Accuracy of 8 intraocular lens power calculation formulas in pediatric cataract patients.

PURPOSE: To compare the accuracy of the eight formulas for intraocular lens (IOL) power calculation in pediatric cataract patients. METHODS: A retrospective study. 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 or axial length (AL). RESULTS: The mean age at surgery was 34.07 ± 24.60 months and mean AL was 21.12 ± 1.42 mm. The mean prediction errors (PE) 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 < 0.0001), while no significant difference of absolute PE was found among the 8 formulas in all patients (p = 0.053). Moreover, in patients younger than 2 years old or with AL ≤ 21 mm, SRK/T formula was relatively accurate in 34% and 39% of eyes, respectively. While in patients older than 2 or with AL > 21 mm, Barrett and Haigis formulas were better (58% and 47% for Barrett, 52% and 53% for Haigis). CONCLUSION: Overall, in patients younger than 2 years old or with AL ≤ 21 mm, SRK/T formulas were relatively accurate, while Barrett and Haigis formulas were better in patients older than 2 or with AL > 21 mm.

The impact of glistenings on the optical quality of a hydrophobic acrylic intraocular lens.

PURPOSE: To study the effect of glistenings on the optical quality of a hydrophobic acrylic intraocular lens (IOL). SETTING: David J. Apple Laboratory, Heidelberg, Germany. DESIGN: An in vitro laboratory study. METHODS: An accelerated aging protocol was used to induce glistenings (microvacuoles) in 38 hydrophobic acrylic IOLs. The IOLs were warmed to 45°C and then cooled to 37°C. Image analysis of light-microcopy photographs determined the number and size of microvacuoles (MV). A classification was applied based on the glistening number per mm2: grade 0 (none), grade 1 (1-100), grade 2 (101-200), grade 3 (201-500) and grade 4 (more than 500). An optical bench was used to measure each IOL's modulation transfer function (MTF) and Strehl ratio to evaluate the impact of glistenings on image quality. RESULTS: Glistenings were observed in all IOLs. The mean glistening numbers ± SD (MV/mm2) in grades 1 through 4 were 74 ± 12.7, 142 ± 22.2, 297 ± 76.2, and 1509 ± 311.9, respectively. The mean glistening sizes in grades 1 through 4 were 13.28 ± 3.85 µm, 15.88 ± 2.08 µm, 16.85 ± 3.23 µm, and 15.27 ± 2.25 µm, respectively. Statistical analysis showed that grades 1 through 3 did not change the optical quality; however, in grade 4, the MTF and the Strehl ratio were significantly affected. CONCLUSION: A limited number of glistenings (<500 MV/mm2) had no effect on the image quality. Although statistically significant deteriorations in the MTF and the Strehl ratio were observed in grade 4, the effects found were small and are unlikely to affect the visual quality.

Keratometric measurements and IOL calculations in pseudophakic post-DSAEK patients.

BACKGROUND: To compare different K readings in pseudophakic patients post-Descemet's stripping automated endothelial keratoplasty (DSAEK) and evaluate corresponding prediction errors in intraocular lens (IOL) power calculations. METHODS: Subjects that underwent cataract surgery and DSAEK surgery at least 3 and 6 months prior, respectively, and IOL implantation in the capsular bag were included in this study. Manifest refraction and IOL information were recorded. A Scheimpflug keratometer (Pentacam) was used for corneal measurements, including the mean anterior and posterior radii of curvature, simulated keratometer (SimK), true net power (TNP), and equivalent K reading (EKR) at the 4.0-mm zone. Conventional keratometry was acquired using the IOLMaster (KMaster). The four K measurements were evaluated for calculating the predicted refraction. RESULTS: The study included 20 eyes from 19 subjects. The ratio of the posterior to the anterior corneal radius was 74.1 ± 3.24%. Comparison of the four keratometric methods (KMaster, SimK, EKR, and TNP) revealed statistically significant differences among all the methods besides KMaster and SimK. Of the four IOL calculation methods(KMaster, SimK, EKR and TNP method),the arithmetic prediction error of the KMaster, SimK, and EKR methods featured nonsignificant differences from zero(p = 0.07, 0.19 and 0.84 respectively); the EKR method calculated the highest percentage of eyes with IOLs within the prediction error. CONCLUSIONS: IOL calculations in post-DSAEK eyes using KMaster, SimK, and EKR can yield small refractive errors after surgery. The EKR (4.0-mm diameter) method was found to be the most accurate.

