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6. A Constants and IOL Formulawww.medsalesacademy.co.uk

Today we will learn๏๏๏๏๏๏About A Constants, Optical and UltrasoundHow to calculate IOL Power?Which constants used in different formula?What is ELP & How does it effect calculation?Which formula are best for which type of eye?What formula for patients with prior refractivesurgery?www.medsalesacademy.co.uk

A Constants๏Each formula has a “number” or “constant” to representthe lens๏Takes into account-Lens placement-Curvature of Lens-Density of Lens๏Ultrasound and Optical measure slightly differently๏Use Ultrasound and Optical “A” constantswww.medsalesacademy.co.uk

Measuring ALMOptical 23.5mmUS 23.2mmwww.medsalesacademy.co.uk

Calculating Lens PowerBasic formulaD A - 2.5 ALM - 0.9 KD IOL PowerA A constantALM Axial LengthK K Readingwww.medsalesacademy.co.uk

Calculation D A - 2.5ALmm - 0.9KD–Eg SupaLens A constant 118–K Reading 43–ALM 23.5 optical and 23.2 with Ultrasound DOpt 118 - (2.5 x 23.5) - (0.9 x 43)–DOpt 20.55 DUS 118 - (2.5 x 23.2) - (0.9 x 43)–DUS 21.3 Use the right A Constants!www.medsalesacademy.co.uk

ULIB๏Data from worldwide surgeons๏Out of date๏Surgeons recommended to optimise๏Contact IOL Manufacturerwww.medsalesacademy.co.uk

Different Formula/ Different Term๏SRK/T - A Constant eg 118.0๏Haigis - 3 Constants eg a0- 0.466, a1- 0.259, a2-0.135๏Hoffer Q - pACD eg 5.04๏Holladay 1 - sf eg 1.27๏If Haigis a1 0.40 a2 0.10 then this has not been optimised, Haigisformula will not give as good results. Use fully optimisedwww.medsalesacademy.co.uk

Question Timewww.medsalesacademy.co.uk

ELP๏๏Effective Lens PositionLens power varies with distancefrom pupil๏Knowing where the lens will sitimproves outcomeswww.medsalesacademy.co.uk

ELP๏First - Before 1980’s ELP was a constant 4mm for everyeye and IOL (Mainly AC)๏Second - In 1980’s Binkhorst used AL as a scaling factorfor ELP๏Third - In 1988 K&AL improved scaling accuracy of ELP๏Fourth - In 1995 Olsen et al improved accuracy byadding 2 more variables PreOp ACD & Lens Thicknesshttps://eyewiki.aao.org/Biometry for Intra-Ocular Lens (IOL) power calculationwww.medsalesacademy.co.uk

Formula Guidelines๏SRK, SRK II and Binkhorst are considered obsolete๏All modern formula (Haigis, SRK/T, Holliday 1 and Hoffer Q) are consideredgood for all eyes, but Hoffer Q and Haigis may be better for short eyes๏Optimising A constants can improve predictability by as much as 20% thepercentage of eyes within /- 1Dwww.medsalesacademy.co.uk

Formulawww.medsalesacademy.co.uk

SRK/T๏Most used formula๏Good for normal eyes๏Designed by Sanders, Retzlaff & Kraft๏Uses A Constant๏Needs K reading & Axial Lengthwww.medsalesacademy.co.uk

HofferQ๏Designed by Ken Hoffer๏Good for short eyes๏Uses PACD (Personalised)๏Needs Axial Length measurement and K Readingwww.medsalesacademy.co.uk

Haigis๏Designed by Professor Haigis๏Uses Anterior Chamber depth as well as Kreading and Axial Length๏Accurate over a wide range of lenses if optimisedwww.medsalesacademy.co.uk

Holladay๏Jack Holladay๏Good for longer eyes๏Uses SF (Surgeon Factor)๏Needs K reading & Axial Lengthwww.medsalesacademy.co.uk

Question Timewww.medsalesacademy.co.uk

Prior Refractive Surgery๏K’s have been altered so any formula based onK’s will not work.๏Point to ASCRS Formula page http://iolcalc.ascrs.org๏Drs may use one of the more modern formulaslike Barratt or Olsen๏They should check topography as refractivesurgery may make cornea irregularwww.medsalesacademy.co.uk

Potvin Shammas Hill‣True Net uk

Holladay 2๏Jack Holladay designed this software which isgood for ALL odd eyes, very short, post LASIK etc๏Pay for use๏Needs normal measurements plus Lens Thickness๏Holladay also has some solutions using thePentacam (EKR) and OPD Scan (ECCP)www.medsalesacademy.co.uk

Haigis L๏On modern IOL masters for Hyperopia andMyopic patients๏Works on a regression formula๏Only available on IOL Masterwww.medsalesacademy.co.uk

ASCRS๏Features many formula๏Can just type in as much information as you edsalesacademy.co.uk

Today we have learnt About A Constants Optical and UltrasoundHow to calculate IOL Power?Which constants used in different formula?What is ELP & How does it effect calculation?Which formula are best for which type of eye?What formula for patients with prior refractivesurgery?www.medsalesacademy.co.uk

Thank you!๏We will email you some questions.๏Please send your questions and comments toemma@medsalesacademy.co.uk๏We look forward to seeing you on the next course Multifocal and Toric IOLswww.medsalesacademy.co.uk

๏ All modern formula (Haigis, SRK/T, Holliday 1 and Hoffer Q) are considered good for all eyes, but Hoffer Q and Haigis may be better for short eyes ๏ Optimising A constants can improve predictability by as much as 20% the percentage of eyes within /- 1D