Preoperative Axial Length Measurements Research Articles

Comparison of axial length measurements in silicone oil-filled eyes using SS-OCT and partial coherence interferometry.

To compare axial length (AL) measurements in silicone oil (SO)-filled eyes using swept-source optical coherence tomography (SS-OCT) (the IOLMaster 700 and OA2000) and partial coherence interferometry (the IOLMaster 500). Zhongshan Ophthalmic Center, Guangzhou, China. Cross-sectional study. We enrolled phakic patients who underwent SO removal surgery. The AL measurements by the IOLMaster 500, IOLMaster 700, and OA2000, both before and after SO removal, were compared. Multiple regression analysis was performed to identify risk factors for the differences between preoperative and postoperative AL measurements. 68 patients (68 eyes) with a mean age of 46.43 ± 13.24 years were included. No statistically significant difference was observed in the preoperative AL measurements between the IOLMaster 500 and IOLMaster 700 (25.48 ± 2.51 mm vs 25.49 ± 2.46 mm; P = .63), whereas the OA2000 yielded shorter AL (25.34 ± 2.36 mm) (both P < .001). After SO removal, the AL measurements showed no statistically significant differences among the 3 devices. In reference to the postoperative AL, the IOLMaster 500 and IOLMaster 700 tended to overestimate the AL in SO-filled eyes (both P < .001), and this measurement error increased with longer AL (β = 0.08 and 0.05, respectively; both P < .001). No statistically significant difference was observed between preoperative and postoperative AL measurements by the OA2000 ( P = .18). The OA2000 is the preferred biometer for AL measurement in SO-filled eyes, whereas the IOLMaster 500 and IOLMaster 700 overestimate the AL especially for long eyes, which needs adjustment in clinical use.

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

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

Accuracy and feasibility of axial length measurements by a new optical low-coherence reflectometry-based device in eyes with posterior subcapsular cataract

To evaluate the feasibility and accuracy of measuring axial length (AL) by a new optical low-coherence reflectometry (OLCR)-based device in eyes with central posterior subcapsular cataract (PSC). Department of Ophthalmology, Assaf-Harofeh Medical Center, Zerifin, Israel. Retrospective case series. Consecutive cases of patients who had uneventful cataract surgery and whose preoperative AL measurements were not feasible with the partial coherence interferometry (PCI) device because of a central PSC were assessed. Preoperative AL was measured by the OLCR device and immersion ultrasound (US). Preoperative results were compared with the postoperative AL measurements obtained by the PCI. Twenty-seven patients (27 eyes) were enrolled in the study. The median difference between the OLCR and the PCI AL measurements (0.07mm) was lower than the median difference between the US and the PCI AL measurements (0.13mm)(P=.016). The ranges of the limits of agreement were 0.15mm between OLCR and PCI, and 0.88mm between US and PCI. The proportion of eyes with an AL difference of less than 0.1mm was significantly higher between the OLCR and the PCI devices (24 eyes [88.9%]) than between the US and the PCI devices (9 eyes [33.3%]) (P=.001). The OLCR-based device successfully measured the preoperative AL in all eyes with central PSC for which preoperative PCI scans were not feasible. These measurements had a high level of agreement with the postoperative AL measurements obtained by the PCI device.

Accurate biometry in silicone oil-filled eyes

Sir, Kunavisarut et al1 should be congratulated on their study ‘Accuracy and reliability of IOL master and A-scan immersion biometry in silicone oil-filled eyes'. This is an important work, given the difficulties that can be encountered in IOL power prediction in these cases. As stated by the authors, it is not always possible to obtain accurate axial length measurements in these eyes preoperatively and the use of data from the fellow eye can be inaccurate. This paper compared the preoperative axial length measurements for IOL master and immersion ultrasound in oil-filled eyes with the measurement from the IOL master taken after removal of the oil. Accurate axial length measurement is a critical part of biometry in cataract surgery, as an error in this measurement is multiplied by a factor of around 2.5 in the process of intraocular lens power calculation.2 In this study, the authors used correlation coefficients to compare the axial length measurements obtained pre and post oil removal. Although the IOL master axial length measurements for silicone oil-filled eyes showed a high correlation with the postoperative axial length measurement (0.966), the postoperative refractive outcomes varied between −2.74 and +2.33 for this relatively small sample of eyes. As stated by Bland and Altman,3 the use of correlation coefficients to compare two different measurements of the same thing is problematic since even a very high correlation does not necessarily translate into useful clinical agreement. The method described by Bland and Altman allows 95% limits of agreement to be calculated. To achieve this, the differences between the measured values are plotted against their means. This method may have better illustrated why there were clinically significant errors in the refractive outcomes for the IOL master, despite a high correlation between the axial length measurements and no statistically significant difference between the mean measurements taken pre and post oil removal.

