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Higher-order aberrations and visual function in pseudophakic eyes with a toric intraocular lens
ARTICLE
Higher-order aberrations and visual function in pseudophakic eyes with a toric intraocular lens Ken Hayashi, MD, Hiroyuki Kondo, MD, Motoaki Yoshida, MD, Shin-ichi Manabe, MD, Akira Hirata, MD
PURPOSE: To compare higher-order aberrations (HOAs) and visual function in eyes with a toric intraocular lens (IOL) and eyes with a nontoric IOL. SETTING: Hayashi Eye Hospital, Fukuoka, Japan. DESIGN: Case-control study. METHODS: Eyes that had phacoemulsification were enrolled in 1 of the following 3 groups: (1) preoperative corneal astigmatism of 1.00 diopter (D) with a toric IOL (toric group), (2) astigmatism of 1.00 D or more with a nontoric IOL (high-astigmatism group), and (3) astigmatism less than 1.00 D with a nontoric IOL (low-astigmatism group). Ocular and corneal HOAs were measured using a wavefront analyzer. Photopic and mesopic visual acuities at high- to low-contrast visual targets were measured using a contrast sensitivity tester. RESULTS: The mean ocular and corneal total HOAs and 3rd-order aberrations in the toric and highastigmatism groups tended to be greater than in the low-astigmatism group; HOAs and 3rd-order aberrations at 3 months and HOAs at 6 months were significantly different (P%.0403). The mean corrected visual acuity did not differ significantly between groups. However, photopic low-contrast visual acuity (LCVA) and mesopic high- to low-contrast visual acuity was significantly worse in the toric and high-astigmatism groups than in the low-astigmatism group (P%.0210). CONCLUSION: Postoperatively, ocular and corneal HOAs were greater in eyes with a toric IOL and in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism, which impaired photopic LCVA and mesopic visual acuity. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2012; 38:1156–1165 Q 2012 ASCRS and ESCRS
Since the 1990s, many models of toric intraocular lenses (IOLs) for aphakic eyes to correct preexisting corneal astigmatism after cataract surgery have been introduced.1–5 Because early toric IOL models were rotationally unstable in the capsular bag, their correcting effect on preexisting corneal astigmatism was limited. A hydrophobic acrylic toric IOL with a single-piece design (Acrysof IQ toric SN6AT, Alcon Laboratories, Inc.) recently became available worldwide. Because the rotational stability of the single-piece acrylic IOL is better than that of the multipiece IOL or plate-haptic IOL,6,7 the Acrysof toric IOL effectively decreases preexisting corneal astigmatism and provides excellent uncorrected distance visual acuity (UDVA).8–13 Several previous studies14–16 found that implantation of an iris-supported or posterior chamber toric phakic IOL improves corrected distance visual acuity 1156
Q 2012 ASCRS and ESCRS Published by Elsevier Inc.
(CDVA) or contrast sensitivity. This might be the result of the precise correction of a moderate to high degree of myopic astigmatism and that the crystalline lenses in young eyes might prevent deterioration of optical quality. This finding may not extend to pseudophakic eyes that have implantation of a toric IOL. To date, however, optical quality and visual function have not been studied in pseudophakic eyes that had implantation of a toric IOL. The purpose of the present study was to examine the amount of ocular or corneal wavefront higher-order aberrations (HOAs) and visual function in pseudophakic eyes with a high preexisting corneal astigmatism that received a toric IOL. To evaluate these outcomes, eyes with high or low preexisting corneal astigmatism that received a nontoric aspheric IOL served as controls. 0886-3350/$ - see front matter doi:10.1016/j.jcrs.2012.02.032
HOAS AND VISUAL FUNCTION WITH TORIC IOLS
PATIENTS AND METHODS All patients scheduled to have cataract surgery at Hayashi Eye Hospital between October 2009 and July 2010 were sequentially screened by a clinical research coordinator. Included eyes were recruited into 1 of 3 groups as follows: (1) eyes with preexisting corneal astigmatism of 1.00 diopter (D) or greater having Acrysof SN60T IOL implantation (toric group), (2) eyes with corneal astigmatism of 1.00 D or greater having Acrysof IQ SN60WF nontoric aspheric IOL implantation (high-astigmatism group), and (3) eyes with corneal astigmatism of less than 1.00 D having Acrysof IQ SN60WF nontoric IOL implantation (low-astigmatism group) (all IOLs by Alcon Laboratories, Inc.). The research adhered to the tenets of the Declaration of Helsinki. An institutional review board approved the study protocol, and all patients provided informed consent. Exclusion criteria were pathology of the cornea, vitreous, macula, or optic nerve; preoperative regular corneal astigmatism greater than 4.00 D or extensive irregular corneal astigmatism determined using corneal topography; planned extracapsular cataract extraction; a history of ocular surgery or inflammation; a pupil diameter less than 5.0 mm with full mydriasis; patient refusal; and anticipated difficulties with the examinations, analyses, or follow-ups.
Intraocular Lens Power Calculation The Acrysof IQ toric IOL used in this study is a yellowtinted single-piece model comprising a hydrophobic acrylic polymer. The IOL has a 6.0 mm asymmetric biconvex optic. The haptics are made of the same acrylic polymer as the optic and have a modified L-shaped design with no angulation. The posterior surface of the optic has a toric component and 3 reference indentations on each side, which indicate the flattest meridian of the optic. The spherical power of this toric IOL is available from 12.00 to 25.00 D in 0.50 D increments. Three toric models are currently available: the SN60T3, SN60T4, and SN60T5 with cylinder powers at the IOL plane (average corneal plane) of 1.50 D (1.03 D), 2.25 D (1.55 D), and 3.00 D (2.06 D), respectively. The nontoric control IOL (Acrysof IQ, SN60WF) is constructed using the same material and design as the toric IOL models except it does not have a toric component or the axis indentations. The spherical power of the IOL in each case was calculated using the SRK/T formula. The axial length (AL) was measured using the IOLMaster biometer (Carl Zeiss Meditec AG), and keratometry (K) readings were taken using an autokerato-refractometer (KR-7100, Topcon Corp.); the
Submitted: August 17, 2011. Final revision submitted: February 8, 2012. Accepted: February 10, 2012. From Hayashi Eye Hospital (Hayashi, Yoshida, Manabe), Fukuoka, the Department of Ophthalmology (Kondo), University of Occupational and Environmental Health, Fukuoka, and the Department of Ophthalmology (Hirata), Saga University Faculty of Medicine, Saga, Japan. Corresponding author: Ken Hayashi, MD, Hayashi Eye Hospital, 4-23-35 Hakataekimae, Hakata-Ku, Fukuoka 812-0011, Japan. E-mail: [email protected].
