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.

Good Visual Performance Despite Reduced Optical Quality during the First Month of Orthokeratology Lens Wear.

Purpose: To measure changes in visual performances and optical quality in myopic children during the first month of wearing orthokeratology lens, and to reveal the association between those two.Methods: Thirty-five myopic children participated in this study. Visual performances were evaluated with visual acuity and shape discrimination threshold (SDT) for radial frequency patterns. Placido disc-based corneal topography for central 4 mm and 6 mm zones was collected and decomposed by Fourier analysis into the spherical, asymmetric, and regular astigmatic components. Root-mean-square of third-order, fourth-order, and total higher-order aberrations (HOA) were extracted for the 4 mm and 6 mm zones. All examinations were conducted at baseline, 1-week, and 1-month after lens dispensing. The changing trends over time and association between SDT and optical quality were analysed with linear-mixed model.Results: All subjects' uncorrected visual acuity improved to 0.1 logMAR or better at 1-week and 1-month lens wear (P < .01). SDT did not change significantly from the baseline at 1-week and 1-month after lens wear (P > .05). For the two zones with diameters of 4 mm and 6 mm, the spherical component decreased significantly at 1-week (P < .01) and remained stable thereafter (P < .01); the asymmetric component increased significantly at 1-week (P < .01) and remained high at 1-month (P < .01); and the regular astigmatism did not show any significant change throughout (P > .05). At the two zones with diameters of 4 mm and 6 mm, the third-order, fourth-order, and total HOA increased significantly over time (P < .05). Change of SDT did not correlate with impairments in optical quality (P > .05 for all parameters).Conclusions: While corneal optical quality decreased steadily during the first month following lens wearing, the visual acuity and shape discrimination sensitivity assessed by SDT remained very satisfactory.

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.

Ensuring Scientific Publishing Credibility in Translational Biomedical Optics.

Editor-in-Chief Brian Pogue writes about publishing credibility in the field of translational biomedical optics.

Reevaluation of Current Prism Standards With Recommendations to Increase Accuracy in the Measurement of Strabismus.

PURPOSE: To critically evaluate the traditional standards for holding single prisms in measuring strabismus, with the specific goal being to increase the overall accuracy of clinical measurements. DESIGN: Reliability and validity analysis. METHODS: Using an analysis involving geometric optics, the effective prism power (EPP), measured in prism diopters (PD), was calculated for glass and acrylic prisms and was the main outcome measure. These results were also validated using optical bench measurements. No patients were involved. RESULTS: Plotting the calculated effective prism power as a function of rotational angle produced curves demonstrating that the frontal plane position lies along the flatter portions of the curves, while the Prentice position lies along the steeper portions of the curves. Calculated values of prism power for the standard clinical positions as well as the percentage errors from accepted standards were compared. Acrylic prisms can be held in the frontal plane position with acceptable amounts of error (<5%) for prisms up to 50 PD. Glass prisms are capable of producing significant errors for measurements much greater than 10 PD. CONCLUSIONS: The use of glass prisms as currently calibrated should be abandoned or at least limited to small measurements. Acrylic prisms produce acceptable errors if careful attention is given to their position.

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.

In vitro optical quality of monofocal aspheric toric intraocular lenses: effect of cylindrical power.

PURPOSE: To assess the in vitro optical quality of monofocal aspheric toric intraocular lenses (IOLs) as a function of the cylindrical power. METHODS: The in vitro optical quality of the AcrySof IQ Toric IOLs SN6AT2, SN6AT3, SN6AT4, SN6AT5 and SN6AT6 (Alcon Laboratories Inc., Forth Worth, TX, USA) was assessed with an instrument conceived for measuring Zernike's coefficients at 3.0- and 5.0-mm apertures. As a reference, the aspheric monofocal lens AcrySof IQ Aspheric SN60WF (Alcon Laboratories Inc., Forth Worth, TX, USA) was also measured. The area of visibility and cut-off frequency were used to describe the modulation transfer function (MTF) of each lens; meanwhile, the light in the bucket and the diameter of a circular area centred on the point-spread function (PSF) peak that captures 50% of the light energy were used to describe the PSF of each lens. Finally, an image simulation was computed from the Zernike values with reference purposes. RESULTS: Small differences were found on the metrics used for describing the MTF and PSF of the lenses at both tested apertures, but these were not statistically significant (p > 0.05). Furthermore, the image simulation showed that these differences would not have clinical relevance at all. CONCLUSIONS: The optical performance of the AcrySof IQ toric IOLs in terms of MTF and PSF is good and seems to be independent of the cylindrical power and similar to a non-toric aspheric lens.

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.

Solid tissue simulating phantoms having absorption at 970 nm for diffuse optics.

Tissue simulating phantoms can provide a valuable platform for quantitative evaluation of the performance of diffuse optical devices. While solid phantoms have been developed for applications related to characterizing exogenous fluorescence and intrinsic chromophores such as hemoglobin and melanin, we report the development of a poly(dimethylsiloxane) (PDMS) tissue phantom that mimics the spectral characteristics of tissue water. We have developed these phantoms to mimic different water fractions in tissue, with the purpose of testing new devices within the context of clinical applications such as burn wound triage. Compared to liquid phantoms, cured PDMS phantoms are easier to transport and use and have a longer usable life than gelatin-based phantoms. As silicone is hydrophobic, 9606 dye was used to mimic the optical absorption feature of water in the vicinity of 970 nm. Scattering properties are determined by adding titanium dioxide, which yields a wavelength-dependent scattering coefficient similar to that observed in tissue in the near-infrared. Phantom properties were characterized and validated using the techniques of inverse adding-doubling and spatial frequency domain imaging. Results presented here demonstrate that we can fabricate solid phantoms that can be used to simulate different water fractions

A Surface-Coupled Optical Trap with 1-bp Precision via Active Stabilization.

