Influence of severity of nuclear cataract on optical biometry

Comparison of the ocular ultrasonic and optical biometry devices in the different quality measurements

PURPOSE

To compare the reliability and agreement of axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) measurements obtained with optical biometry based on swept-source optical coherence tomography (IOLMaster 700; Carl Zeiss, Germany) and an ultrasound biometry device (Nidek; US-4000 Echoscan, Japan) in different qualities of AL measurement.

METHODS

A total of 239 consecutive eyes of 239 cataract surgery candidates with a mean age of 56 ± 14 years were included. The quality measurements were grouped according to the quartiles of SD of the measured AL by IOLMaster 700. The first and fourth quartile's SD are defined as high and low-quality measurement, respectively, and the second and third quartiles' SD is defined as moderate-quality.

RESULTS

The reliability of AL and ACD between the two devices in all patients and in different quality measurement groups was excellent with highly statistically significant (AL: all ICC=0.999 and P<0.001, ACD: all ICC>0.920 and P<0.001). AL and ACD in all quality measurements showed a very strong correlation between devices with highly statistically significant. However, there was poor (ICC=0.305), moderate (ICC=0.742), and good (ICC=0.843) reliability in measuring LT in low-, moderate-, and high-quality measurements, respectively. LT showed a very strong correlation (r = 0.854) with highly statistically significant (P<0.001) between devices only in patients with high-quality measurements.

CONCLUSIONS

AL and ACD of the IOLMaster700 had outstanding agreements with the US-4000 ultrasound in different quality measurements of AL and can be used interchangeably. But LT should be used interchangeably cautiously only in the high-quality measurements group.

Relationship between the main components of the crystalline lens and the anterior chamber depth after cataract formation

PURPOSE

To assess the relationship between anterior chamber depth (ACD) and lens thickness (LT), as well as its three main components (anterior and posterior cortex and nucleus thickness), in cataractous and non-cataractous eyes, depending on the axial length (AxL).

METHODS

Anterior and posterior cortex and nucleus thickness of the crystalline lens, ACD, and AxL were measured using optical low-coherence reflectometry in cataractous and non-cataractous eyes. They were also classified into hyperopia, emmetropia, myopia, and high myopia, depending on AxL; thus, eight subgroups were created. A minimum sample size of 44 eyes (of 44 patients) for each group was recruited. Linear models were fitted for the whole sample and each AxL subgroup to assess if there were differences in the relationships between the crystalline lens variables and ACD, including age as a covariate.

RESULTS

Three hundred seventy cataract patients (237 females, 133 males) and 250 non-cataract controls (180 females, 70 males), aged 70.5 ± 9.4 and 41.9 ± 15.5 years, respectively, were recruited. The mean AxL, ACD, and LT for the cataractous and non-cataractous eyes were 23.90 ± 2.05, 24.11 ± 2.11, 2.64 ± 0.45, and 2.91 ± 0.49, 4.51 ± 0.38, 3.93 ± 0.44 mm, respectively. The inverse relationship of LT, anterior and posterior cortex, and nucleus thickness with ACD was not significantly (p ≥ 0.26) different between cataractous and non-cataractous eyes. Further subclassification of the sample depending on AxL showed that the inverse relationship between the posterior cortex and ACD was no longer significant (p > 0.05) for any non-cataractous AxL group. LT, anterior and posterior cortex, and nucleus thickness was not significantly (p ≥ 0.43) different between cataractous and non-cataractous eyes for the whole sample, and all AxL groups after adjusting for age.

CONCLUSIONS

The presence of cataracts does not modify the inverse relationship of the LT, anterior and posterior cortex, and nucleus with ACD. And this relationship does not seem to depend importantly on AxL. Besides, the possible differences in LT, anterior and posterior cortex, and nucleus between cataractous and non-cataractous eyes may not be caused by lens opacification, but possibly by the progressive lens growth due to aging.

