SPS-209 Pre-operative Testing & IOL Power Calculations | ASCRS
2020 ASCRS Virtual Annual Meeting

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Papers in this Session
Expand each tab below to view the paper abstract for each paper within this session.
Applying Vector Analysis to Assess Refraction Precision and Agreement between Three Devices for Preoperative Keratometry Measurements
Authors
David A. Price
Francis W. Price Jr., MD

Purpose
To report a novel application of vector analysis to better evaluate keratometric agreement between three imaging devices, assess preoperative variance in astigmatism measurement, and determine the resulting uncertainty in post-operative outcomes.

Methods
Data from 60 patients who had implantable collamer lens surgery and preoperative same day imaging with biometry (Lenstar LS 900, Haag-Streit AG, Switzerland), topography (TMS-4, Tomey, Nagoya, Japan), and Scheimpflug imaging (Pentacam HR, Oculus Optikgeräte GmbH, Wetzlar, Germany) was retrospectively analyzed. Keratometry, cylinder axis and magnitude, and Jackson cross-cylinders were compared. Vector analysis was used to calculate a difference vector (DV) between astigmatism measurements. The use of vector analysis is standard in refractive surgery reporting but novel in this context. Multivariate analysis assessed factors influencing axis and vector agreement at a 5% significance level.

Results
Cylinder ranged from 0.17 - 3.24 D in the 60 eyes, average 1.37 D. The mean vector astigmatism difference between each pair of devices was not significantly different and exceeded 0.25 D: DV was 0.32 ± 0.17 D for Lenstar vs. Pentacam, 0.33 ± 0.22 D for TMS4 vs. Pentacam, and 0.38 ± 0.24 D for TMS4 vs. Lenstar. The DV between Pentacam and the other machines increased when cylinder was higher (p = 0.01 for both) indicating decreased overall agreement, whereas the DV between Lenstar and TMS-4 measurements did not increase with increasing cylinder (p = 0.51). The axis agreement was tighter between all machines with increased cylinder (p < 0.01 for all).

Conclusion
Cylinder vector agreement is superior to comparing cylinder magnitude and axis agreement separately, because it is an integrated measure and provides an estimate of the range of potential outcomes in surgery planning. The average DV is above 0.25 D, indicating uncertainty in cylinder measurement is a limiting factor in refractive surgical outcomes.
Accuracy of 8 Intraocular Lens Power Calculation Formulas in Pediatric Cataract Patients
Author
Yune Zhao, MD

Purpose
To compare the accuracy of the eight formulas for intraocular lens (IOL) power calculation in pediatric cataract patients.

Methods
A total of 68 eyes (68 patients) that underwent uneventful cataract surgery and posterior chamber IOL implantation in the capsular bag were enrolled. We compared the calculation accuracy of the 8 formulas at 1 month postoperatively and performed subgroup analysis according to age and axial length (AL).

Results
The mean age at surgery was 34.07 ± 24.60 months and mean AL was 21.12 ± 1.42mm. The mean prediction errors of eight formulas for all patients were as follows: SRK II (-0.66), SRK/T (-0.44), Holladay 1 (-0.36), Hoffer Q (-0.09), Olsen (0.71), Barrett (0.37), Holladay 2 (-0.70), and Haigis (0.50). There was significant difference among the 8 formulas (p < 0.01), while no significant difference of absolute PE was found among the 8 formulas in all patients (p = 0.053). In patients younger than 2 years old and with AL ≤ 21mm, SRK/T formula was relatively accurate in 34% and 39% of eyes, respectively. While in patients older than 2 and with AL > 21mm, Barret and Haigis formulas was better.

Conclusion
Overall, in patients younger than 2 years old and with AL ≤ 21mm, SRK/T formulas was relatively accurate, while Barrett and Haigis formulas were better in patients older than 2 and with AL >21mm.
Results with the New Hoffer QS IOL Power Formula
Authors
Kenneth J. Hoffer, MD, ABO
Giacomo Savini, MD

Purpose
To evaluate and compare the clinical results of the Hoffer QS formula.

Methods
The 18,000 eye Melles study showed the biometric parameters under which the the Hoffer Q formula deteriorates. Original studies showed it was most accurate in eyes <22 mm. After considerations of new parameters for the formula, the Hoffer QS was produced. We compared this new formula in a large series of eyes to all the latest formulas available.

