Filomena Ribeiro

Personalized Pseudophakic Model for Refractive Assessment

Purpose To test a pseudophakic eye model that allows for intraocular lens power (IOL) calculation, both in normal eyes and in extreme conditions, such as post-LASIK. Methods Participants: The model’s efficacy was tested in 54 participants (104 eyes) who underwent LASIK and were assessed before and after surgery, thus allowing to test the same method in the same eye after only changing corneal topography. Modelling The Liou-Brennan eye model was used as a starting point, and biometric values were replaced by individual measurements. Detailed corneal surface data were obtained from topography (Orbscan®) and a grid of elevation values was used to define corneal surfaces in an optical ray-tracing software (Zemax®). To determine IOL power, optimization criteria based on values of the modulation transfer function (MTF) weighted according to contrast sensitivity function (CSF), were applied. Results Pre-operative refractive assessment calculated by our eye model correlated very strongly with SRK/T (ru200a=u200a0.959, p<0.001) with no difference of average values (16.9±2.9 vs 17.1±2.9 D, p>0.05). Comparison of post-operative refractive assessment obtained using our eye model with the average of currently used formulas showed a strong correlation (ru200a=u200a0.778, p<0.001), with no difference of average values (21.5±1.7 vs 21.8±1.6 D, p>0.05). Conclusions Results suggest that personalized pseudophakic eye models and ray-tracing allow for the use of the same methodology, regardless of previous LASIK, independent of population averages and commonly used regression correction factors, which represents a clinical advantage.

Comparison of astigmatic prediction errors associated with new calculation methods for toric intraocular lenses

PURPOSEnTo compare the prediction errors in residual astigmatism associated with new calculation methods for toric intraocular lenses (IOLs).nnnSETTINGnHospital da Luz, Lisbon, Portugal.nnnDESIGNnRetrospective case series.nnnMETHODSnIn eyes having cataract surgery with toric IOL implantation (Acrysof IQ), the predicted residual astigmatism by each calculation method was compared with the manifest refractive astigmatism. The prediction error in residual astigmatism was calculated by vector analysis.nnnRESULTSnThe study evaluated 86 eyes (86 patients). All calculation methods resulted in overcorrection of with-the-rule astigmatism and undercorrection of against-the-rule astigmatism. For the original Alcon calculator, the centroid prediction error was 0.43 @ 170, which was reduced by the application of the Baylor nomogram (0.35 @ 169) or the Abulafia-Koch formula (0.34 @ 170). For the Holladay toric calculator, the centroid prediction error was 0.40 @ 168, which was reduced by the Baylor nomogram (0.35 @ 169), the Abulafia-Koch formula (0.25 @ 158), and the Goggin coefficient of adjustment (0.38 @ 170). The Barrett calculator and the newly introduced Alcon calculator yielded the lowest centroid prediction errors (0.17 @ 165 and 0.19 @ 164, respectively). The centroid prediction error of ray-tracing calculations (PhacoOptics) using real posterior corneal surface measurements was 0.32 @xa0171.nnnCONCLUSIONSnThe Barrett toric calculator and the new Alcon calculator yielded the lowest astigmatic prediction errors. Of the nomogram methods, application of the Abulafia-Koch formula achieved the best results. The outcomes of toric IOL implantation might be improved by using 1 of these calculation methods.

Refractive Error Assessment: Influence of Different Optical Elements and Current Limits of Biometric Techniques

