Estimation of effective lens position using a method independent of preoperative keratometry readings

Influence of corneal astigmatism on near and far vision in eyes with bifocal intraocular lenses

Here, we present a full wave propagation model that quantitatively assesses the effect of astigmatism on visual functions in eyes with diffractive bifocal IOLs. The proposed model with bifocal IOLs evaluated the image quality of each focus at varying degrees of corneal astigmatism with the metrics of modulation transfer function and light-in-the-bucket. The results show that corneal astigmatism alters the distance-near image quality balance. Positive (negative) astigmatism has more detrimental effects on far (near) vision. Additionally, bifocal IOLs are more vulnerable to corneal astigmatism, highlighting the need to consider multifocal toric IOLs with astigmatism greater than 1.0 D. The numerical results closely agreed with previous relevant clinical findings, suggesting the clinical usability of the presented method in predicting the postoperative visual function of patients.

Accuracy of intraocular lens calculation formulas for flanged intrascleral intraocular lens fixation with double-needle technique

PURPOSE

To evaluate the refractive prediction error (RPE) of intraocular lens (IOL) calculation formulas in eyes that have undergone the Yamane technique for scleral fixation of IOLs.

SETTING

Alkek Eye Center, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.

DESIGN

Retrospective case series from electronic chart review.

METHODS

Patients who had undergone scleral fixation of secondary IOLs were selected. The IOL RPEs for 4 IOL prediction formulas-Barrett Universal II, Holladay 1, Hoffer Q, and SRK/T formulas-were obtained by subtracting the predicted spherical equivalent from the postoperative spherical equivalent. The arithmetic mean RPE, mean absolute error (MAE), and percentages of eyes with prediction error of 0.50 diopter (D) or lesser and 1.00 D or lesser were calculated and compared.

RESULTS

Forty eyes of 40 patients met inclusion criteria. All formulas produced hyperopic mean arithmetic RPE. MAE values were 0.73 D for Holladay 1, 0.76 D for Barrett Universal II, 0.80 D for SRK/T, and 0.86 D for Hoffer Q formulas. The percentage of eyes with prediction error of 0.50 D or lesser and 1.00 D or lesser with these formulas were 45% (18 eyes) and 75% (30 eyes) for Holladay 1, 38.5% (15 eyes) and 77% (30 eyes) for Barrett Universal II, 32.5% (13 eyes) and 67.5% (27 eyes) for SRK/T, and 27.5% (11 eyes) and 62.5% (25 eyes) for Hoffer Q formulas. There were no statistically significant differences in prediction errors between the 4 formulas.

CONCLUSIONS

Refractive outcomes of the Yamane technique were less predictable than those of standard cataract surgery. Arithmetic RPE ranged from hyperopic to predicted values for all formulas tested.

Using a multilayer perceptron in intraocular lens power calculation

PURPOSE

To determine the capabilities of a multilayer perceptron (MLP) for calculating the power of an intraocular lens (IOL) to be implanted and in achieving a given postoperative stable refraction.

SETTING

Cuban Institute of Ophthalmology, Havana, Cuba.

DESIGN

Retrospective review.

METHODS

The study comprised data of patients who had uneventful phacoemulsification cataract surgery with implantation of a biconvex acrylic foldable IOL (type RYCF, model Ocuflex) in the capsular bag over 6 years. Exclusion criteria were previous intraocular or refractive corneal surgery, any corneal disease, pathological or complicated cataracts, intraoperative complications, preoperative astigmatism beyond 3.0 diopters (D), postoperative corrected distance visual acuity worse than 20/40, missing postoperative refractive information, eyes with an axial length (AL) shorter than 19.36 mm, eyes with an AL longer than 27.0 mm, average corneal keratometry (K) power lower than 36.0 D or higher than 50.9 D, and refractive surprises greater than ±3.0 D. The data were used to train an MLP to predict the value of the IOL power required for attaining a given postoperative refraction. Using AL, K value, and predicted and real postoperative refraction as input data, the output of the MLP was the IOL power.

RESULTS

The study comprised 15 728 eyes of 15 728 patients. The trained neural networks predicted the value of the implanted IOL with an error less than 0.5 D in more than 95% of patients, even for a case in which a surgeon was not included in the training process.

CONCLUSIONS

The accuracy attained by the trained MLP is high, indicating the feasibility of a prospective study leading to a new method of predicting the IOL power in refractive surgery with an error lower than the current prediction methods.