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K readings were used to calculate the IOL power and to calculate the power and axis placement of the toric IOL. In patients with dense cataract, the AL was measured using an ultrasonic applanation biometer (Ocuscan, Alcon Biophysics). Calculations of the toric IOL power and axis placement to achieve emmetropia were performed using a web-based toric IOL calculator program.A Preoperative keratometry and biometry data, incision location and size, and the surgeon’s estimated surgically induced corneal astigmatism were used to determine the appropriate toric IOL model, spherical equivalent (SE) IOL power, and axis of placement in the eye.
Surgical Technique The same surgeon (K.H.) performed all surgical procedures. Preoperatively, with the patient seated upright at the slitlamp to compensate for cyclorotation, the surgeon marked the corneal limbus at the 0-degree, 90-degree, and 180-degree positions using a marker after vertical alignment of the patient’s head. At the beginning of the surgery, the steepest meridian of the corneal limbus was identified and marked with a diamond knife using a toric IOL marker (9-705R-1, Duckworth & Kent) with the aid of the preplaced reference points. The surgeon made a 2.50 mm clear corneal incision (CCI) horizontally in eyes with against-the-rule or oblique corneal astigmatism and superiorly in eyes having with-the-rule astigmatism; the horizontal incision was created temporally in the right eye and nasally in the left eye. Phacoemulsification was performed using a previously described technique.17 First, a continuous curvilinear capsulorhexis measuring approximately 5.5 mm in diameter was created using a bent needle. After hydrodissection, phacoemulsification of the nucleus and aspiration of the cortex were performed. The wound was enlarged to 2.65 mm using a steel keratome for implantation of the IOL. The lens capsule was inflated with sodium hyaluronate 1% (Healon), after which the IOL was implanted in the capsular bag. The toric IOL was rotated until the axis indentations were aligned with the corneal cylinder axis marked at the steepest meridian. The ophthalmic viscosurgical device was thoroughly removed, with attention given to avoiding rotation of the IOL. The IOL axis alignment was confirmed by stromal hydration after would closure. No eye received limbal relaxing incisions or astigmatic keratotomy.
Outcome Measures All patients were examined for ocular and corneal wavefront aberrations, UDVA, CDVA, refractive status, keratometric cylinder, and pupil diameter preoperatively and 3 and 6 months postoperatively. The KR-1W system (Topcon Corp.) combines Hartmann-Shack ocular aberrometry, which was used to measure ocular wavefront aberrations, and Placido disk videokeratography, which was used to measure corneal wavefront aberrations; thus, the system provides aberration values for the whole eye and cornea. The details of this apparatus have been described.18 In brief, after full mydriasis, pupils were measured at least 3 times. The Hartmann-Shack aberrometer projects light onto the retina, and the light reflected from the retina passes through the internal oculus. The reflected light passes through the Hartmann plate and becomes a spot of light, which forms an image on a charge-coupled device camera. Displacement of the image formation is analyzed as wavefront distortion. The wavefront aberrations (1st- to 6th-order wavefront
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Zernike coefficients) were calculated from the displacement and expanded with the Zernike polynomials. After full mydriasis, analysis of wavefront aberrations was performed by measuring the central 4.0 mm and 6.0 mm using the aperture. The root-mean-square (RMS) value of the 3rd-order Zernike coefficients was used to represent 3rd-order aberrations (coma-like aberrations), and the RMS of the 4th-order Zernike coefficients was used to represent 4th-order aberrations (spherical-like aberrations). Total HOAs were defined as the sum of the RMS of the 3rd- to 6th-order coefficients. For example, 3rd-order aberrations were defined as the RMS of all 4 Zernike 3rd-order terms. Videokeratography was performed simultaneously, and corneal 3rd-order aberrations, 4th-order aberrations, and total HOAs were determined. In addition, assuming a simple model for the eye, wavefront aberrations of the internal optics (internal optic aberrations) were obtained by direct subtraction of the corneal aberrations from the ocular aberrations.18–20 The refractive spherical power, cylindrical power, and axis were examined with the autokerato-refractometer used in the preoperative examination; the manifest SE value was determined as the spherical power plus one half the cylindrical power. The corneal powers at the steepest and flattest meridians were also measured using the autokerato-refractometer. The keratometric cylindrical power and axis were determined for each cornea and used to calculate the surgically induced corneal astigmatism. The surgically induced corneal astigmatism was calculated using the polar value analysis described by Naeser et al.21,22 In addition, the polar coordinate system was converted to the vector coordinate system (change vector magnitude and meridian). The UDVA and CDVA were examined using decimal charts and converted to a logMAR scale for statistical analysis. Pupil diameter was measured using a Colvard pupillometer (Oasis Medical). Six months postoperatively, all eyes had high- to lowcontrast visual acuity measurement with and without a glare source after distance correction using the Contrast Sensitivity Accurate Tester (CAT-2000, Menicon Co. Ltd.). This device measures logMAR CDVA with a range of 1.0 and 0.1 using visual targets with 5 contrast levels (100%, 25.0%, 10.0%, 5.0%, and 2.5%) under photopic and mesopic conditions. Measurement under photopic conditions was performed with chart lighting of 100 candelas (cd)/m2 and under mesopic conditions with chart lighting of 2 cd/m2. For measurement of glare visual acuity, a glare source of
200 lux was located in the periphery 20 degrees around the visual axis. Ophthalmic technicians unaware of the purpose of the study performed all measurements.
