Improving the prediction accuracy of the SRK/T formula: The T2 formula

Sheard, Richard; Smith, Guy T; Cooke, David L.

doi:10.1016/j.jcrs.2010.05.031

Cited by 91 publications

(79 citation statements)

References 4 publications

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“…In our case, we chose the rigid PMMA model 6.0 mm optic because the subluxated IOL had to be explanted. Using the A constant for the negative-powered IOLs, according to the modified SRK/T formula (ie, SRK/ T2), 7 we obtained an SE approaching emmetropia. In addition to published results for iris-claw IOLs, the iris-claw myopic IOL is a good alternative to avoid the expected hyperopic refractive result when an IOL must be explanted due to IOL dislocation.…”

Section: Discussionmentioning

confidence: 96%

Myopic iris-claw intraocular lens for late intraocular lens–capsular bag complex dislocation using the T2 formula

Huerva¹

2014

Journal of Cataract and Refractive Surgery Online Case Reports

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A 75-year-old white woman with a history of high myopia and bilateral cataract surgery presented with dislocation of the intraocular lens (IOL)-capsular bag complex in her left eye. Exchange of the complex and an iris-claw IOL aphakia model were proposed. Because the lowest power for this IOL was C2.0 diopters (D), an Artisan IOL (À3.0 D) with an estimated A-constant of 103.8 for negative powered IOLs using the SRK/T2 formula was implanted. Three months after selective sutures were removed, the refraction was C0.75 À1.25 Â 100 (spherical equivalent [SE] C0.125 D) and the corrected distance visual acuity was 20/100 (Snellen). The iris-claw IOL model for myopia correction may be used in cases of IOL-capsular bag complex dislocation in patients with high myopia. The outcome may be more predictable with the SRK/T2 formula.Financial Disclosure(s): The author has no financial or proprietary interest in any material or method mentioned. JCRS Online Case Reports 2014; 2:e38-e40 Q 2014 ASCRS and ESCRSDislocation of an intraocular lens (IOL) within the capsular bag may occur many years after uneventful cataract surgery as a result of previous progressive zonular disintegration and capsule shrinkage. 1,2 The most commonly reported associated condition is pseudoexfoliation. 3,4 However, a recent study 5 reports that high myopia may be the main risk factor for late inthe-bag IOL dislocation.When in-the-bag IOL dislocation occurs, intervention measures must be performed immediately because of the imminent risk for IOL-capsular bag complex dislocation into the vitreous cavity. It is usually preferable to intervene surgically while an anterior approach is still possible. Management includes IOL exchange, replacement with an anterior chamber IOL, or suturing the IOL through the bag to the iris or the sclera. 3-5 The advantage of repositioning and suturing the IOL is that it avoids a large incision. 6 However, this is not possible in some cases due to the IOL dislocation into the vitreous cavity or the appearance of the vitreous in the anterior chamber; instead, exchange of the IOL-capsular bag complex and anterior vitrectomy may be preferable. Aphakia correction can be performed using a new sulcus-sutured or glued IOL, an anterior angle-supported IOL, or an iris-claw IOL. Iris-claw IOLs with a diopter (D) power range of C2.0 to C30.0 D are available for aphakia correction. In some highly myopic patients, emmetropia cannot be achieved within this range. Other models designed to correct myopia should be used instead. However, calculating the power of these IOLs in these patients is challenging. We present the treatment of late in-the-bag IOL dislocation in a highly myopic patient involving exchange of the dislocated IOL-capsular bag complex and implantation of an iris-claw IOL using the SRK/T2 formula. 7 CASE REPORTA 75-year-old white woman with a history of high myopia and bilateral cataract surgery in 1996 presented with visual disturbances of 1-month duration in the left eye in July 2013. She did not report the amount of previou...

