Comparison of anterior segment parameters and axial length measurements performed on a Scheimpflug device with biometry function and a reference optical biometer

Biometry combining Scheimpflug imaging and partial coherence interferometry versus standard partial coherence interferometry biometry

PURPOSE

To compare measurements of mean keratometry (K), axial length (AL), Jackson first and second astigmatism vector (J0 and J45), astigmatism magnitude, white-to-white (WTW) diameter and anterior chamber depth (ACD) values between two biometers, the Pentacam® AXL and the IOL Master 500.

SETTING

Public hospital in Belgium.

DESIGN

Retrospective instrument reliability analysis.

METHODS

Eyes of cataract or refractive lens exchange patients were examined preoperatively on a device combining Scheimpflug imaging and partial coherence interferometry (Pentacam® AXL) and a reference optical biometer (IOL Master 500). K, AL, J0, J45, astigmatism, WTW and ACD values were compared.

RESULTS

Three hundred and twenty-eight eyes of 187 cataract or refractive lens exchange patients (mean age 68years) were examined preoperatively. Measurements of mean keratometry, axial length, ACD, white-to-white and astigmatism were significantly different (P<0.05) between the two devices. Measurements of J0 and J45 did not significantly differ. Keratometry measurements with the Pentacam® AXL were significantly flatter than those measured with the IOL Master 500. Axial length measured with Pentacam® AXL was significantly greater when measured with the IOL Master 500, but this difference was not clinically relevant (0.015mm).

CONCLUSIONS

The Pentacam® AXL and the IOL Master 500 cannot be used interchangeably.

Analysis of preoperative ocular optical parameters in patients with cataract

This study aims to evaluate the distribution of preoperative corneal parameters obtained using the Pentacam anterior segment analyzer in Chinese male and female patients with cataracts and to investigate the correlation between these parameters and related factors. Preoperative examination data of the eyes of 1,255 patients who underwent cataract surgery were retrospectively analyzed. The Pentacam AXL was used to extract preoperative corneal measurements, and the total corneal measurement data were analyzed. The average age of the patients was 52.9 ± 21.3 years. The mean simulated keratometry values and corneal curvature of total corneal refractive power were positively correlated with age (both P < 0.01). Spearman's correlation analysis revealed a positive association between age and anterior corneal spherical aberration, posterior corneal spherical aberration, and total corneal spherical aberration changes. A negative correlation was found between age and with-the-rule astigmatism, and it was positively correlated with the ratios of against-the-rule and oblique astigmatism. A significant between-eye correlation was observed regarding spherical aberration (Z40), horizontal coma (Z31), vertical coma (Z3-1), and horizontal trefoil (Z33). The corneal curvature in females was significantly steeper than that in males (P < 0.01). Corneal curvature, corneal spherical aberration, and corneal astigmatism were found to change with age. Additionally, we found physiological differences between the sexes. Individual measurements could be taken preoperatively to facilitate the development of personalized surgical plans. By identifying age- and gender-related corneal variations, this study enables more personalized cataract surgery planning, potentially improving refractive outcomes and reducing postoperative complications through tailored surgical techniques and intraocular lens selection.

Comparison of measurements and calculated lens power using three biometers: a Scheimpflug tomographer with partial coherence interferometry and two swept source optical coherence tomographers

PURPOSE

To compare the biometric measurements obtained from the Pentacam AXL Wave, IOLMaster 700, and ANTERION and calculate the recommended intraocular lens power using the Barrett Formulae.

METHODS

This was a retrospective cross-sectional study of patients who underwent biometry using the Pentacam AXL Wave, IOLMaster 700, and ANTERION. Flat keratometry (K1), steep keratometry (K2), anterior chamber depth (ACD), and axial length (AL) from each device were measured and compared. These parameters were used to calculate the recommended IOL powers using the Barrett formula.

RESULTS

The study included 252 eyes of 153 patients. The IOLMaster had the highest acquisition rate among the two biometers. The Pentacam obtained the shortest mean AL, the IOLMaster measured the highest mean keratometry values, and the ANTERION measured the highest mean ACD. In terms of pairwise comparisons, keratometry and axial length were not significantly different between the Pentacam-IOLMaster and ANTERION-IOLMaster groups, while the rest of the pairwise comparisons were statistically significant. In nontoric and toric eyes, 35-45% of patients recommended the same sphere of IOL power. In another 30-40%, the Pentacam and ANTERION recommended an IOL power one step greater than that of the IOLMaster-derived data. 50% of the study population recommended the same toric-cylinder IOL power.

CONCLUSIONS

The Pentacam AXL Wave, IOLMaster 700, and ANTERION can reliably provide data for IOL power calculations; however, these data are not interchangeable. In nontoric and toric eyes, 35-45% of cases recommended the same sphere IOL power, and in another 30-40%, the Pentacam and ANTERION recommended one-step higher IOL power than the IOLMaster-derived data. In targeting emmetropia, selecting the first plus IOL power is advisable when using the Pentacam and ANTERION to approximate the IOL power calculations recommended by the IOLMaster 700.