Evaluation of Ocular Biometric Parameters Following Cataract Surgery

Background: The aim of this study was to highlight the structural changes in patients with cataract following surgery and the repercussions on the anterior pole. Methods: A total of 83 patients diagnosed with cataract who underwent uneventful phacoemulsification was included. Every patient was examined one week prior to and two weeks after the surgery. Pre- and postoperative assessment included examination of the anterior and posterior segment, keratometry, and optical biometry. Results: The pre- vs. postoperative axial length (AL) mean difference was 0.07 ± 0.18 mm (p < 0.001).The mean difference of the postoperative anterior chamber depth (ACD) vs. preoperative ACD values (1.11 ± 0.50 mm) was also statistically significant (p < 0.001). The linear regression function postoperative central corneal thickness (CCT) = 0.9004 × (preoperative CCT) + 0.0668, where it characterized a reduced positive correlation (R2) of 68.89% between the postoperative CCT and preoperative CCT. The mean pre-/post-operative differences in the K1 values were 0.08 ± 0.38 D, with a statistically significant difference between the two datasets (p = 0.0152). The mean pre/postoperative difference in the K2 values was 0.002 ± 0.58 D (p = 0.4854). Conclusions: ACD deepened significantly postoperatively. Regarding AL, there was a decrease after surgery, and a very good positive correlation between the post and preoperative values. The CCT values decreased with age. The 2.2-mm corneal incision during cataract surgery resulted in a relatively small postoperative residual astigmatism.

Preliminary demonstration of a novel intraocular lens power calculation: the O formula

PURPOSE

To evaluate the performance of a new formula of intraocular lens (IOL) power calculation (the O formula) based on ray tracing without commonly used parameters, including ultrasound-compatible axial length, keratometry readings, and A-constant.

SETTING

Tokyo Medical Center, Tokyo, Japan.

DESIGN

Retrospective consecutive case series.

METHODS

423 eyes (423 patients) implanted with a single-piece, L-loop, acrylic IOL were enrolled. All biometric data for the O formula were obtained by anterior segment swept-source optical coherence tomography (SS-OCT) and SS-OCT-based biometer. The performance of the O formula was compared with those of the Barrett Universal II (BUII) and Kane formulas at 1 month postoperatively. Statistical analysis was applied according to a heteroscedastic test with SD of prediction errors as the main parameter for formula performance.

RESULTS

The SD of the O formula (0.426) was statistically significantly lower than that of the BUII formula (0.464, P = .034) but not statistically significantly different from that of the Kane formula (0.433, P = .601). The percentages of patients with refractive prediction errors within ±0.50 diopter (D) and ±1.00 D of the O, BUII, and Kane formulas were 75.4% and 98.6%, 77.1% and 97.9%, and 76.6% and 98.1%, respectively.

CONCLUSIONS

The O formula, based on ray tracing using SS-OCT-based devices, is one of the promising approaches for IOL power calculation, although additional larger scale studies are needed. It may be used as an alternative in IOL power calculation because of its independence from commonly used parameters.

Ocular biometry in dense cataracts: Comparison of partial-coherence interferometry, swept-source optical coherence tomography and immersion ultrasound

Purpose:

To assess the axial length (AL) measurement failure rate using partial-coherence interferometry (PCI) and swept-source optical coherence tomography (SS-OCT) in dense cataracts. As a secondary outcome, the SS-OCT biometry was compared to immersion ultrasound.

Methods:

This is a prospective cross-sectional and comparative study. Seventy eyes from 70 patients with dense cataracts were enrolled in this study. Dense cataract was defined according to the Lens Opacities Classification System III (LOCS III) scores equal to or more than NO4, NC4, C4, and P3. The failure rate of AL measurement was evaluated using PCI and SS-OCT. Anterior chamber depth (ACD), lens thickness (LT), and AL measurements obtained by SS-OCT were compared with IUS.

Results:

AL measurement failure rate with PCI was 68.57% and 21.43% with SS-OCT (P = 0.007). AL measurement was achieved in 69.23% of NO4, 66.6% of P3, and 15.3% of mixed cataracts using PCI, while SS-OCT was achieved in 100% of NO4, NO5, P3, and P5 and 76.9% of mixed cataracts. Cortical cataracts alone did not influence AL measurement. Biometric data of ACD, LT, and AL were statistically different comparing US and SS-OCT with a good correlation of AL.

Conclusion:

SS-OCT significantly improves the rate of successful AL measurements when compared to PCI in dense cataracts. The LOCS III clinical cut-off for the use of SS-OCT ocular biometry may well be up to P4 and NO5.

