Partial Coherence Interferometry Research Articles

Biometry measurements using a new large-coherence–length swept-source optical coherence tomographer

To evaluate the repeatability and reproducibility of the measurements obtained with the Argos, a new biometer with swept-source optical coherence tomography (SS-OCT), and to compare them with the results obtained with the IOLMaster 500 (partial-coherence interferometry [PCI]) and the Lenstar LS 900 (optical low-coherence reflectometry [OLCR]) biometers. Private practice, Lynwood, California, USA. Prospective observational study. All measurements were performed with the SS-OCT tomographer, the PCI biometer, and the OLCR biometer. Eyes (n = 107) were measured to evaluate the axial length (AL), central corneal thickness (CCT), aqueous depth, anterior chamber depth (ACD), lens thickness, pupil size, corneal diameter, and anterior corneal radius of curvature (RAV). Repeatability and reproducibility of the SS-OCT measurements showed comparable values and a low variation rate, with an interset mean difference of 0.01 mm for AL, 0.01 mm for CCT, 0.01 mm for aqueous depth and ACD, 0.03 mm for lens thickness, 0.10 mm for pupil size, 0.14 mm for corneal diameter, and 0.02 mm for RAV. The SS-OCT device correctly measured the AL in 96% of the cases compared with 79% for the OLCR device and 77% for the PCI device. Comparisons between the PCI device and SS-OCT device were -0.01 ± 0.05 mm for AL, -0.17 ± 0.20 mm for ACD, and -0.01 ± 0.05 mm for RAV. Comparison between the OLCR device and the SS-OCT device was 0.01 ± 0.06 mm for AL, 0.08 ± 0.15 mm for ACD, 0.00 ± 0.05 mm for RAV, 0.00 ± 0.01 mm for CCT, 0.07 ± 0.14 mm for aqueous depth, -0.23 ± 0.22 mm for lens thickness, -0.29 ± 0.53 mm for pupil size, and -0.34 ± 0.76 mm for corneal diameter. Axial length measurements with the new SS-OCT biometer were comparable to the PCI and OLCR measurements with a higher AL acquisition rate. Dr. Shammas is a consultant to Movu, Inc. Drs. Ortiz, Kim, and Chong have proprietary interest in the new technology.

Comparison of refractive error in phacovitrectomy for epiretinal membrane using ultrasound and partial coherence interferometry.

To compare the postoperative refractive error (RE) using A-scan ultrasound (US) and partial coherence interferometry (PCI) after phacovitrectomy for idiopathic epiretinal membrane (iERM) and cataract. Eighty-eight participants (88 eyes) with iERM and cataracts underwent phacovitrectomies with internal limiting membrane removal. Postoperative RE was the main outcome measured, calculated by subtracting intended spherical equivalent (SE) from 6-month postoperative SE. Secondary outcomes included axial length (AL) measured by 2 methods, change in best-corrected visual acuity (BCVA), and change in central subfield thickness (CSFT). Mean postoperative RE using US showed greater myopic shift compared with that using PCI (-0.569 ± 0.571 D vs -0.169 ± 0.415 D, respectively, p<0.001). The 6-month postoperative RE was within ±0.50 D in 43.2% (38/88) using US vs 84.1% (74/88) using PCI and within ±1.00 D in 84.1% (74/88) using US vs 96.6% (85/88) using PCI. Mean AL measured by US was shorter than that measured by PCI (23.50 ± 1.27 mm vs 23.58 ± 1.30 mm, respectively, p<0.001). Postsurgery, BCVA improved from 0.374 ± 0.264 logMAR to 0.144 ± 0.124 logMAR (p<0.001), and CSFT decreased from 449.2 ± 78.5 µm to 378.2 ± 47.0 µm (p<0.001). The BCVA improvement significantly correlated with decreased CSFT (R = 0.268, p = 0.011). Estimation of intraocular lens power for phacovitrectomies for iERM and cataracts is more accurate when assessed by PCI than by US.