Agreement between IOLMaster 700 and Pentacam AXL for IOL power measurement in patients with high myopia

PURPOSE

The anterior segment in individuals with high myopia has different features compared to those without myopia. IOLMaster 700 and Oculus Pentacam AXL are two accurate optical biometers. Both devices measure the cornea differently and thus yield different results when measuring intraocular lens (IOL) power. The purpose of this study is to assess the agreement of the IOL power calculation between IOLMaster 700 and Oculus Pentacam AXL in patients with high myopia.

METHODS

A prospective, analytical cross-sectional study was conducted to assess the agreement between the IOL power calculation with IOLMaster 700 and Oculus Pentacam AXL. In this study, 44 eyes were examined using Oculus Pentacam AXL and IOLMaster 700, and IOL power was calculated using the Barret Universal II formula and the AMO Sensar AR40E. The Bland-Altman plot was used to evaluate the agreement between the two devices.

RESULTS

Based on the IOLMaster 700 examination, 44 eyes with high myopia had axial lengths ranging from 26.05 to 34.02 mm. The mean IOL power was 8.26 ± 4.755 and 8.58 ± 4.776 based on IOLMaster 700 and Oculus Pentacam AXL, respectively. The Bland-Altman plot revealed good agreement between the two devices, with a mean difference of -0.3182 in the IOL power calculation and a 95% LoA of 0.88099-0.24462 with a 95% confidence interval.

CONCLUSION

Both devices showed good agreement in the IOL power calculation in patients with high myopia.

Clinical Evaluation of a New Spectral-Domain Optical Coherence Tomography-Based Biometer

The VEMoS-AXL system is a new optical biometer based on spectral domain optical coherence tomography (SD-OCT) that has been tested in terms of intrasession repeatability and compared with a swept-source optical coherence tomography biometer (SS-OCT), which is recognized as the gold standard for the performance of an agreement analysis. A biometric analysis was performed three consecutive times in 120 healthy eyes of 120 patients aged between 18 and 40 years with the SD-OCT system, and afterwards, a single measurement was obtained with the SS-OCT system. Within-subject standard deviations were 0.004 mm, 4.394 µm, and 0.017 mm for axial length (AL), central corneal thickness (CCT), and anterior chamber depth (ACD) measures obtained with the SD-OCT biometer, respectively. The agreement between devices was good for AL (limits of agreement, LoA: -0.04 to 0.03 mm) and CCT (LoA: -4.36 to 14.38 µm), whereas differences between devices were clinically relevant for ACD (LoA: 0.03 to 0.21 mm). In conclusion, the VEMoS-AXL system provides consistent measures of anatomical parameters, being most of them interchangeable with those provided by the SS-OCT-based gold standard.

Comparison of a new implantable collamer lens formula to standards formulas using spectral domain optical coherence tomography

PURPOSE

To use spectral-domain optical coherence tomography (SD-OCT) data to develop a new implantable collamer lens (ICL) sizing formula and compare vault outcomes with the Online Calculation and Ordering System™ (OCOS) and the NK2 formula.

METHODS

Consecutive eyes (n = 237) were evaluated that had undergone ICL/toric ICL implantation. Actual ICL vaults were measured, and a what-if analysis was performed to predict vault values with the NK2 formula using SD-OCT data. To develop a new formula (EPB), multiple regression analysis was performed with different parameters than the NK2 formula. Predicted vaults with NK2 and EPB formulas were compared to the actual vaults.

RESULTS

Parameters that were correlated with optimal ICL size were white-to-white, anterior chamber width, lens rise and desired refractive correction. The mean postoperative vault was 489 ± 258 μm. At last visit, 94.5% of eyes were within the manufacturer's acceptable vault range. Predicted vaults in the acceptable range were 74 and 87% with the NK2 and EPB formulas, respectively. Six percent had a predicted vault less than 100 μm with the EPB formula compared to 1% for actual outcomes. The NK2 formula resulted in a shift toward higher predicted vaults while the EPB formula was similar to the actual postoperative vaults but with slightly more cases with extremely low and high vaults.

CONCLUSION

SD-OCT data with OCOS result in good postoperative vaults. Further refinement is required to the NK2 for use with SD-OCT data. Although the EPB formula provides acceptable predicted vaults, further refinement with a larger sample size is needed.

Anterior eye parameters and lens thickness measured by an intraoperative OCT and a swept-source OCT: comparison of hyperopic, emmetropic and myopic eyes

PURPOSE

To evaluate if anterior chamber depth (ACD) and lens thickness (LT) measured by two different devices are affected by different eye lengths.

METHODS

ACD and LT of 251 eyes (44 hyperopic, 60 myopic, 147 emmetropic) of 173 patients received with an iOCT-guided femtosecond laser-assisted lens surgery (FLACS) and the IOL Master 700 were compared.

RESULTS

ACD measured with the IOL Master 700 was -0.026 ± 0.125 mm smaller (p = 0.001) than that with the iOCT for all eye-groups (hyperopic: p = 0.601, emmetropic: p = 0.003; myopic: p = 0.094). However, differences in all groups were not clinically relevant. LT measurements (all eyes: -0.0642 ± 0.0504 mm) shows a statistically significant difference in all evaluated groups (p < 0.001). Only myopic eyes showed a clinically relevant difference in LT.

CONCLUSION

The two devices show no clinically relevant differences in the eye-length groups (myopic, emmetropic, and hyperopic) for all ACD measurements. LT data shows a clinically relevant difference only for the group of myopic eyes.

