Accuracy of newer intraocular lens power formulas in short and long eyes using sum-of-segments biometry.

PURPOSE: To analyze the accuracy of newer intraocular lens power formulas in long and short eyes measured using the sum-of-segments biometry. SETTING: Private practice, Lynwood, California. DESIGN: Retrospective observational study. METHODS: 595 patients scheduled for cataract surgery had their eyes measured using the sum-of-segments biometry. The expected residual refractions were calculated using Barrett Universal II (B II), Barrett True Axial Length (BTAL), Emmetropia Verifying Optical (EVO), Hill-RBF, Hoffer QST, Holladay 2, Holladay 2-NLR, K6, Kane, Olsen, PEARL-DGS, T2, and VRF formulas and compared with the traditional Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. RESULTS: In the 102 long eyes, all new formulas had a mean absolute error (MAE) equal or lower than the traditional formulas, ranging from 0.29 to 0.32 diopter (D). In the 78 short eyes, BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas had the lowest MAE (0.33 D, 0.33 D, 0.31 D, 0.36 D, 0.32 D, and 0.32 D, respectively), whereas all traditional formulas exceeded 0.36 D. CONCLUSIONS: All new formulas performed equal or better than the traditional formulas with the sum-of-segments biometry. The best overall results in the short and long eyes as well as in the very short and very long eyes were noted with the BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas, closely followed by the B II and Kane formulas.

Predicted vs measured posterior corneal astigmatism for toric intraocular lens calculations.

PURPOSE: To evaluate the astigmatic correction obtained with a toric intraocular lens using the keratometric readings (Ks) from a swept-source optical coherence tomography (SS-OCT) biometer and the Barrett toric formula with its predicted posterior corneal astigmatism (PCA) value and to compare the results with those expected by using the OCT Ks and a measured PCA from a scheimpflug topographer and by using the SimKs and the measured PCA from the Scheimpflug topographer. SETTING: Private practice, Lynwood, California. DESIGN: Retrospective observational study. METHODS: All measurements were performed by the SS-OCT biometer and the Scheimpflug topographer and using the Barrett toric formula. RESULTS: We evaluated 122 eyes of 122 patients. The mean absolute errors in predicted residual astigmatism for the entire series were 0.41 ± 0.19 diopters (D) (0.00 to 0.85 D) using the OCT Ks and predicted PCA, 0.45 ± 0.25 D (0.00 to 1.01 D) using the OCT Ks and measured PCA, and 0.49 ± 0.25 D (0.00 to 1.30 D) using the SimKs and measured PCA. The statistically significant differences between the errors had a P value of .062 for the entire series (n = 122), .26 for the subgroup with against-the-rule astigmatism (n = 68), .47 for the subgroup with oblique astigmatism (n = 11), and .05 for the subgroup with with-the-rule astigmatism (n = 43). The percentage of eyes within ±0.50 D were 74% (n = 90), 71% (n = 87) and 64% (n = 78) (P = .13) and within ±0.75 D were 99% (n = 121), 95% (n = 116) and 84% (n = 102) (P < .001), respectively. CONCLUSIONS: The Barrett toric formula and its predicted PCA performed better with the OCT K readings than with the topographer SimKs and a measured PCA.

Effects on IOL Power Calculation and Expected Clinical Outcomes of Axial Length Measurements Based on Multiple vs Single Refractive Indices.

PURPOSE: To compare axial length measurements based on multiple specific refractive indices for each segment of the eye to those obtained using a single refractive index for the entire eye and to evaluate the subsequent effects on IOL power calculation. SETTING: One site in Lynwood, CA. DESIGN: Single-arm, non-interventional, non-randomized retrospective chart review. METHODS: Eyes undergoing cataract surgery where biometry and IOL power calculations were based on axial length calculated with multiple specific refractive indices (multiple) were evaluated. A simulated axial length based on using a single refractive index was calculated for each case (single). The expected residual refractions based on different IOL formulas were calculated for both single and multiple groups. Formulas were then optimized, and the mean prediction errors (MPE) and mean absolute prediction errors (MAE) were calculated, based on the difference between the (optimized) expected value and the actual refractive outcome. RESULTS: A total of 595 eligible eyes were evaluated. Differences between the axial lengths determined in the single and multiple groups ranged from +0.28 mm to -0.14 mm, with a significant correlation between the difference in AL and average AL (r2 = 0.73, p < 0.001). AL differences between groups were statistically significant in long and short eyes (p < 0.001) but not in average eyes or overall (p > 0.25). In nearly all cases, the average MPE in the multiple group was lower than that for the single group across all axial lengths and formulas. When larger differences in MAE were present, the multiple group results were more often lower (better). CONCLUSION: Differences were found between axial lengths calculated using a single refractive index and multiple refractive indices, mainly in the short and long eyes. Differences had some effect on IOL power calculation. Such effects may become increasingly important as the precision of formulas increases.