The measurement of ocular axial length in normal human eyes based on an improved Twyman-Green interferometer

In order to meet the demands of myopia prevention, as well as the increasing needs of measurement for refractive and cataract operations in China, a new axial length (AL) measurement system combining an improved Twyman-Green interferometer with digital signal processing has been established. The ALs of 33 eyes of different optical refractive subjects (-8.50 ~ 0.50 D) were measured with the New AL and intraocular lens (IOL) master. The repeatability of measurements with the New AL was assessed using coefficient of variation (CoV) and intra-group correlation coefficient (ICC). Comparison, correlation, linear regression and agreement of AL between devices were analyzed. There was good repeatability (CoV = 0.0617%, ICC = 0.9999) with the New AL and great agreement has been obtained with both devices. These show that the New AL is capable of providing precise AL values over the normal AL range compared to the IOL master, and indicate that the New AL developed can be used for routine clinical AL measurements.

Axial Length Change in Pseudophakic Eyes Measured by IOLMaster 700

Purpose

The purpose of this study was to investigate the change in axial length (AL) after cataract surgery measured by swept source optical coherence tomography (IOLMaster 700), and explore ways to eliminate this AL measurement error in pseudophakic eyes.

Methods

Patients with cataract who underwent unilateral phacoemulsification with four types of intraocular lens (IOLs) implantation (Asphina 509M, Tecnis PCB00, enVista MX60, and Acrysof SN60WF) were enrolled. Bilateral AL measurements were performed before and 1 month after cataract surgery utilizing IOLMaster 700. The postoperative AL of the operated eye was evaluated using three different modes (phakic, aphakic, and pseudophakic), and the fellow eye was measured by phakic mode. Associations among the AL change and cataract grade, lens thickness, preoperative AL, or refractive index of IOL were investigated using stepwise multivariate linear regression.

Results

A total of 305 patients with cataract with mean age of 65.97 ± 13.39 years were recruited. The mean postoperative AL was 0.10 mm and 0.21 mm shorter than the pre-operative AL utilizing pseudophakic and phakic modes, respectively (P < 0.001). No significant difference was observed between pre-operative and postoperative AL using aphakic mode (P = 0.264). There were no significant associations among AL change in pseudophakic eye and cataract grade, lens thickness, pre-operative AL, or refractive index of IOL (P > 0.05).

Conclusions

A correction factor of 0.10 mm is suggested to eliminate AL measurement error of IOLMaster 700 in pseudophakic eyes before further improvement of AL measurement accuracy.

Translational Relevance

Our study may help to eliminate the AL measurement error of IOLMaster 700 in pseudophakic eyes.

Effect of cataract-induced refractive change on intraocular lens power formula predictions

Cataract-induced refractive change (CIRC) is the change in refraction induced by a cataract. It can amount to several diopters (D). It alters predicted errors in refraction following cataract surgery through changes in axial length measurement. This study determined the effect of CIRC on the accuracy of intraocular lens power formula predictions of refraction in 872 eyes of 662 patients. Regression of results gave -0.030 D prediction error per 1 D of CIRC, i.e. cataract-induced myopia and hyperopia tended to yield postoperative hyperopia and myopia, respectively. Theoretical determinations with a model eye supported this result. There was significant correlation of nuclear cataract opalescence with CIRC. Although these effects are difficult to identify based on changes in refraction, if biometers were able to identify cataract density and automatically adjust axial length measurement, IOL power predictions might improve.

Could anatomical changes occurring with cataract surgery have a clinically significant effect on effective intraocular lens position?

PURPOSE

To assess if the calculation of the effective lens position (ELP) of two different monofocal intraocular lenses (IOLs) could be optimized by considering the potential anatomical changes occurring after cataract surgery.

METHODS

Prospective, descriptive, single-center study involving 472 eyes of 280 subjects (mean age 73.5 years) undergoing cataract surgery that were divided into two groups according to the IOL implanted: group 1330 eyes with AcrySof IQ SN60WF (Alcon), and group 2142 eyes with Akreos MI60L (Bausch + Lomb). Refractive and biometric changes were evaluated during a period of 6-month follow-up with an optical biometer (considering potential measurement artifacts). Comparison of ELP estimated with the SRK-T formula (ELP_SRK-T) and ELP calculated considering clinical real data was made (ELP_{AXL-corrected clinical}).