The Guiding Significance of Ocular Biometry in Evaluating the Refractive Status of Preschool Children

INTRODUCTIONS

This study aimed to analyze the correlation between refractive status and ocular biological parameters in preschool-age children (3-6 years old), establish a regression curve, guide the clinical judgment of children's refractive status, and improve the accuracy of refractive screening for this age group.

METHODS

A total of 508 children, aged 3-6 years, were admitted to the hospital, exhibiting symptoms of ametropia and a need for dilation optometry. Among these, 326 children were included in the statistics group, having been examined between August 2021 and October 2022, and 182 children were included in the validation group, having been examined between November 2022 and March 2023. Using IOL Master700, ocular biometry parameters were measured for all participants, including axial length (AL), keratometry readings (K1 and K2), anterior chamber depth (ACD), lens thickness (LT), and central corneal thickness (CCT). One percent atropine sulfate eye gel was administered, and then the spherical equivalent (SE) was calculated by Bennett's formula. The correlation between SE and other ocular biometrics was analyzed, followed by the establishment of an SE prediction equation. The SE prediction equation was used to calculate the spherical equivalent (SE#) using ocular biometry data from the validation group, and the consistency between SE and SE# was evaluated.

RESULTS

SE showed a negative correlation with AL/CR (r = -0.936), AL (r = -0.811), ACD (r = -0.500), age (r = -0.396), and Km (r = -0.213) (p < 0.001), and positive correlation with LT (r = 0.301), LP (r = 0.176) (p < 0.001). A multiple linear regression equation was established for SE using the stepwise selection method, SE = 49.232 - 23.583 × AL/CR + 1.703 × ACD + 0.589 × Km - 0.609 × LP + 1.103 × LT (R2 = 0.997). Based on the regression equation, the predicted SE# highly correlated with SE after cycloplegia in the validation group (r = 0.998, p < 0.001).

CONCLUSION

The main ocular biological factors of ocular diopter in children aged 3-6 years are AL/CR, ACD, Km, LP, and LT, which are jointly influenced by multiple factors. Ocular biometry is a reliable predictor of real refraction among children aged 3-6.

Technical failure rates for biometry between swept-source and older-generation optical coherence methods: a review and meta-analysis

PURPOSE

Precise ocular measurements are fundamental for achieving excellent target refraction following both cataract surgery and refractive lens exchange. Biometry devices with swept-source optical coherence tomography (SS-OCT) employ longer wavelengths (1055-1300 nm) in order to have better penetration through opaque lenses than those with partial coherence interferometry (PCI) or low-coherence optical reflectometry (LCOR) methods. However, to date a pooled analysis showing the technical failure rate (TFR) between the methods has not been published. The aim of this study was to compare the TFR in SS-OCT and in PCI/LCOR biometry.

METHODS

PubMed and Scopus were used to search the medical literature as of Feb 1, 2022. The following keywords were used in various combinations: optical biometry, partial coherence interferometry, low-coherence optical reflectometry, swept-source optical coherence tomography. Only clinical studies referring to patients undergoing routine cataract surgery, and employing at least two (PCI or LCOR vs. SS-OCT) optical methods for optical biometry in the same cohort of patients were included.

RESULTS

Fourteen studies were included in the final analysis, which presented results of 2,459 eyes of at least 1,853 patients. The overall TFR of all included studies was 5.47% (95% confidence interval [CI]: 3.66-8.08%; overall I² = 91.49%). The TFR was significantly different among the three methods (p < 0.001): 15.72% for PCI (95% CI: 10.73-22.46%; I² = 99.62%), 6.88% for LCOR (95% CI: 3.26-13.92%; I² = 86.44%), and 1.51% for SS-OCT (95% CI: 0.94-2.41%; I² = 24.64%). The pooled TFR for infrared methods (PCI and LCOR) was 11.12% (95% CI: 8.45-14.52%; I² = 78.28%), and was also significantly different to that of SS-OCT: 1.51% (95% CI: 0.94-2.41%; I² = 24.64%; p < 0.001).

CONCLUSIONS

A meta-analysis of the TFR of different biometry methods highlighted that SS-OCT biometry resulted in significantly decreased TFR compared to PCI/LCOR devices.

Optical Biometry and IOL Calculation in a Commercially Available Optical Coherence Tomography Device and Comparison With Pentacam AXL

PURPOSE

Optical devices are the gold standard for ocular biometry; however, they are unable to obtain high-quality optical coherence tomography (OCT) images. The current study aimed to evaluate ocular measurements and intraocular lens (IOL) calculation used in an anterior/posterior segment OCT device and to compare the results with those of a validated biometer.

DESIGN

Prospective evaluation of a diagnostic tool.

METHODS

This study enrolled healthy subjects at the Hygeia Clinic, Gdańsk, Poland, between October 2021 and November 2021. All individuals had ocular biometry measured with a validated biometer (Pentacam AXL) and with a new module of an anterior/posterior segment OCT device (Revo 80, Optopol Technologies). All IOL calculations were performed for the right eye with keratometric values from the Pentacam for one IOL: the Alcon AcrySof IQ SN60WF, with plano target setting.

