Thyroid-associated orbitopathy (TAO) with corneal exposure is classified using the VISA classification. The 'S' (Strabismus) component is graded by:
- A Motility restriction — from no restriction (0) to all positions restricted with incapacitating diplopia in primary and reading position (grade 4) ✓
- B Degree of exophthalmos in millimeters by Hertel exophthalmometry
- C Thickness of extraocular muscles on orbital CT in millimeters
- D Patient-reported diplopia frequency over 24 hours on a visual analogue scale
Explanation
The VISA (Vision, Inflammation, Strabismus, Appearance) classification for TAO grades strabismus (motility) as: Grade 0 — no strabismus or restrictions; Grade 1 — intermittent or only in extremes of gaze; Grade 2 — constant diplopia in one or more positions (but not primary gaze); Grade 3 — constant diplopia in primary gaze or down gaze (reading); Grade 4 — constant diplopia in all gaze positions including primary. The inferior rectus is most commonly involved in TAO (inferior rectus fibrosis causing hypotropia and upgaze restriction). The clinical activity score (CAS) separately measures disease activity. Strabismus surgery is performed after the disease is quiescent (stable CAS) and after orbital decompression if needed.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.