Intraocular lens power calculation after corneal refractive surgery: double-K method

Area of Science:

• Ophthalmology
• Refractive Surgery
• Biomedical Engineering

Background:

• Accurate intraocular lens (IOL) power calculation is crucial for visual outcomes after cataract surgery.
• Corneal refractive surgery, such as LASIK and PRK, alters corneal curvature, complicating pre-operative IOL power calculations.
• Existing formulas may not adequately account for these post-refractive surgery corneal changes.

Purpose of the Study:

• To evaluate the accuracy of a modified SRK/T formula for IOL power calculation in patients who have undergone prior corneal refractive surgery.
• To compare the refractive outcomes using the standard SRK/T formula versus the modified "double-K" SRK/T formula.

Main Methods:

• The SRK/T formula was adapted to incorporate pre-refractive surgery keratometry (Kpre) for effective lens position and post-refractive surgery keratometry (Kpost) for IOL power calculation.
• Kpre was determined via keratometry or topography, and Kpost via clinical history.
• The modified formula was tested on 9 patients who had cataract surgery after LASIK or PRK.

Main Results:

• The modified "double-K" SRK/T formula resulted in a mean spherical equivalent (SE) of +0.13 D, compared to +1.82 D with the standard SRK/T formula.
• 66.7% of patients achieved a refractive outcome within +/- 0.5 D SE using the "double-K" method, versus 0% with the standard formula.

Conclusions:

• The "double-K" modification of the SRK/T formula significantly enhances the accuracy of IOL power calculation after LASIK and PRK.
• This improved accuracy leads to better refractive outcomes in cataract surgery patients with a history of corneal refractive procedures.