Validity of Barrett’s Index in diagnosing dysthyroid optic neuropathy in a United Kingdom population
Author: Edward Rule
Base Hospital / Institution: University Hospital of Wales
ePoster presentation
Abstract ID: 25-258
Purpose
Barrett’s Index (BI) is a radiological measurement of the size of the extraocular muscles (EOM) as a percentage of the height or width of the orbit. We aimed to evaluate the clinical usefulness of BI in diagnosing dysthyroid optic neuropathy (DON) in a United Kingdom population, and to assess EOM diameter changes and clinical signs of DON in thyroid eye disease (TED).
Methods
This retrospective case-control study was conducted at a UK tertiary ophthalmology centre. Medical records and imaging from TED patients from 2003 to 2024 were reviewed. Cases (DON) and controls (TED without DON) were identified based on clinical criteria. A masked ophthalmologist and radiologist measured BI and maximum EOM diameters on CT and MRI. Concordance between ophthalmology and radiology BI measurements was assessed. Sensitivity and specificity of BI thresholds were calculated.
Results
91 orbits from 39 patients were analysed. Reduced visual acuity, colour vision defects, RAPD, optic nerve swelling, and visual field defects were significantly associated with DON. Proptosis was significantly greater in cases compared to controls. EOMs were significantly enlarged in cases, supporting the theory of EOM enlargement causing compressive optic neuropathy. BI was significantly higher in cases compared to controls (P < 0.001). There was good concordance between BI measurements taken by ophthalmology and radiology. A BI threshold of 50% demonstrated a sensitivity of 60% and specificity of 81% for DON, comparable to expert review of imaging. Horizontal and vertical BI thresholds of 41.61% and 57.25%, respectively, provided optimal diagnostic performance.
Conclusion
BI is a reliable and accessible aid to DON diagnosis, performing comparably to specialist image interpretation. This study supports using BI as a screening tool for early DON identification in TED patients. BI may be useful to alert clinicians to the possibility of DON where specialist image interpretation is not immediately available.
Additional Authors
| First name | Last name | Base Hospital / Institution |
|---|---|---|
| Ebony | Smith | Sydney Eye Hospital |
| Maggie | Hourihan | University Hospital of Wales |
| William | Pinzón Pérez | Queensland Cyber Infrastructure Foundation |
| Rachel | Dillon | University Hospital of Wales |
| Anjana | Haridas | University Hospital of Wales |
