Investigation Of The Myopic Outcome Of The Newer Intraocular Lens Calculation Formulas In Long Asian Eyes.

To investigate the underlying cause of the myopic results of the newer formulas(Barrett Universal ll, EVO 2.0, Kane, and PEARL-DGS) in long(axial length over 26mm, 133 out of 3100 total eyes) Asian eyes implanting Alcon TFNT intraocular lens(IOL). 

Miracle Eye Clinic, Seoul, Korea.

The reference back-calculated effective lens position(ELP)s from the postoperative outcome of the Haigis formula with conventional axial length(AL), and the Cooke-modified-Axial-Length(CMAL) were plotted. The predicted ELP of each single and triple optimized, AL-applied and CMAL-applied Haigis formula were plotted and compared. The relationship between the anterior chamber depth(ACD) and AL in our population was also illustrated. The graphs depicting the predicted and reference back-calculated Theoretical Internal Lens Position(TILP) of the PEARL-DGS formula, and the relationship between the ACD and AL of the base population in which the PEARL formula was developed, were compared with our results. 

Contrary to the AL-applied Haigis formula, the predicted ELP curve of the CMAL-applied, single-optimized Haigis formula, which more or less simulates the working of the newer formulas(using optical vergence formula, modified AL and single constant), revealed a significant upward deviation from the back-calculated ELP in the long eyes, consequently resulting in myopic outcomes. The predicted ELP curve of the CMAL-applied, triple-optimized Haigis formula displayed better fitting to the back-calculated ELP. 

The relationship between the AL and ACD in our population and the base population of the PEARL formula, both similar to the back-calculated ELP or TILP curve of each formula, showed differences from each other in long eyes. 

The myopic outcomes in the long eyes appear to originate from the ethnic difference in the AL-ACD relationship. Our result suggests that, due to the relatively shallow ACD in the long eyes of our population, particularly with the application of the modified AL like the CMAL, the ELP was not formed as deeply as the newer formulas' algorithms expected. Contrarily, the CMAL-applied, triple-optimized Haigis formula could predict well by linking the ELP prediction only to the ACD change.

Regardless of the complexity of the ELP prediction algorithm, using a single constant might not be as resilient as using multiple constants to cope with populations of different characteristics from the population in which each formula was developed.