Purpose
To measure the effect of spherical aberration correction by aspheric intraocular lenses (IOLs) based on pupil diameter, and to determine the minimum pupil diameter for each aspheric IOL.
Design
Retrospective cross-sectional study.
Methods
Eight-six patients (169 eyes) who were implanted with a HOYA AF-1 NY-60 (HOYA Corporation) or Tecnis ZCB00 1-piece IOL (Abbott Medical Optics Inc) were enrolled. Ocular, corneal, and internal spherical aberrations were measured at the 1-month postoperative visit using the Wavefront Analyzer KR-1W (Topcon). Minimum pupil diameter, which is required for each aspheric IOL to be effective, was calculated using a regression equation.
Results
The mean value of internal spherical aberration of the Tecnis ZCB00 group (−0.09 ± 0.094 μm) was lower than that of the HOYA NY-60 group (−0.05 ± 0.072 μm) ( P = .005). The original negative spherical aberrations of the HOYA NY-60 (−0.18 μm) were measured at a pupil diameter of 5.6 mm, and for the Tecnis ZCB00 (−0.27 μm) at a pupil diameter of 6.1 mm. The aspheric IOL efficiency dropped to 0% when the pupil diameter was 3.47 mm for the Tecnis ZCB00 group and 3.71 mm for the HOYA NY-60 group.
Conclusions
When the pupil diameters of patients are smaller than 3.4 mm for the Tecnis ZCB00 and 3.7 mm for the HOYA NY-60, the spherical aberration correction using these aspheric IOLs seems to be ineffective. Approximately 10% of the eyes showed smaller pupil size than the minimum effective diameter under mesopic conditions.
Phacoemulsification with foldable intraocular lens (IOL) implantation is one of the most common ophthalmic surgeries. Owing to advances in surgical techniques and IOLs, postoperative vision has greatly improved. The knowledge of ocular wavefront aberrations has led to new approaches for vision correction in cataract surgery.
The cornea has positive spherical aberrations, and a young healthy crystalline lens has negative spherical aberrations, which compensate for part of the corneal aberrations. The aberrations of the cornea increase with age, and this increase is consistent with a decrease in imaging quality and visual perception. Implantation of spherical IOLs with positive spherical aberrations causes an increase in positive spherical aberrations after cataract surgery and leads to diminished retinal image quality compared to a young healthy crystalline lens. Therefore, aspheric IOLs were designed to have negative spherical aberrations to balance the positive spherical aberrations of the cornea.
Previous studies demonstrated the advantages of aspheric IOLs, including improvement in contrast sensitivity and reduction in spherical aberrations. However, one previous study suggested that aspheric IOLs became ineffective when the pupil diameter was smaller than 3.0 mm. In the case of small pupil diameter, the spherical aberrations of the cornea and the compensatory effect of aspheric IOLs are insufficient to affect postoperative visual function. In general, pupil diameter decreases as people age. Therefore, the cost-effectiveness of aspheric IOLs should be evaluated based on the pupil diameter because most patients undergoing cataract surgery are elderly.
To assess the cost-effectiveness of aspheric IOLs, the minimum pupil diameter for each aspheric IOL to be effective should be evaluated. The minimum pupil diameter for each aspheric IOL may differ depending on the amount of negative spherical aberration in each aspheric IOL. This study was designed to measure the effect of spherical aberration corrections by aspheric IOLs based on pupil diameter, and to determine the minimum pupil diameter for each aspheric IOL.
Methods
Study Population
This retrospective cross-sectional study included 169 eyes from 86 consecutive patients who underwent phacoemulsification and aspheric IOL implantation at our institute between May 1, 2011 and February 29, 2012. One of 2 aspheric IOLs, HOYA AF-1 NY-60 (HOYA Corporation, Tokyo, Japan) and Tecnis ZCB00 1-piece IOL (Abbott Medical Optics Inc, Santa Ana, California, USA), was implanted in the patient. Patients who had best-corrected visual acuities better than 20/30 after cataract surgery were included. We excluded patients with traumatic cataracts, previous ocular surgery, complicated surgery such as posterior capsule rupture, postoperative complications, or any other ocular diseases such as glaucoma, and retinal abnormalities. Approval for the retrospective review of patient data was obtained from the Korea University Guro Hospital Institutional Review Board, Seoul, Korea. All research and data collection followed the tenets of the Declaration of Helsinki. Patients were divided into 2 groups, a HOYA NY-60 group (89 eyes of 46 patients) and a Tecnis ZCB00 group (80 eyes of 40 patients).
Surgical Technique
All phacoemulsification and IOL implantation procedures were performed by a single experienced surgeon (J.S.S.). After achieving topical anesthesia with Alcaine (proparacaine hydrochloride 0.5%; Alcon Laboratories, Inc, Fort Worth, Texas, USA), a 2.2-mm temporal clear corneal incision was made, and a 5.0- to 5.5-mm continuous curvilinear capsulorrhexis was created with a 26-gauge needle. A standard phacoemulsification technique was used and an aspheric IOL was inserted into the capsular bag using an injector system.
Patient Examination
One month after surgery, all patients underwent a complete ophthalmic examination, including slit-lamp biomicroscopy, autorefraction, and best-corrected distance visual acuity (BCDVA) assessment. The ocular, corneal, and internal spherical aberrations and pupil diameter under high mesopic conditions (8 lux) were measured using a wavefront analyzer (KR-1W; Topcon, Tokyo, Japan). The KR-1W includes 3 technologies: Hartmann-Shack wavefront system, Placido disk topographic system, and standard autorefraction. This device has the advantage that measurements of the ocular and corneal spherical aberrations are performed on the same axis and using the same reference for centration, because those measurements are performed in 1 device. Thus, internal aberration can be accurately calculated. The KR-1W provides a measured value of the 4-mm and 6-mm optical zones for spherical aberrations. Therefore, if the pupil diameter was less than 4 mm, the measured value was displayed in the 4-mm optical zone. When the pupil diameter was between 4 mm and 6 mm, the measured value was shown in the 6-mm optical zone. All measurements of the KR-1W were taken by a single experienced technician who was unaware of the type of aspheric IOL.