RESULTS

Besides significant changes in refraction (p ≤ 0.020), a significant increase in anterior chamber depth (ACD) (p < 0.001) and a significant reduction in the axial length (AXL) (p < 0.001) were detected at 1 month after surgery. Mean 1-month postoperative AXL change was - 0.08 ± 0.06 and - 0.10 ± 0.11 mm in groups 1 and 2, respectively (p = 0.001), with no significant changes afterward. Mean difference between ELP_SRK-T and ELP_{AXL-corrected clinical} was 0.17 ± 0.39 and - 0.23 ± 0.43 mm in groups 1 and 2, respectively (p < 0.001). A strong and statistically significant correlation of these differences with the prediction refractive error was found in both groups (group 1, r =  - 0.723; group 2, r =  - 0.819; p < 0.001).

CONCLUSIONS

The estimation of ELP using the SRK-T formula for the two IOLs evaluated may be optimized considering biometric changes with surgery, helping to understand better some problems of refractive unpredictability.

Comparison of composite and segmental methods for acquiring optical axial length with swept-source optical coherence tomography

This study compared the optical axial length (AL) obtained by composite and segmental methods using swept-source optical coherence tomography (SS-OCT) devices, and demonstrated its effects on the post-operative refractive errors (RE) one month after cataract surgery. Conventional AL measured with the composite method used the mean refractive index. The segmented-AL method used individual refractive indices for each ocular medium. The composite AL (24.52 ± 2.03 mm) was significantly longer (P < 0.001) than the segmented AL (24.49 ± 1.97 mm) among a total of 374 eyes of 374 patients. Bland–Altman analysis revealed a negative proportional bias for the differences between composite and segmented ALs. Although there was no significant difference in the RE obtained by the composite and segmental methods (0.42 ± 0.38 D vs 0.41 ± 0.36 D, respectively, P = 0.35), subgroup analysis of extremely long eyes implanted with a low power intraocular lens indicated that predicted RE was significantly smaller with the segmental method (0.45 ± 0.86 D) than that with the composite method (0.80 ± 0.86 D, P < 0.001). Segmented AL with SS-OCT is more accurate than composite AL in eyes with extremely long AL and can improve post-operative hyperopic shifts in such eyes.

The influence of low signal-to-noise ratio of axial length measurement on prediction of target refraction, achieved using IOLMaster

Purpose

To evaluate the influence of low signal-to-noise ratio (SNR) of axial length measurement, achieved using IOLMaster, on prediction of target refraction.

Methods

A total of 131 eyes of 131 patients who underwent phacoemulsification with posterior chamber lens implantation were enrolled. Preoperative axial length measurements were performed with the IOLMaster 500 (Carl Zeiss Meditec, Germany); preoperative SNR values were used to divide the eyes into three groups (Group 1; SNR <10, Group 2; 10 ≤ SNR <50, Group 3; 50 ≤ SNR <100). One month and 6 months after cataract surgery, the manifest refraction spherical equivalents (MRSE) were measured. The mean numeric errors (MNE), the mean of the difference between postoperative MRSE, and preoperative target refraction, using the various intraocular lens (IOL) formulas, were calculated and compared among the three groups.

Results

One month after cataract surgery, postoperative MRSE was more hyperopic than preoperative target refraction, calculated by the Haigis formula in group 1, and by the SRK/T formula in group 2. After 6 months, for all formulas in group 1, there were significantly hyperopic results (approximately 0.35 diopter). Upon comparison of MNE among the three groups, group 1 was statistically significantly different from the other groups by Haigis formula.

Conclusions

When the SNR values in biometry, using IOLMaster, are <10, careful attention should be given to determining IOL power, as postoperative spherical equivalents are more hyperopic than preoperative target refraction by IOL formula.

Comparison of optical biometry versus ultrasound biometry in cases with borderline signal-to-noise ratio

Purpose

To ascertain if optical biometry determination of axial length (AL) and intraocular lens (IOL) power is significantly different compared to ultrasound (US) biometry in cases with borderline signal-to-noise ratio (SNR).

Patients and methods

Sixty patients who had cataract and IOL Master biometry with borderline SNR (1.6–2.0) were included. A retrospective chart review was performed to compare data collected with optical biometry and US biometry in cataract cases with borderline SNR.

Results

Results showed that optical biometry IOL and AL measurements were not significantly different from the US measurements. Analysis also demonstrated good agreement between the two methods.

Conclusion

Our study suggests that, in cases of borderline quality data, IOL power and AL measurements with optical biometry are still useful in surgical planning and that additional US measurements may be used more as a corroborative tool.