RESULTS

The mean age of the 144 participants was 25.23 ± 7.15 years. The axial length measured with Revo was longer than with Pentacam AXL (24.08 ± 1.13 vs 23.98 ± 1.13; P < .0001), a 0.10 ± 0.04 mm difference. This translated into a significantly lower IOL power to achieve emmetropia for all formulas (-0.34 ± 0.15, -0.32 ± 0.13, -0.34 ± 0.19, and -0.30 ± 0.15 for the Hoffer Q, Holladay I, Haigis, and SRK/T formulas, respectively). The study showed high agreement between the devices: nearly 90% of eyes were within ±0.50 diopters for all of the analyzed formulas (r > 0.99).

CONCLUSIONS

The present study demonstrates that the results of IOL calculation with the OCT biometer have a very strong correlation with those obtained with the Pentacam AXL; however, axial length measurements and calculated IOL power cannot be considered interchangeable.

Comprehensive comparisons of ocular biometry: A network-based big data analysis

PURPOSE

To systematically compare and rank ocular measurements with optical and ultrasound biometers based on big data.

METHODS

PubMed, Embase, the Cochrane Library and the US trial registry ( www.

CLINICALTRIAL

gov ) were used to systematically search trials published up to October 22nd, 2020. We included comparative studies reporting the following parameters measured by at least two devices: axial length (AL), flattest meridian keratometry (Kf), steepest meridian keratometry (Ks), mean keratometry (Km), astigmatism (AST), astigmatism vectors J₀ and J₄₅, anterior chamber depth (ACD), aqueous depth (AQD), central corneal thickness (CCT), corneal diameter (CD) and lens thickness (LT). A network-based big data analysis was conducted using STATA version 13.1.

RESULTS

Across 129 studies involving 17,181 eyes, 12 optical biometers and two ultrasound biometers (with both contact and immersion techniques) were identified. A network meta-analysis for AL and ACD measurements found that statistically significant differences existed when contact ultrasound biometry was compared with the optical biometers. There were no statistically significant differences among the four swept-source optical coherence tomography (SS-OCT) based devices (IOLMaster 700, OA-2000, Argos and ANTERION). As for Ks, Km and CD, statistically significant differences were found when the Pentacam AXL was compared with the IOLMaster and IOLMaster 500. There were statistically significant differences for CCT when the OA-2000 was compared to Pentacam AXL, IOLMaster 700, Lenstar, AL-Scan and Galilei G6.

CONCLUSION

For AL and ACD, contact ultrasound biometry obtains the lower values compared with optical biometers. The Pentacam AXL achieves the lowest values for keratometry and CD. The smallest value for CCT measurement is found with the OA-2000.

A formula to improve the reliability of optical axial length measurement in IOL power calculation

To verify the influence of axial length (AL) variations after cataract surgery in IOL power calculation. Patients underwent ophthalmic evaluation before surgery, including optical biometry with IOLMaster 500. Same exams were repeated 2 months after surgery: AL of operated eye was evaluated using two modes (pseudophakic/aphakic options). Mean Keratometry and AL changes were analyzed. Furthermore, refractive prediction error (PE) was back-calculated with Barrett Universal-II, Hoffer-Q, Holladay-1 and SRK/T formulas. To eliminate any systematic error, the mean error (ME) was zeroed-out for each formula. MEs and median absolute errors (MedAEs) of PEs were analyzed. Two-hundred-one operated eyes of 201 patients and 201 opposite eyes were evaluated. In operated eyes, mean AL difference was - 0.11 ± 0.07 mm (p < 0.001) with pseudophakic option and 0.00 ± 0.07 mm (p = 0.922) with aphakic option. There were not-statistically significant differences between MedAE of PEs calculated after zeroing-out the ME with different ALs (p > 0.05). Instead, only MEs of PEs obtained with postoperative ALs-pseudophakic option were not-statistically different from zero (p > 0.05). AL measurement change after cataract surgery is probably due to a systematic error in optical biometer in case of phakic eyes. A correction factor applied to preoperative AL could eliminate any systematic error in IOL power calculation without modifying the lens constant.

Agreement of predicted intraocular lens power using swept-source optical coherence tomography and partial coherence interferometry

PURPOSE

To analyze the agreement of the predicted intraocular lens (IOL) power obtained with ANTERION, IOLMaster 700 and Pentacam AXL biometers.

METHODS

We calculated the monofocal and trifocal IOL power using the SRK/T, Haigis, Barrett Universal II and Hoffer Q formulas for 106 eyes. IOL power agreement between devices was evaluated using the Bland-Altman method.

RESULTS

We found significant differences between biometers comparisons (p < 0.001). ANTERION and IOLMaster 700 did not produce significant IOL power differences (p > 0.05), with the same outcomes for medium- and long-eyes. No significant differences were found using the SRK/T, Haigis, or Hoffer Q formulas for short-eyes (p > 0.1). However, Barrett Universal II formula produced significant differences (p < 0.05) and these differences lay between the ANTERION and Pentacam AXL. ANTERION versus IOLMaster 700 comparison showed limits of agreement (LoA) varying from 1.1071D in SRK/T monofocal medium-eyes to 1.6828D in Hoffer Q trifocal all-eyes. The largest LoA (about 3.0D) was found for short-eyes when comparing the Pentacam AXL with the other two devices.