Comparison of 3 biometry devices in cataract patients

Accurate biometry is an obligatory preoperative measurement for refractive surgery as well as cataract surgery. A new device based on partial coherence interferometry was compared with 2 currently used biometry devices. Department of Ophthalmology, Saarland University Medical Center, Homburg, Germany. Prospective case series. Eyes of cataract patients were examined with a functional prototype of the new optical low-coherence reflectometry (OLCR) biometer OA-2000, the standard OLCR biometer Lenstar, and the partial coherence interferometry (PCI) biometer IOLMaster. The results were compared using a Wilcoxon-Mann-Whitney U test and Pearson correlation calculations. A total of 138 eyes of 74 cataract patients were examined. Pearson correlation showed excellent correlation for axial length, anterior chamber depth and keratometry among the 3 devices tested. The highest correlation was found between standard OLCR biometer and PCI biometer for AL, R1, and R2 (r = 1.0, r = 0.936, r = 0.952, respectively; all P ≤ .001). For anterior chamber depth (ACD), the highest correlation was found between the standard OLCR biometer and the new OLCR biometer (r = 0.943; P ≤ .001). The mean values of AL/ACD/R1/R2 differed very little, but the differences were significant (all P ≤ .05) (new OLCR biometer 23.31/3.21/7.74/7.64 mm; standard OLCR biometer 23.30/3.13/7.80/7.60 mm; PCI biometer 23.37/3.00/7.78/7.6 mm). Compared with other clinical instruments, the new OLCR biometer generated the most accurate results. Differences especially in measurement of axial length were statistically but not clinically significant. The new OLCR biometer yielded results that correlated very well with the values of the PCI biometer and standard OLCR biometer. None of the authors has a financial or proprietary interest in any material or method mentioned.

Comparison of 2 optical biometers and evaluation of the Camellin-Calossi intraocular lens formula for normal cataractous eyes

To compare the measurements and intraocular lens (IOL) power calculations obtained with an optical biometer (AL-Scan) and partial coherence interferometry (PCI) device (IOLMaster 500), and to evaluate the accuracy of the Camellin-Calossi IOL formula in virgin eyes. Saiseikai Kurihashi Hospital, Saitama, Japan. Prospective comparative study. Measurements were compared from 262 patients (450 eyes) scheduled for cataract surgery. Axial length (AL), keratometry (K), anterior chamber depth (ACD), and number of eyes that were successfully measured were compared. Comparisons were performed of the residual postoperative refractive error with the SRK/T, Haigis, and Camellin-Calossi IOL formulas with optical biometer data. The IOL constant was optimized for 81 eyes that had iSertMicro 251 IOL implantation. The mean difference in AL between biometers was -0.012 mm ± 0.031 (SD) (P < .0001). Correlation coefficients (r) for AL, keratometry, and ACD were 0.9997, 0.9836, and 0.9571, respectively. The calculated IOL constant for the Camellin-Calossi formula was 119.3. The optimized IOL constant for the SRK/T was 118.8, the same as that of the User Group for Laser Interference Biometry for the PCI device. For the Haigis formula, only a0 was optimized, and it was 1.390. After optimizing the A-constant for the Camellin-Calossi formula, the residual postoperative refractive error of the Camellin-Calossi formula was not statistically significantly different in comparison to those obtainied with the Haigis and SRK/T formulas. Ocular biometry measurements were equivalent for both devices, indicating that the AL-Scan can be used for routine preoperative cataract assessment. The predictive accuracy of the Camellin-Calossi formula included in the optical biometer was equivalent to common IOL formulas for virgin eyes. No author has a financial or proprietary interest in any material or method mentioned.