PURPOSEnTo identify and quantify sources of error on refractive assessment using exact ray tracing.nnnMETHODSnThe Liou-Brennan eye model was used as a starting point and its parameters were varied individually within a physiological range. The contribution of each parameter to refractive error was assessed using linear regression curve fits and Gaussian error propagation analysis. A MonteCarlo analysis quantified the limits of refractive assessment given by current biometric measurements.nnnRESULTSnVitreous and aqueous refractive indices are the elements that influence refractive error the most, with a 1% change of each parameter contributing to a refractive error variation of +1.60 and -1.30 diopters (D), respectively. In the phakic eye, axial length measurements taken by ultrasound (vitreous chamber depth, lens thickness, and anterior chamber depth [ACD]) were the most sensitive to biometric errors, with a contribution to the refractive error of 62.7%, 14.2%, and 10.7%, respectively. In the pseudophakic eye, vitreous chamber depth showed the highest contribution at 53.7%, followed by postoperative ACD at 35.7%. When optic measurements were considered, postoperative ACD was the most important contributor, followed by anterior corneal surface and its asphericity. A MonteCarlo simulation showed that current limits of refractive assessment are 0.26 and 0.28 D for the phakic and pseudophakic eye, respectively.nnnCONCLUSIONSnThe most relevant optical elements either do not have available measurement instruments or the existing instruments still need to improve their accuracy. Ray tracing can be used as an optical assessment technique, and may be the correct path for future personalized refractive assessment.

Clinical Outcomes After Cataract Surgery With a New Transitional Toric Intraocular Lens.

PURPOSEnTo evaluate the visual outcomes of patients who underwent cataract surgery with implantation of a transitional toric monofocal intraocular lens (IOL) (Precizon Toric IOL, model 565; Ophtec BV, Groningen, The Netherlands).nnnMETHODSnIn this prospective case series, 51 eyes of 39 patients with cataract and regular keratometric astigmatism between 1.00 and 4.50 diopters (D) that had phacoemulsification with implantation of a Precizon Toric IOL were included. Over a 4-month follow-up period, the main outcome measures were uncorrected and corrected distance visual acuities (UDVA and CDVA, respectively), spherical equivalent (SE) refraction, astigmatism outcomes evaluated according to the Alpins method, the IOLs rotational stability, and higher order aberrations.nnnRESULTSnAt the 4-month follow-up visit, mean UDVA was 0.06 ± 0.1 logMAR (range: 0.4 to -0.18 logMAR) (P < .001) and mean CDVA was -0.00 ± 0.07 logMAR (range: 0.15 to -0.18 logMAR) (P < .001). UDVA was 0.3 logMAR or better in 50 (98%) eyes and 0.1 logMAR or better in 42 (82%) eyes. Mean SE refraction was -0.19 ± 0.38 D (range: -1.13 to +0.50 D), with 44 (86%) eyes within ±0.50 D of the attempted correction. Mean target induced astigmatism was 1.96 ± 0.94 D (range: 0.70 to 4.50 D) and mean surgically induced astigmatism was 1.85 ± 1.01 D (range: 0.07 to 4.64 D). Mean correction index was 0.87 (range: 0.07 to 2.29 D). Mean toric IOL axis rotation was 1.98° ± 1.78° (range: 0° to 7°). Ocular aberrometry was within normal values.nnnCONCLUSIONSnThe implantation of the Precizon Toric IOL in patients with cataract and corneal astigmatism provided excellent visual outcomes, predictability of refractive results, rotational stability, and good optical performance. [J Refract Surg. 2016;32(7):452-458.].

Ocular biometric measurements in cataract surgery candidates in Portugal

Objective Describe the ocular biometric parameters and their associations in a population of cataract surgery candidates. Methods A cross-sectional study of 13,012 eyes of 6,506 patients was performed. Biometric parameters of the eyes were measured by optical low-coherence reflectometry. The axial length (AL), mean keratometry (K) and astigmatism, anterior chamber depth (ACD) (epithelium to lens), lens thickness (LT), and Corneal Diameter (CD) were evaluated. Results The mean age was 69 ± 10 years (44–99 years). Mean AL, Km, and ACD were 23.87 ± 1.55 mm (19.8–31.92 mm), 43.91 ± 1.71 D (40.61–51.14 D), and 3.25 ± 0.44 mm (2.04–5.28 mm), respectively. The mean LT was 4.32 ± 0.49 mm (2.73–5.77 mm) and the mean CD was 12.02 ± 0.46 mm (10.50–14.15 mm). The mean corneal astigmatism was 1.08 ± 0.84 D (0.00–7.58 D) and 43.5% of eyes had astigmatism ≥ 1.00 D. Male patients had longer AL and ACDs (p < .001) and flatter corneas (p < .001). In regression models considering age, gender, Km, ACD, LT, and CD, a longer AL was associated with being male and having higher ACD, LT and CD. Conclusions These data represent normative biometric values for the Portuguese population. The greatest predictor of ocular biometrics was gender. There was no significant correlation between age and AL, ACD, or Km. These results may be relevant in the evaluation of refractive error and in the calculation of intraocular lens power.

