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Letters
July 2012

Toric Intraocular Lens Calculations—Reply

Author Affiliations

Author Affiliations: Department of Ophthalmology, Queen Elizabeth Hospital and Health Service, Woodville South, and South Australian Institute of Ophthalmology, University of Adelaide (Drs Goggin and Moore), and Sansom Institute of Health Research and School of Nursing and Midwifery, University of South Australia (Prof Esterman), Adelaide, Australia.

Arch Ophthalmol. 2012;130(7):947-949. doi:10.1001/archophthalmol.2012.700

In reply

We thank Dr Simpson for pointing out the typographical error in our article.1 He is correct. The formula should have read E = F /[1 + (d /1.336) F]. All calculations in the article were done using this correct formula, and the formula in the article has been corrected. With regard to the suitability of this formula for the task of predicting toric IOL outcome, we have demonstrated that it predicted the outcome better than the Alcon online calculator. He is right that it is related to the formula for adjusting effective powers between contact lenses and spectacle lenses, but the incorporation of an index of refraction for aqueous and cornea (1.336) makes it suitable for calculation of equivalent powers within the eye. The US patent application document for the online Alcon toric calculator2 uses such formulas in a more detailed manner, calculating vergence at the cornea and the first and second principal planes of the IOL.

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