Intraocular lens power calculation in cases with posterior keratoconus

To compare the calculation errors of intraocular lens (IOL) power in patients with posterior keratoconus and to determine which corneal refractive power is suitable for these calculations. Chukyo Hospital, Nagoya, Japan. Retrospective case series. This retrospective chart review was performed to identify eyes diagnosed with posterior keratoconus using anterior segment optical coherence tomography (AS-OCT). The keratometry (K) values were measured using an autokeratometer and partial coherence interferometry (PCI) (IOLMaster). The AS-OCT measured the total refractive corneal power and the anterior to posterior corneal curvature (A/P) ratio. Predicted refractive errors were calculated from K values based on the postoperative subjective refractive errors. The chart review of 4621 eyes found that 4 eyes of 4 patients (mean age 74.8 years ± 13.0 [SD]) were diagnosed with posterior keratoconus. The total refractive corneal power values were the smallest among all of the corneal refractive powers in all 4 eyes. The preoperative A/P ratio was 1.45 (Case 1), 1.26 (Case 2), 1.25 (Case 3), and 1.44 (Case 4). When the PCI measured K values were applied for the IOL power calculations, all of the eyes became hyperopic with postoperative refractive errors of +1.51 diopters (D) (Case 1), +0.34 D (Case 2), +0.97 D (Case 3), and +1.08 D (Case 4). When the total refractive corneal power values were applied, the errors were +0.10 D (Case 1), -0.18 D (Case 2), -0.61 D (Case 3), and -0.65 D (Case 4). The real corneal power values that take both the anterior and posterior corneal curvatures into consideration should be applied for IOL power calculations in cases with posterior keratoconus. No author has a financial or proprietary interest in any material or method mentioned.

Clinical comparison of a new swept-source optical coherence tomography–based optical biometer and a time-domain optical coherence tomography–based optical biometer

To evaluate the repeatability and reproducibility of a newer swept-source optical biometer and to compare it with a standard partial coherence interferometry (PCI) biometer. Siriraj Hospital, Mahidol University, Bangkok, Thailand. Prospective comparative study. One hundred eyes from 100 cataract patients were enrolled in this study. Each patient was measured with 2 optical biometers, a newer swept-source optical biometer (IOLMaster 700) and a standard partial coherence interferometry biometer (IOLMaster 500) by 2 independent operators. The keratometry, axial length (AL), anterior chamber depth, white-to-white corneal diameter, and intraocular lens (IOL) power, calculated by the SRK/T and the Haigis formulas for each device, were recorded. Intraoperator repeatability and interoperator reproducibility of both devices were analyzed using intraclass correlation coefficients (ICCs). Agreement of ocular biometry and IOL power between the 2 devices was evaluated using the Bland-Altman method. The repeatability and reproducibility of the swept-source and standard biometers were high for all ocular biometry parameters (ICC, 0.93-1.00). The agreement between the 2 biometers was also high (ICC, 0.92-1.00). The IOL powers obtained from both devices were not distinct. Because of the density of the cataracts, the AL in 5 eyes could be measured only by the swept-source biometer. Repeatability and reproducibility of a swept-source optical biometer was excellent and agreement with a standard biometer was very high. Better lens penetration ability and AL measurements were obtained with the swept-source biometer than with the standard biometer. No author has a financial or proprietary interest in any material or method mentioned.

Anterior chamber depth studies

To compare the anterior chamber depth (ACD; corneal epithelium to lens) using 3 modalities and compare the change 1 day and 3 months postoperatively. Private practice, Santa Monica, California, USA. Nonrandomized prospective series. The mean optical pachymetry and immersion ultrasound (US) of the ACD and partial coherence interferometry (PCI) were measured. Optical pachymetry ACD was measured in 675 eyes postoperatively at 1 day and 3 months. The optical pachymetry ACD in 492 eyes was 3.17 mm ± 0.42 (SD); by immersion US, it was 2.99 ± 0.51 mm (0.18 mm deeper; P < .0001). In 178 eyes, the optical pachymetry ACD was 3.23 ± 0.45 mm; the PCI was 3.19 ± 0.48 mm (0.04 mm deeper), which was not statistically different (P > .05). In 675 eyes, optical pachymetry ACD preoperatively was 3.19 ± 0.40 mm. The postoperative 1-day optical pachymetry ACD was 4.35 ± 0.35 mm with a mean refractive error of -0.30 diopter (D); the final 3-month optical pachymetry ACD was 4.47 ± 0.31 mm, with a mean refractive error of -0.07 D (P < .0001). This is a mean intraocular lens (IOL) position shift of +0.12 mm posteriorly; the +0.23 D change represents a ratio of 1.92 D/mm of IOL axial movement. The PCI ACD was comparable with optical pachymetry, but careful immersion US led to a 0.18 mm shorter ACD reading that cannot be corrected by sound velocity. The posterior capsule contracted and moved the IOL posteriorly 0.12 mm, resulting in 0.23 D hyperopic shift. Dr. Hoffer owns the registered trademark name "Hoffer(®)" and receives royalties for its commercial use from Alcon Laboratories, Inc., Appasamy Associates, Carl Zeiss Meditec AG, DGH Technology, Inc., Ellex iScience, Inc., Haag-Streit AG, Nidek Co., Ltd., Tomey Corp., Topcon Medical Systems, Inc., and Ziemer USA, Inc., as well as royalties from Slack, Inc. for the textbook IOL Power. Neither author has a financial or proprietary interest in any material or method mentioned.

