Personal A-constant in relation to axial length with various intraocular lenses

Preliminary demonstration of a novel intraocular lens power calculation: the O formula

PURPOSE

To evaluate the performance of a new formula of intraocular lens (IOL) power calculation (the O formula) based on ray tracing without commonly used parameters, including ultrasound-compatible axial length, keratometry readings, and A-constant.

SETTING

Tokyo Medical Center, Tokyo, Japan.

DESIGN

Retrospective consecutive case series.

METHODS

423 eyes (423 patients) implanted with a single-piece, L-loop, acrylic IOL were enrolled. All biometric data for the O formula were obtained by anterior segment swept-source optical coherence tomography (SS-OCT) and SS-OCT-based biometer. The performance of the O formula was compared with those of the Barrett Universal II (BUII) and Kane formulas at 1 month postoperatively. Statistical analysis was applied according to a heteroscedastic test with SD of prediction errors as the main parameter for formula performance.

RESULTS

The SD of the O formula (0.426) was statistically significantly lower than that of the BUII formula (0.464, P = .034) but not statistically significantly different from that of the Kane formula (0.433, P = .601). The percentages of patients with refractive prediction errors within ±0.50 diopter (D) and ±1.00 D of the O, BUII, and Kane formulas were 75.4% and 98.6%, 77.1% and 97.9%, and 76.6% and 98.1%, respectively.

CONCLUSIONS

The O formula, based on ray tracing using SS-OCT-based devices, is one of the promising approaches for IOL power calculation, although additional larger scale studies are needed. It may be used as an alternative in IOL power calculation because of its independence from commonly used parameters.

Long-Term Changes in Manifest Refraction Subsequent to Cataract Surgery

PURPOSE

To examine the long-term refractive changes after stabilization of surgically induced changes (SICs) subsequent to cataract surgery.

SETTING

Private hospital.

DESIGN

Case-control study.

METHODS

Manifest refraction of 300 eyes of 300 patients that underwent phacoemulsification and 300 eyes of 300 age- and sex-matched patients without surgery was examined the day on which SICs stabilized (baseline) and ≥7 years postbaseline using an autorefractometer. Refraction was divided into 3 components: spherical power (M), vertical/horizontal astigmatism (J0), and oblique astigmatism (J45) using power vector analysis, and the components were compared between the 2 time-points and between groups.

RESULTS

In the surgery group, the mean M and J45 did not change significantly between baseline and ≥7 years postbaseline, but the J0 significantly decreased between the 2 time-points (P < .001), indicating an against-the-rule (ATR) shift. In the non-surgery group, the mean M significantly increased and J0 significantly decreased between the time-points (P < .001), whereas J45 did not change significantly. The mean change in M between the 2 time-points was significantly smaller in the surgery group (P < .001), whereas the changes in J0 and J45 did not differ significantly between the time-points.

CONCLUSION

Spherical power did not change and refractive astigmatism significantly changed toward ATR astigmatism during the more than 7-year follow-up after stabilization of SICs in pseudophakic eyes, while hyperopic and ATR shifts occurred in phakic eyes, and the astigmatic changes were comparable between pseudophakic and phakic eyes.

Does Every Calculation Formula Fit for All Types of Intraocular Lenses? Optimization of Constants for Tecnis ZA9003 and ZCB00 Is Necessary

Background and Objectives: To evaluate the performance of intraocular lenses (IOLs) using power calculation formulas on different types of IOL. Materials and Methods: 120 eyes and four IOL types (BioLine Yellow Accurate Aspheric IOL (i-Medical), TECNIS ZCB00, TECNIS ZA9003 (Johnson & Johnson) (3-piece IOL) and Softec HD (Lenstec)) were analyzed. The performance of Haigis, Barret Universal II and SKR-II formulas were compared between IOL types. The mean prediction error (ME) and mean absolute prediction error (MAE) were analyzed. Results: The overall percentage of eyes predicted within ±0.25 diopters (D) was 40.8% for Barret; 39.2% Haigis and 31.7% for SRK-II. Barret and Haigis had a significantly lower MAE than SRK-II (p < 0.05). The results differed among IOL types. The largest portion of eyes predicted within ±0.25 D was with the Barret formula in ZCB00 (33.3%) and ZA9003 (43.3%). Haigis was the most accurate in Softec HD (50%) and SRK-II in Biolline Yellow IOL (50%). ZCB00 showed a clinically significant hypermetropic ME compared to other IOLs. Conclusions: In general, Barret formulas had the best performance as a universal formula. However, the formula should be chosen according to the type of IOL in order to obtain the best results. Constant optimizations are necessary for the Tecnis IOL ZCB00 and ZA9003, as all of the analyzed formulas achieved a clinically significant poor performance in this type of IOL. ZCB00 also showed a hypermetropic shift in ME in all the formulas.