Results
The Hoffer QS resulted in a MedAE of 0.200 with 58% of the eyes within ±0.25 D of prediction; 88% within ±0.50 D and 97% within ±0.75 D. These results were superior to the Barrett UII, EVO, Holladay 2AL, Panacea, RBF and VRF and equal to the Kane formula.

Conclusion
The modification of the Hoffer Q formula leads to superior clinical results with the majority of eyes within ±0.25 D and almost 90% within ±0.50 D.
AL Measurements Using Component-Specific Indices of Refraction Vs a Composite Index: Effect on IOL Power Calculation and Clinical Outcomes
Author
H. John Shammas, MD

Purpose
1.Evaluate the difference between the Sum-of Segments axial length measurement (AL-SOS) and a simulated axial length that mimics the IOLMaster 500 (AL-SIM) 2.Evaluate the effects of AL changes on the predicted refraction error for the commonly used formulas

Methods
A total of 595 eyes of 595 patients undergoing cataract surgery were measured with the Argos biometer. AL-SOS is taken from the biometer’s print-out, while AL-SIM is calculated. The predicted refraction errors were calculated for the commonly used formulas using AL-SOS versus AL-SIM while keeping the K readings and ACD measurements same. All included eyes received a monofocal Alcon SN60WF IOL and had a final visual acuity of 20/40 with no other ocular pathology. All constants were optimized and the eyes were stratified into 3 AL classes: short (<22.0mm), average and long (>25.0mm)

Results
The Mean Absolute Error (MAE), Median Absolute Error (MedAE), Standard Deviation (SD) and the Maximal Absolute Error (MaxAE) were calculated and showed an improvement in all these parameters with AL-SOS versus AL-SIM, especially in the short and long eyes. The percentage of eyes within +/- 0.25 D and +/-0.50D also improved when the AL-SOS is used.

Conclusion
Axial length measurement using component-specific indices of refraction resulted in an improvement in the clinical results when compared to the use of a composite index of refraction, especially in the short and long eyes.
Autorefraction Versus Manifest Refraction in Pseudophakic Eyes: Implications for Optimization of Intraocular Lens Power Formulas.
Authors
Kendrick M. Wang
John G Ladas, MD, PhD
Albert S. Jun, MD, PhD, ABO
Irene C. Kuo, MD

Purpose
Manifest refraction (MRx) is important for intraocular lens (IOL) power formula optimization, but MRx is subjective and time-consuming relative to autorefraction. We compared MRx to autorefraction in pseudophakic eyes and examined associations between biometric variables and increased accuracy of autorefraction to optimize IOL power calculation.

Methods
This is a retrospective chart review of eyes that underwent uncomplicated cataract surgery by one surgeon at Johns Hopkins University School of Medicine. Pseudophakic eyes with BSCVA worse than 20/40 with toric, multifocal, or accommodating IOLs were excluded. The median absolute error, between autorefraction (VISUREF 100, Carl Zeiss AG, Germany) and MRx in spherical equivalent (SE), sphere, and cylinder, was analyzed. Subgroup analysis was performed to examine association of age, gender, axial length, anterior chamber depth, and keratometry with accuracy of autorefraction relative to MRx. Additionally, optimization of multiple IOL formulas using autorefraction versus MRx was investigated.

Results
Out of a total of 93 eyes, there was a trend of more myopic MRx compared with autorefraction; the mean error between MRx and autorefraction was 0.193 D (paired T-test, p < 0.05). Comparing autorefraction to MRx, the median absolute error (MedAE) of the SE was 0.375 D (IQR [0.188, 0.563]). The MedAE of sphere and of cylinder were both 0.250 D (Wilcoxon signed rank test, p <0.05). 48.4% of eyes had an autorefraction SE within ± 0.25 D of the MRx SE, and 79.6% were within ± 0.50 D. Biometric variables associated with lowest MedAE (increased accuracy of autorefraction relative to MRx) in SE, sphere, and cylinder and impact on optimization of IOL power calculations will also be presented.