Ocular biometry in the adult population in rural central China: a population-based, cross-sectional study.

To describe the distribution and determinants of ocular biometric parameters and to ascertain the relative importance of these determinants in a large population of adults in rural central China. A population-based, cross-sectional study performed in rural central China included 1721 participants aged 40 or more years. Ocular biometrical parameters including axial length (AL), anterior chamber depth (ACD), radius of corneal curvature (K) and horizontal corneal diameter [white-to-white (WTW) distance] were measured using non-contact partial coherence interferometry [intraocular lens (IOL)-Master]. Ocular biometric data on 1721 participants with a average age of 57.0±8.7y were analyzed at last. The general mean AL, ACD, mean corneal curvature radius (MCR), WTW were 22.80±1.12, 2.96±0.36, 7.56±0.26 and 11.75±0.40 mm, respectively. The mean values of each parameter in 40 to 49, 50 to 59, 60 to 69, and 70 to 91 years age groups were as follows: AL, 22.77±0.87, 22.76±1.06, 22.89±1.41, 22.92±0.80 mm; ACD, 3.10±0.32, 2.98±0.34, 2.86±0.36, 2.77±0.35 mm; MCR, 7.58±0.25, 7.54±0.26, 7.55±0.26, 7.49±0.28 mm; WTW, 11.79±0.38, 11.75±0.40, 11.72±0.41, 11.67±0.41 mm. The AL, ACD, MCR and WTW were correlated with age and the AL was correlated with height and weight. Our findings can serve as an important normative reference for multiple purposes and may help to improve the quality of rural eye care.

Validation of a partial coherence interferometry method for estimating retinal shape.

To validate a simple partial coherence interferometry (PCI) based retinal shape method, estimates of retinal shape were determined in 60 young adults using off-axis PCI, with three stages of modeling using variants of the Le Grand model eye, and magnetic resonance imaging (MRI). Stage 1 and 2 involved a basic model eye without and with surface ray deviation, respectively and Stage 3 used model with individual ocular biometry and ray deviation at surfaces. Considering the theoretical uncertainty of MRI (12-14%), the results of the study indicate good agreement between MRI and all three stages of PCI modeling with <4% and <7% differences in retinal shapes along horizontal and vertical meridians, respectively. Stage 2 and Stage 3 gave slightly different retinal co-ordinates than Stage 1 and we recommend the intermediate Stage 2 as providing a simple and valid method of determining retinal shape from PCI data.