Comparison of a new biometer using swept-source optical coherence tomography and a conventional biometer using partial coherence interferometry

The aim of this study was to compare the axial lengths (ALs) using a new biometer with swept-source optical coherence tomography (Argos) versus ALs using a conventional biometer with partial coherence interferometry (IOL Master, version 5). The ALs in 48 eyes of 48 cataract patients were measured with Argos using refractive indexes that correspond to the particular tissue and with IOL Master using a single refractive index. The eyes were divided into three subgroups by AL length: short-AL group (n = 16), <23.27 mm; intermediate-AL group (n = 16), 23.27–24.03 mm; long-AL group (n = 16), ≥24.04 mm. The ALs (mm) measured with the Argos and IOL Master biometers, respectively, were 22.77 ± 0.43 and 22.74 ± 0.44, 23.63 ± 0.21 and 23.62 ± 0.21, and 26.00 ± 1.61 and 26.05 ± 1.64 in the short-, intermediate-, and long-AL groups, respectively. The mean ALs with the Argos biometer were longer than those with the IOL Master biometer in the short-AL group (P = 0.002) There was no significant difference in the intermediate-AL groups (P = 0.14). In contrast, the mean ALs with the Argos biometer were shorter than those with the IOL Master biometer in the long-AL group (P < 0.001). Differences between the ALs measured with the two biometers were statistically significant in short- and long-AL subgroups. However, the differences might not be clinically significant.

Refractive Results Using a New Optical Biometry Device: Comparison With Ultrasound Biometry Data

The aim of the study was to compare the measurements of optical (AL-Scan; Nidek Co., Ltd.) and ultrasonic (Echo Scan US-800; Nidek Co., Ltd.) biometry devices and to assess refractive results after cataract surgery. Eighty-one cataractous eyes of 81 patients were included in this study. Biometry was performed using the AL-Scan and an ultrasonic biometer (USB). Axial length (AL), keratometry (K) data, and intraocular lens (IOL) power calculations using the SRK/T formula were compared. Bland-Altman analysis was used to assess the extent of agreement between AL-Scan and USB data in terms of AL measurement and IOL power calculation. The K measurements of the AL-Scan were compared to autorefractor data (Canon Autorefractor RK-F1). The AL-Scan assessed the AL as longer (average difference 0.06 ± 0.18 mm; ICC = 0.987; P < 0.001) and the IOL power as greater (average difference 0.19 ± 0.66 D; ICC = 0.964; P < 0.001) than the USB. The AL-Scan also measured average K values (average difference 0.25 ± 0.25 D; ICC = 0.985; P < 0.001) greater than those given by the autorefractor. The postoperative mean absolute error was +0.30 ± 0.04 D (minimum: -0.51 D, maximum +1.04 D). The postoperative mean K value change was 0.36 ± 0.29 D (P < 0.05). The differences between measurements afforded by the AL-Scan and USB may be clinically acceptable. Keratometric changes that develop after cataract operations compromise the attainment of good refractive outcomes.

Factors Affecting the Accuracy of Intraocular Lens Power Calculation with Lenstar

This retrospective study was performed to compare refractive outcomes measured by conventional methods and by use of the Lenstar biometer and to investigate the factors affecting intraocular lens (IOL) power calculation with Lenstar with and without IOL-constant optimization. The study included 100 eyes of 86 patients who underwent cataract surgery. Corneal curvature was measured with a manual keratometer (MK), automated keratometer (AK), and the Lenstar biometer, and axial length (AL) was measured by A-scan and Lenstar. Mean numerical error (MNE) and mean absolute error (MAE) were compared between AK and MK with A-scan, and Lenstar with and without optimization. Factors affecting the accuracy of the IOL power calculation by use of Lenstar with and without optimization were analyzed. No significant differences were observed in the MNE or MAE among the devices. The proportion of MAE within 0.5 D was higher for Lenstar with optimization (62.7%) than without optimization (46.2%). The proportion of MAE within 0.5 D was 62% and 58% for MK and AK with A-scan, respectively. Without optimization, the MAE was smaller in eyes with ALs between 23 mm and 25 mm (p=0.03), whereas it was smaller at higher corneal powers when the IOL constant was optimized (>44 D, p=0.03). The IOL power calculations showed no significant differences among the devices, but the results of MAE within 0.5 D by use of Lenstar without optimization were worse than those of conventional methods. The AL influenced the accuracy of refractive outcomes determined by using Lenstar without optimization, and corneal curvature was shown to affect the accuracy of refractive measurements using Lenstar with optimization.

