Stabilization of refractive error and associated factors following small incision phacoemulsification cataract surgery

Background Accumulating evidence suggests that refractive stabilization occurs rapidly following small incision cataract surgery. Nonetheless, many guidelines still suggest waiting four to 6 weeks before prescribing corrective lenses. This study was undertaken to supplement the existing literature regarding refractive stabilization, and evaluate multiple contributing factors that could dissuade clinicians from confidently correcting refractive error in the early post-operative course following routine cataract surgeries. Methods Adult patients undergoing phacoemulsification cataract surgery with uncomplicated surgeries and post-surgical courses at the Calgary Ophthalmology Centre (Calgary, Alberta, Canada) were included in this prospective observational case series. Exclusion criteria included known corneal dystrophies, infectious keratitis, complicated surgery or toric/multifocal IOLs. Data was collected at weekly intervals for a total of 6 weeks. Collected data included autorefraction, visual acuity, corneal pachymetry, and effective lens position. Results One hundred six eyes of 104 patients were included in this study. Post-operative sphere, cylinder and spherical equivalent were not significantly different at any post-operative week compared with week six, and 80–86% of patients were within 0.5D of last follow-up spherical equivalent at any week. The secondary outcomes of central corneal thickness, effective lens position and visual acuity did, however, exhibit significant differences between early post-operative weeks and last follow-up values. Conclusions These data suggest that refractive error can be effectively measured and corrected as early as one-week post-operatively in the majority of patients, though other measures of post-operative stability including central corneal thickness, effective lens position and visual acuity can require up to 4 weeks to stabilize. Thus a conservative and pragmatic approach may be to wait until 4 weeks post-operatively prior to obtaining refractive correction following uncomplicated phacoemulsification cataract surgery.

Effect of eccentricity of overnight lenses on 2-year axial growth and visual quality

AIM: To explore the effect of eccentricity of overnight orthokeratology (OK) lenses on 2-year eye axial growth and visual quality. METHODS: Based on the degree of eccentricity of OK lenses, patients were divided into three groups: a low degree of eccentricity group (degree of eccentricity ≤0.5 mm), a group of moderate eccentricity (eccentric degree >0.5-1.0 mm) and a group with a high degree of eccentricity (eccentric degree >1-1.5 mm). The degree of eccentricity of the OK lens, spherical equivalent (SE), the uncorrected visual acuity (UCVA) after wearing OK lenses, axial length (AL) before and after wearing OK lenses, total higher-order aberrations (HOA), comas, and spherical aberrations (SA) for 3 mm pupils were analyzed. The difference among the three groups for all parameters was compared using the Kruskal-Wallis H Rank-Sum test. RESULTS: The study retrospectively analyzed 75 cases (139 eyes). In the low eccentricity group (53 eyes), the mean age was 11.4±2.4y, SE was -3.24±1.48 D, and AL was 24.85±1.01 mm. In the moderate eccentricity group (53 eyes), the mean age was 11.4±2.2y, SE was -3.22±1.29 D, and AL was 25.15±0.92 mm. In the high eccentricity group (31 eyes), the mean age was 11.5±1.9y, SE was -3.54±1.43 D, and AL was 24.95±0.84mm. After two years, there was no significant difference in the changes of the axis among the three groups (P=0.089). The HOA, SA, and coma in the high eccentric group were significantly higher than in the middle eccentric group (P<0.05). The HOA, SA, and coma in the high eccentric group were also significantly higher than those in the low eccentric group (P<0.05). CONCLUSION: For OK lenses, it is unnecessary to strictly require the absolute centralization of the lens position. An unnecessary change of the lenses may delay the eye-axis control. However, the balance between axial control and visual quality should be assessed.