Comparability of anterior chamber depth measurements with partial coherence interferometry and optical low-coherence reflectometry in pseudophakic eyes

To assess whether anterior chamber depth (ACD) measurements in pseudophakic eyes obtained with partial coherence interferometry (PCI) and optical low-coherence reflectometry (OLCR) devices can be used interchangeably. Vienna Institute for Research in Ocular Surgery, A Karl Landsteiner Institute, Hanusch Hospital, Vienna, Austria. Prospective case series. The ACD measurements in 1 eye of each pseudophakic patient were performed with the PCI-based ACMaster device and the OLCR-based Lenstar LS900 device at least 1 day postoperatively. The study comprised 65 eyes of 65 patients with a mean age of 71.7 years ± 9.0 (SD) (range 39 to 91 years). In 15 eyes, no valid ACD readings could be obtained with the OLCR device. No obvious reason for these measurement failures was identified; however, tear-film alterations shortly after surgery were suspected. No significant difference in the mean ACD in the remaining 50 eyes was found between PCI measurements (5019 ± 660 μm; range 4008 to 6181 μm) and OLCR measurements (5015 ± 663 μm; range 4017 to 6163 μm) (P = .06). Three (6%) of 50 measurements were not within the 95% limits of agreement in the Bland-Altman analysis. Pseudophakic ACD measurements with the PCI and OLCR devices can be used interchangeably. The OLCR device proved to be more user-friendly and faster; however, in a substantial number of eyes, no usable values were obtainable. No author has a financial or proprietary interest in any material or method mentioned.

Refractive outcomes of Descemet membrane endothelial keratoplasty triple procedures (combined with cataract surgery)

To describe the refractive outcomes of triple Descemet membrane endothelial keratoplasty (DMEK). Retrospective case series. The study included patients with Fuchs endothelial dystrophy and cataract without coincident pathology. Outcomes of 108 sequential triple DMEK procedures were evaluated. With a mean follow-up of 11.9 months, the median corrected distance visual acuity (CDVA) was 20/20 (range 20/15 to 20/40) and the median uncorrected distance visual acuity in eyes with a distance target (n = 84) was 20/40 (range 20/20 to 20/200). Forty-five percent of patients gained 3 or more lines of CDVA. The median refractive error was +0.43 diopter (D) (interquartile range, -0.34 to +1.17 D). Aspheric intraocular lenses (IOLs) (n = 91) did not significantly change refractive astigmatism (mean: preoperative +0.926 D ± 0.144 [SD]; postoperative +0.945 ± 0.129 D) (P = .83), while toric IOLs (n = 9) did (mean: preoperative +2.47 ± 0.36 D; postoperative +0.94 ± 0.90 D) (P = .0015). The anterior curvature measured by Scheimpflug imaging (Pentacam) did not significantly change (mean -0.06 ± 0.47) (P = .41); however, keratometry by partial coherence interferometry (IOLMaster) did (mean -0.6 ± 0.9 D) (P < .0001). Triple DMEK safely achieved excellent CDVA. Selection of the optimum IOL power is complicated by several factors. Because Fuchs dystrophy induces changes predominately in the central cornea, measurements averaging curvature over a larger area might underreport significant refractive deviations. In the absence of an algorithm to more precisely individualize IOL calculations, a refractive target of -0.75 to -1.00 D will help reduce the proportion of eyes left hyperopic. No author has a financial or proprietary interest in any material or method mentioned.

English

Abstract This cross-sectional study aimed to describe the variation in ocular biometry and investigate the relationship among the parameters of the adult cataract surgery candidates at the Zhongshan Hospital, Fudan University, Shanghai, China. The study included 1975 cataract patients (1975 eyes) aged from 18 to 95 years old. Axial length (AL), corneal curvature, anterior chamber depth (ACD) and horizontal corneal diameter (white-to-white [WTW] distance) were optically measured by partial coherence interferometry (IOL Master). Spearman rank correlation coefficients were used to evaluate bivariate correlations. The average AL and the mean corneal curvature were 24.86 ± 2.72 mm and 44.13 ± 1.58 D, respectively. The mean ACD and WTW were 3.11 ± 0.50 mm and 11.83 ± 0.42 mm, respectively. The mean corneal curvature was negatively correlated with AL, especially in the range of AL from 22 mm to 25 mm, while ACD and WTW were positively correlated with AL. However, the correlation coefficient between AL and WTW was relatively low. Slight corneal astigmatism, especially against-the-rule (ATR) astigmatism, was common in cataract patients. Corneal curvature seemed to be relatively flat to compensate for the long axial length achieving the emmetropic state in limited range. Corneal expansion was limited with the increasing of axial length.