CONCLUSIONS

These devices provided statistically significant but clinically insignificant mean differences in predicted IOL power. However, wide LoA values suggest that for specific eyes these outcomes could be clinically significant.

Inter-device measurement variability of vital data parameters for keratorefractive and cataract refractive surgery

Introduction:

The measurements of corneal white-to-white (WTW) diameter and pupil size are critical for decision making in refractive surgery. Currently, automatic measurement of keratometry, corneal WTW, and pupil size are implemented in several ocular devices. The purpose of this study was to examine the agreement between two commonly used devices, an autorefractor and an optical biometer, for these parameters.

Methods:

Measurements were performed with both a Lenstar LS-900 and Nidek ARK-1 by an experienced examiner in random order. The devices were placed in close proximity within the same dimly lit room.

Results:

The measurements of 65 right eyes were analyzed. The results of the flat, steep, and mean keratometric reading were not significantly different (p = 0.96, p = 0.90, p = 0.93, respectively). Corneal WTW distances showed only moderate agreement between devices and were found to be significantly different (r = 0.8071; p < 0.01). Pupil diameters showed poor agreement between devices and were significantly different (r = 0.4890; p < 0.01). Agreement between implantable contact lens sizing, based on the measurements obtained by the two devices, was achieved for 19 of the 51 eyes (37.3%).

Conclusion:

We found a significant difference in WTW and pupil size measurements between ARK-1 and Lenstar. Results for both of the devices cannot be considered interchangeable for these data parameters.

Megalocornea, anterior megalophthalmos, keratoglobus and associated anterior segment disorders: A review

Megalocornea and anterior megalophthalmos (megalocornea spectrum) disorders are typically defined by corneal diameter > 12.5 mm in the absence of elevated intraocular pressure. Clinical features overlap with keratoglobus but are distinct from buphthalmos and severe (globus) keratoconus. Megalocornea spectrum disorders and keratoglobus are primarily congenital disorders, often with syndromic associations; both can present with large and thin corneas, creating difficulty in diagnosis, however, only keratoglobus is typically progressive. Molecular genetics provide significant insight into underlying aetiologies. Nonetheless, careful clinical assessment remains intrinsic to diagnosis. Surgical management can be challenging due to the enlarged ciliary ring and weakened zonules in megalocornea spectrum disorders and the extreme corneal thinning of keratoglobus. In this review, the established literature on measurement of corneal diameter, diagnosis of megalocornea, anterior megalophthalmos and keratoglobus, differentiation from severe keratoconus, recent molecular genetics research and key surgical modalities in the management of these rare disorders are outlined and discussed.

Ocular biometry with swept-source optical coherence tomography

This study aimed to summarize the outcomes reported when swept-source optical coherence tomography (SS-OCT) is used for ocular biometry. A literature search was performed to identify publications reporting clinical outcomes of patients measured with commercial SS-OCT. Twenty-nine studies were included in this review. A comprehensive analysis of the available data was performed, focusing on parameters used for intraocular lens (IOL) power calculation in cataract surgery, including keratometry, central corneal thickness, white-to-white distance, anterior chamber depth, lens thickness, axial length, IOL power, and pupil diameter. Different metrics for repeatability, reproducibility, and agreement between devices were analyzed. In general, SS-OCT biometers provide excellent repeatability and reproducibility outcomes; however, the differences obtained for some parameters measured in agreement studies should be carefully analyzed to validate the interchangeability between devices. The good outcomes reported lead us to conclude that optical biometers based on SS-OCT technology are likely to become the gold standard for ocular biometry.

Agreement Between Two Optical Biometers Based on Large Coherence Length SS-OCT and Scheimpflug Imaging/Partial Coherence Interferometry

PURPOSE

To evaluate the agreement between measurements obtained with a new optical biometer (Argos; Movu Inc) using large coherence length swept-source optical coherence tomography (SS-OCT) and those obtained with an optical biometer with a rotating Scheimpflug camera, combined with partial coherence interferometry (PCI) (Pentacam AXL; Oculus Optikgeräte GmbH) in adults.

METHODS

The following measurements were examined and evaluated: axial length, central corneal thickness (CCT), anterior chamber depth (ACD), mean keratometry, J₀ and J₄₅ vectors, and corneal diameter. Measurements with the two biometers were conducted in triplicate per instrument in a random order by the same examiner. Paired t tests were employed to compare the difference between the two devices. The Bland-Altman method was implemented to assess their agreement.

RESULTS

A total of 145 patients were enrolled in the study. The differences between the Scheimpflug/PCI-based biometer and the SS-OCT biometer were as follows: -0.02 ± 0.05 mm for axial length, 1.15 ± 5.79 µm for CCT, -0.04 ± 0.04 mm for ACD, -0.28 ± 0.16 diopters (D) for mean keratometry, 0.01 ± 0.11 D for J₀, -0.02 ± 0.10 D for J₄₅, and -1.03 ± 0.62 mm for corneal diameter. Bland-Altman plots showed narrow ranges in axial length, CCT, ACD, mean keratometry, and J₀ and J₄₅, which implied excellent agreement between the two biometers. Corneal diameter displayed poor agreement, with a 95% limits of agreement ranging from -2.25 to 0.19 mm.

