As a working rule of thumb in horizontal strabismus surgery planning, how much change in ocular alignment does 1 mm of recession or resection of a horizontal rectus muscle produce?

• A Approximately 2 to 3 prism dioptres ✓
• B Approximately 1 prism dioptre
• C Approximately 5 prism dioptres
• D Approximately 10 prism dioptres

Explanation

Standard surgical planning tables and Indian textbook teaching hold that 1 mm of recession or resection of a horizontal rectus muscle alters the deviation by roughly 2 to 3 prism dioptres, allowing the surgeon to convert a measured angle into millimetres of surgery. One dioptre per millimetre underestimates the effect and would leave a large residual deviation, while 5 or 10 dioptres per millimetre grossly overestimates it and would cause severe overcorrection even for modest angles.

Reference: Khurana's Comprehensive Ophthalmology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.