Short-Term Changes in Prediction Error after Cataract Surgery in Eyes Receiving 1 of 3 Types of Single-Piece Acrylic Intraocular Lenses

PURPOSE

To compare short-term changes in refractive prediction error (PE) after phacoemulsification among eyes receiving different types of single-piece acrylic intraocular lenses (IOLs).

DESIGN

Randomized clinical trial.

METHODS

A total of 195 eyes of 195 patients scheduled for implantation of a single-piece acrylic IOL were randomly assigned to receive 1 of 3 IOLs: 1) an Alcon model SN60WF, 2) a Hoya model XY-1, or 3) an AMO model ZCB00V. Manifest spherical equivalent (MRSE) value, PE, and changes in PE were examined at 1 day and at 1 and 2 months postoperatively and were compared among groups.

RESULTS

The mean MRSE and PE significantly changed toward myopia between 1 day and 2 months postoperatively in all groups (P < .0001). The MRSE and PE did not differ significantly among groups at 1 day and 1 month postoperatively and were significantly smaller in the SN60WF group than in the XY-1 and ZCB00V groups at 2 months (P ≤ .0006). The PE change between 1 day and 2 months postoperatively was significantly smaller in the SN60WF group than in the other groups (P = .0062). IOL type and changes in anterior chamber depth and corneal curvature independently correlated with PE changes.

CONCLUSIONS

The MRSE and PE showed a significant myopic change for 2 months postoperatively in eyes implanted with 1 of 3 types of single-piece acrylic IOLs and were significantly smaller in the SN60WF than in the XY-1 and ZCB00V groups. Changes in PE during the 2 postoperative months were smaller in the SN60WF IOLs than in the other IOLs, suggesting that postoperative refractive stability differs among single-piece acrylic IOLs.

Influence of Patient Age on Intraocular Lens Power Prediction Error

PURPOSE

To examine whether intraocular lens (IOL) power prediction error (PE) after cataract surgery differs according to patient age.

DESIGN

Prospective cohort study.

METHODS

We consecutively enrolled 75 eyes of 75 patients 59 years of age or younger, and 150 eyes of 150 patients in each of 3 age groups (60-69, 70-79, and 80-89 years), for whom phacoemulsification and implantation of a single-piece acrylic IOL was planned. The IOL power was calculated using the optimized SRK/T formula. Objective refraction was measured using an autorefractometer at approximately 3 months postoperatively, and the mean arithmetic PE and median absolute PE were compared among age groups.

RESULTS

The mean preoperative refractive error predicted by the SRK/T formula was similar among age groups (P = .4179). The mean postoperative spherical equivalent was significantly more myopic in younger patients (P < .0001). Mean PE was -0.24 diopters (D) in those ≤59 years of age, -0.17 D in those 60-69 years of age, -0.11 D in those 70-79 years of age, and -0.05 D in those 80-89 years of age; the mean PE was less myopic in older patients (P = .0008). The median absolute PE did not differ significantly among groups (P = .6192). Mean PE was positively correlated with age (P < .0001). Multiple regression analysis revealed that age, preoperative axial length, average corneal curvature, and anterior chamber depth were independent predictors of the age-related difference in PE.

CONCLUSION

PE was less myopic by approximately 0.06 D per decade as age increased, suggesting that patient age should be considered when selecting IOL power.