Statistical Analysis Ocular, corneal, and internal optic HOAs; UDVA; CDVA; high-to low-contrast visual acuity with and without glare; manifest SE; corneal astigmatism; pupil diameter; and other continuous variables were compared between the toric, high-astigmatism, and low-astigmatism groups using the Kruskal-Wallis test. The surgically induced corneal astigmatism determined using the polar coordinate system was compared between groups using a multivariate analysis of variance (ANOVA).21,22 Categorical variables were compared between the 3 groups using the chi-square goodness-of-fit test. When a statistically significant difference was found between the 3 groups, the difference between each combination of 2 groups was further compared using the Mann-Whitney U test for continuous variables and the chi-square test for discrete variables with the Bonferroni adjustment for multiple comparisons. The vector magnitude of the surgically induced corneal astigmatism was correlated with ocular or corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations using the simple regression analysis. Differences with a P value less than 0.05 were considered statistically significant.
RESULTS Screening was continued until 50 eyes were recruited into each of the 3 groups. Of the 150 patients enrolled, 18 were lost to follow-up. Twelve patients did not appear for the scheduled follow-up, 3 were referred to other hospitals, 1 moved from the area, and 2 refused examinations. Accordingly, 48 eyes in the toric group, 42 in the high-astigmatism group, and 42 in the lowastigmatism group remained for analysis. The mean age of all patients (66 men and 66 women) was 69.0 years G 9.0 (SD) (range 40 to 85 years). Table 1 shows the patients’ demographics by group. The age, sex, ratio of left eyes to right eyes, manifest SE value, and pupil diameter did not differ significantly between groups. The mean preoperative
Table 1. Patient characteristics. Group Parameter Mean age (y) Sex (M/F), n (%) Left/right eyes, n (%) Mean keratometric cylinder (D) Mean refractive cylinder (D) Mean MRSE (D)
Toric
High Astigmatism
Low Astigmatism
P Value
70.3 G 8.81 27/21 21/27 1.80 G 0.61 2.43 G 1.13 1.73 G 3.2
69.6 G 8.8 20/22 23/19 1.38 G 0.49 1.67 G 1.45 1.39 G 3.2
66.9 G 9.1 19/23 20/22 0.46 G 0.25 0.91 G 0.72 1.23 G 3.7
.1921 .5417 .5752 !.0001* !.0001* .2522
MRSE Z manifest refraction spherical equivalent Means G SD *Statistically significant difference between the 3 groups.
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corneal astigmatism and refractive astigmatism were highest in the toric group followed by the highastigmatism group and the low-astigmatism group (P%.0001). The toric IOL models used were SN6AT3 in 21 eyes, SN6AT4 in 18 eyes, and SN6AT5 in 9 eyes. All surgeries were uneventful, and no eye required sutures. The HOA values could be obtained with a 4.0 mm pupil in 128 eyes (97.7%) and with a 6.0 mm pupil in 58 eyes (43.9%) postoperatively. With a 4.0 mm pupil, there was no significant difference preoperatively in the mean ocular total HOAs, 3rd-order aberrations, or 4th-order aberrations between the 3 groups (PR.1408). Postoperatively, the mean ocular total HOAs were significantly greater in the toric group and highastigmatism group than in the low-astigmatism group at 3 months and 6 months (P%.0365) (Figure 1); the ocular total HOAs did not differ significantly between the toric group and the high-astigmatism group. The ocular 3rd-order aberrations were also greater in the toric and high-astigmatism groups than in the
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low-astigmatism group; the difference between the 3 groups was significant at 3 months (PZ.0403) and marginally significant at 6 months (PZ.0574). There were no significant between-group differences in ocular spherical-like 4th-order aberrations. With a 4.0 mm pupil (Figure 2) and a 6.0 mm pupil (Figure 3), there was no significant difference preoperatively in the mean corneal total HOAs, 3rd-order aberrations, or 4th-order aberrations between groups (PR.1133). Postoperatively, however, the mean corneal total HOAs were significantly greater in the toric and high-astigmatism groups than in the low-astigmatism group at 3 months and 6 months (P%.0330); the corneal total HOAs did not differ significantly between the toric group and high-astigmatism group. The corneal 3rd-order aberrations were also greater in the toric and highastigmatism groups than in the low-astigmatism group; the difference between the 3 groups was significant at 3 months (P%.0163). There was no significant difference in corneal 4th-order aberrations between groups. Regarding internal optic aberrations, no statistically
Figure 1. Comparison of the mean G SD ocular HOAs in the toric group, high-astigmatism group, and low-astigmatism group. Mean ocular total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the low-astigmatism group after cataract surgery, although there was no significant difference preoperatively. J CATARACT REFRACT SURG - VOL 38, JULY 2012
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Figure 2. Comparison of the mean G SD corneal HOAs for a 4.0 mm pupil in the toric group, high-astigmatism group, and low-astigmatism group. Mean corneal total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the lowastigmatism group after cataract surgery, although there was no significant difference preoperatively.