Comparability and repeatability of different methods of corneal astigmatism assessment

Purpose To assess the comparability and repeatability of keratometric and astigmatism values measured by four techniques: Orbscan IIz® (Bausch and Lomb), Lenstar LS 900® (Haag-Streit), Cassini® (i-Optics), and Total Cassini (anterior + posterior surface), in healthy volunteers. Patients and methods Fifteen healthy volunteers (30 eyes) were assessed by the four techniques. In each eye, three consecutive measures were performed by the same operator. Keratometric and astigmatism values were recorded. The intraclass correlation coefficient (ICC) was used to assess comparability and repeatability. Agreement between measurement techniques was evaluated with Bland–Altman plots. Results Comparability was high between all measurement techniques for minimum keratometry (K1), maximum keratometry (K2), astigmatism magnitude, and astigmatism axis, with ICC >0.900, except for astigmatism magnitude measured by Cassini compared to Lenstar (ICC =0.798) and Orbscan compared to Lenstar (ICC =0.810). However, there were some differences in the median values of K1 and K2 between measurement techniques, and the Bland–Altman plots showed a wide data spread for all variables, except for astigmatism magnitude measured by Cassini and Total Cassini. For J0 and J45, comparability was only high for J0 between Cassini and Orbscan. Repeatability was also high for all measurement techniques except for K2 (ICC =0.814) and J45 (ICC =0.621) measured by Cassini. Conclusion All measurement techniques showed high comparability regarding K1, K2, and astigmatism axis. Although posterior corneal surface is known to influence these measurements, comparability was high between Cassini and Total Cassini regarding astigmatism magnitude and axis. However, the wide data spread suggests that none of these devices should be used interchangeably.

A novel color-LED corneal topographer to assess astigmatism in pseudophakic eyes.

Purpose To assess the accuracy of corneal astigmatism evaluation measured by four techniques, Orbscan IIz®, Lenstar LS900®, Cassini®, and Total Cassini (anterior + posterior surface), in pseudophakic eyes. Patients and methods A total of 30 patients (46 eyes) who had undergone cataract surgery with the implantation of a monofocal intraocular lens (AcrySof IQ) were assessed after surgery. For each eye, subjective assessment of astigmatism and its axis was performed. Minimum, maximum, and mean keratometry and astigmatism and its axis were evaluated using the four measurement techniques. All measurements were compared with the subjective measurements. Agreement between each measurement technique and subjective assessment was evaluated using Bland–Altman plots. Linear regressions were performed and compared. Results Linear regression analysis of astigmatism axis showed very high R2 for all models, with Total Cassini showing the least difference to the unit slope (0.052) and the least difference to a null constant (3.790), although not statistically different from the other models. Regarding astigmatism value, the Cassini and Total Cassini models were similar and statistically better than the Lenstar model. Cassini and Total Cassini showed better J0 compared with Orbscan. Conclusion On linear regression models, Cassini and Total Cassini showed the best performance regarding astigmatism value. Cassini and Total Cassini also showed the least J0 deviation from the Cartesian origin compared with Orbscan, which had the lowest performance. Total corneal measurement with the color LED topographer seems to be a better technique for astigmatism assessment.

Assessment of Image Quality Using a Pseudophakic Eye Model for Refractive Evaluation

In the refractive assessment by optical evaluation based on ray-tracing, the definition of the best focus plane remains a challenge. We simulated 100 pseudophakic eye models using a Montecarlo analysis with ray-tracing evaluation. The image quality resulting from optimization with the Visual Strehl ratio computed in frequency domain weighted by the neural contrast sensitivity function (VSMTF), a metric that has been shown to have a good correlation with defocus detection by the human eye, and with the Root-Mean-Square of Wavefront (RMSW) error, the most commonly used optimization metric, was assessed. For objective assessment, we designed an index to detect increasing stages of defocus. For subjective assessment, we designed a force choice test that was completed by 20 observers. Results show that both for objective and subjective evaluation, VSMTF performed better than RMSW. Therefore, VSMTF is a good metric for the refractive assessment of human eye models with ray-tracing.