Gradient Boosting Decision Tree Algorithm for the Prediction of Postoperative Intraocular Lens Position in Cataract Surgery

Purpose

To develop a method for predicting postoperative anterior chamber depth (ACD) in cataract surgery patients based on preoperative biometry, demographics, and intraocular lens (IOL) power.

Methods

Patients who underwent cataract surgery and had both preoperative and postoperative biometry measurements were included. Patient demographics and IOL power were collected from the Sight Outcomes Research Collaborative (SOURCE) database. A gradient-boosting decision tree model was developed to predict the postoperative ACD. The mean absolute error (MAE) and median absolute error (MedAE) were used as evaluation metrics. The performance of the proposed method was compared with five existing formulas.

Results

In total, 847 patients were assigned randomly in a 4:1 ratio to a training/validation set (678 patients) and a testing set (169 patients). Using preoperative biometry and patient sex as predictors, the presented method achieved an MAE of 0.106 ± 0.098 (SD) on the testing set, and a MedAE of 0.082. MAE was significantly lower than that of the five existing methods (P < 0.01). When keratometry was excluded, our method attained an MAE of 0.123 ± 0.109, and a MedAE of 0.093. When IOL power was used as an additional predictor, our method achieved an MAE of 0.105 ± 0.091 and a MedAE of 0.080.

Conclusions

The presented machine learning method achieved greater accuracy than previously reported methods for the prediction of postoperative ACD.

Translational Relevance

Increasing accuracy of postoperative ACD prediction with the presented algorithm has the potential to improve refractive outcomes in cataract surgery.

Anterior chamber depth - a predictor of refractive outcomes after age-related cataract surgery

Background

Anterior chamber depth (ACD) is becoming a hot topic and plays an important role in correcting the refractive errors (REs) after cataract surgery. The aim of this study was to assess the ACD changes and their relationship with the REs after phacoemulsification and intraocular lens (IOL) implantation in patients with age-related cataracts.

Methods

One hundred forty-five eyes of 125 age-related cataract patients from the Department of Ophthalmology, Tangdu Hospital, China, were recruited. IOL Master was used for axial length (AL) and the IOL power calculation measurements, and the Pentacam HR device was used for the ACD and lens thickness (LT) measurements. Every patient underwent uncomplicated phacoemulsification by a single surgeon using a single technique. Postoperative refraction results were obtained at 1 month. The appropriate formula used for the IOL power calculation was chosen depending on the AL, specifically the Hoffer Q (AL < 22.0 mm), SRK/T (22.0 mm ≤ AL ≤ 30.0 mm), and Haigis (AL > 30.0 mm) formulas.

Results

The postoperative ACD was deepened and tended to stabilize gradually after 2 weeks. A concurrent hyperopic shift (0.57 ± 0.47 D) was observed when the change in the ACD was less than 1.65 mm, whereas a myopic shift (− 0.18 ± 0.62 D) occurred contrarily, and the difference between the two groups was statistically significant (P < 0.0001). The change in ACD was significantly larger in the shallow anterior chamber (1.92 ± 0.40 mm) than in the deep chamber (1.33 ± 0.42 mm) (P < 0.0001). Similarly, the change in ACD was larger in the short AL (2.12 ± 0.37 mm) than in the long AL (1.32 ± 0.49 mm). The postoperative ACD and refractive changes were correlated with the preoperative ACD and AL (P < 0.0001), respectively. Two regression formulas were proposed: postoperative ACD = 3.524 + 0.294 × preoperative ACD and postoperative ACD = 3.361 + 0.228× (preoperative ACD + 1/2 LT).

Conclusions

The results of this study showed that the ACD deepened and was associated with a concurrent RE after cataract surgery. Postoperative changes in the ACD were related to the preoperative ACD and AL, which determined the refraction status and visual quality. The regression formula of the postoperative ACD could provide a theoretical basis for predicting refractive errors in the clinic.

Effects of Residual Anterior Lens Epithelial Cell Removal on Axial Position of Intraocular Lens after Cataract Surgery

Purpose

The aim of this study was to assess the effects of residual anterior lens epithelial cell (LEC) removal by anterior capsule polishing on the effective lens position (ELP) and axial position stability of the intraocular lens (IOL) after cataract surgery via postoperative measurement of the anterior chamber depth.

