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Review Intraocular Lenses Effective Ocular Biometry and Intraocular Lens Power Calculation Magdalena Turczynowska, 1 Katarzyna Ko ź lik-Nowakowska, 2 Magdalena Gaca-Wysocka 2 and Andrzej Grzybowski 2,3 1. Department of Ophthalmology, Stefan Ż eromski Specialist Municipal Hospital, Cracow, Poland; 2. Department of Ophthalmology, Poznan City Hospital, Poland; 3. Department of Ophthalmology, University of Warmia and Mazury, Olsztyn, Poland S ince the introduction of phacoemulsification, cataract surgery has evolved remarkably. The use of premium intraocular lenses (IOLs) (aspheric, toric, multifocal), refractive lens exchange and patients after refractive surgery procedures require extremely precise clinical measurements and IOL calculation formulas to achieve desired postoperative refraction. For many years, ultrasound biometry has been the standard for measurement of ocular parameters. The introduction of optical biometry (fast and non-invasive) has replaced ultrasound methods and is now considered as the clinical standard for ocular biometry. Recently, several modern optical instruments have been commercially launched and there are new methods available, including the empirical, analytical, numerical or combined methods to determine IOL power. The aim of this review is to present current techniques of ocular biometry and IOL power calculation formulas, which will contribute to achieve highly accurate refractive outcomes. Keywords Biometry, ocular biometry, optical biometry, optical biometry devices, intraocular lenses, IOLs, IOL power calculation, IOL power calculation formulas Disclosure: Magdalena Turczynowska, Katarzyna Koźlik-Nowakowska, Magdalena Gaca-Wysocka and Andrzej Grzybowski have nothing to disclose in relation to this article. No funding was received in the publication of this article. This study involves a review of the literature and did not involve any studies with human or animal subjects performed by any of the authors. Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit. Received: 16 August 2016 Accepted: 18 September 2016 Citation: European Ophthalmic Review, 2016;10(2):94–100 Corresponding Author: Magdalena Turczynowska, Department of Ophthalmology, Stefan Ż eromski Specialist Municipal Hospital in Kraków, os. Na Skarpie 66, 31-913 Kraków, Poland. E: Cataract surgery is currently the most frequently performed surgical technique worldwide. Since the introduction of phacoemulsification by Kelman in 1967, surgical technology and construction of implanted intraocular lenses (IOLs) have undergone considerable improvement. Small, sutureless incisions and the use of foldable intraocular lenses reduced the incidence of complications and surgically induced astigmatism. 1,2 Furthermore, the use of premium intraocular lenses (aspheric, toric, multifocal or a combination) allows the patient to become fully spectacle-independent. 3 The improvement of surgical treatment results in rising expectations of patients. The key issue is to achieve the desired refractive outcome. Essential for this purpose are precise measurements of the eye and selection of the optimal IOL calculation formula. The aim of this article is to present current techniques of ocular biometry and IOL power calculation formulas, which will contribute to achieve highly accurate refractive outcomes. Ocular biometry The first step to achieve satisfactory postoperative refractive outcome is accurate ocular biometry. Biometry enables the measurement of the various dimensions of the eye, including axial length (AL), anterior chamber depth (ACD), lens thickness (LT) or central corneal thickness (CCT). These values, together with the keratometry are essential for the IOL power calculation. Precision of measurements is crucial, as a 0.1 mm error in AL results in a refractive error of about 0.27 diopter (D). 4 Ultrasound biometry For many years, the only way to measure the AL of the eye was with ultrasound biometry. This technique measures the distance from the surface of the corneal apex to the internal limiting membrane (ILM). Good alignment along the ocular axis is important and that requires patient cooperation (which can be difficult in children or patients with mental disorders). In cases where a probe has direct contact with the cornea, there is a risk of a corneal damage or infection. Therefore, a topical anaesthetic and proper disinfection of the probe are required. Occurring inter-individual differences are highly dependent on the pressure exerted on the eye by the ultrasound probe. High pressure results in corneal indentation and shortening of the AL. Immersion ultrasound minimises the indentation of the cornea as it uses a saline-filled shell between the probe and the eye. Clinical studies have shown that immersion biometry is more accurate and more reliable than ultrasound biometry performed in contact mode. 5–8 A limitation of ultrasound biometry is low image resolution, as a consequence of using a long, low-resolution wavelength (10 MHz) to measure small dimensions. In addition, differences in retinal thickness near the fovea or the presence of other macular pathologies contribute to inconsistent measurements. 9,10 Optical biometry The introduction of optical biometry has steadily replaced ultrasound methods and is now considered the clinical standard for ocular biometry. The results are comparable to those achieved 94 TOU C H ME D ICA L ME D IA