A patient with thyroid eye disease (TED) develops compressive optic neuropathy. The MOST sensitive clinical indicator of this complication is:

• A Severity of proptosis (>25 mm)
• B Visual evoked potential (VEP) delay and colour vision (Ishihara) defect ✓
• C Degree of chemosis and conjunctival redness
• D Corneal exposure and punctate epithelial erosions

Explanation

Compressive optic neuropathy (CON) in TED is caused by apical muscle crowding at the orbital apex compressing the optic nerve. It may occur with minimal proptosis if muscles are predominantly enlarged apically. The most sensitive early indicators are reduced colour vision (especially red desaturation), relative afferent pupillary defect (RAPD), and VEP latency delay — often preceding detectable visual acuity loss. Proptosis degree does not correlate reliably. Chemosis and corneal exposure reflect corneal risk rather than optic nerve status.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.