• 2550 Willow Street
    Vancouver, BC, V5Z 3N9
    Tel: 604.875.4407
  • 13490 104th Avenue
    Surrey, BC V3T1V8
    Tel: 604.930.1010

Post Refractive IOL Calculation

IOL calculation in patients who have had prior refractive surgery can be challenging. Based on the results of the 173 eye McCarthy et al. study1, we selected the top performing formulas and created a simple calculator that can be used as an adjunct for IOL calculations in eyes which have had prior myopic LASIK/PRK.

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The calculator provides surgeons with a spectrum of  IOL powers based on a selection of the top formulas from the study. The following formula combinations are currently available in the calculator:

  • Shammas No-History2,3
  • Masket with the Hoffer Q4
  • Clinical history method (single and double K) with the Hoffer Q5
  • Latkany Flat K with the SRK/T6
  • Corneal bypass method with the Holladay7

INSTRUCTIONS: The IOL calculator is NOT indicated for eyes which have had prior radial keratotomy or hyperopic refractive surgery. We strongly recommend using it in conjunction with the Haigis-L and other standard methods of post refractive IOL calculation, such as those available on the Lenstar LS 900 and IOL Master, and the American Society of Cataract and Refractive Surgery (ASCRS) IOL calculator.

The calculator has two sheets: the Formula Input Sheet where patient information is input and the Formula Output Sheet where the IOL powers are generated. If a formula does not have sufficient information to complete the calculations the output will be returned as “NA.” Formulas are arranged such that the formlas that on average (as per our study) produce the most myopic results are at the top of the Formula Output Sheet and the ones that behave most emmetropic are on the bottom. Pop-ups should appear when hovering over certain cells to help users with data input.

As added functionality, the calculator provides an automated risk assessment based on the agreement between certain formulas and patient biometry. If sufficient data is available, IOL calculations receive either a “Low” or High” risk classification. This feature is intended as a rough indicator of the reliability of the calculations. Additionally, the calculator includes a set of warnings for eyes that have biometry associated with poorer outcomes (outlier keratometry, axial lengths and historical refractions). In cases where the automated risk assessment is HIGH or the calculator gives a warning for outlier biometry, we usually repeat the measurements and consider selecting for a myopic outcome to reduce the risk of hyperopia.

Whenever possible, individual surgeon optimized lens constants should be used. Alternatively, the User Group for Laser Interference Biometry provides a comprehensive list of lens constants that have been optimized based on multiple surgeon clinical outcomes with the IOL Master, available here.

Please consult the references at the bottom of the page for further information on the formulas and their indications for use.

DISCLAIMER: The calculator was made to be used in conjunction with existing standard methods for post refractive IOL calculation and is intended as a supplement ONLY.  Physicians who use the calculator remain solely responsible for their outcomes and by using the calculator agree to hold harmless the authors for any and all claims or liability that may arise through use or misuse of this tool.

ACCESS OUR ONLINE CALCULATOR HERE.

Please note that we do not store any data on our servers and, consequently, are not able to retrieve past calculations.

REFERENCES:

  1. McCarthy M, Gavanski GM, Paton KE, Holland SP. Intraocular
    lens power calculations after myopic laser refractive
    surgery: a comparison of methods in 173 eyes. Ophthalmology
    2011;118:940–4.
  2. Shammas HJ, Shammas MC, Garabet A, et al. Correcting the
    corneal power measurements for intraocular lens power calculations
    after myopic laser in situ keratomileusis. Am J
    Ophthalmol 2003;136:426 –32.
  3. Shammas HJ, Shammas MC. No-history method of intraocular
    lens power calculation for cataract surgery after myopic laser in
    situ keratomileusis. J Cataract Refract Surg 2007;33:31–6.
  4. Masket S, Masket SE. Simple regression formula for intraocular
    lens power adjustment in eyes requiring cataract surgery
    after excimer laser photoablation. J Cataract Refract Surg
    2006;32:430–4.
  5. Aramberri J. Intraocular lens power calculation after corneal
    refractive surgery: double-K method. J Cataract Refract Surg
    2003;29:2063– 8.
  6. Latkany RA, Chokshi AR, Speaker MG, et al. Intraocular lens
    calculations after refractive surgery. J Cataract Refract Surg
    2005;31:562–70.
  7. Walter KA, Gagnon MR, Hoopes PC Jr, Dickinson PJ. Accurate
    intraocular lens power calculation after myopic laser in
    situ keratomileusis, bypassing corneal power. J Cataract Refract
    Surg 2006;32:425–9.