significant differences were found in total HOAs, 3rd-order aberrations, or 4th-order aberrations preoperatively or 3 or 6 months postoperatively. The mean residual refractive astigmatism in the toric and low-astigmatism groups was significantly less than in the high-astigmatism group 3 months and 6 months after surgery (P%.0001). The mean manifest SE value in the toric and low-astigmatism groups was significantly lower than in the high-astigmatism group after surgery (P%.0040). Accordingly, the mean postoperative UDVA was significantly better in the toric and low-astigmatism groups than in the high-astigmatism group at 3 months and 6 months (P%.0001). The mean postoperative CDVA was not significantly different between the 3 groups at 3 months or 6 months (PR.1466) (Table 2). The mean photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity was significantly worse in the toric and high-astigmatism groups than in the low-astigmatism group (P%.0210) (Figure 4). Statistical analysis of mesopic visual acuity at 2.5% contrast could not be obtained because it was
worse than the detection limit (1.0 logMAR) in most eyes. High- to low-contrast visual acuity in the presence of glare also tended to be worse in the toric and high-astigmatism groups than in the lowastigmatism group. Except for mesopic visual acuity with glare at 100% contrast, the difference did not reach statistical significance (Figure 5). Specifically, mesopic visual acuity with glare at 10.0%, 5.0%, and 2.5% contrast could not be analyzed because the visual acuity with glare at these contrasts was worse than the detection limit in most eyes. The mean postoperative pupil diameter was similar between the 3 groups at 3 months and 6 months (PR.2137) (Table 3). The mean corneal astigmatism at 3 months and 6 months was highest in the toric group followed by the high-astigmatism group and the low-astigmatism group (P%.0001). Using a univariate comparison test, the vector magnitude of the surgically induced corneal astigmatism tended to be greater in the toric and high-astigmatism groups than in the low-astigmatism group; the difference between the 3 groups was significant at 3 months
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Figure 3. Comparison of the mean G SD corneal HOAs for a 6.0 mm pupil in the toric group, high-astigmatism group, and low-astigmatism group. Mean corneal total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the lowastigmatism group after cataract surgery, although there was no significant difference preoperatively.
(PZ.0156) and marginally significant at 6 months (PZ.0661). Using multivariate ANOVA, however, the mean surgically induced corneal astigmatism was not significantly different between the 3 groups (PR.6445). Using simple regression analysis, the vector magnitude of the surgically induced corneal astigmatism
Table 2. Comparison of mean logMAR CDVA between the 3 groups. Mean LogMAR CDVA G SD Exam
Toric
High Low P Astigmatism Astigmatism Value
Preop 0.61 G 0.32 0.56 G 0.33 0.64 G 0.39 .4722* 3 mo postop 0.01 G 0.61 0.01 G 0.05 0.03 G 0.04 .1467* 6 mo postop 0.02 G 0.06 0.01 G 0.06 0.03 G 0.04 .1742* CDVA Z corrected distance visual acuity *No significant difference.
correlated significantly with ocular and corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations 3 months and 6 months after cataract surgery (Table 4). In addition, the determination coefficients of corneal HOAs, 3rd-order aberrations, and 4th-order aberrations were greater than those of ocular HOAs. Furthermore, the vector magnitude of the surgically induced corneal astigmatism correlated significantly with the change in ocular and corneal total HOAs and 3rd-order aberrations (Table 5). A larger magnitude of surgically induced corneal astigmatism was significantly correlated with a greater change in corneal total HOAs (Pearson r Z 0.304, PZ.0004) (Figure 6). DISCUSSION In our study, we found that ocular total HOAs and 3rd-order coma-like aberrations were significantly greater after cataract surgery in eyes with high preexisting corneal astigmatism that had toric or nontoric
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Figure 4. Comparison of the mean G SD visual acuity at high- to low-contrast visual targets under photopic and mesopic conditions in the toric group, highastigmatism group, and lowastigmatism group. Mean photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity was worse in the toric and high-astigmatism groups than in the low-astigmatism group (P %.0210). Mesopic visual acuity at 2.5% contrast could not be analyzed, because mesopic visual acuity at this contrast was worse than the detection limit in most eyes.
IOL implantation than in eyes with low preexisting corneal astigmatism that had nontoric IOL implantation; the values were similar in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation. In addition, ocular 4th-order sphericallike aberrations did not differ significantly between the 3 groups. These results suggest that the optical quality after cataract surgery may be worse in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism.
Similarly, the corneal total HOAs and 3rd-order aberrations in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL were significantly greater than in eyes with low preexisting corneal astigmatism that received a nontoric IOL. In addition, there was no significant difference in the HOAs of the internal optics. Furthermore, in most eyes, the corneal total HOAs and 3rd-order aberrations increased postoperatively, while the ocular HOAs decreased. These findings suggest that corneal
Figure 5. Comparison of the mean G SD visual acuity at high- to lowcontrasts in the presence of a glare under photopic and mesopic conditions in the toric group, highastigmatism group, and lowastigmatism group. Mean high- to low-contrast visual acuity with glare tended to be worse in the toric and high-astigmatism groups than in the low-astigmatism group, but the difference did not reach statistical significance except for mesopic visual acuity with glare at 100% contrast. Mean mesopic visual acuity with glare at 10%, 5%, and 2.5% contrast could not be analyzed, because the mesopic visual acuity at these contrasts was worse than the detection limit in most eyes.