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

PURPOSE: 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. SETTING: Private practice, Lynwood, California, USA. DESIGN: Prospective observational study. METHODS: All measurements were performed with the SS-OCT tomographer, the PCI biometer, and the OLCR biometer. RESULTS: 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. CONCLUSION: Axial length measurements with the new SS-OCT biometer were comparable to the PCI and OLCR measurements with a higher AL acquisition rate. FINANCIAL DISCLOSURE: Dr. Shammas is a consultant to Movu, Inc. Drs. Ortiz, Kim, and Chong have proprietary interest in the new technology.

Improving the preoperative prediction of the anterior pseudophakic distance for intraocular lens power calculation.

PURPOSE: To establish a new formula for intraocular (IOL) power calculation. SETTING: Private practice, Lynwood, California, USA. DESIGN: Retrospective observational and prospective evaluation. METHODS: In this 2-part retrospective observational study followed by a prospective evaluation, the postoperative anterior pseudophakic distance (APD) was correlated with the ante-nucleus distance (AND), the nucleus thickness (NT) of the cataractous lens, and the axial length. An estimated APD (EAPD) equation was established and used prospectively in a new formula on eyes scheduled for cataract surgery. RESULTS: Correlations were made in 90 operated eyes, and the EAPD equation was used in a new formula on 110 eyes scheduled for cataract surgery. Using the new IOL power formula, the median absolute error was 0.28 D with 82.7% of the eyes within ±0.50 D and 100% within ±1.00 D. CONCLUSIONS: The new IOL power formula with its incorporated EAPD equation performed well. FINANCIAL DISCLOSURE: H.J.S. has a pending patent on this system and method for determining IOL lens power.

Measuring the cataractous lens.

PURPOSE: To evaluate the lens thickness, anterior cortex space, nucleus thickness, and posterior cortex space in cataractous eyes and compare them with those in eyes of younger patients with clear lenses. SETTING: Private practice, Lynwood, California, USA. DESIGN: Retrospective observational study. METHODS: The study evaluated a group of cataractous eyes and compared them with a group of eyes of younger patients with clear lenses. All measurements were performed with a biometer (Lenstar LS 900). RESULTS: The cataractous group (200 eyes) had a greater mean lens thickness (4.65 mm ± 0.41 [SD]) than the control group (80 eyes) (4.09 ± 0.33 mm). The mean measured values for the cataractous groups and control groups were 0.84 ± 0.21 mm and 0.35 ± 0.11 mm for anterior cortex space, 3.31 ± 0.25 mm and 3.27 ± 0.27 mm for mean nucleus thickness, and 0.51 ± 0.16 mm and 0.48 ± 0.13 mm for mean posterior cortex space, respectively. Anterior cortex space, nucleus thickness, and posterior cortex space correlated positively with lens thickness (r = 0.69, r = 0.69, and r = 0.59, respectively). Lens thickness, anterior cortex space, nucleus thickness, and posterior cortex space showed a weak inverse correlation with axial length (r = 0.06, r = 0.08, r = 0.10, and r = 0.10, respectively) and an inverse correlation with anterior chamber depth (r = 0.57, r = 0.43, r = 0.42, and r = 0.22, respectively). Lens thickness showed a positive correlation with age (r = 0.28), as did the anterior cortex space (r = 0.32) and posterior cortex space (r = 0.26), but nucleus thickness did not show a positive correlation (r = 0.02). CONCLUSION: Lens thickness increased with age and with cataract formation and was mostly attributable to an increase in the anterior cortex space. FINANCIAL DISCLOSURE: Neither author has a financial or proprietary interest in any material or method mentioned.

Scheimpflug corneal power measurements for intraocular lens power calculation in cataract surgery.

PURPOSE: To compare the keratometric (K) readings from the Pentacam-HR (High Resolution) unit with the automated K values from the IOLMaster keratometer (KIOLM), and to evaluate them in the commonly used intraocular lens (IOL) power calculation formulas for routine cataract surgery. DESIGN: Prospective, comparative observational study. METHODS: setting: Private practice, Lynwood, California. study population: Fifty cataractous eyes scheduled for surgery between July and August 2012. observation procedure: The K readings from the Pentacam-HR unit taken at the 2-, 3-, 4-, and 5-mm zones and the 2-, 3-, 4-, and 5-mm rings, respectively, from 3 different maps: sagittal corneal front (KF), true net power (KTNP), and total refractive power (KRP) are compared with KIOLM. IOL power calculations were performed with each of the 25 sets of K readings. main outcome measures: The IOL prediction median absolute error (MedAE) obtained with each measurement. RESULTS: KF averaged 0.03-0.13 diopter (D) higher than KIOLM (P > .05), KTNP averaged 1.16-1.21 D lower than KIOLM (P > .001), and KRP averaged 0.23-0.72 D lower than KIOLM (P > .001), with large variations in the measurements. The MedAE obtained with the different Pentacam K readings ranged from 0.44-0.64 D vs 0.52 D obtained with KIOLM (P > .05). MedAE was lower in all categories when the pupil was 3 mm or smaller. CONCLUSION: The Pentacam KF values were the closest to KIOLM and the KF readings from the 2-mm ring yielded the best results for IOL power calculation.