Comparison of Methods Study between a Photonic Crystal Biosensor and Certified ELISA to Measure Biomarkers of Iron Deficiency in Chronic Kidney Disease Patients.

The total analytical error of a photonic crystal (PC) biosensor in the determination of ferritin and soluble transferrin receptor (sTfR) as biomarkers of iron deficiency anemia in chronic kidney disease (CKD) patients was evaluated against certified ELISAs. Antigens were extracted from sera of CKD patients using functionalized iron-oxide nanoparticles (fAb-IONs) followed by magnetic separation. Immuno-complexes were recognized by complementary detection Ab affixed to the PC biosensor surface, and their signals were followed using the BIND instrument. Quantification was conducted against actual protein standards. Total calculated error (TEcalc) was estimated based on systematic (SE) and random error (RE) and compared against total allowed error (TEa) based on established quality specifications. Both detection platforms showed adequate linearity, specificity, and sensitivity for biomarkers. Means, SD, and CV were similar between biomarkers for both detection platforms. Compared to ELISA, inherent imprecision was higher on the PC biosensor for ferritin, but not for sTfR. High SE or RE in the PC biosensor when measuring either biomarker resulted in TEcalc higher than the TEa. This did not influence the diagnostic ability of the PC biosensor to discriminate CKD patients with low iron stores. The performance of the PC biosensor is similar to certified ELISAs; however, optimization is required to reduce TEcalc.

Confocal laser method for quantitative evaluation of critical optical properties of toric intraocular lenses.

PURPOSE: To present a proof-of-concept study on the development and implementation of an innovative confocal laser method platform for precise quantitative evaluation of critical optical properties unique to toric intraocular lenses (IOLs). SETTING: U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA. DESIGN: Experimental study. METHODS: The optical properties of hydrophobic toric IOLs were evaluated with a confocal laser method that was modified to isolate the 2 planes of focus that are observed with toric IOLs. RESULTS: The results show the confocal laser method has the potential to measure the orthogonally separated optical powers and then calculate them to the commonly referenced spherical equivalent and cylinder powers of toric IOLs with high accuracy (≤1 µm of focal length measurement). Furthermore, the proposed confocal laser method design includes a new component for precise differentiation of the 2 focal planes and isolation of the 2 focal points, and thus for accurate measurement of the anterior cylinder axis of toric IOLs. CONCLUSION: The modifications to the confocal laser method platform enabled the quantitative evaluation of optical properties attributed to toric IOLs. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Effect of trabeculectomy on the accuracy of intraocular lens calculations in patients with open-angle glaucoma.

BACKGROUND: The objective of the study is to examine the effect of trabeculectomy on intraocular lens power calculations in patients with open-angle glaucoma (OAG) undergoing cataract surgery. DESIGN: The design is retrospective data analysis. PARTICIPANTS: There are a total of 55 eyes of 55 patients with OAG who had a cataract surgery alone or in combination with trabeculectomy. METHODS: We classified OAG subjects into the following groups based on surgical history: only cataract surgery (OC group), cataract surgery after prior trabeculectomy (CAT group), and cataract surgery performed in combination with trabeculectomy (CCT group). MAIN OUTCOME MEASURES: Differences between actual and predicted postoperative refractive error. RESULTS: Mean error (ME, difference between postoperative and predicted SE) in the CCT group was significantly lower (towards myopia) than that of the OC group (P = 0.008). Additionally, mean absolute error (MAE, absolute value of ME) in the CAT group was significantly greater than in the OC group (P = 0.006). Using linear mixed models, the ME calculated with the SRK II formula was more accurate than the ME predicted by the SRK T formula in the CAT (P = 0.032) and CCT (P = 0.035) groups. CONCLUSIONS: The intraocular lens power prediction accuracy was lower in the CAT and CCT groups than in the OC group. The prediction error was greater in the CAT group than in the OC group, and the direction of the prediction error tended to be towards myopia in the CCT group. The SRK II formula may be more accurate in predicting residual refractive error in the CAT and CCT groups.