Intraocular lens power measured by partial coherence interferometry

PURPOSE

To compare the accuracy of the intraocular lens (IOL) power calculation of the Zeiss IOLMaster versus conventional automated keratometry and contact acoustic biometry after personalized optimization.

METHODS

Three hundred twenty eyes of 249 patients consecutively receiving phacoemulsification and IOL implantation with the sutureless clear cornea approach were enrolled. Preoperative biometry was derived from the Zeiss IOLMaster and an acoustic device (Alcon OcuScan RxP), and keratometry was measured by the Zeiss IOLMaster and a conventional automated keratometer (Topcon KR-8800). One month after surgery, refraction was measured and the predicted refractive errors were calculated with personalized optimization.

RESULTS

For eyes responsive to all devices, IOLMaster biometry + IOLMaster keratometry had the best predictability for postoperative refraction, with a mean absolute error (MAE) of 0.38 ± 0.28D, followed by OcuScan RxP biometry + IOLMaster keratometry (MAE, 0.49 ± 0.34D) and OcuScan RxP biometry + KR-8800 keratometry (MAE, 0.54 ± 0.37D) (P < 0.05 for all paired comparisons). For eyes that could not be measured by IOLMaster biometry, the MAE was smaller with IOLMaster keratometry (0.62 ± 0.56D) than with KR-8800 keratometry (0.57 ± 0.52D) (P = 0.03). The variables of age, diabetes mellitus, severity of cataract, axial length, and corneal curvature were unrelated to the predictability of postoperative refraction.

CONCLUSIONS

The Zeiss IOLMaster yielded more accurate refractive outcomes than the conventional automated keratometry and contact acoustic biometry after personalized optimization. For eyes irresponsive to axial length measurement by the IOLMaster, keratometry of the IOLMaster was still superior to conventional automated keratometry.

Comparison of postoperative refractive outcomes: IOLMaster® versus immersion ultrasound

BACKGROUND AND OBJECTIVE

To compare the postoperative refractive outcomes between IOLMaster biometry (Carl Zeiss Meditec, Inc., Dublin, CA) and immersion ultrasound biometry for axial length measurements.

PATIENTS AND METHODS

Refractive outcomes in 354 eyes were compared using the IOLMaster and the immersion ultrasound biometry. Predicted refraction was determined using manual keratometry and the SRK-T formula with personalized A-constant.

RESULTS

The axial lengths measured using the IOLMaster and immersion ultrasound were 24.49 ± 2.11 and 24.46 ± 2.11 mm, respectively, and the difference was significant (P < .05). The mean errors were 0.000 ± 0.578 D with the IOLMaster, and 0.000 ± 0.599 D with the immersion ultrasound, but the difference was not significant. The mean absolute error was smaller with the IOLMaster than with immersion ultrasound (0.463 ± 0.341 vs 0.479 ± 0.359 D), but the difference was not significant.

CONCLUSION

IOLMaster biometry yields highly accurate results in cataract surgery. However, if the IOLMaster is unavailable, immersion ultrasound biometry with personalized intraocular lens constants is an acceptable alternative.

Assessment of a new averaging algorithm to increase the sensitivity of axial eye length measurement with optical biometry in eyes with dense cataract

PURPOSE

To assess the capability of new software to decrease the proportion of eyes that have insufficient signal-to-noise ratio (SNR) in optical biometry.

SETTING

Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom.

DESIGN

Evaluation of diagnostic test or technology.

METHODS

In a prospective study, consecutive cataract patients coming for biometry who were unsuccessfully measured with the former software (version 4) of the IOLMaster partial coherence interferometry (PCI) device were reevaluated with the new composite software (version 5). Subsequently, in a retrospective study, consecutive cataract patients were measured with software version 5. For unsuccessful scans, the type and intensity of cataract were assessed at the slitlamp.

RESULTS

Altogether, 2713 eyes (1956 patients) were included in the study. The prospective study comprised 458 eyes (244 patients), 10.6% of which could not be measured successfully with software version 4. With the composite software, 30% of cases were measured successfully, with a higher proportion (42%) in the posterior subcapsular cataract subgroup. In the retrospective study, of 2255 eyes (1712 patients), 4.7% were not measured successfully using the new algorithm because of white cataract (70 eyes), posterior subcapsular cataract (14 eyes), or dense nuclear cataract combined with posterior subcapsular cataract (13 eyes) or for other reasons (8 eyes).

