title: Challenges and approaches in modern biometry and IOL calculation.
abstract: The introduction of new intraocular lenses (IOLs), industry marketing to the public and patient expectations has warranted increased accuracy of IOL power calculations. Toric IOLs, multifocal IOLs, aspheric IOLs, phakic lenses, accommodative lenses, cases of refractive lens exchange and eyes that have undergone previous refractive surgery all require improved clinical measurements and IOL prediction formulas. Hence, measurement techniques and IOL calculation formulas are essential factors that affect the refractive outcome. Measurement with ultrasound has been the historic standard for measurement of ocular parameters for IOL calculation. However the introduction of optical biometry using partial coherence interferometry (PCI) has steadily established itself as the new standard. Additionally, modern optical instruments such as Scheimpflug cameras and optical coherence tomographers are being used to determine corneal power that was normally the purview of manual keratometry and topography. A number of methods are available to determine the IOL power including the empirical, analytical, numerical or combined methods. Ray tracing techniques or paraxial approximation by matrix methods or classical analytical 'IOL formulas' are actively used in for the prediction of IOL power. There is no universal formula for all cases - phakic and pseudophakic cases require different approaches, as do short eyes, long eyes, astigmatic eyes or post-refractive surgery eyes. Invariably, IOLs are characterized by different methods and lens constants, which require individual optimization. This review describes the current methods for biometry and IOL calculation.
authors: Department of Ophthalmology, University of Wuerzburg, Germany.
authors: Wolfgang
authors: W
authors: Haigis
keywords: Cataract surgery; Corneal power; IOL calculation; Keratometer index; Optical biometry; Post-refractive surgery IOL; Problem eyes
references: J Cataract Refract Surg. 2005 Jul;31(7):1338-44
references: 16105604
references: J Cataract Refract Surg. 2009 Apr;35(4):650-62
references: 19304085
references: Am J Ophthalmol. 1956 Mar;41(3):488-98
references: 13302351
references: Eye (Lond). 2009 Jan;23(1):149-52
references: 17721503
references: J Cataract Refract Surg. 2005 May;31(5):1020-4
references: 15975473
references: Br J Ophthalmol. 2009 Jun;93(6):807-10
references: 19289385
references: Br J Ophthalmol. 2009 Jul;93(7):949-53
references: 19380310
references: J Cataract Refract Surg. 2006 Dec;32(12):2004-14
references: 17137976
references: J Cataract Refract Surg. 2004 Apr;30(4):892-900
references: 15093657
references: J Cataract Refract Surg. 2009 Feb;35(2):330-4
references: 19185251
references: J Cataract Refract Surg. 2006 Mar;32(3):419-24
references: 16631049
references: J Cataract Refract Surg. 2007 Jan;33(1):31-6
references: 17189790
references: J Cataract Refract Surg. 2011 Nov;37(11):1984-7
references: 21889873
references: J Cataract Refract Surg. 2010 Apr;36(4):644-8
references: 20362858
references: J Cataract Refract Surg. 2008 Mar;34(3):368-76
references: 18299059
references: J Cataract Refract Surg. 2008 Oct;34(10):1658-63
references: 18812114