Methods

We enrolled 30 patients (60 eyes) requiring bilateral cataract surgery for age-related cataracts. Meticulous anterior capsule polishing and removal of residual LECs under the capsule were performed using a bimanual irrigation/aspiration system for one randomly selected eye in each patient. The eye without polishing served as a control. ELP was measured at five different time points after surgery, and axial shifting of IOL was determined at each visit by comparison with the position at the previous visit.

Results

The polishing and control groups showed significant differences with regard to the mean ELP at 1 (3.40 ± 0.29 versus 3.53 ± 0.32 mm, resp.; p=0.026) and 2 months (3.42 ± 0.32 versus 3.61 ± 0.35 mm, resp.; p=0.001) after surgery, the mean standard deviation for the five ELP values (0.087 ± 0.093 versus 0.159 ± 0.138 mm, p=0.001), and the root mean square of the change in ELP at each follow-up visit (0.124 ± 0.034 versus 0.246 ± 0.038 mm, p=0.047). The eyes in the control group exhibited a tendency for backward IOL movement with a concurrent hyperopic shift in refraction of approximately 0.2 diopter at 2 months after surgery.

Conclusion

Our findings suggest that residual anterior LEC polishing enhances the axial position stability of IOLs, without any complications, after cataract surgery.

Change of Capsulotomy Over 1 Year in Femtosecond Laser-Assisted Cataract Surgery and Its Impact on Visual Quality

PURPOSE

To compare the shape of the capsulotomy, its change, and its impact on visual quality over 1 year using the femtosecond laser system from the manual technique.

METHODS

In this two-center cross-sectional study from May 2012 to June 2013, each patient had femtosecond laser-assisted cataract surgery in one eye (FLACS group) and conventional phacoemulsification cataract surgery in the other eye (CPCS group). An evaluation of the capsulotomy was performed using retroillumination slit-lamp photographs at 7 days, 6 months, and 1 year after surgery. Effective lens position (ELP), refractive error, and corrected distance visual acuity (CDVA) were analyzed.

RESULTS

Thirty-three patients were included in the study. Diameters of capsulorhexis were more precise and deviation surfaces were lower in the FLACS group than in the CPCS group at each evaluation (P < .05). Femtosecond laser capsulotomies were less modified over time than manual continuous curvilinear capsulorhexis. No significant differences were observed for CDVA, refractive error, and ELP between groups.

CONCLUSIONS

More precise capsulotomy sizing can be achieved with the femtosecond laser compared to continuous curvilinear capsulorhexis. Femtosecond laser capsulotomies are less modified over time but did not improve ELP or visual quality. [J Refract Surg. 2017;33(1):44-49].

Changes in Axial Length and Refractive Error After Noninvasive Normalization of Intraocular Pressure From Elevated Levels

PURPOSE

To explore the changes in axial length and refractive error after noninvasive normalization of intraocular pressure (IOP) from elevated levels.

DESIGN

A prospective observational study.

METHODS

We enrolled 51 consecutive patients with abnormally elevated unilateral IOP (≥10 mm Hg compared with that of the fellow eye, in which the IOP was ≤21 mm Hg). In all patients, the keratometric value and axial length were obtained with the aid of an IOLMaster before and after IOP normalization (defined as attainment of an IOP difference of ≤3 mm Hg compared with the fellow eye, with or without topical application of ocular hypotensive therapy). We focused principally on IOP, axial length, the keratometric value, and the predicted refractive difference (the predicted refractive error after IOP normalization upon placement of an IOL with a power for emmetropia correction determined prior to IOP normalization).

RESULTS

The axial length was significantly reduced from 23.5 to 23.3 mm after IOP normalization, from 45.9 mm Hg to 14.3 mm Hg (P < .001). The change in IOP correlated with that of the axial length (r = 0.826, P < .001), but not with the change in the keratometric value (P = .618). The change in axial length per 10 mm Hg IOP decrease was -0.06 mm (P < .001). The IOP change was correlated with the predicted refractive difference (r = 0.693, P < .001); the predicted refractive difference per 10 mm Hg IOP decrease was +0.15 diopter (P < .001).

CONCLUSIONS

The axial length decreased and the predicted refractive difference increased (hyperopia) as IOP decreased. Therefore, a possible risk of postoperative hyperopic shift should be considered when biometric examination for IOL power calculation is performed in a patient with an abnormally elevated IOP.