CONCLUSIONS

Excellent agreement was established between the measurements provided by the new optical biometer based on SS-OCT and the optical biometer using Scheimpflug imaging and PCI, except for corneal diameter. [J Refract Surg. 2020;36(7):459-465.].

Repeatability and agreement of biometric measurements using spectral domain anterior segment optical coherence tomography and Scheimpflug tomography in keratoconus

PURPOSE

To compare the repeatability and agreement in biometric measurements using Spectral Domain Anterior Segment OCT (AS-OCT, REVO-NX, Optopol) and Scheimpflug tomography (Pentacam-AXL, Oculus) in keratoconus.

METHODS

Prospective case series at a university hospital tertiary center. Axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), and thinnest corneal thickness (TCT) were measured using both devices in patients with keratoconus. Three groups were analyzed: eyes with no prior crosslinking or contact lens wear (Group A), eyes with prior crosslinking (Group B), and eyes with prior contact lens wear (Group C). Repeatability and agreement of measurements were analyzed.

RESULTS

The study comprised of 214 eyes of 157 subjects. In Group A (n = 95 eyes), Group B (n = 86 eyes), and Group C (n = 33 eyes), intraclass correlation coefficient (ICC) was higher than 0.90 for all examined parameters, except for ACD readings in Group A with the REVO-NX (ICC = 0.83). Differences in ACD, TCT, and CCT were significantly different between the two devices for Groups A, B and C (p<0.05). AL measurements differed significantly in Groups A and B (p<0.05) but not in Group C (p = 0.18). Repeatability did not vary significantly between Groups A, B, or C in any parameter with both devices (p>0.05). There was poor agreement between the two devices across all parameters (p<0.05).

CONCLUSIONS

Both devices demonstrated good repeatability but poor agreement across AL, ACD, CCT and TCT measurements. There was no significant difference in repeatability in virgin eyes compared to eyes with prior crosslinking or contact lens wear, however, the interchangeable use of the two devices is not recommended.

Ocular biometry through fully refocused steady-state magnetic resonance imaging sequence: reliability and agreement with the IOLMaster® 500

PURPOSE

To evaluate the reliability and agreement between Fully Refocused Steady-State magnetic resonance sequences (FRSS) and the IOLMaster^® 500 optical biometer for measuring anterior chamber depth (ACD) and axial length (AL).

METHODS

In a sample of 32 healthy volunteers, separate observers measured the ACD and AL of both eyes using both techniques (inter-method) and through repeated FRSS measurements (interobserver) and by the same observer (intraobserver). We employed the Bland-Altman method to determine the agreement between FRSS and partial coherence interferometry (using the IOLMaster^®) and the interobserver and intraobserver variability, providing the limits of agreement (LoA, or mean difference ± 1.96 SD). Correlation coefficients and intraclass correlation coefficients were also provided.

RESULTS

For ACD measurements with FRSS in pseudo-color scale, we obtained an LoA of 0.016 ± 0.266 mm compared with partial coherence interferometry. For AL with FRSS in greyscale, the LoA was 0.019 ± 0.383 mm. Maximum interobserver variability showed a  - 0.036 ± 0.247 mm LoA for ACD with FRSS in pseudo-color scale. Maximum intraobserver variability was 0.000 ± 0.157 mm LoA for AL with FRSS in greyscale.

CONCLUSIONS

ACD and AL measurements using FRSS sequencing present high LoA and reliability when compared with partial coherence interferometry using the IOLMaster^® 500. The results were better for FRSS in pseudo-color scale in ACD determination and for FRSS in greyscale in AL determination. FRSS would not be recommended for IOL power calculation due to variability of AL measurement.

Evaluation and comparison of a novel Scheimpflug-based optical biometer with standard partial coherence interferometry for biometry and intraocular lens power calculation

In the present study, the axial length (AL), corneal curvature, anterior chamber depth (ACD) and white-to-white (WTW) distance were assessed using the Pentacam AXL (Oculus Optikgeraete GmbH), a novel Scheimpflug-based optical biometer with standard partial coherence interferometry (PCI). The Pentacam AXL and PCI biometer (IOLMaster 500; Carl Zeiss AG) were compared in terms of their intraocular lens (IOL) power calculations. The medical records of patients (eyes, n=190) who underwent cataract surgery were retrospectively reviewed. Biometry measurements involved the eyes of patients with cataract and were performed by the same examiner with the Pentacam AXL biometer and the IOLMaster 500 device. Following determination of the AL, mean keratometry (Km), ACD and WTW distance, the IOL power calculation was compared between the two devices using the Sanders, Retzlaff and Kraff theoretical (SRK/T) and Haigis formulas. The AL, Km and WTW values for the Pentacam AXL group were significantly lower compared with those of the IOLMaster 500 group. The difference was -0.02±0.04 mm, -0.20±0.28 D and -0.10±0.20 mm, respectively (P<0.001). The ACD for the Pentacam AXL group was higher compared with that of the IOLMaster 500 group with a difference of 0.02±0.13 mm (P=0.13). The IOL power calculated using the SRK/T and Haigis formulas exhibited significant differences between the two devices (t=11.48 and 10.97, respectively; P<0.001). In conclusion, the AL, ACD, WTW measurement and IOL power indicated optimal agreement and strong correlations between the two devices. However, constant optimization may be necessary for the novel biometer Pentacam AXL.