Effect of keratoconus grades on repeatability of keratometry readings: Comparison of 5 devices

To determine the repeatability of keratometry (K) measurements of a Scheimpflug pachymeter (Pentacam), Placido topographer (Eyesys), scanning-slit corneal topographer (Orbscan), partial coherence interferometry (PCI) device (IOLMaster), and Javal manual keratometer with different grades of keratoconus. Noor Eye Hospital, Tehran, Iran. Retrospective case series. Keratometry was performed first with Scheimpflug pachymetry followed, in order, by Placido topography, scanning-slit corneal topography, PCI, and manual keratometry. Repeatability was examined in groups with a maximum K of less than 50.0 diopters (D), 50.0 to 55.0 D, and more than 55.0 D. Seventy-eight eyes of 45 keratoconus patients were assessed. In Group 1, repeatability was highest with Scheimpflug pachymetry and lowest with scanning-slit corneal topography (0.36 to 1.24). In Group 2, the intraclass correlation coefficients (ICCs) for maximum K ranged from 0.823 with the scanning-slit corneal topography to 0.974 with Scheimpflug pachymetry. The repeatability index for minimum K (0.53 to 2.11) and maximum K (0.60 to 1.92) in this group was highest with Scheimpflug pachymetry and with for scanning-slit corneal topography. In Group 3, the ICCs for minimum K and maximum K ranged from 0.890 to 0.990, and the repeatability index for minimum K varied between 1.66 with Scheimpflug pachymetry to 2.98 with Placido topography; for maximum K, the index was from 2.15 with PCI to 2.81 with the manual keratometer. In mild keratoconus, the 5 devices had acceptable repeatability in K readings. In cases with a maximum K reading greater than 55.0 D, all devices had reduced repeatability as a result of measurement errors; thus, measurements might not be so reliable.

Effect of pupil dilation on biometry measurements with partial coherence interferometry and its effect on IOL power formula calculation.

To determine if there are any differences between eye parameters measured by the IOLMaster (Carl Zeiss Meditec AG, Jena, Germany) biometer before and after dilating the pupil. The effect of those changes on intraocular lens (IOL) power calculation is also analyzed. A prospective observational study was carried out including 107 right eyes of 107 patients with cataract and no other ocular morbidity. An IOLMaster baseline measurement included axial length (AL), mean keratometry (K), and anterior chamber depth (ACD) (corneal epithelium to lens). A second measurement was taken 45 minutes after instillation of topical tropicamide and phenylephrine. Biometric variation was analyzed and prediction for IOL power based on the Haigis and the Sanders/Retzlaff/Kraff Theoretical (SRK/T) formulas was calculated for both measurements. The ACD increased significantly after dilation (+0.12 ± 0.12 mm; p&lt;0.01). The AL and K variation was not significant: +0.00 ± 0.02 mm (p = 0.62) and +0.01 ± 0.22 D (p = 0.57), respectively. Pupil dilation did not affect IOL power calculation based on SRK/T formula either targeting emmetropia (-0.02 ± 0.26, p = 0.30) or the lowest myopic residual refraction (-0.03 ± 0.34, p = 0.30). However, using the Haigis formula significantly changed calculations for emmetropia (0.07 ± 0.34, p = 0.03) and for the lowest myopic refraction (0.10 ± 0.40, p = 0.01). Pupil pharmacologic dilation produces a significant increase in ACD when measured by the IOLMaster. This change results in a different IOL power prediction according to the Haigis formula, which calculates the effective lens position taking into account the ACD.

Longitudinal Relationship between Axial Length and Height in Chinese Children: Guangzhou Twin Eye Study.