Ray tracing intraocular lens calculation performance improved by AI-powered postoperative lens position prediction

AimsTo assess whether incorporating a machine learning (ML) method for accurate prediction of postoperative anterior chamber depth (ACD) improves cataract surgery refraction prediction performance of a commonly used ray tracing power calculation suite (OKULIX).Methods and analysisA dataset of 4357 eyes of 4357 patients with cataract was gathered at the Kellogg Eye Center, University of Michigan. A previously developed machine learning (ML)–based method was used to predict the postoperative ACD based on preoperative biometry measured with the Lenstar LS900 optical biometer. Refraction predictions were computed with standard OKULIX postoperative ACD predictions and ML-based predictions of postoperative ACD. The performance of the ray tracing approach with and without ML-based ACD prediction was evaluated using mean absolute error (MAE) and median absolute error (MedAE) in refraction prediction as metrics.ResultsReplacing the standard OKULIX postoperative ACD with the ML-predicted ACD resulted in statistically significant reductions in both MAE (1.7% after zeroing mean error) and MedAE (2.1% after zeroing mean error). ML-predicted ACD substantially improved performance in eyes with short and long axial lengths (p<0.01).ConclusionsUsing an ML-powered postoperative ACD prediction method improves the prediction accuracy of the OKULIX ray tracing suite by a clinically small but statistically significant amount, with the greatest effect seen in long eyes.

Prediction of effective Lens position using anterior segment optical coherence tomography in Chinese subjects with angle closure

Purpose To assess the accuracy of biometric parameters measured by anterior segment optical coherence tomography (AS-OCT) and partial coherence interferometry (PCI) in prediction of effective lens position (ELP) compared with previous formulas in PACG patients. Methods 121 PACG eyes were randomly divided into training set (85 eyes) and validation set (36 eyes) with same procedure including AS-OCT, PCI, phacoemulsification and IOL implantation surgery. Preoperative anterior chamber depth (pre-ACD), scleral spur depth (SSD), scleral spur width (SSW), lens vault (LV) and cornea thickness (CT) were measured from AS-OCT image. Axial length (AL) and corneal power (K) were measured by PCI. All the 7 parameters were analyzed by multiple linear regression in training set and a statistic regression formula was developed. In validation set, one-way ANOVA was applied to compare the new regression formula with Sanders-Retzlaff-Kraff theoretic (SRK/T), Holladay 1, Haigis, and a regression formula developed in previous study. Results The coefficient of determination (R2) of different parameter combinations are 0.19 (pre-ACD, AL), 0.25 (AL, K) and 0.49 (SSD, AL, SSW) in training set. In validation set, the correlation between predicted and measured ELP are: new formula (R2 = 0.50, P = 0.9947) Holladay 1 (R2 = 0.12, P < 0.0001), SRK/T (R2 = 0.11, P < 0.0001) and Haigis (R2 = 0.06, P < 0.0001). Conclusion Among 7 tested parameters, pre-ACD contribute little in ELP prediction. Formula consist of SSD, AL and SSW showed better accuracy than other formulas tested.

Nasal trabeculo-ciliary angle and relative lens vault as predictors for intraocular pressure reduction following phacoemulsification

Purpose To evaluate quantitative relationships between biometric measurements and expected intraocular pressure reduction following phacoemulsification. Design A prospective, comparative clinical study. Methods Forty nine candidates for phacoemulsification were included. Intraocular pressure was measured preoperatively and after 7 and 30 days. Ocular biometrics were measured using optical biometry and ultrasound biomicroscopy preoperatively and 1 month postoperatively. Results Patients were sub-grouped into open-angle glaucoma (12 eyes), angle-closure glaucoma (18 eyes), and cataract-only groups (19 eyes). The mean intraocular pressure reduction was −1.67 ± 2.73, −13.11 ± 7.98, and −7.50 ± 3.58 mmHg in the cataract-only, angle-closure glaucoma, and open-angle glaucoma groups ( p = 0.001). The delta-intraocular pressure at day 7 showed positive correlations with lens vault and relative-lens vault ( p = 0.005 and 0.001). It showed negative correlations with lens position, relative-lens position, anterior chamber depth, aqueous depth, and nasal and temporal angles in addition to lens thickness, anterior vault, nasal trabeculo-ciliary angle, and temporal-trabeculo-ciliary angle at the end of the follow-up period. Regression analysis revealed significant associations between preoperative intraocular pressure and both nasal-trabeculo-ciliary angle and anterior vault ( p = 0.038 and 0.019) and delta-intraocular pressure and both nasal-trabeculo-ciliary angle and relative-lens vault ( p = 0.001 and ≤0.001) with an area under the curve of 0.71 for relative-lens vault. For every degree decrease in nasal-trabeculo-ciliary angle, there was an expected 0.33 mmHg intraocular pressure reduction with no expected change if nasal-trabeculo-ciliary angle decreased to <22°. Conclusions The relationship between anterior-segment-biometrics could determine intraocular pressure behavior after phacoemulsification. The preoperative nasal-trabeculo-ciliary angle and relative-lens vault could be significant predictors for postoperative intraocular pressure reduction.