Lenstar LS 900 versus Pentacam-AXL: analysis of refractive outcomes and predicted refraction

Analysis of refractive outcomes, using biometry data collected with a new biometer (Pentacam-AXL, OCULUS, Germany) and a reference biometer (Lenstar LS 900, HAAG-STREIT AG, Switzerland), in order to assess differences in the predicted and actual refraction using different formulas. Prospective, institutional study, in which intraocular lens (IOL) calculation was performed using the Haigis, SRK/T and Hoffer Q formulas with the two systems in patients undergoing cataract surgery between November 2016 and August 2017. Four to 6 weeks after surgery, the spherical equivalent (SE) was derived from objective refraction. Mean prediction error (PE), mean absolute error (MAE) and the median absolute error (MedAE) were calculated. The percentage of eyes within ± 0.25, ± 0.50, ± 1.00, and ± 2.00 D of MAE was determined. 104 eyes from 76 patients, 35 males (46.1%), underwent uneventful phacoemulsification with IOL implantation. Mean SE after surgery was − 0.29 ± 0.46 D. Mean prediction error (PE) using the SRK/T, Haigis and Hoffer Q formulas with the Lenstar was significantly different (p > 0.0001) from PE calculated with the Pentacam in all three formulas. Percentage of eyes within ± 0.25 D MAE were larger with the Lenstar device, using all three formulas. The difference between the actual refractive error and the predicted refractive error is consistently lower when using Lenstar. The Pentacam-AXL user should be alert to the critical necessity of constant optimization in order to obtain optimal refractive results.

Comparison of postoperative anterior segment changes associated with pars plana vitrectomy with and without vitreous base shaving

AIM

To compare changes in anterior segment topography and axial length (AL) evaluated with Pentacam and IOL Master after pars plana vitrectomy (PPV) performed with and without vitreous base shaving.

METHODS

This prospective study included patients who underwent PPV or phacoemulsification+PPV (Phaco+PPV) for various indications. Patients who underwent total posterior hyaloid detachment and excessive vitreous base shaving with scleral indentation were referred to as complete PPV (c-PPV). The patients whom posterior hyaloid was separated as far as the posterior arcades and vitreous base shaving with scleral depression was not performed were classified as the partial PPV (p-PPV) group. All patients underwent detailed ophthalmologic examinations preoperatively and 1wk, 1, and 3mo postoperatively. Changes in the anterior chamber depth (ACD), anterior chamber volume (ACV), iridocorneal angle (ICA), central corneal thickness (CCT), and keratometric measurements (K₁ and K₂) were evaluated with Pentacam HR. Changes in the AL measurements were analyzed with IOL Master.

RESULTS

A significant increase in ACD was observed in c-PPV cases (P=0.02), but this increase was not significant in the p-PPV group (P=0.053). In contrast, ICA increased significantly in the c-PPV group (P=0.02) but decreased in the p-PPV group (P=0.09). BCVA was significantly improved in the c-PPV group from week 1 (P<0.001) while the increase in the p-PPV group reached significance at 3mo (P=0.035). CCT increased in the first week and later returned to baseline in both groups. No significant differences in the other parameters were observed between the groups, and there were no significant changes in intraocular pressure, ACV, AL, K₁ or K₂ values (P>0.05 for all).

CONCLUSION

Incomplete posterior hyaloid excision and not removing the vitreous base in PPV surgeries may create a more stable anterior chamber, thus preventing the downward movement of the lens-iris diaphragm, and may cause ciliary body retraction, thereby reducing ICA. Awareness of these effects can provide some amount of guidance to physicians in selecting the appropriate PPV procedure and preempting surgical complications.

Comparison of Anterior Segment Parameters and Axial Length Using Two Scheimpflug Devices with Integrated Optical Biometers

Purpose

To assess the repeatability of anterior segment parameters and axial length (AL) using Pentacam AXL and Galilei G6 and the agreement between both devices.

Materials and Methods

Eighty-four eyes of 84 participants were measured prospectively with two devices. Outcome measurements included corneal curvatures, anterior chamber depth (ACD), AL, pupil size, and white-to-white distance (WTW). Intra-device repeatability was assessed using intraclass correlation coefficient (ICC), within-subject standard deviation (Sw), test-re-test repeatability (TRT=2.77 Sw), and coefficient of variation (CoV). Agreement between two devices was analyzed using Bland-Altman plots.

Results

For each device, the Sw of corneal curvatures, ACD, and AL were lower than 0.25 D, 0.04 mm, and 0.04 mm, respectively. The ICC was higher than 0.90 in all parameters measured by Pentacam AXL, whereas three parameters measured by Galilei G6 (steep meridian at anterior and posterior cornea, and pupil size) were lower than 0.90. Comparing to Galilei G6, Pentacam AXL led to significantly lower mean anterior cornea curvatures (Km) with the mean difference (95% level of agreement; LoA) of -0.12 D (-0.36, 0.12, P<0.001). For ACD, there was no significant difference between the two devices. Pentacam AXL led to significantly lower AL, pupil size, and WTW, with the mean differences (95% LoA) of -0.04 mm (-0.35, 0.27), -0.18 mm (-0.71, 0.35), and -0.35 mm (-0.61, -0.10), respectively.