CONCLUSION

The composite software (version 5) enhanced the SNR, allowing valid measurements in eyes in which optical biometry had previously failed, especially in cases of posterior subcapsular cataract.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosure is found in the footnotes.

Relationship between postoperative refractive outcomes and cataract density: multiple regression analysis

PURPOSE

To evaluate the relationship between cataract density and the deviation from the predicted refraction.

SETTING

Department of Ophthalmology, Nara Medical University, Kashihara, Japan.

METHODS

Axial length (AL) was measured in eyes with mainly nuclear cataract using partial coherence interferometry (IOLMaster). The postoperative AL was measured in pseudophakic mode. The AL difference was calculated by subtracting the postoperative AL from the preoperative AL. Cataract density was measured with the pupil dilated using anterior segment Scheimpflug imaging (EAS-1000). The predicted postoperative refraction was calculated using the SRK/T formula. The subjective refraction 3 months postoperatively was also measured. The mean absolute prediction error (MAE) (mean of absolute difference between predicted postoperative refraction and spherical equivalent of postoperative subjective refraction) was calculated. The relationship between the MAE and cataract density, age, preoperative visual acuity, anterior chamber depth, corneal radius of curvature, and AL difference was evaluated using multiple regression analysis.

RESULTS

In the 96 eyes evaluated, the MAE was correlated with cataract density (r = 0.37, P = .001) and the AL difference (r = 0.34, P = .003) but not with the other parameters. The AL difference was correlated with cataract density (r = 0.53, P<.0001).

CONCLUSION

The postoperative refractive outcome was affected by cataract density. This should be taken into consideration in eyes with a higher density cataract.

Value of dual biometry in the detection and investigation of error in the preoperative prediction of refractive status following cataract surgery

PURPOSE

To report the value of dual biometry in the detection of biometry errors.

METHODS

Study 1: retrospective study of 224 consecutive cataract operations. The intraocular lens power calculation was based on immersion biometry. Study 2: immersion biometry was compared with optical coherence biometry (OCB) in terms of axial length, anterior chamber depth, keratometry readings and the recommended lens power to achieve emmetropia. Study 3: prospective study of 61 consecutive cataract operations. Both immersion and OCB were performed, but lens power calculation was based on the latter.

RESULTS

Study 1: 115 (86%), 101 (75.4%), 90 (67.2%) and 50 (37.3%) of postoperative spherical equivalents were within +/-1.5 dioptres (D), +/-1.25 D, +/-1 D and +/-0.5 D of the target, respectively. Study 2: excellent agreement between axial length readings, anterior chamber depth readings and keratometry readings by immersion biometry and OCB was observed (reflected in a mean bias of -0.065 mm, -0.048 mm and +0.1803 D, respectively, in association with OCB). Agreement between the lens power recommended by each technique to achieve emmetropia was poor (mean bias of +1.16 D in association with OCB), but improved following appropriate modification of lens constants in the Accutome A-scan software (mean bias with OCB = -0.4 D). Study 3: 37 (92.5%) and 23 (57.5%) of operated eyes achieved a postoperative refraction within +/-1 D and +/-0.5 D of target, respectively.

CONCLUSION

Systematic errors in biometry can exist, in the presence of acceptable postoperative refractive results. Dual biometry allows each biometric parameter to be scrutinized in isolation, and identify sources of error that may otherwise go undetected.

Comparison of intraocular lens power calculation by the IOLMaster in phakic and eyes with hydrophobic acrylic lenses

PURPOSE

To compare the optical biometry measurements and intraocular lens (IOL) power estimation using the IOLMaster (Carl Zeiss Meditec, Dublin, CA) in phakic eyes and eyes with hydrophobic acrylic lenses.

DESIGN

Observational cross-sectional study.

PARTICIPANTS

A total of 156 patients (226 eyes).

METHODS

The IOLMaster measurements (IOLM-1) were performed before phacoemulsification and reexamined 3 months postoperatively (IOLM-2). One of the foldable acrylic IOLs (AcrySof SA60AT, SN60WF, or SN60D3, Alcon Laboratories Inc., Dallas, TX) was implanted.