To understand the growth model of axial length (AL) and height, and to explore the relationship between the two with the passage of time. We followed twins in the Guangzhou Twin Eye Study for five years. The AL of both eyes was measured by partial coherence interferometry, and height was measured by a standard scale during each visit. A multivariate multilevel mixed model was adopted for data analysis. A total of 1217 children were included in the study. Both AL and height increased, but the rate of growth slowed down with age. The mitigation rate of height growth was -0.34 cm/year; while that of AL growth was -0.01 mm/year. AL was positively related to height, with a relevant coefficient of R = 0.22 (Cov [height intercept, AL intercept] = 1.56, 95% CI = 1.14 to 1.99). The growth rates of AL and height were also positively related, with a relevant coefficient of R=0.18 (Cov [height slope, AL slope] = 0.03, 95% CI = 0.01 to 0.05). However, taller children had slower rates of height increases, with a relevant coefficient of R = -0.12 (Cov [height intercept, height slope] = -1.33, 95% CI = -2.25 to -0.42); but had faster AL growth, with a relevant coefficient of R = (Cov [height intercept, AL slope] = 0.02, 95% CI = -0.05 to 0.08, R = 0.02). AL and its growth rate were positively related to each other, with a relevant coefficient of R = (Cov [AL intercept, AL slope] = 0.04, 95%CI = 0.03 to 0.05, R = 0.3); while the growth rates of AL and height were negatively related to each other, with a relevant coefficient of R = (Cov [AL intercept, height slope] = -0.03 95%CI = -0.16 to 0.1, R = -0.02). The increase in children's AL is relevant to their height increases. The faster their height increases, the faster their AL increases.

Comparison of corneal astigmatism measurements of 2 optical biometer models for toric intraocular lens selection

To compare corneal astigmatism measurements obtained using a new optical biometer (AL-Scan) and a standard biometer based on partial coherence interferometry (IOLMaster 500) for toric intraocular lens (IOL) selection. Siriraj Hospital, Mahidol University, Bangkok, Thailand. Prospective comparative study. Keratometry (K) readings were taken with the 2 biometers in eyes of cataract patients. The corneal astigmatism readings from the 2 devices were compared. The cylinder measurements were transformed into J0 and J45 vector components for analysis, and the devices' values were compared using the paired t test. Correlation coefficients were calculated. The Bland-Altman method was used to evaluate the agreement between the sets of measurements. One hundred thirty-seven eyes (81 patients) were enrolled. The magnitude of astigmatism between the new biometer 2.4 mm zone and the standard biometer was similar (P = .19). There was a statistically significant difference between values from the new biometer 3.3 mm zone and the standard biometer (P < .05). There was good correlation in the overall magnitude of astigmatism between devices. There was a trend of low correlation toward the flat cornea (K <43.0 diopters [D]), low corneal cylinder (<1.0 D), and with-the-rule astigmatism. The IOL toricity calculated from both devices was similar. Corneal astigmatism measurements with the 2 biometers were similar in magnitude, especially in 2.4 mm zone of the new biometer. There was no difference in the toric IOL selections between the devices. No author has a financial or proprietary interest in any material or method mentioned.

Medical Optical Coherence Tomography (OCT) and Medical Partial Coherence Interferometry (PCI)

This paper gives a short introduction to optical coherence tomography (OCT) and partial coherence interferometry (PCI). Basic principles and important techniques are explained. Recent papers describing applications of OCT and PCI in the medical field are reviewed.

Effect of a capsular tension ring on axial intraocular lens position.

To assess the effect of a capsular tension ring (CTR) on the postoperative anterior chamber depth (ACD). Vienna Institute for Research in Ocular Surgery, Department of Ophthalmology, Hanusch Hospital, Vienna, Austria. Prospective observer- and patient-masked randomized trial. Bilateral small-incision cataract surgery with implantation of a hydrophobic acrylic single-piece intraocular lens (IOL) (Tecnis ZCB00) was performed using a standard technique. Each patient received a CTR in 1 eye (CTR group) and no CTR in the fellow eye (control group). The ACD was measured preoperatively with biometry (IOLMaster 500) and at 1 hour and 12 weeks postoperatively using partial coherence interferometry (ACMaster). The subjective refraction was assessed at 12 weeks. Sixty eyes (30 patients) were included. Preoperatively, the mean axial length was 23.36 mm ± 1.55 (SD) (range 21.01 to 29.46 mm) in the CTR group and 23.37 ± 1.70 mm (range 21.14 to 28.84 mm) in the control group and the mean ACD was 3.06 ± 0.45 mm (range 2.25 to 4.16 mm) and 3.03 ± 0.47 mm (range 2.18 to 4.10 mm), respectively. The differences were not statistically significant (P=.148 and P=.074, respectively). The mean postoperative ACD was 4.83 ± 0.46 mm (range 3.84 to 5.76 mm) in the CTR group and 4.81 ± 0.43 mm (range 3.67 to 5.65 mm) in the control group. The difference between the groups was not statistically significant (P=.329). Implantation of a CTR had no significant influence on the postoperative axial IOL position. No author has a financial or proprietary interest in any material or method mentioned.

