation and documentation of extraocular motility measurement, ptosis evaluation as measured by marginal reflex distance, and assessment of effacement of the perineural fat at the orbital apex, as measured on coronal CT

References (11)

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Manuscript no. 2011-1494.

Financial Disclosure(s): The authors have no proprietary or commercial interest in any of the materials discussed in this article.

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