MAIN OUTCOME MEASURES

The expected refraction and estimation error calculated from IOLM-1 using the SRK II, SRK/T, and Haigis formulae were compared with the residual refraction 3 months postoperatively. The power of the implanted IOL and IOLM-2 measurement data were used to re-estimate the postoperative expected refraction in pseudophakic eyes. The difference in expected refraction and estimation error between phakic and pseudophakic eyes was studied. Differences in the anterior chamber depth and axial length measured by IOLM-1 and IOLM-2 were analyzed and correlated with the estimation error.

RESULTS

The IOLMaster measured an axial length 0.10+/-0.15 mm shorter in pseudophakic eyes (P<0.001). Calculations from IOLM-2 gave a significantly more hyperopic expected refraction than IOLM-1, with an averaged 0.20+/-0.46 diopters (D), 0.18+/-0.45 D, and 0.65+/-0.59 D calculated by the SRK II, SRK/T, and Haigis formulae, respectively. There was no significant difference among the 3 IOLs. The difference in estimation error correlated with the difference in axial length and anterior chamber depth (P<0.001 for the SRK II, SRK/T, and Haigis formulae). However, the correlation was strongest when the Haigis formula was used for the calculation.

CONCLUSIONS

The expected refraction in pseudophakic eyes differed significantly from that in phakic eyes by the IOLMaster depending on the IOL formulae used for the calculation rather than the type of IOL. An adjustment of target refraction by 0.20 to 0.65 D toward the hyperopic side of the desired refraction could be considered when using optical biometry data in pseudophakic eyes to achieve postoperative emmetropia.

Refractive predictability of partial coherence interferometry and factors that can affect it

PURPOSE

To evaluate the refractive predictability of a partial coherence interferometry (PCI) biometry device (IOL Master) for cataract surgery and to investigate factors that may affect it.

METHODS

Retrospective review of 209 eyes from 151 patients that had undergone preoperative PCI biometry and an uneventful phacoemulsification cataract surgery with posterior chamber intraocular lens (IOL) implantation was conducted. Prediction error defined as the intended refraction minus the postoperative refraction in spherical equivalent (SE) and the absolute error were analyzed according to IOL calculation formulas, patient characteristics, preoperative visual acuity (VA) and refraction, posterior subcapsular cataract (PSC), signal-to-noise ratio (SNR), and axial length (AL).

RESULTS

The overall refractive predictability of the PCI device was good. Generally, the SRK/T formula performed better than the SRK-II formula. Refractive predictability was slightly worse in eyes with >or=+2.0 diopters (D) of preoperative SE (with both SRK-II and SRK/T) and in eyes with an AL<or=23.0 mm (only with SRK-II. No other factors significantly affected the refractive predictability of the PCI, although poor VA, dense PSC, and poor SNR were closely interrelated.

CONCLUSIONS

The SRK/T formula performed significantly better than the SRK-II formula. Eyes with an AL<or=23.0 mm were associated with significantly greater hyperopic shifts in postoperative refraction with the SRK-II formula, but not with the SRK/T formula. A preoperative SE>or=+2.0D was related to a significantly greater hyperopic shift in postoperative refraction. With proper verification of measured data and a suitable IOL calculation formula, good refractive predictability is expected from PCI biometry regardless of patient characteristics, preoperative VA, SNR, PSC, and AL.

Biometry and intraocular lens power calculation

PURPOSE OF REVIEW

Heightened patient expectations for precise postoperative refractive results have spurred the continued improvements in biometry and intraocular lens calculations. In order to meet these expectations, attention to proper patient selection, accurate keratometry and biometry, and appropriate intraocular lens power formula selection with optimized lens constants are required. The article reviews recent studies and advances in the field of biometry and intraocular lens power calculations.

RECENT FINDINGS

Several noncontact optical-based devices compare favorably, if not superiorly, to older ultrasonic biometric and keratometric techniques. With additional improvements in the internal acquisition algorithm, the new IOL Master software version 5 upgrade should lessen operator variability and further enhance signal acquisition. The modern Haigis-L and Holladay 2 formulas more accurately determine the position and the shape of the intraocular lens power prediction curve.

SUMMARY

Postoperative refractive results depend on the precision of multiple factors and measurements. The element with the highest variability and inaccuracy is, ultimately, going to determine the outcome. By understanding the advantages and limitations of the current technology, it is possible to consistently achieve highly accurate results.