Conclusion
Certain biometric variables are associated with increased accuracy of autorefraction relative to manifest refraction in pseudophakic eyes. These associations have implications for optimizing IOL power formulas.
Effectiveness and Agreement of 3 Optical Biometers in Measure Axial Length in Patients with Mature Cataracts.
Authors
Ramiro A. Almeida Jr., MD
Maria A. Henriquez, MD, PhD
Raúl A. Zúñiga Iracheta, MD
Josselyne G. Lopez, MD
Gustavo A. Hernandez Sahagun, MD
Carmen Maldonado, MSc
Jose Chauca, MSc
Luis Izquierdo, MD, PhD

Purpose
To evaluate the effectiveness and agreement of 3 optical biometers in measure axial length, and biometric parameters in patients with mature cataract.

Methods
Setting: Oftalmosalud Instituto de Ojos, Peru, between September 2018 to January 2019. Prospective, comparative study included 45 eyes with mature cataract were analyzed. Three consecutive scans were acquired with each device Pentacam AXL, Galilei G6 and IOL Master 700. The following parameters was recorded: Axial Length (AL), Anterior Flat keratometry (K1), Steep Keratometry (K2), Anterior Astigmatism (Ast), Mean K, Anterior Chamber Depth (ACD), Central Corneal Thickness (CCT) and Lens Thickness (LT). Correlations between devices was assessed using Coefficient of Concordance and Correlation (CCC).

Results
After three attempts the acquisition success rate in measuring mature cataracts was 84.4% (38/45), 42.2% (19/45) and 37.7% (17/45) for the IOL master, the Galilei and the Pentacam respectively. Significant differences were found between the Pentacam AXL and the IOL master 700 in terms of AL, K2 and CCT. Significant differences were found in terms K1, K2, Km, ACD and CCT between the Pentacam and Galilei and significant differences were found in AL, K1, Km, and ACD between the Galilei and the IOL master (p < 0.05 all). Good correlations was found between devices ( > 0.90) in terms of keratometries and axial length.

Conclusion
The IOL master 700 had the highest AL acquisition success rate when compared with the Pentacam AXL and Galilei G6. Good agreement between devices was found in terms of axial length and keratometry.
Optical Biometers: A Review of Published Comparative Evidence
Authors
William B. Trattler, MD, ABO
Carine C.W. Hsiao, MS
Shantanu Jawla, MS
Carlos Buznego, MD, ABO
Matthew D. Shulman, MD

Purpose
Optical biometry is a non-invasive, automated method for measuring anatomical details of the eye that are critical for precise intraocular lens power calculation during cataract surgery. The purpose of this study was to collate and report published comparative evidence for ARGOS biometer versus IOLMaster 500, IOLMaster 700 and LENSTAR biometers.

Methods
A literature review was conducted to identify published studies comparing ARGOS to either IOLMaster 500, IOLMaster 700 or LENSTAR biometers, for use in Cataract surgery. Medical literature databases Embase, Medline and Cochrane Library were searched using a predefined search strategy via Ovid platform (period: database inception – 14 May 2019). The search results were limited to English language, with no restrictions on the study design or study type. Comparative data on the following outcomes was collated: axial length (AL) measurements, acquisition rates (AR) (including dense cataract cases), predictive accuracy (PA) and Keratometry measurements.

Results
Nine publications were included. In 2 publications, ARGOS showed numerically higher AR for ARGOS (97.6%,99.4%) vs IOLMaster 700 (92.6%,97.1%). In 4 publications, AR for ARGOS (99.4%,97.7%,98.2%,96.0%) was numerically higher vs IOLMaster 500 (77.0%,80.7%,84.7%,87.30%) and 1 publication comparing ARGOS to LENSTAR showed numerically higher AR for ARGOS (96.0%) vs LENSTAR (79.0%). In dense cataracts, 1 publication showed higher AR for ARGOS (89.9%) vs IOLMaster 700 (63.6%). AL measurements (in 8 publications) and Keratometry measurements (in 3 publications) with ARGOS showing good correlation with either of the three biometers. One publication found similar PA with ARGOS and IOLMaster 500.

Conclusion
The findings from this literature search showed that ARGOS had higher acquisition rates compared to IOLMaster 500, IOLMaster 700 and LENSTAR biometers, with comparable outcomes in terms of AL measurements, predictive accuracy and Keratometry measurements.

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