Partial coherence interferometry versus immersion ultrasonography for axial length measurement in children

To determine whether measurements obtained by partial coherence interferometry (PCI) correlate well with measurements obtained using immersion ultrasound (US) in children. Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, USA. Evaluation of a diagnostic test or technology. The charts of pediatric patients who had cataract surgery from August 2008 to September 2009 were reviewed. Axial length (AL) measurements in the operative eye were obtained using PCI at the preoperative clinic visit and then using immersion US in the operating room before surgery. The data were compared to determine the degree of agreement. The charts of 18 patients (27 eyes) were reviewed. Preoperative AL measurements by PCI were obtained in 21 eyes (78%). On average, the PCI-measured ALs were 0.1 mm less than the immersion US values (95% confidence interval, -0.2 to -0.1; P = .002). All eyes with an AL of 23.5 mm or less had lower PCI values than immersion US values. There was no systematic pattern of 1 measurement being greater or less than the other in eyes with an AL longer than 23.5 mm. There was a systematic difference in AL measurement between PCI and immersion US, with PCI tending to give lower values, particularly in eyes with an AL of 23.5 mm or less. Depending on the length of the eye, a 0.1 mm error in AL measurement could result in a 0.25 to 0.75 diopter difference in intraocular lens calculation that could be clinically significant in some patients.

Investigating a possible cause of the myopic shift after combined cataract extraction, intraocular lens implantation, and vitrectomy for treatment of a macular hole

Objective: It has been documented that combination surgery (phacoemulsification, intraocular lens implantation, and vitrectomy) produces a postoperative myopic shift. We hypothesize that the myopic shift seen in patients treated with combination surgery, membrane stripping, and injection of C 3F 8 for treatment of a macular hole is due to an erroneously short preoperative axial length measurement by the IOLMaster. Study Design: Retrospective chart review. Participants: Eleven eyes of 10 patients treated for a stage III or IV macular hole were recruited from a database search of 1 vitreoretinal practice in Regina, Sask. Methods: All eyes included in the study underwent combination surgery, membrane stripping, and injection of C 3F 8. None of the patients demonstrated concurrent eye pathology. Postoperative axial length measurements by the IOLMaster were obtained and compared with the same preoperative measurements. Results: The mean (SD) postoperative myopic shift seen in the study eyes was −0.76 (0.65) D ( z = −2.578, p < 0.01 ).The mean (SD) preoperative and postoperative axial length measurements were 23.54 (1.02) mm and 23.53 (1.01) mm, respectively. No significant difference in axial length was found between the preoperative and postoperative axial length measurements ( t = 0.43, df = 10, p = 0.68). Conclusions: These findings do not support our hypothesis of an erroneous preoperative axial length measurement by the IOLMaster in patients with a stage III or IV macular hole treated with combination surgery, membrane stripping, and injection of C 3F 8. Further studies are required to determine the precise cause of the postoperative myopic shift.

Factors related to corneal endothelial damage after phacoemulsification in eyes with occludable angles

To evaluate the influence of preoperative variables and early postoperative intraocular pressure (IOP) on the loss of corneal endothelial cells after phacoemulsification in eyes with occludable angles. Taipei Veterans General Hospital, Taipei, Taiwan. Sixty patients with occludable angles having phacoemulsification were prospectively enrolled. Corneal endothelial cell evaluation was conducted preoperatively and 3 months postoperatively. Three months postoperatively, the mean corneal endothelial cell density decreased by 14.5% +/- 25.8% (SD) (P < .001). Greater corneal endothelial cell loss was associated with shorter axial length (AL) (P = .008), steeper anterior corneal curvature (P = .03), greater nuclear opalescence (P = .04), and higher IOP measured 4 to 8 hours after surgery (P = .04) and the following morning (P = .002). Multiple linear regression analysis identified AL and the IOP measured 4 to 8 hours after surgery as the best predictors of postoperative corneal endothelial cell loss after adjusting for nuclear opalescence and phacoemulsification time (R2 = 0.40, P = .001). The corneal endothelial cell loss after phacoemulsification in eyes with occludable angles was associated with preoperative AL measurement and postoperative IOP within 24 hours. To minimize corneal endothelial cell damage, it is critical to avoid an IOP spike during the early postoperative period and to exercise extreme caution intraoperatively in eyes with an AL less than 22.6 mm.