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Table 3. Comparison of the mean pupil diameter in the 3 groups. Mean Pupil Diameter (mm) G SD Parameter
Toric
High LowP Astigmatism Astigmatism Value
†
Far (mm) Preop 3 mo postop 6 mo postop Near (mm)z Preop 3 mo postop 6 mo postop
3.6 G 0.6 3.4 G 0.5 3.5 G 0.5
3.5 G 0.8 3.4 G 0.6 3.3 G 0.5
3.6 G 0.5 3.5 G 0.6 3.5 G 0.5
.7663 .4906* .2137*
3.1 G 0.6 2.9 G 0.5 3.0 G 0.5
3.1 G 0.6 2.9 G 0.5 2.9 G 0.5
3.1 G 0.5 3.0 G 0.5 3.0 G 0.5
.9476 .4022* .2794
*No significant difference † Pupil diameter at far distance z Pupil diameter at near distance
HOAs, specifically 3rd-order aberrations, are induced more after cataract surgery in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism. The mean CDVA did not differ significantly between the 3 groups. Photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity, however, were significantly worse in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation than in eyes with low preexisting corneal astigmatism that had nontoric IOL implantation. Furthermore, high- to low-contrast visual acuity in the presence of a glare source tended to be worse in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation. These results indicate that visual function in eyes with high preexisting
Table 4. Simple regression analysis between the vector magnitude of surgically induced corneal astigmatism and ocular total HOAs and 3rd-order aberrations and between the vector magnitude of surgically induced corneal astigmatism and corneal total HOAs and 3rd-order aberrations. Analysis
R2*
P Value
Between ocular HOAs and vector magnitude of SIA 3 months Total HOAs 0.148 !.0001† 3rd-order aberrations 0.126 !.0001† 6 months Total HOAs 0.137 !.0001† 3rd-order aberrations 0.075 .0045† Between corneal HOAs and vector magnitude of SIA 3 months Total HOAs 0.188 !.0001† 3rd-order aberrations 0.154 !.0001† 6 months Total HOAs 0.194 !.0001† 3rd-order aberrations 0.141 !.0001† HOAs Z higher-order aberrations; SIA Z surgically induced astigmatism *Determination coefficient † Statistically significant correlation
corneal astigmatism that received a toric or nontoric IOL was worse than that in eyes with low preexisting corneal astigmatism that received a nontoric IOL. Thus, the visual function outcomes were consistent with the ocular HOAs and optical quality results. Previous studies14–16 found that implantation of a posterior chamber or iris-supported toric phakic IOL improved CDVA or contrast sensitivity. This finding might be the result of the precise correction of a moderate to high degree of myopic astigmatism
Table 5. Simple regression analysis between the vector magnitude of surgically induced corneal astigmatism and changes in corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations 3 months after surgery. Analysis
R 2*
P Value
Between ocular HOAs and vector magnitude of SIA Total HOAs 0.061 .0126† 3rd-order aberrations 0.085 .0042† 4th-order aberrations 0.018 .1966 Between corneal HOAs and vector magnitude of SIA Total HOAs 0.092 .0004 3rd-order aberrations 0.092 .0006 4th-order aberrations 0.022 .1023 HOAs Z higher-order aberrations; SIA Z surgically induced astigmatism *Determination coefficient † Statistically significant correlation
Figure 6. Correlation between the vector magnitude of surgically induced astigmatism (SIA) and change in corneal total HOAs from baseline at 3 months after cataract surgery. A larger vector magnitude of the SIA correlated significantly with a greater change in corneal total HOAs (Pearson r Z 0.304, PZ.0004).
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and that a young crystalline lens might preclude the deterioration of the optical quality of the eye. Accordingly, this does not likely hold true for pseudophakic eyes that have implantation of a toric IOL for aphakia. We believe that our study is the first to show that ocular HOAs are greater and visual function is worse after cataract surgery in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL than in eyes with low preexisting astigmatism that received a nontoric IOL. The difference in ocular and corneal total HOAs and 3rd-order aberrations after cataract surgery is predominantly attributed to the difference in induced irregular corneal astigmatism caused by CCIs. The vector magnitude of the surgically induced corneal astigmatism was greater in the toric group and highastigmatism group than in the low-astigmatism group based on univariate analysis, although no significant difference was found using multivariate analysis. Furthermore, the vector magnitude of the surgically induced corneal astigmatism was significantly correlated with ocular and corneal HOAs, which represent irregular astigmatism, as well as with changes in corneal HOAs resulting from the cataract surgery. Based on these results, we believe that the cataract incision induces more irregular astigmatism and regular astigmatism in eyes with high preexisting corneal astigmatism than in eyes with low preexisting corneal astigmatism. In contrast, because there was no significant between-group difference in the HOAs of the internal optics, which are derived mainly from the IOL,18–20 the toric IOL component may not markedly influence HOAs or optical quality. In conclusion, after cataract surgery, ocular and corneal HOAs, specifically 3rd-order coma-like aberrations, were greater in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL than in eyes with low preexisting corneal astigmatism that received a nontoric IOL, which led to the impairment in photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity in eyes with high preexisting astigmatism that received a toric or nontoric IOL. Based on the results in the present study, we believe that corneal HOAs are induced more in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism and that a greater degree of HOAs does not derive mainly from the toric IOL component. It is conceivable, however, that ocular wavefront aberrations are markedly induced when there is marked axis misalignment of the toric IOL. Further study is needed to examine the effect of the toric component of the IOL on ocular HOAs, particularly when there is marked axis misalignment of the toric IOL.
WHAT WAS KNOWN Previous studies show that implantation of a toric IOL improves CDVA or contrast sensitivity. To date, however, optical quality such as HOAs and visual function have not been studied in pseudophakic eyes that had toric IOL implantation. WHAT THIS PAPER ADDS After cataract surgery, corneal HOAs, specifically thirdorder aberrations, were induced more in eyes with high preexisting corneal astigmatism that received a toric IOL or nontoric IOL than in eyes with low preexisting corneal astigmatism that received a nontoric IOL. This increase in corneal HOAs led to the impairment of contrast sensitivity in eyes with high preexisting astigmatism that received a toric IOL or a nontoric IOL.