Can the accuracy of multifocal intraocular lens power calculation be improved to make patients spectacle free?

PURPOSE: To optimise intraocular lens (IOL) power calculation techniques for a segmental multifocal IOL, LENTIS™ MPlus(®) (Oculentis GmbH, Berlin, Germany) and assess outcomes. METHODS: A retrospective consecutive non-randomised case series of patients receiving the MPlus(®) IOL following cataract surgery or clear lens extraction was performed at a privately owned ophthalmic hospital, Midland Eye, Solihull, UK. Analysis was undertaken of 116 eyes, with uncomplicated lens replacement surgery using the LENTIS™ MPlus(®) lenses. Pre-operative biometry data were stratified into short (<22.00 mm) and long axial lengths (ALs) (≥22.00 mm). IOL power predictions were calculated with SRK/T, Holladay I, Hoffer Q, Holladay II and Haigis formulae and compared to the final manifest refraction. These were compared with the OKULIX ray tracing method and the stratification technique suggested by the Royal College of Ophthalmologists (RCOphth). RESULTS: Using SRK/T for long eyes and Hoffer Q for short eyes, 64% achieved postoperative subjective refractions of ≤±0.25 D, 83%≤±0.50 D and 93%≤±0.75 D, with a maximum predictive error of 1.25D. No specific calculation method performed best across all ALs; however for ALs under 22 mm Hoffer Q and Holliday I methods performed best. CONCLUSIONS: Excellent but equivalent overall refractive results were found between all biometry methods used in this multifocal IOL study. For eyes with ALs under 22 mm Hoffer Q and Holliday I performed best. Current techniques mean that patients are still likely to need top up glasses for certain situations.

Optical quality comparison between 2 collagen copolymer posterior chamber phakic intraocular lens designs.

PURPOSE: To compare the optical quality in vitro of 2 designs of the Visian Implantable Collamer Lens phakic intraocular lens (pIOL) for different powers and optical apertures. SETTING: University of Valencia, Valencia, Spain. DESIGN: Experimental study. METHODS: The Nimo TR1504 deflectometry device was used to measure the V4c pIOL, which has a smaller optic diameter, and the V5 pIOL, which has a larger optic diameter. The pIOLs were measured for -3.00 diopters (D), -6.00 D, -9.50 D, and -10.50 D at different optical apertures from 3.00 to 6.00 mm depending on the IOL power and model. The root mean square of higher-order aberrations (RMS HOAs) was analyzed. The Strehl ratio, point-spread functions (PSFs), and simulated images were calculated from wavefront aberrations. RESULTS: There were no statistically significant differences in any Zernike RMS or RMS HOAs between the 2 pIOL models with the same power and optical aperture (P > .05). Both pIOLs had negative spherical aberration that increased with the pIOL power. Strehl ratio values showed no statistically significant differences between the pIOLs with the same power and pupil aperture. Minimal differences were seen in the PSFs and simulated images between the pIOLs. CONCLUSIONS: Both pIOLs showed good and comparable in vitro optical quality similar that of a perfect lens in that they should not affect visual performance after implantation. Patients with larger pupil diameters could benefit from the pIOL with the larger optic diameter because it showed better in vitro optical quality than the previous design with a smaller optic diameter. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Standardized ex vivo comparison of different upper urinary tract biopsy devices: impact on ureterorenoscopes and tissue quality.