Influence of severity of nuclear cataract on optical biometry

To compare preoperative and postoperative measurements of the axial length (AL) performed with the IOLMaster (Carl Zeiss Meditec) to evaluate the effect of nuclear cataract on the optical biometry. Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. In 245 consecutive eyes of 162 patients scheduled for cataract surgery, type and severity of cataract was evaluated using the Lens Opacities Classification System III. Preoperative and postoperative axial length measurements were performed with the IOLMaster. The postoperative readings of AL were corrected for the IOL optic material implanted. The preoperative AL measurements were 0.07 mm +/- 0.05 (SD) (range -0.18 to 0.11 mm) longer than the postoperative measurements (P<.001). These differences in AL were only weakly correlated (r = -0.28, P = .01) with the nuclear cataract grade, mean 3.5 +/- 0.9. In this study, AL measurements with optical biometry using the IOLMaster were not influenced by the severity of nuclear cataract to a clinically relevant degree. Furthermore, it was found that AL in the phakic eye was overestimated by about 0.07 mm because of a slightly too low value of the group refractive index used for the crystalline lens.

Factors influencing the accuracy of the SRK formula in the intraocular less power calculation.

Several intraocular lens (IOL) power calculation formulas (either theoretical or empirical) are used to determine the emmetropic IOL power) The Sanders-Retzlaff-Kraff (SRK) linear regression formula is among the most widely recognized empirical ones. In the present study intraocular lens power calculation aiming at emmetropia was performed, using SRK formula, in 145 cataractous eyes undergoing lens implantation. The final refraction was evaluated at 8 to 12 months after surgery. The purpose of this study was the identification and quantitative evaluation of the factors which influence significantly the accuracy of SRK in the intraocular lens power calculation. The following factors were studied: (1) the error in preoperative biometry with regard to the difference between post and preoperative axial length measurements, (2) the position of the implantation of the intraocular lens (anterior versus posterior chamber), (3) the intraocular lens style, (4) the intraocular lens power level, (5) the preoperative corneal astigmatism, (6) the surgically induced corneal astigmatism, and (7) the postoperative astigmatism. Multiple regression and stepwise regression analysis showed a strong correlation (R2 = 0.65; p < 0.001) between postoperative refractive error (Rf) and error in preoperative biometry (delta AL), surgically induced corneal astigmatism (SIA) and postoperative astigmatism (Ap) only. This correlation is expressed by the following equation: Rf = 0.07 -2.55 delta AL -0.42 SIA + 0.34 Ap. This equation indicates the quantitative effect of each factor on the accuracy of the SRK formula, by defining the pattern of the fluctuations of the amount or state (myopic or hyperopic) of refractive error induced by changes of variables delta AL, SIA and Ap.

The Effect of Cataract Type on the Intraocular Lens Power Calculation Using the SRK Formula

OBJECTIVE: To evaluate the effect of the cataract type on the preoperative axial length measurements by ultrasonography, the intraocular lens (IOL) power calculation and the actual postoperative refractive error using the SRK formula. STUDY DESIGN: Comparative study of preand postoperative biometry data and determination of the refractive errors 3–6 months after surgery. SETTING: University Eye Clinic of Ioannina, Greece. PATIENTS: 145 adults divided into four groups according to the cataract type: group A, subcapsular; group B, nuclear; group C, mature and group D, intumescent. MAIN OUTCOME MEASURES: Preoperatively—measurements of axial length and calculation of IOL power using the SRK formula and aiming at emmetropia. Postoperatively—measurements of axial length and refraction. RESULTS: Statistical analysis (one-way analysis of variance) showed no significant differences between: (1) the mean values of differences in pre- and postoperative biometry ( F = 0.26, P = 0.85) and (2) the mean values of actual refractive error ( F = 2.34, P = 0.08), among the four groups of patients. CONCLUSIONS: The cataract type itself does not seem to influence significantly either the preoperative biometry and consequently the intraocular lens power calculation, or the actual postoperative refractive error, using the SRK formula.

Factors contributing to corneal decompensation with the Stableflex lens

A retrospective review was conducted on 38 eyes with Stableflex intraocular lenses in which the lenses were removed or the eye had penetrating keratoplasty. Preoperative axial length measurements were significantly lower in eyes with Stableflex lenses than in control eyes. Based on these data, axial length measurements may be valuable in predicting which eyes will develop corneal problems with small-diameter, closed-loop anterior chamber lenses. Axial lengths may also be beneficial in deciding preoperatively which eyes may need smaller-size anterior chamber lenses of other designs. This is believed to be the first report linking short axial lengths to problems with anterior chamber lenses and recommending the use of axial length measurements for preoperative sizing of anterior chamber lenses.