Optical traps can measure bead motions with Å-scale precision. However, using this level of precision to infer 1-bp motion of molecular motors along DNA is difficult, since a variety of noise sources degrade instrumental stability. In this chapter, we detail how to improve instrumental stability by (1) minimizing laser pointing, mode, polarization, and intensity noise using an acousto-optical-modulator mediated feedback loop and (2) minimizing sample motion relative to the optical trap using a three-axis piezo-electric-stage mediated feedback loop. These active techniques play a critical role in achieving a surface stability of 1 Å in 3D over tens of seconds and a 1-bp stability and precision in a surface-coupled optical trap over a broad bandwidth (Δf = 0.03-2 Hz) at low force (6 pN). These active stabilization techniques can also aid other biophysical assays that would benefit from improved laser stability and/or Å-scale sample stability, such as atomic force microscopy and super-resolution imaging.

Continuous Wave Spectroscopy with Diffusion Theory for Quantification of Optical Properties: Comparison Between Multi-distance and Multi-wavelength Data Fitting Methods.

Typically, continuous wave spectroscopy (CWS) can be used to accurately quantify biological tissue optical properties (µ a and µ s ') by employing the diffuse reflectance information acquired at multiple source-detector separations (multi-distance). On the other hand, sample optical properties can also be obtained by fitting multi-wavelength light reflectance acquired at a single source detector separation to the diffusion theory equation. To date, multi-wavelength and multi-distance methods have not yet been rigorously compared for their accuracy in quantification of the sample optical properties. In this investigation, we compared the accuracy of the two above-mentioned quantifying methods in the optical properties recovery. The liquid phantoms had µ a between 0.004 and 0.011 mm(-1) and µ s ' between 0.55 and 1.07 mm(-1) whose optical properties mimic the human breast. Multi-distance data and multi-wavelength data were fitted to the same diffusion equation for consistency. The difference between benchmark µ a and µ s ' and the fitted results, ΔError (ΔE) was used to evaluate the accuracy of the two methods. The results showed that either method yielded ΔE within 15-30 % when values were within certain limits to standard values applicable to µ s ' and µ a for human adipose tissue. Both methods showed no significant differences in ΔE values. Our results suggest that both multi-distance and multi-wavelength methods can yield similar reasonable optical properties in biological tissue with a proper calibration.

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.

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.

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.

In vitro optical quality comparison between the Mini WELL Ready progressive multifocal and the TECNIS Symfony.

PURPOSE: To compare the optical quality between two intraocular lenses (IOLs): the Mini WELL Ready progressive multifocal (SIFI Medtech, Catania, Italy), and the TECNIS Symfony (Abbott Laboratories, Illinois, USA), which both provide a continuous range of vision from far to near positions. METHODS: The in vitro optical quality of each lens was assessed with an instrument conceived for measuring the modulation transfer function (MTF). The optical quality of each lens was described in terms of MTF, through-focus MTF, defocus tolerance, pupil dependence, and Strehl ratio MTF. These metrics were assessed for the best lens far focus, and at four vergences (from -1.5 to -3.0 D in 0.5-D steps), at 3.0 and 4.5 mm apertures. RESULTS: The through-focus curves of each lens showed two main areas: one corresponding to far-distance vision, and another to intermediate- and near-distance vision. Both lenses showed similar MTF curves and Strehl ratio values at both apertures. The optical quality of both lenses slightly decreased with the aperture for all vergences. Nevertheless, the quality of the progressive multifocal lens increased with the aperture at far-distance vision. This lens also showed the largest defocus tolerance at near-distance vision for both apertures. CONCLUSIONS: The results obtained in the present study suggest that both designs might enlarge the depth of focus. Whereas, the Mini WELL Ready showed better optical quality than the TECNIS Symfony at far vision with 4.5 mm aperture, and larger defocus tolerance than the diffractive lens at near-distance vision.

Double-integrating-sphere system at the National Institute of Standards and Technology in support of measurement standards for the determination of optical properties of tissue-mimicking phantoms.

There is a need for a common reference point that will allow for the comparison of the optical properties of tissue-mimicking phantoms. After a brief review of the methods that have been used to measure the phantoms for a contextual backdrop to our approach, this paper reports on the establishment of a standardized double-integrating-sphere platform to measure absorption and reduced scattering coefficients of tissue-mimicking biomedical phantoms. The platform implements a user-friendly graphical user interface in which variations of experimental configurations and model-based analysis are implemented to compute the coefficients based on a modified inverse adding-doubling algorithm allowing a complete uncertainty evaluation. Repeatability and validation of the measurement results of solid phantoms are demonstrated for three samples of different thicknesses, d = 5.08 mm, 7.09 mm, and 9.92 mm, with an absolute error estimate of 4.0% to 5.0% for the absorption coefficient and 11% to 12% for the reduced scattering coefficient (k = 2). The results are in accordance with those provided by the manufacturer. Measurements with different polarization angles of the incident light are also presented, and the resulting optical properties were determined to be equivalent within the estimated uncertainties.