A patient is planned for phacoemulsification. Axial length (AL) = 23.5 mm, keratometry = 44.0 D in both meridians. The SRK/T formula yields IOL power = 21.0 D. The surgeon uses the Haigis formula and obtains 20.5 D. For this patient's AL, which formula is considered MOST accurate?

• A Haigis or Barrett Universal II (fourth generation) ✓
• B SRK II formula
• C Holladay I formula
• D SRK/T formula (third generation)

Explanation

IOL power calculation accuracy by axial length: for average eyes (AL 22-25 mm), third-generation formulas (SRK/T, Holladay I, Hoffer Q) are adequate. However, for short eyes (<22 mm), long eyes (>25 mm), and post-refractive surgery eyes, fourth-generation formulas (Haigis using three constants a0/a1/a2, Barrett Universal II, Olsen) are significantly more accurate because they better account for the effective lens position (ELP). At 23.5 mm (average), the difference is small, but Haigis and Barrett are generally preferred for precision.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.