Related Experiment Video
Updated: May 12, 2026
Correction of Presbyopia by Monocular Bi-Aspheric Ablation Profile
Published on: September 20, 2024
Intraocular lens power calculation in eyes with previous hyperopic laser in situ keratomileusis
H John Shammas1, Maya C Shammas, Warren E Hill
1Department of Ophthalmology, the Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. jshammas@shammaseye.com
Purpose:
To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data.
Setting:
Private practices, Lynwood, California, and Mesa, Arizona, USA.
Design:
Retrospective comparative observational study.
Methods:
The corrected corneal power (Kc) was calculated in each eye by adding the refractive change at the corneal level to the pre-LASIK keratometric (K) readings. By comparing Kc with the measured post-LASIK K readings (Kpost), the following equation was derived: Kc = 1.0457 Kpost-1.9538. This equation was combined with the Shammas original formula to obtain the Shammas-PHL formula.
Results:
The new formula was evaluated in 18 eyes with previous LASIK data and in 24 eyes with no previous LASIK data. Using the Shammas-PHL formula, the mean arithmetic prediction error was -0.03 diopter (D) ± 0.72 (SD) (range -1.57 to +1.54 D) and the median absolute error was 0.38 D in 18 eyes with available pre-LASIK data and 0.05 ± 0.58 D (range -0.56 to +1.40 D) and 0.43 D, respectively, in the 24 eyes with no pre-LASIK data.
Conclusion:
The Shammas-PHL formula can be used in post-hyperopic LASIK cases whether or not the pre-LASIK data are available.
Related Concept Videos
01:16Focusing of Light in the Eye
01:28Angle Closure Glaucoma: Treatment