Intraocular lens power calculation in eyes with previous hyperopic laser in situ keratomileusis.

PURPOSE: To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data. SETTING: Private practices, Lynwood, California, and Mesa, Arizona, USA. DESIGN: Retrospective comparative observational study. METHODS: The corrected corneal power (Kc) was calculated in each eye by adding the refractive change at the corneal level to the pre-LASIK keratometric (K) readings. By comparing Kc with the measured post-LASIK K readings (Kpost), the following equation was derived: Kc = 1.0457 Kpost-1.9538. This equation was combined with the Shammas original formula to obtain the Shammas-PHL formula. RESULTS: The new formula was evaluated in 18 eyes with previous LASIK data and in 24 eyes with no previous LASIK data. Using the Shammas-PHL formula, the mean arithmetic prediction error was -0.03 diopter (D) ± 0.72 (SD) (range -1.57 to +1.54 D) and the median absolute error was 0.38 D in 18 eyes with available pre-LASIK data and 0.05 ± 0.58 D (range -0.56 to +1.40 D) and 0.43 D, respectively, in the 24 eyes with no pre-LASIK data. CONCLUSION: The Shammas-PHL formula can be used in post-hyperopic LASIK cases whether or not the pre-LASIK data are available.

Improving the second-eye refractive error in patients undergoing bilateral sequential cataract surgery.

PURPOSE: To assess the refractive error in the second eye to undergo surgery when the intraocular lens (IOL) power was modified to correct 50% of the error from the first eye when such an error exceeded 0.50 diopter (D). DESIGN: Prospective, observational case series. PARTICIPANTS: Two hundred fifty patients with bilateral, sequential cataract surgery. METHODS: Two hundred fifty consecutive patients who underwent the first-eye cataract operation 1 to 3 months earlier were scheduled for cataract surgery in the second eye. When choosing the IOL power for the second eye, the calculations were adjusted to correct 50% of the first-eye refractive error (FERE). The adjusted second-eye refractive error (aSERE) was evaluated 6 to 8 weeks after surgery. It was compared with the FERE, with a potential nonadjusted SERE, and with a potential fully adjusted SERE. MAIN OUTCOME MEASURES: Postoperative refractive error. RESULTS: The median aSERE was significantly lower in the second eye compared with the median FERE in the 47 cases in which the FERE ranged from -0.50 to -1.00 D (-0.12 vs. -0.66 D), in the 15 cases in which the FERE exceeded -1.00 D (-0.12 vs. -1.25 D), in the 24 cases in which the FERE ranged from 0.50 to 1.00 D (-0.03 vs. 0.65 D), and in the 11 cases in which the FERE exceeded 1.00 D (-0.29 vs. 1.19 D). The difference was statistically significant in all categories (P<0.00001). CONCLUSIONS: In patients undergoing bilateral sequential cataract surgery and in cases in which the FERE exceeded 0.50 D, the refractive error of the second eye can be improved by modifying the IOL power to correct up to 50% of the error from the first eye. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Management of acute Stevens-Johnson syndrome and toxic epidermal necrolysis utilizing amniotic membrane and topical corticosteroids.

PURPOSE: To describe the results of a novel treatment approach to the acute ophthalmic management of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). DESIGN: Retrospective interventional case series. METHODS: setting: Institutional. study population: Sixteen eyes of 8 patients with acute, biopsy-proven SJS or TEN and significant ophthalmic involvement. interventional procedure(s): Application of amniotic membrane to the ocular surface, either in the operating room or at the bedside, and short-term use of intensive topical corticosteroid medication. main outcome measures: Visual acuity, slit-lamp appearance of the ocular surface, and patients' subjective impression of ocular comfort. RESULTS: Two patients expired during the hospitalization. Mean follow-up time for the surviving patients was 7.7 months. Four surviving patients in whom the entire ocular surface (ie, the cornea, bulbar and palpebral conjunctiva, and eyelid margins) was treated with amniotic membrane retained visual acuities of 20/40 or better and an intact ocular surface. In contrast, the initial 2 patients in the study who were treated with only a Prokera device or unsutured amniotic membrane sheets, leaving the palpebral conjunctiva and eyelid margins uncovered, developed more significant ocular surface abnormalities, and 1 developed a corneal perforation. CONCLUSIONS: Amniotic membrane coverage of the ocular surface in its entirety coupled with the use of intensive short-term topical corticosteroids during the acute phase of SJS and TEN is associated with the preservation of good visual acuity and an intact ocular surface. Partial amniotic membrane coverage of the ocular surface may not serve to minimize the cicatrizing ocular sequelae of SJS and TEN as effectively as complete coverage.