Main Outcome Measure(s)
Aspheric IOL efficiency (%) was defined as the spherical aberration measured using the wavefront analyzer divided by the designed negative spherical aberration of the IOL (−0.18 μm for HOYA NY-60 and −0.27 μm for Tecnis ZCB00), and then multiplied by 100.
Statistical Analysis
Statistical analyses were performed using Fisher exact test, Student t test, regression analysis, and Spearman rank correlation analysis in SPSS version 12.0 (SPSS Inc, Chicago, Illinois, USA). Results were considered statistically significant if the P value was less than .05.
Results
This study evaluated 169 eyes of 86 patients. Of the 86 patients, 32 were men and 54 were women. The mean age was 66.5 ± 10.7 years (range, 40-88 years). The mean calculated IOL power, preoperative targeted refraction, axial length, corneal power, sex, age at the time of surgery, and pupil diameters under mesopic conditions are shown in Table 1 . There was no statistically significant difference in the characteristics of subjects between the 2 groups.
| All Patients | HOYA NY-60 Group | Tecnis ZCB00 Group | P Value | |
|---|---|---|---|---|
| Designed spherical aberration correction (μm) | −0.18 | −0.27 | – | |
| Eyes (patients) | 169 (86) | 89 (46) | 80 (40) | – |
| Sex (M:F) | 32 : 54 | 15 : 31 | 17 : 23 | .378 a |
| Age (y) | 66.5 ± 10.7 | 67.8 ± 10.0 | 65.1 ± 11.3 | .100 b |
| IOL power (D) | 20.7 ± 2.9 | 20.5 ± 3.0 | 20.8 ± 2.7 | .522 b |
| Targeted refraction (D) | −0.28 ± 0.44 | −0.26 ± 0.32 | −0.30 ± 0.54 | .497 b |
| Axial length (mm) | 23.5 ± 2.0 | 23.5 ± 1.1 | 23.6 ± 2.6 | .892 b |
| Corneal power (D) | 43.84 ± 2.06 | 43.96 ± 2.60 | 43.70 ± 1.20 | .431 b |
| Pupil diameter | 4.30 ± 0.74 | 4.27 ± 0.64 | 4.33 ± 0.84 | .600 b |
Figure 1 shows the corneal spherical aberrations of all patients from both the HOYA NY-60 and Tecnis ZCB00 groups based on the pupil diameter. There was no statistically significant difference in the corneal spherical aberrations between the 2 groups ( P = .387) ( Table 2 ). The mean ocular, corneal, and internal spherical aberrations of the HOYA NY-60 and Tecnis ZCB00 groups are shown in Table 2 . The mean value of ocular spherical aberration of the Tecnis ZCB00 group (0.02 ± 0.04 μm) was significantly lower than that of the HOYA NY-60 group (0.04 ± 0.05 μm) ( P = .008). Although there was no significant difference in corneal spherical aberrations, the internal spherical aberration of the Tecnis ZCB00 group (−0.09 ± 0.09 μm) was significantly lower than that of the HOYA NY-60 group (−0.05 ± 0.07 μm) ( P = .005).
| HOYA NY-60 Group | Tecnis ZCB00 Group | P Value a | |
|---|---|---|---|
| Ocular spherical aberrations (μm) | 0.04 ± 0.05 | 0.02 ± 0.04 | .008 |
| Corneal spherical aberrations (μm) | 0.09 ± 0.09 | 0.11 ± 0.11 | .387 |
| Internal spherical aberrations (μm) | −0.05 ± 0.07 | −0.09 ± 0.09 | .005 |
Figure 2 shows the ocular, corneal, and internal spherical aberrations based on the pupil diameter. According to the regression equations for the internal spherical aberrations of the 2 groups (Y = −0.0065 × X 2 − 0.0319 × X + 0.2070, R 2 = 0.659, P < .001 and Y = −0.0025 × X 2 − 0.0792 × X + 0.3051, R 2 = 0.832, P < .001, respectively), the negative spherical aberration of the HOYA NY-60 group was −0.18 μm at a pupil diameter of 5.6 mm, which is the amount of negative spherical aberration presented by the manufacturer, and that of the Tecnis ZCB00 group was −0.27 μm at a pupil diameter of 6.1 mm.
Correlation analysis revealed a positive correlation between corneal spherical aberrations, aspheric IOL efficiency, and pupil diameter. Correlation analysis showed a negative correlation between internal spherical aberrations and pupil diameter in both groups ( Table 3 ). However, there was no correlation between ocular spherical aberrations and pupil diameter ( Table 3 ).
| HOYA NY-60 Group | Tecnis ZCB00 Group | |||
|---|---|---|---|---|
| r | P Value | r | P Value | |
| Ocular SA | 0.194 | .069 | 0.081 | .476 |
| Corneal SA | 0.648 | <.001 | 0.805 | <.001 |
| Internal SA | −0.727 | <.001 | −0.882 | <.001 |
| Aspheric IOL efficiency a | 0.727 | <.001 | 0.882 | <.001 |
a Aspheric IOL efficiency (%) was defined as the spherical aberration measured using the wavefront analyzer divided by the designed negative spherical aberration of the IOL (−0.18 μm for HOYA NY-60 and −0.27 μm for Tecnis ZCB00), and then multiplied by 100.
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