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Section: Discussionmentioning

confidence: 96%

Myopic iris-claw intraocular lens for late intraocular lens–capsular bag complex dislocation using the T2 formula

Huerva¹

2014

Journal of Cataract and Refractive Surgery Online Case Reports

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“…26 The Haigis formula is reported to give accurate predictions for both short 27 and long eyes, 28 but Olsen's formula may produce results slightly better than Haigis'. 29 The Holladay 2 formula is suggested to be 'one of the more accurate formulas available', 8 but there is little systematic evidence for this assertion.…”

Section: Formula Choicementioning

confidence: 99%

Optimising biometry for best outcomes in cataract surgery

Sheard

2013

Eye

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Biometry has become one of the most important steps in modern cataract surgery and, according to the Royal College of Ophthalmologists Cataract Surgery Guidelines, what matters most is achieving excellent results. This paper is aimed at the NHS cataract surgeon and intends to be a critical review of the recent literature on biometry for cataract surgery, summarising the evidence for current best practice standards and available practical strategies for improving outcomes for patients. With modern optical biometry for the majority of patients, informed formula choice and intraocular lens (IOL) constant optimisation outcomes of more than 90% within ± 1 D and more than 60% within ± 0.5 D of target are achievable. There are a number of strategies available to surgeons wishing to exceed these outcomes, the most promising of which are the use of strict-tolerance IOLs and second eye prediction refinement.

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“…The individual steps of the SRK/T formula were examined with reference to a database of biometry and refractive outcomes in 11.189 eyes by Sheard et al[5*] They observed a nonphysiologic behavior in the calculation of corrected axial length and corneal height. They developed the T2 formula using a regression formula for corneal height derived from the development subset and they concluded that any surgeon who uses the SRK/T formula could switch to using the T2 formula and improve refractive outcomes by 10%.…”

Section: Intraocular Lens Power Calculationmentioning

confidence: 99%

“…Numerous devices and formulas are currently available, allowing accurate determination of the IOL power needed to reach the target refraction. [1–3,4**,5*,6–9,10*,11–16, 17*–18] In order to accomplish target refraction, axial length (AL), anterior chamber depth (ACD), and corneal radii (K1and K2) need to be accurately measured. Moreover, proper choices of IOL power calculation formulas are important, as are the use of accurate IOL constants, depending on the type of IOL and post-operative IOL location.…”

Section: Introductionmentioning

confidence: 99%

Clinically relevant biometry

Şahin

Hamrah

2012

Current Opinion in Ophthalmology

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Purpose of review Obtaining precise post-operative target refraction is of utmost importance in today’s modern cataract and refractive surgery. Given the growing number of patients undergoing premium intraocular lens implantations, patient expectation continues to rise. In order to meet heightened patient expectations, it is crucial to pay utmost attention to patient selection, accurate keratometry and biometry readings, as well as to the application of correct intraocular lens power formula with optimized lens constants. This article reviews recent advances in the field of clinical biometry and intraocular lens power calculations. Recent findings Recently developed low-coherence reflectometry optical biometry is comparable to older ultrasonic biometric and keratometric techniques. In addition, the new IOL Master software upgrade has improved reproducibility and enhanced signal acquisition. Further, the modern lens power formulas currently determine the effective lens position and the shape of the intraocular lens power prediction curve more accurately. Summary In order to reach target refraction, precise biometric measurements are imperative. Understanding the strengths and limitations of the currently available biometry devices, allows prevention of high variability and inaccuracy, ultimately determining the refractive outcomes.

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Improving the prediction accuracy of the SRK/T formula: The T2 formula

Abstract: The SRK/T formula has nonphysiologic behavior that contributes to IOL power prediction errors. A modification to the formula algorithm, the T2 formula, can be directly substituted for SRK/T, resulting in significantly improved prediction accuracy.

Cited by 91 publications

References 4 publications

Myopic iris-claw intraocular lens for late intraocular lens–capsular bag complex dislocation using the T2 formula

Myopic iris-claw intraocular lens for late intraocular lens–capsular bag complex dislocation using the T2 formula

Optimising biometry for best outcomes in cataract surgery

Clinically relevant biometry

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