REFERENCES 1. Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while controlling axis shift. J Cataract Refract Surg 1994; 20:523–526 2. Sun X-Y, Vicary D, Montgomery P, Griffiths M. Toric intraocular lenses for correcting astigmatism in 130 eyes. Ophthalmology 2000; 107:1776–1781; discussion by RM Kershner, 17811782 3. Ruhswurm I, Scholz U, Zehetmayer M, Hanselmayer G, Vass C, Skorpik C. Astigmatism correction with a foldable toric intraocular lens in cataract patients. J Cataract Refract Surg 2000; 26:1022–1027 4. Till JS, Yoder PR Jr, Wilcox TK, Spielman JL. Toric intraocular lens implantation: 100 consecutive cases. J Cataract Refract Surg 2002; 28:295–301 5. De Silva DJ, Ramikissoon YD, Bloom PA. Evaluation of a toric intraocular lens with a Z-haptic. J Cataract Refract Surg 2006; 32:1492–1498 6. Chang DF. Comparative rotational stability of single-piece openloop acrylic and plate-haptic silicone toric intraocular lenses. J Cataract Refract Surg 2008; 34:1842–1847 7. Koshy JJ, Nishi Y, Hirnschall N, Crnej A, Gangwani V, Maurino V, Findl O. Rotational stability of a single-piece toric acrylic intraocular lens. J Cataract Refract Surg 2010; 36:1665–1670 s8. Mendicute J, Irigoyen C, Aramberri J, Ondarra A, Monte R. Foldable toric intraocular lens for astigmatism correcMico tion in cataract patients. J Cataract Refract Surg 2008; 34:601–607 9. Bauer NJC, de Vries NE, Webers CAB, Hendrikse F, Nuijts RMMA. Astigmatism management in cataract surgery with the AcrySof toric intraocular lens. J Cataract Refract Surg 2008; 34:1483–1488 nchez D, Dıaz-Alvarez 10. Ruız-Mesa R, Carrasco-Sa SB, Ruız Mateos MA, Ferrer-Blasco T, Montes-Mico R. Refractive lens exchange with foldable toric intraocular lens. Am J Ophthalmol 2009; 147:990–996 11. Lane SS, Ernest P, Miller KM, Hileman KS, Harris B, Waycaster CR. Comparison of clinical and patient-reported outcomes with bilateral AcrySof toric or spherical control intraocular lenses. J Refract Surg 2009; 25:899–901
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12. Holland E, Lane S, Horn JD, Ernest P, Arleo R, Miller KM. The AcrySof toric intraocular lens in subjects with cataracts and corneal astigmatism; a randomized, subject-masked, parallelgroup, 1-year study. Ophthalmology 2010; 117:2104–2111 13. Ernest P, Potvin R. Effects of preoperative corneal astigmatism orientation on results with a low-cylinder-power toric intraocular lens. J Cataract Refract Surg 2011; 37:727–732 14. Dick HB, Tehrani M, Aliyeva S. Contrast sensitivity after implantation of toric iris-claw lenses in phakic eyes. J Cataract Refract Surg 2004; 30:2284–2289 15. Kamiya K, Shimizu K, Aizawa D, Igarashi A, Komatsu M, Nakamura A. One-year follow-up of posterior chamber toric phakic intraocular lens implantation for moderate to high myopic astigmatism. Ophthalmology 2010; 117:2287–2294 16. Schallhorn S, Tanzer D, Sanders DR, Sanders ML. Randomized prospective comparison of Visian Toric Implantable Collamer Lens and conventional photorefractive keratectomy for moderate to high myopic astigmatism. J Refract Surg 2007; 23:853–867 17. Hayashi K, Yoshida M, Hayashi H. Corneal shape changes after 2.0-mm or 3.0-mm clear corneal versus scleral tunnel incision cataract surgery. Ophthalmology 2010; 117:1313–1323 18. Hayashi K, Yoshida M, Hayashi H. Correlation of higher-order wavefront aberrations with visual function in pseudophakic eyes. Eye 2008; 22:1476–1482. Available at: http://www. nature.com/eye/journal/v22/n12/pdf/6702921a.pdf. Accessed March 9, 2012
19. Artal P, Guirao A, Berrio E, Williams DR. Compensation of corneal aberrations by the internal optics in the human eye. J Vis 2001; 1(1):1–8. Available at: http://www.journalofvision. org/content/1/1/1.full.pdf. Accessed March 9, 2012 nez-Alfaro I. Optical aberrations of 20. Barbero S, Marcos S, Jime intraocular lenses measured in vivo and in vitro. J Opt Soc Am Opt Image Sci Vis 2003; 20:1841–1851 21. Naeser K, Knudsen EB, Hansen MK. Bivariate polar value analysis of surgically induced astigmatism. J Refract Surg 2002; 18:72–78 22. Naeser K, Hjortdal JØ. Bivariate analysis of surgically induced regular astigmatism. Mathematical analysis and graphical display. Ophthalmic Physiol Opt 1999; 19:50–61
OTHER CITED MATERIAL
A. Alcon, Inc. AcrySofÒ Toric IOL Web Based Calculators. Available at: http://www.acrysoftoriccalculator.com. Accessed March 9, 2012
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First author: Ken Hayashi, MD Hayashi Eye Hospital, Fukuoka, Japan
Higher-order aberrations and visual function in pseudophakic eyes with a toric intraocular lens Ken Hayashi, MD, Hiroyuki Kondo, MD, Motoaki Yoshida, MD, Shin-ichi Manabe, MD, Akira Hirata, MD
PURPOSE: To compare higher-order aberrations (HOAs) and visual function in eyes with a toric intraocular lens (IOL) and eyes with a nontoric IOL. SETTING: Hayashi Eye Hospital, Fukuoka, Japan. DESIGN: Case-control study. METHODS: Eyes that had phacoemulsification were enrolled in 1 of the following 3 groups: (1) preoperative corneal astigmatism of 1.00 diopter (D) with a toric IOL (toric group), (2) astigmatism of 1.00 D or more with a nontoric IOL (high-astigmatism group), and (3) astigmatism less than 1.00 D with a nontoric IOL (low-astigmatism group). Ocular and corneal HOAs were measured using a wavefront analyzer. Photopic and mesopic visual acuities at high- to low-contrast visual targets were measured using a contrast sensitivity tester. RESULTS: The mean ocular and corneal total HOAs and 3rd-order aberrations in the toric and highastigmatism groups tended to be greater than in the low-astigmatism group; HOAs and 3rd-order aberrations at 3 months and HOAs at 6 months were significantly different (P%.0403). The mean corrected visual acuity did not differ significantly between groups. However, photopic low-contrast visual acuity (LCVA) and mesopic high- to low-contrast visual acuity was significantly worse in the toric and high-astigmatism groups than in the low-astigmatism group (P%.0210). CONCLUSION: Postoperatively, ocular and corneal HOAs were greater in eyes with a toric IOL and in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism, which impaired photopic LCVA and mesopic visual acuity. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2012; 38:1156–1165 Q 2012 ASCRS and ESCRS
Since the 1990s, many models of toric intraocular lenses (IOLs) for aphakic eyes to correct preexisting corneal astigmatism after cataract surgery have been introduced.1–5 Because early toric IOL models were rotationally unstable in the capsular bag, their correcting effect on preexisting corneal astigmatism was limited. A hydrophobic acrylic toric IOL with a single-piece design (Acrysof IQ toric SN6AT, Alcon Laboratories, Inc.) recently became available worldwide. Because the rotational stability of the single-piece acrylic IOL is better than that of the multipiece IOL or plate-haptic IOL,6,7 the Acrysof toric IOL effectively decreases preexisting corneal astigmatism and provides excellent uncorrected distance visual acuity (UDVA).8–13 Several previous studies14–16 found that implantation of an iris-supported or posterior chamber toric phakic IOL improves corrected distance visual acuity 1156
Q 2012 ASCRS and ESCRS Published by Elsevier Inc.
