EFFECT OF DECENTRATION ON THE QUALITY OF VISION: A COMPARISON BETWEEN ASPHERIC BALANCE CURVE DESIGN AND POSTERIOR ASPHERIC DESIGN INTRAOCULAR LENSES

Effect of decentration on the quality of vision in two aspheric posterior chamber intraocular lenses: A contralateral eye study

PURPOSE

To perform an intraindividual comparison of the quality of vision and the effect of decentration between two aspheric intraocular lenses: aspheric balanced curve (ABC) design Vivinex iSert XY1 (Hoya Surgical Optics, Singapore) and anterior aspheric design Tecnis ZCB00 (Abbott Medical Optics, CA).

SETTING

Tertiary Eye Care Centre.

DESIGN

Prospective, randomized comparative study using a random number table.

METHODS

Thirty patients were randomized to the implantation of Vivinex iSert XY1 in one eye and Tecnis ZCB00 in the contralateral eye. Then, 12 weeks postoperatively, a laser ray-tracing aberrometer was used to evaluate the visual Strehl ratio, higher-order aberrations (HOA), decentration of IOL from the visual axis and geometric axis, angle alpha, and angle kappa. Contrast sensitivity was measured using the functional visual analyzer.

RESULTS

The visual internal Strehl ratio was higher ( P < 0.05) at all pupil sizes and the spherical aberrations values were lower ( P < 0.05) at larger pupil sizes (5 mm and 6 mm) in the Vivinex group. The mean decentration from the visual axis in the Vivinex group was significantly more than that in the Tecnis group ( P < 0.01). With an increase in angle alpha, there was a greater decline in the visual Strehl ratio for Tecnis; however, there was a statistically significant decline at 3 mm pupil size for Tecnis ZCB00 ( P = 0.028). The contrast sensitivity was similar for both IOLs.

CONCLUSION

In comparison to an anterior aspheric design IOL, the ABC design IOL yielded better quality of vision, neutralized spherical aberrations to a larger extent, and provided a relatively superior quality of vision with decentration.

Risk factors associated with intraocular lens decentration after cataract surgery

PURPOSE

To identify risk factors associated with intraocular lens (IOL) decentration after uneventful phacoemulsification with IOL implantation.

DESIGN

A prospective cohort study METHODS: All patients underwent a general ophthalmologic examination. One month postoperatively, the magnitude and orientation of IOL decentration relative to the visual axis center were assessed using an OPD-Scan III aberrometer, and the vertical and horizontal decentration values were determined. Univariate and multivariate linear regression analyses were performed to evaluate the association between the IOL decentration and ocular biometric parameters.

RESULTS

In total, 143 eyes of 143 patients were enrolled. The mean decentration magnitude was 0.27±0.15 mm, and the decentration axis appeared at any orientation, with no orientation tendency. The horizontal and vertical decentration were -0.02±0.22 mm and 0.01±0.22 mm, respectively. Multivariate regression analysis showed that the white-to-white distance (WTW) and the magnitude of angle α were positively associated with the decentration magnitude (P<0.001, adj. R²=0.121), the horizontal angle κ and horizontal angle α were positively associated with the horizontal decentration (P<0.001, adj. R²=0.209), and the anterior chamber depth (ACD) and vertical angle κ were positively associated with the vertical decentration (P<0.001, adj. R²=0.152).

CONCLUSIONS

The IOL decentration magnitude was greater in patients with a larger WTW and a larger angle α, the horizontal decentration was greater in patients with a larger horizontal angle κ and a larger horizontal angle α, and the vertical decentration was greater in patients with a deeper ACD and a larger vertical angle κ. In these patients, premium IOLs should be implanted cautiously.

Geometry of Acrylic, Hydrophobic IOLs and Changes in Haptic-Capsular Bag Relationship According to Compression and Different Well Diameters: A Bench Study Using Computed Tomography

Introduction

Characteristics of the haptics and optic–haptic junction (OHJ) of an intraocular lens (IOL) affect IOL position in the capsular bag, positional stability, and the development of posterior capsule opacification. Therefore, the haptics and OHJ have a role in determining initial and long-term visual outcomes after cataract surgery. Understanding differences in the haptics and OHJ of available IOLs and in the relationships between the haptics of each IOL and the capsular bag across a range of capsular bag sizes might inform selection of an IOL model for individuals.

Purpose

To evaluate the geometry of five currently marketed, commonly used one-piece hydrophobic acrylic monofocal IOLs and changes in haptic–capsular bag relationships according to capsular bag size using a range of compression well diameters.

Methods

AcrySof SN60WF, CT LUCIA 621PY, enVista MX60, TECNIS ZCB00, and Vivinex XY1 IOLs were scanned with computed tomography (CT) in a dry, uncompressed state for quantitative analyses of haptic and OHJ dimensions and qualitative assessment of geometry. CT scanning was done after IOL placement into a series of compression wells (11.5, 11.0, 10.0, and 9.0 mm) for analyses of haptic angle of contact (AoC) and capsular bag contact (CBC). IOL axial alignment and haptic–capsular bag relationships were assessed on side-view and 3-dimensional top-view images, respectively.

Results

The qualitative and quantitative evaluations highlighted differences in haptic and OHJ geometry and dimensions across the five IOLs. All haptic dimensions (length, thickness, surface area, volume) and all OHJ dimensions (surface area and volume) were greatest for the CT LUCIA 621PY IOL. Compared to the IOL that had the smallest measurement for each parameter, the value for the CT LUCIA 621PY IOL was 31–91% larger. The lens with the largest OHJ surface area and volume showed values that were 500% and 240% greater than the corresponding values for the lens with the smallest OHJ surface area and OHJ volume. The AoC and CBC values decreased with increasing well size for all IOLs. The CT LUCIA 621PY had the greatest AoC and CBC values for all well sizes and the smallest percentage change in AoC and CBC comparing the values from the 9.0 mm and 11.5 mm wells.

Conclusion

The in vitro evaluations in this study highlight differences in the haptic and OHJ geometric characteristics of the five IOLs studied. The collected evidence refutes opinions that all hydrophobic acrylic one-piece IOLs are the same and supports the idea that individual IOLs can have relative advantages and disadvantages that depend on the individual case. We believe the knowledge of geometry is necessary for the surgeon to have the opportunity to select the best “customized” option in the individual case as a result of anatomical conditions and secondary diagnoses. Our bench study shows how big the differences are in currently available monofocal hydrophobic acrylic lenses.