OBJECTIVES: To evaluate the influence of different biopsy forcipes on the deflection, irrigant flow, and optical characteristics of flexible ureterorenoscopes and to assess tissue quality for histopathologic evaluation in an ex vivo setting. MATERIALS AND METHODS: The following five different biopsy forcipes were compared: Olympus (FB-56D-1; diameter 5Fr.), R. Wolf (829.601; 3Fr.), Karl Storz Medical (11275ZE; 3Fr.), Boston Scientific (Piranha; 505-160; 3 Fr.), and Cook BIGopsy (115CM; 2.4 Fr.). The devices were tested in 3 different ureterorenoscopes: Storz 11278 VU (Flex-X(2)), Storz 11278 V (Flex-X(C)), and Wolf Cobra (7326071/-6). Tissue samples were obtained from porcine upper urinary tracts. RESULTS: Baseline irrigation flow rates with empty channels were significantly higher in the Wolf Cobra than in Storz ureterorenoscopes (30.5 vs. 23 and 21 ml/min). The BIGopsy forceps allowed for higher flow rates in both Storz ureterorenoscopes (2.2 and 1.3, respectively) when compared to the other devices (0.5 and 0.6 ml/min). The Storz and Wolf biopsy forcipes resulted in the highest impairment of the deflection angle. In all 3 ureterorenoscopes, flow rates and deflection angle were least impaired by the BIGopsy. However, BIGopsy compromised the field of view (20 % reduction vs. 12 % by others). The largest sample of renal pelvis and ureter biopsies was obtained with BIGopsy and Storz(®) forcipes, respectively. The extent of artifacts and denuded urothelium were comparable in all samples. CONCLUSIONS: The various biopsy devices showed different impacts on irrigation flow, deflection, and field of view. The Cook BIGopsy best retains irrigation flow in single-channel flexible ureterorenoscopes and deflection. However, a smaller field of view may complicate handling and tissue acquisition.

Comparison of the ultrasonographic method with 2 partial coherence interferometry methods for intraocular lens power calculation.

BACKGROUND: The accuracy of biometric measurements, particularly axial length, is critical for precise intraocular lens (IOL) power calculation and predictable refractive outcomes after cataract surgery. Partial coherence interferometry-based systems represent progress toward measurements that are more precise and reliable. The purpose of this study was to evaluate a new noncontact optical biometer (Lenstar; Haag-Streit AG, Koeniz, Switzerland) using optical low-coherence reflectometry and to compare the biometric measurements (including axial length, keratometry, anterior chamber depth, and IOL power) with those obtained from current clinical instrumentation. METHODS: Biometric measurements were obtained with Lenstar, IOL Master V.5 (Carl Zeiss Meditec AG, Jena, Germany), and A-scan applanation ultrasound scan combined with a Javal-type keratometer in 234 eyes of 234 subjects scheduled for cataract surgery. IOL power was calculated using Sanders, Retzlaff, Kraff II, Hoffer Q, and Holladay 1 formulas. RESULTS: The axial length readings were similar (P = 0.997). The anterior chamber depth measurements obtained by IOL Master were slightly smaller than those obtained with other devices (P = 0.092). The means of the average keratometry readings were 0.65 and 0.61 diopters lower when measured with Lenstar as compared with IOL Master and the Javal-type keratometer, respectively (P = 0.002). All of the measurements were tightly correlated (P < 0.001). For anterior chamber depth measurements, however, the correlation was slightly weaker. Using the above-mentioned formulas, the mean IOL power measurements were similar. These measurements were tightly correlated (P < 0.001). The level of agreement was acceptable and comparable between devices. CONCLUSIONS: The findings from this study show the validity and clinical utility of Lenstar compared with instrumentation currently used in clinical practice for assessing ocular biometry and IOL power calculation in cataractous eyes.