Comparison of Surgically Induced Astigmatism and Morphologic Features Resulting From Femtosecond Laser and Manual Clear Corneal Incisions for Cataract Surgery

PURPOSEnTo compare the surgically induced astigmatism (SIA) vector, flattening effect, torque, and wound architecture following femtosecond laser and manual clear corneal incisions (CCIs).nnnMETHODSnIn a double-armed, randomized, prospective case series, cataract surgery was performed for 600 eyes using femtosecond laser (300 eyes) or manual (300 eyes) 2.4-mm CCIs in temporal or superior oblique locations. SIA, flattening effect, torque, and the summated vector mean for SIA were calculated. Correlation with individual features was established and incision morphology was investigated by anterior segment optical coherence tomography at 3 months of follow-up.nnnRESULTSnThe SIA, flattening effect, and torque were lower in the femtosecond laser group for both incision locations, although the differences were not significant (all P > .05). The femtosecond laser group showed less dispersion of SIA magnitude and flattening effect. Temporal and superior oblique incisions resulted in flattening effect values of -0.11 and -0.21 diopters (D), respectively, in the femtosecond laser group and -0.13 and -0.34 D, respectively, in the manual group. Significant correlations with individual features were only found in the femtosecond laser group, with preoperative astigmatism being the only significant SIA predictor by multiple regression analysis (P = .003). Femtosecond laser CCIs showed less deviation from the intended length, wound enlargement, endothelial misalignment, and Descemet membrane detachments (all P < .037).nnnCONCLUSIONSnFemtosecond laser CCIs were more reproducible. Although SIAs were smaller in femtosecond laser CCIs than in manual CCIs for both temporal and superior oblique incisions, the difference was not statistically significant. Association with individual features is highly variable. [J Refract Surg. 2018;34(5):322-329.].

Comparative analysis of clinical outcomes of a monofocal and an extended-range-of-vision intraocular lens in eyes with previous myopic laser in situ keratomileusis

PURPOSEnTo compare the clinical outcomes after cataract surgery with implantation of a monofocal or an extended-range-of-vision intraocular lens (IOL).nnnSETTINGnHospital da Luz, Lisbon Portugal.nnnDESIGNnProspective case series.nnnMETHODSnPatients who previously had myopic laserxa0inxa0situ keratomileusis (LASIK) had cataract surgery with bilateral implantation of an extended-range-of-vision IOL (Tecnis Symfony) or axa0monofocal IOL (Tecnis ZCB00). Visual acuity, refraction, defocus curve, contrast sensitivity, photic phenomena, spectacle independence, and patient satisfaction were evaluated at 4 months postoperatively.nnnRESULTSnThe study comprised 44 patients (88 eyes), with 22 patients in each IOL group. No significant differences between groups were found postoperatively for most visual and refractive parameters (all Pxa0≥xa0.27). However, binocular uncorrected intermediate and near visual acuities were significantly better in the extended-range-of-vision group (Pxa0<xa0.01). The defocus curve of both IOLs differed more with increasing negative defocus (Pxa0<xa0.01). No significant differences between IOLs were found in contrast sensitivity for any spatial frequency evaluated (Pxa0≥xa0.05). Most of the patients did not perceive photic phenomena with either IOL. Mild glare was reported in 22.7% of the extended-range-of-vision patients and 9.1% of the monofocal group; mild halos were comparable with 13.6% in both groups. Spectacle dependence for intermediate vision and near vision was higher in the monofocal IOL group.nnnCONCLUSIONnThe extended-range-of-vision IOL was a useful option to restore visual function after cataract surgery in eyes that previously had myopic LASIK surgery, offering levels of visual quality comparable to those achieved with the monofocal IOL.