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Calculating Contact Lens Power In Aphakia

Methods

Trivedi-Wilson (TW) Regression Formula

Contact Lens power = 84.4 -(3.2 x Axial Eye Length mm)

The TW formula was derived from 50 eyes of infants who underwent cataract surgery before 1 year of age (mean age 2.4 months) using SilSoft silicone elastomer lenses. The R² was 0.82

https://www.aao.org/education/editors-choice/guidelines-selecting-contact-lens-power-in-aphakic

SRK/T formula

SRK/T formula Input the following:

  • A-constant = 112.176
  • Keratometry readings
  • Axial Eye Length

SRK/T at eyecalcs.com
SRK/T at EyeCalc.org

In the IATS cohort, using the SRK/T formula yielded a mean prediction error of −2.0 D and mean absolute PE of 2.9 D.

Aphakic Contact Lens (aCL) Formula

Contact lens power = (1334/Axial Length mm) - 0.6685 Mean Keratometry D -15.25 + Desired Target Refraction

Christoph Lwowski et al developed the aCL formula, and showed median absolute prediction error of only 0.53 D, comparable to retinoscopy (0.69 D) and substantially outperforming the TW formula (median AE 3.25 D) and the default +32 D lens (median AE 2.63 D). [3]

References

  1. Selection of an Initial Contact Lens Power for Infantile Cataract Surgery Without Primary Intraocular Lens Implantation. Trivedi RH, Wilson ME. Ophthalmology. 2013;120(10):1973-6
  2. The Role of Preoperative Biometry in Selecting Initial Contact Lens Power in the Infant Aphakia Treatment Study. Trivedi RH, Lambert SR, Lynn MJ, Wilson ME. Journal of AAPOS : The Official Publication of the American Association for Pediatric Ophthalmology and Strabismus. 2014;18(3):251-4
  3. Correction of Aphakia Using Biometry-Based Contact Lens Calculation in Pediatric Cataract Extraction: Introducing the Aphakic Contact Lens Formula. Lwowski C, Kaiser KP, Wenner Y, et al. Graefe's Archive for Clinical and Experimental Ophthalmology = Albrecht Von Graefes Archiv Fur Klinische Und Experimentelle Ophthalmologie. 2026;:10.1007/s00417-026-07370-6
  4. Rigid Gas-Permeable Contact Lenses Fitting Philosophy for Unilateral Aphakic Infants. Zhang X, Zeng J, Zhai Z, Li C, Yang X. Eye & Contact Lens. 2020;46(6):381-384
  5. Predictability of Intraocular Lens Power Calculation Formulae in Infantile Eyes With Unilateral Congenital Cataract: Results From the Infant Aphakia Treatment Study. Vanderveen DK, Trivedi RH, Nizam A, Lynn MJ, Lambert SR. American Journal of Ophthalmology. 2013;156(6):1252-1260.e2
  6. Accuracy of Intraocular Lens Power Calculation Formulas in Pediatric Cataract Patients: A Systematic Review and Meta-Analysis. Zhong Y, Yu Y, Li J, et al. Frontiers in Medicine. 2021;8:710492
  7. Association of Contact Lens Adherence With Visual Outcome in the Infant Aphakia Treatment Study. Cromelin CH, Drews-Botsch C, Russell B, Lambert SR, Infant Aphakia Treatment Study Group. JAMA Ophthalmology. 2018;136(3):279-285