Conclusion

We found good repeatability of corneal curvature, ACD, and AL in both devices. Most parameters obtained from Pentacam AXL were statistically significantly different from those obtained from Galilei G6, except for steep meridians and ACD.

Application of a Partial Least Squares Regression Algorithm for Posterior Chamber Phakic Intraocular Lens Sizing and Postoperative Vault Prediction

PURPOSE

To develop and validate a new algorithm for predicting the postoperative vault of the myopic EVO Visian Implantable Collamer Lens (ICL) V4c (STAAR Surgical AG).

METHODS

This study included 81 eyes of 43 patients who had undergone ICL implantation. Preoperative data obtained by swept-source optical coherence tomography, Scheimpflug camera, and anterior segment optical coherence tomography were applied to develop a new partial least squares (PLS) regression algorithm. ICL sizing was performed using the standard white-to-white method with the online calculation and ordering system. The postoperative vault was assessed based on anterior segment optical coherence tomography. The PLS approach was applied to create the calibration model for predicting the postoperative vault. The new PLS model was cross-validated using the leave-one-out method and compared to a recently published linear regression model. Agreement between the actual and predicted vault values for the two methods was assessed by the Bland-Altman method.

RESULTS

There was a statistically significant correlation (P < .001, r = 0.73) between the postoperative vault values and those predicted by the PLS algorithm. Validation of the PLS model yielded lower mean differences and limits of agreement (0 and 410 µm, respectively) than the linear regression method (400 and 750 µm, respectively).

CONCLUSIONS

The PLS algorithm increases the precision of ICL vault prediction. However, it shows a tendency to overestimate small vault values and underestimate high vaults. [J Refract Surg. 2020;36(9):606-612.].

Intraocular Lens Power Formulas, Biometry, and Intraoperative Aberrometry: A Review

The refractive outcome of cataract surgery is influenced by the choice of intraocular lens (IOL) power formula and the accuracy of the various devices used to measure the eye (including intraoperative aberrometry [IA]). This review aimed to cover the breadth of literature over the previous 10 years, focusing on 3 main questions: (1) What IOL power formulas currently are available and which is the most accurate? (2) What biometry devices are available, do the measurements they obtain differ from one another, and will this cause a clinically significant change in IOL power selection? and (3) Does IA improve refractive outcomes? A literature review was performed by searching the PubMed database for articles on each of these topics that identified 1313 articles, of which 166 were included in the review. For IOL power formulas, the Kane formula was the most accurate formula over the entire axial length (AL) spectrum and in both the short eye (AL, ≤22.0 mm) and long eye (AL, ≥26.0 mm) subgroups. Other formulas that performed well in the short-eye subgroup were the Olsen (4-factor), Haigis, and Hill-radial basis function (RBF) 1.0. In the long-eye group, the other formulas that performed well included the Barrett Universal II (BUII), Olsen (4-factor), or Holladay 1 with Wang-Koch adjustment. All biometry devices delivered highly reproducible measurements, and most comparative studies showed little difference in the average measures for all the biometric variables between devices. The differences seen resulted in minimal clinically significant effects on IOL power selection. The main difference found between devices was the ability to measure successfully through dense cataracts, with swept-source OCT-based machines performing better than partial coherence interferometry and optical low-coherence reflectometry devices. Intraoperative aberrometry generally improved outcomes for spherical and toric IOLs in eyes both with and without prior refractive surgery when the BUII and Hill-RBF, Barrett toric calculator, or Barrett True-K formulas were not used. When they were used, IA did not result in better outcomes.

García Á, Piñero DP. Comparison of Standard and Total Keratometry Astigmatism Measured with three Different Technologies

Purpose:

To compare the keratometric and total corneal astigmatism measures provided by three different technologies as well as to assess the level of interchangeability among them.

Methods:

A Prospective, comparative study enrolling 94 eyes from 53 patients (age, 29-77 years) was carried out. All participants were patients with the diagnosis of cataract or patients with a transparent crystalline lens but seeking surgical presbyopia correction. A complete eye examination was performed in all eyes, including corneal analysis with three different devices: IOL-Master 700 (Carl Zeiss Meditec), Cassini (i-Optics), and Pentacam (Oculus Optikgeräte GmbH). Interchangeability of standard and total keratometric readings (equivalent keratometric readings for Pentacam) and astigmatism measures with these three systems were evaluated with the Bland-Altman analysis.

Results:

Significantly higher standard and total keratometric readings were obtained with the IOL-Master compared to the other two systems (p<0.001). Likewise, a significantly higher magnitude of standard and total keratometric astigmatism was obtained with the Cassini system (p<0.001). Ranges of the agreement for corneal power measurements between devices varied from 0.58 D to 1.53 D, whereas they ranged from 0.46 D to 1.37 D for standard and total astigmatism measurements.

Conclusion:

Corneal power and astigmatism measures obtained with IOL-Master 700, Cassini, and Pentacam systems cannot be used interchangeably. The impact of these differences on the refractive predictability achieved with different types of intraocular lenses (IOL) should be evaluated in the future in order to define which is the best corneal evaluation approach for optimizing the IOL power calculations.