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T. D. Padrick, E. Sarver; IOL Power Calculations Using Aphakic Spherical Equvalent. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5446.
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To determine if accurate IOL power calculations can be done utilizing the intraoperative aphakic spherical equivalent (IASE) data obtained with the WaveTec Vision ORange system.
IOL power calculations require the keratometric power (K) of the cornea, the axial length (AL) of the eye, the expected lens position (ELP) of the IOL once implanted into the eye and the desired post operative refraction. Traditional IOL power calculation methods utilize K values, AL determined by either ultrasound or partial optical coherence tomography and one of several IOL power calculation formulas which modify the manufacturers lens constant to an ELP for the patient’s eye. We have determined a relationship between the ELP calculated by standard formulas and the IASE. This ELP value, K values, IASE and desired post operative refraction are utilized in a refractive vergence formula to calculate the power of the IOL. We refer to this intraoperative calculation as the ORange method.
The IASE was obtained for 125 eyes undergoing routine cataract surgery. The ORange method was used to calculate the predicted post operative refraction for the particular IOL that was implanted. This value was compared to the 30 day manifest refraction spherical equivalent to determine the ORange method prediction error. The absolute value prediction error for the 125 eyes was 0.49 D +/- 0.35 D. We further selected a subset of 18 eyes implanted with the same IOL (Alcon SN60WF) and used this data in a regression formula that included not only the aphakic refraction spherical equivalent but also the white-to-white (corneal diameter) measurement. For this subset, the ORange absolute value prediction error was 0.28 D +/- 0.16 D.
Utilization of IASE measured during cataract surgery provides an effective basis for calculating IOL power.
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