Optical Design of Improved Offner Imaging Spectrometer

An improved Offner imaging spectrometer was proposed based on the optical system characteristics of Offner imaging spectrometer, which can ensure perfect imaging quality in a wider annular region. The operating wavelength of the improved Offner imaging spectrometer ranges from 900nm to 1700nm, and the magnification is 1. Improved Offner imaging spectrometer can be obtained by changing the meniscus lens position and further optimizing the design. The results indicate that the improved Offner imaging spectrometer can effectively improve compactness and lightweight, and reduce the difficulty of optical adjustment, which is conducive to the stability of practical application.

Trans-optic Suture Fixation of Subluxated Intraocular Lenses

PurposeTo report a technique for fixating posterior chamber intraocular lenses (PCIOLs) to the sclera by passing sutures through the lens materialMethodsCases in which PCIOLs were fixated to the sclera using trans-optic sutures were included in this series. Intra and post-operative complications were recorded, and lens position was assessed using slit lamp examination.ResultsFourteen cases were included in this series. In 9 cases the procedure was performed using 9-0 polypropylene in pseudophakic eyes to correct subluxation, centration, tilt or to replace a broken haptic. In 5 cases this technique was used for primary PCIOL fixation using a flanged 6-0 polypropylene suture in aphakic eyes. In all cases the lenses remained centered and stable at the end of follow up, and no post-operative complications occurred.ConclusionTrans-optic suturing is a safe and effective alternative method for fixation of IOLs in a variety of pseudophakic and aphakic clinical scenarios.

An Ensemble-Based Approach for Estimating Personalized Intraocular Lens Power

This study introduced a new approach for the calculation of personalized intraocular lens power, which used an ensemble of regression models to devise a more accurate and robust prediction of the effective lens position. The concept of cross-validation is used to rigorously assess the performance of the devised formula against the most commonly used published formulae. The results from this study show that overall, the proposed approach outperforms the most commonly used modern formulae (namely, SRK/T, Hoffer Q, Holladay I, and Haigis) in terms of mean absolute prediction errors and prediction accuracy i.e., the percentage of eyes within ± 0.5D and ± 1 D ranges of prediction, for various ranges of axial lengths of the eyes. The results are obtained using three models of lens (two monofocal and one multifocal). Furthermore, the proposed formula exhibited some promising features in terms of robustness. This particular characteristic enables the new formula to cope with the variations in the axial length, the pre-operative anterior chamber depth as well as the keratometric readings of the corneal power; hence mitigating the impact of measurement accuracy for these parameters.

Relationship between Medium-Term Changes in Intraocular Lens Position and Refraction after Cataract Surgery with Two Different Models of Monofocal Lenses

The aim of this prospective descriptive study was to characterize the variations of the clinical effective lens position (ELP) (considering paraxial optics and postoperative data) and the intraocular lens (IOL) position, using “eye” data gathered from a 6-month follow-up of patients who underwent uneventful cataract surgery. Patients were implanted with two different monofocal IOLs: AcrySof IQ SN60WF (Alcon) (Group 1, 247 eyes) and Akreos MI60L (Bausch & Lomb) (Group 2, 104 eyes). No significant differences were found between groups concerning spherical equivalent (SE), axial length, and clinical ELP changes, from 1 to 6 months after surgery (p ≥ 0.516). A more positive change in postoperative anterior chamber depth was found in Group 2, but the difference did not reach statistical significance (p = 0.065). No significant moderate to strong correlations were found between the changes in clinical ELP and preoperative data. The correlation between the changes in SE and clinical ELP over time was strong and statistically significant (groups 1 and 2: r = 0.957 and r = 0.993, p < 0.001). In conclusion, changes in refraction from 1 to 6 months after cataract surgery, with single-piece monofocal IOLs, are not clinically relevant, which correlates with the presence of good positional stability. These changes cannot be predicted preoperatively and considered in IOL power calculations.