(CDVA) or contrast sensitivity. This might be the result of the precise correction of a moderate to high degree of myopic astigmatism and that the crystalline lenses in young eyes might prevent deterioration of optical quality. This finding may not extend to pseudophakic eyes that have implantation of a toric IOL. To date, however, optical quality and visual function have not been studied in pseudophakic eyes that had implantation of a toric IOL. The purpose of the present study was to examine the amount of ocular or corneal wavefront higher-order aberrations (HOAs) and visual function in pseudophakic eyes with a high preexisting corneal astigmatism that received a toric IOL. To evaluate these outcomes, eyes with high or low preexisting corneal astigmatism that received a nontoric aspheric IOL served as controls. 0886-3350/$ - see front matter doi:10.1016/j.jcrs.2012.02.032
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PATIENTS AND METHODS All patients scheduled to have cataract surgery at Hayashi Eye Hospital between October 2009 and July 2010 were sequentially screened by a clinical research coordinator. Included eyes were recruited into 1 of 3 groups as follows: (1) eyes with preexisting corneal astigmatism of 1.00 diopter (D) or greater having Acrysof SN60T IOL implantation (toric group), (2) eyes with corneal astigmatism of 1.00 D or greater having Acrysof IQ SN60WF nontoric aspheric IOL implantation (high-astigmatism group), and (3) eyes with corneal astigmatism of less than 1.00 D having Acrysof IQ SN60WF nontoric IOL implantation (low-astigmatism group) (all IOLs by Alcon Laboratories, Inc.). The research adhered to the tenets of the Declaration of Helsinki. An institutional review board approved the study protocol, and all patients provided informed consent. Exclusion criteria were pathology of the cornea, vitreous, macula, or optic nerve; preoperative regular corneal astigmatism greater than 4.00 D or extensive irregular corneal astigmatism determined using corneal topography; planned extracapsular cataract extraction; a history of ocular surgery or inflammation; a pupil diameter less than 5.0 mm with full mydriasis; patient refusal; and anticipated difficulties with the examinations, analyses, or follow-ups.
Intraocular Lens Power Calculation The Acrysof IQ toric IOL used in this study is a yellowtinted single-piece model comprising a hydrophobic acrylic polymer. The IOL has a 6.0 mm asymmetric biconvex optic. The haptics are made of the same acrylic polymer as the optic and have a modified L-shaped design with no angulation. The posterior surface of the optic has a toric component and 3 reference indentations on each side, which indicate the flattest meridian of the optic. The spherical power of this toric IOL is available from 12.00 to 25.00 D in 0.50 D increments. Three toric models are currently available: the SN60T3, SN60T4, and SN60T5 with cylinder powers at the IOL plane (average corneal plane) of 1.50 D (1.03 D), 2.25 D (1.55 D), and 3.00 D (2.06 D), respectively. The nontoric control IOL (Acrysof IQ, SN60WF) is constructed using the same material and design as the toric IOL models except it does not have a toric component or the axis indentations. The spherical power of the IOL in each case was calculated using the SRK/T formula. The axial length (AL) was measured using the IOLMaster biometer (Carl Zeiss Meditec AG), and keratometry (K) readings were taken using an autokerato-refractometer (KR-7100, Topcon Corp.); the
Submitted: August 17, 2011. Final revision submitted: February 8, 2012. Accepted: February 10, 2012. From Hayashi Eye Hospital (Hayashi, Yoshida, Manabe), Fukuoka, the Department of Ophthalmology (Kondo), University of Occupational and Environmental Health, Fukuoka, and the Department of Ophthalmology (Hirata), Saga University Faculty of Medicine, Saga, Japan. Corresponding author: Ken Hayashi, MD, Hayashi Eye Hospital, 4-23-35 Hakataekimae, Hakata-Ku, Fukuoka 812-0011, Japan. E-mail: [email protected].
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K readings were used to calculate the IOL power and to calculate the power and axis placement of the toric IOL. In patients with dense cataract, the AL was measured using an ultrasonic applanation biometer (Ocuscan, Alcon Biophysics). Calculations of the toric IOL power and axis placement to achieve emmetropia were performed using a web-based toric IOL calculator program.A Preoperative keratometry and biometry data, incision location and size, and the surgeon’s estimated surgically induced corneal astigmatism were used to determine the appropriate toric IOL model, spherical equivalent (SE) IOL power, and axis of placement in the eye.
