Corneal ray tracing versus simulated keratometry for estimating corneal power changes after excimer laser surgery

Savini, Giacomo; Calossi, Antonio; Camellin, Massimo; Carones, Francesco; Fantozzi, Marco; Hoffer, Kenneth J.

doi:10.1016/j.jcrs.2013.11.032

Cited by 31 publications

(34 citation statements)

References 29 publications

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“…As of today, however, these clinical data are lacking. Hence, considering that ray tracing has been proven to be highly efficacious in estimating corneal power changes 9 and calculating IOL power after LASIK and PRK by numerous clinical reports 7,8,10 , we believe that ray tracing represents the currently best available benchmark for IOL power calculation in post-SMILE eyes. A plethora of empirically optimized formulas is available in the ASCRS online calculator to accurately predict IOL power after excimer-based keratorefractive surgery (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Conveniently, a range of these formulas is readily accessible in the American Society of Cataract and Refractive Surgeons (ASCRS) post-keratorefractive surgery IOL power online calculator. Avoiding any empirical optimization, ray tracing represents a purely physical approach for IOL power calculation particularly attractive in eyes with previous LASIK or PRK [6][7][8][9][10] . This method involves direct measurement of the posterior corneal curvature (e.g.…”

mentioning

confidence: 99%

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Intraocular Lens Power Calculation after Small Incision Lenticule Extraction

Luft

Schworm

Kreutzer

et al. 2020

Sci Rep

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With more than 1.5 million Small Incision Lenticule Extraction (SMILE) procedures having already been performed worldwide in an ageing population, intraocular lens (IOL) power calculation in post-SMILE eyes will inevitably become a common challenge for ophthalmologists. Since no refractive outcomes of cataract surgery following SMILE have been published, there is a lack of empirical data for optimizing IOL power calculation. Using the ray tracing as the standard of reference-a purely physical method that obviates the need for any empirical optimization-we analyzed the agreement of various IOL power calculation formulas derived from the American Society of Cataract and Refractive Surgeons (ASCRS) post-keratorefractive surgery online calculator. In our study of 88 post-SMILE eyes, the Masket formula showed the smallest mean prediction error [−0.36 ± 0.32 diopters (D)] and median absolute error (0.33D) and yielded the largest percentage of eyes within ±0.50D (70%) in reference to ray tracing. Non-inferior refractive prediction errors and ±0.50D accuracies were achieved by the Barrett True K, Barrett True K No History and the Potvin-Hill formula. Use of these formulas in conjunction with ray tracing is recommended until sufficient data for empirical optimization of IOL power calculation after SMILE is available.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Intraocular Lens Power Calculation after Small Incision Lenticule Extraction

Luft

Schworm

Kreutzer

et al. 2020

Sci Rep

View full text Add to dashboard Cite

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“…Assessing corneal power in patients who have previously undergone keratorefractive surgery has been the subject of a significant amount of research over the past several years . Keratometry and computerised videokeratography fail to provide correct measurements of the corneal power after corneal surgery.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, keratometers and topographers have a central scotoma. The inherit limitations explain why these instruments give inaccurate measurements after corneal surgery . Many formulas have been suggested through the years to circumvent these issues, with The Clinical History Method being one of the most recognised calculations .…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies suggest that devices employing Scheimpflug technology, such as the Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), the Galilei (Ziemer Ophthalmic Systems AG, Port, Switzerland), and the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany), may be used to accurately measure the effective refractive change for surgically treated corneas. The Pentacam HR (Oculus Optikgeräte GmbH) device uses a rotating Scheimpflug camera and presents several methods for calculating corneal power including Gaussian optics and ray tracing (http://www.pentacam.com/sites/calc_corneal_power.php#ptop).…”

Section: Introductionmentioning

confidence: 99%

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Assessing the corneal power change after refractive surgery using Scheimpflug imaging

Gyldenkerne

Ivarsen

Hjortdal

2015

Ophthalmic Physiologic Optic

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Assessing the validity of corneal power estimation using conventional keratometry for intraocular lens power calculation in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty

Diener¹,

Treder²,

Lauermann³

et al. 2020

Graefes Arch Clin Exp Ophthalmol

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Purpose The present retrospective study was designed to test the hypothesis that the postoperative posterior to preoperative anterior corneal curvature radii (PPPA) ratio in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty (DMEK) is significantly different to the posterior to anterior corneal curvature radii (PA) ratio in virgin eyes and therefore renders conventional keratometry (K) and the corneal power derived by it invalid for intraocular lens (IOL) power calculation. Methods Measurement of corneal parameters was performed using Scheimpflug imaging (Pentacam HR, Oculus, Germany). In 125 eyes with Fuch’s dystrophy undergoing DMEK, a fictitious keratometer index was calculated based on the PPPA ratio. The preoperative and postoperative keratometer indices and PA ratios were also determined. Results were compared to those obtained in a control group consisting of 125 eyes without corneal pathologies. Calculated mean ratios and keratometer indices were then used to convert the anterior corneal radius in each eye before DMEK to postoperative posterior and total corneal power. To assess the most appropriate ratio and keratometer index, predicted and measured powers were compared using Bland-Altman plots. Results The PPPA ratio determined in eyes with Fuch’s dystrophy undergoing DMEK was significantly different (P < 0.001) to the PA ratio in eyes without corneal pathologies. Using the mean PA ratio (0.822) and keratometer index (1.3283), calculated with the control group data to convert the anterior corneal radius before DMEK to power, leads to a significant (P < 0.001) underestimation of postoperative posterior negative corneal power (mean difference (∆ = − 0.14D ± 0.30) and overestimation of total corneal power (∆ = − 0.45D ± 1.08). The lowest prediction errors were found using the geometric mean PPPA ratio (0.806) and corresponding keratometer index (1.3273) to predict the postoperative posterior (∆ = − 0.01 ± 0.30) and total corneal powers (∆ = − 0.32D ± 1.08). Conclusions Corneal power estimation using conventional K for IOL power calculation is invalid in eyes with Fuch’s dystrophy undergoing DMEK. To avoid an overestimation of corneal power and minimize the risk of a postoperative hyperopic shift, conventional K for IOL power calculation should be adjusted in eyes with Fuch’s dystrophy undergoing cataract surgery combined with DMEK. The fictitious PPPA ratio and keratometer index may guide further IOL power calculation methods to achieve this.

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Corneal ray tracing versus simulated keratometry for estimating corneal power changes after excimer laser surgery

Abstract: Dr. Calossi is consultant to Costruzione Strumenti Oftalmici. Dr. Carones is consultant to Wavelight Laser Technologie AG. No other author has a financial or proprietary interest in any material or method mentioned.

Cited by 31 publications

References 29 publications

Intraocular Lens Power Calculation after Small Incision Lenticule Extraction

Intraocular Lens Power Calculation after Small Incision Lenticule Extraction

Assessing the corneal power change after refractive surgery using Scheimpflug imaging

Assessing the validity of corneal power estimation using conventional keratometry for intraocular lens power calculation in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty

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