Measurement Reliability of Axial Length of the Human Eye by using Partial Coherence Interferometry

To investigate the minimum near-infrared ray intensity required (quantifiable threshold value) for consistent measurements of axial length (AL) using partial coherence interferometry (PCI), we attached two polarizing lenses (PL) to two types of PCI (IOLmaster, ALscan). The near-infrared ray intensity of PCI was modified by rotating the axis of one PL at intervals of 5 degrees. The right eye of each volunteer was measured three times and the AL and signal-to-noise ratio (SNR) was recorded five times for each measurement. Reduction of light intensity was theoretically estimated using Malus' Law. AL was measured consistently with both IOLmaster and ALscan until they reached 55 degrees (1.33 % of intensity) and 60 degrees (0.77%), respectively (P = 0.343, Log-rank test). In contrast, SNR decreased as light intensity decreased. In addition, to analyze media opacities that precluded measurement of AL, we retrospectively reviewed the medical records of patients unmeasurable by PCI (ALscan) from May to November 2013. Thirty-eight of 473 eyes (8.0%) could not be measured using ALscan due to media opacities, such as severe posterior subcapsular cataract (PSC, 11 eyes), hypermature cataract (9 eyes), and vitreous hemorrhage (18 eyes). The mean grades of vitreous haze and PSC were <TEX>$7.72{\pm}0.96$</TEX> and <TEX>$4.45{\pm}1.04$</TEX>, respectively. In conclusion, up to 0.77-1.33% of near-infrared rays decreased, and AL could be measured consistently.

Short-term refractive change and ocular parameter changes after cycloplegia.

To explore short-term refractive and ocular parameter changes and their correlations after cycloplegia with tropicamide. This study prospectively enrolled 114 right eyes of 114 participants (mean [±SD] age, 9.1 [±2.8] years). Spherical equivalent of refractive error (SER), axial length (AL), corneal curvature (CC), and anterior chamber depth (ACD) were measured before and after 30 minutes from instillation of 0.4% tropicamide. A partial optical coherence interferometry (Zeiss IOLMaster) was used for ocular parameter measurement. Refractive change and ocular parameter changes after cycloplegia and their correlations were evaluated. Spherical equivalent of refractive error, AL, and ACD all positively shifted significantly at 30 minutes after application of 0.4% tropicamide (p < 0.0001 for each parameter measured). After cycloplegia, 28 eyes (24.6%) had a hyperopic shift of more than 0.25 diopters (D), 3 eyes (2.6%) had a myopic shift of more than 0.25 D, and 83 eyes (72.8%) had their SER changes within -0.25 to 0.25 D. The mean, maximum, and minimum keratometric values all decreased (p = 0.005, 0.03, and 0.05, respectively), whereas corneal astigmatism did not change significantly. The changes in AL, ACD, or mean keratometric values contributed little to the refractive changes after cycloplegia by tropicamide (p > 0.05, pr ≤ 0.01 for all values). Spherical equivalent of refractive error, AL, and ACD all positively shifted after cycloplegia with tropicamide. Corneal curvature became flattened after cycloplegia with tropicamide, but the corneal astigmatism did not change significantly. Refractive changes did not correlate with changes in AL, ACD, or CC after cycloplegia with tropicamide.