Scheimpflug photography keratometry readings for routine intraocular lens power calculation.

PURPOSE: To prospectively evaluate keratometry (K) values obtained by Scheimpflug photography in eyes scheduled for cataract surgery, compare the results with K values obtained with an autokeratometer (automated K), and evaluate the K values in commonly used intraocular lens (IOL) power calculation formulas for routine cataract surgery. SETTING: Private clinical ophthalmology practice, Lynwood, California, USA. METHODS: The mean simulated K power (simulated K), equivalent K (equivalent K), and true net power (true net K) readings from the Pentacam Comprehensive Eye Scanner were compared with the automated K readings. Automated K, simulated K, and equivalent K values were compared in commonly used IOL power calculation formulas. RESULTS: The mean automated K value was 43.49 diopters (D)+/-1.75 (SD) and the mean simulated K value, 43.49+/-2.00 D (P> .1). The mean equivalent K value was 43.78+/-1.97 D and exceeded the mean automated K and simulated K by 0.29 D (P> .1). The mean true net K was 42.31+/-2.13 D, which was 1.18 D lower than the automated K and simulated K values (P= .015). The IOL prediction mean absolute error was 0.41+/-0.27 D using the automated K method, 0.50+/-0.36 D using the simulated K method (difference 0.09 D) (P> .1), and 0.65+/-0.35 D using the equivalent K method (difference 0.24 D) (P< .01). CONCLUSION: The K values from Scheimpflug photography did not improve accuracy over autokeratometer values for routine IOL power calculation.

Variability of axial length, anterior chamber depth, and lens thickness in the cataractous eye.

PURPOSE: To review and evaluate the biometry measurements in 750 eyes (first eye developing cataract) of 750 consecutive patients with no retinal pathology. SETTING: Private practice, Lynwood, California, USA. METHODS: All measurements were performed with the I3 system A-scan (Innovative Imaging, Inc.) using an immersion technique. The axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) measurements were evaluated in relation to each other and in relation to age, sex, and keratometric readings. RESULTS: The mean AL was 23.46 mm +/- 1.03 (SD), the mean ACD was 2.96 +/- 0.45 mm, and the mean LT was 4.93 +/- 0.56 mm. Men presented for surgery at an earlier age than women (mean 73 +/- 9.41 years versus 75 +/- 8.55 years) with a longer AL (23.76 +/- 1.00 mm versus 23.27 +/- 1.01 mm). The AL tended to be longer in younger patients (r = -0.127; P<.001); the ACD tended to be deeper in younger patients (r = -0.250; P<.001) and in longer eyes (r = 0.423; P<.001). The LT tended to be thicker in older patients (r = 0.385; P<.001) and in shorter eyes (r = -0.179; P<.001), with large scatter in the distribution. CONCLUSIONS: There was a positive correlation between AL and ACD and an inverse correlation between AL and LT. Also, AL was inversely correlated with age and corneal power.

No-history method of intraocular lens power calculation for cataract surgery after myopic laser in situ keratomileusis.

PURPOSE: To prospectively evaluate the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available. SETTING: Private practice, Lynwood, California, USA. METHODS: The predicted IOL power was calculated in each case. Also calculated were the mean arithmetic and absolute IOL predictor errors, range of the prediction errors, and number of eyes in which the error was within +/-1.00 diopter (D). RESULTS: The mean arithmetic IOL prediction error was -0.003 D +/- 0.63 (SD), and the mean absolute IOL prediction error was 0.55 +/- 0.31 D (range -0.89 to +1.05 D). Fourteen eyes (93.3%) were within +/-1.00 D. The results of the Shammas post-LASIK formula compared favorably to the results obtained with the optimized Holladay 1 (P = .42), Hoffer Q (P = .25), Haigis (P = .30), and Holladay 2 (P = .19) formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005). CONCLUSION: The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.

Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis.

PURPOSE: To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method. DESIGN: Interventional case series. METHODS: Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre - CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost -0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost -6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results. RESULTS: Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram (P <.001), and there was no statistically significant difference between the mean keratometric values (P >.5). CONCLUSIONS: The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.