Surgical Technique The same surgeon (K.H.) performed all surgical procedures. Preoperatively, with the patient seated upright at the slitlamp to compensate for cyclorotation, the surgeon marked the corneal limbus at the 0-degree, 90-degree, and 180-degree positions using a marker after vertical alignment of the patient’s head. At the beginning of the surgery, the steepest meridian of the corneal limbus was identified and marked with a diamond knife using a toric IOL marker (9-705R-1, Duckworth & Kent) with the aid of the preplaced reference points. The surgeon made a 2.50 mm clear corneal incision (CCI) horizontally in eyes with against-the-rule or oblique corneal astigmatism and superiorly in eyes having with-the-rule astigmatism; the horizontal incision was created temporally in the right eye and nasally in the left eye. Phacoemulsification was performed using a previously described technique.17 First, a continuous curvilinear capsulorhexis measuring approximately 5.5 mm in diameter was created using a bent needle. After hydrodissection, phacoemulsification of the nucleus and aspiration of the cortex were performed. The wound was enlarged to 2.65 mm using a steel keratome for implantation of the IOL. The lens capsule was inflated with sodium hyaluronate 1% (Healon), after which the IOL was implanted in the capsular bag. The toric IOL was rotated until the axis indentations were aligned with the corneal cylinder axis marked at the steepest meridian. The ophthalmic viscosurgical device was thoroughly removed, with attention given to avoiding rotation of the IOL. The IOL axis alignment was confirmed by stromal hydration after would closure. No eye received limbal relaxing incisions or astigmatic keratotomy.
Outcome Measures All patients were examined for ocular and corneal wavefront aberrations, UDVA, CDVA, refractive status, keratometric cylinder, and pupil diameter preoperatively and 3 and 6 months postoperatively. The KR-1W system (Topcon Corp.) combines Hartmann-Shack ocular aberrometry, which was used to measure ocular wavefront aberrations, and Placido disk videokeratography, which was used to measure corneal wavefront aberrations; thus, the system provides aberration values for the whole eye and cornea. The details of this apparatus have been described.18 In brief, after full mydriasis, pupils were measured at least 3 times. The Hartmann-Shack aberrometer projects light onto the retina, and the light reflected from the retina passes through the internal oculus. The reflected light passes through the Hartmann plate and becomes a spot of light, which forms an image on a charge-coupled device camera. Displacement of the image formation is analyzed as wavefront distortion. The wavefront aberrations (1st- to 6th-order wavefront
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Zernike coefficients) were calculated from the displacement and expanded with the Zernike polynomials. After full mydriasis, analysis of wavefront aberrations was performed by measuring the central 4.0 mm and 6.0 mm using the aperture. The root-mean-square (RMS) value of the 3rd-order Zernike coefficients was used to represent 3rd-order aberrations (coma-like aberrations), and the RMS of the 4th-order Zernike coefficients was used to represent 4th-order aberrations (spherical-like aberrations). Total HOAs were defined as the sum of the RMS of the 3rd- to 6th-order coefficients. For example, 3rd-order aberrations were defined as the RMS of all 4 Zernike 3rd-order terms. Videokeratography was performed simultaneously, and corneal 3rd-order aberrations, 4th-order aberrations, and total HOAs were determined. In addition, assuming a simple model for the eye, wavefront aberrations of the internal optics (internal optic aberrations) were obtained by direct subtraction of the corneal aberrations from the ocular aberrations.18–20 The refractive spherical power, cylindrical power, and axis were examined with the autokerato-refractometer used in the preoperative examination; the manifest SE value was determined as the spherical power plus one half the cylindrical power. The corneal powers at the steepest and flattest meridians were also measured using the autokerato-refractometer. The keratometric cylindrical power and axis were determined for each cornea and used to calculate the surgically induced corneal astigmatism. The surgically induced corneal astigmatism was calculated using the polar value analysis described by Naeser et al.21,22 In addition, the polar coordinate system was converted to the vector coordinate system (change vector magnitude and meridian). The UDVA and CDVA were examined using decimal charts and converted to a logMAR scale for statistical analysis. Pupil diameter was measured using a Colvard pupillometer (Oasis Medical). Six months postoperatively, all eyes had high- to lowcontrast visual acuity measurement with and without a glare source after distance correction using the Contrast Sensitivity Accurate Tester (CAT-2000, Menicon Co. Ltd.). This device measures logMAR CDVA with a range of 1.0 and 0.1 using visual targets with 5 contrast levels (100%, 25.0%, 10.0%, 5.0%, and 2.5%) under photopic and mesopic conditions. Measurement under photopic conditions was performed with chart lighting of 100 candelas (cd)/m2 and under mesopic conditions with chart lighting of 2 cd/m2. For measurement of glare visual acuity, a glare source of
200 lux was located in the periphery 20 degrees around the visual axis. Ophthalmic technicians unaware of the purpose of the study performed all measurements.
Statistical Analysis Ocular, corneal, and internal optic HOAs; UDVA; CDVA; high-to low-contrast visual acuity with and without glare; manifest SE; corneal astigmatism; pupil diameter; and other continuous variables were compared between the toric, high-astigmatism, and low-astigmatism groups using the Kruskal-Wallis test. The surgically induced corneal astigmatism determined using the polar coordinate system was compared between groups using a multivariate analysis of variance (ANOVA).21,22 Categorical variables were compared between the 3 groups using the chi-square goodness-of-fit test. When a statistically significant difference was found between the 3 groups, the difference between each combination of 2 groups was further compared using the Mann-Whitney U test for continuous variables and the chi-square test for discrete variables with the Bonferroni adjustment for multiple comparisons. The vector magnitude of the surgically induced corneal astigmatism was correlated with ocular or corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations using the simple regression analysis. Differences with a P value less than 0.05 were considered statistically significant.
RESULTS Screening was continued until 50 eyes were recruited into each of the 3 groups. Of the 150 patients enrolled, 18 were lost to follow-up. Twelve patients did not appear for the scheduled follow-up, 3 were referred to other hospitals, 1 moved from the area, and 2 refused examinations. Accordingly, 48 eyes in the toric group, 42 in the high-astigmatism group, and 42 in the lowastigmatism group remained for analysis. The mean age of all patients (66 men and 66 women) was 69.0 years G 9.0 (SD) (range 40 to 85 years). Table 1 shows the patients’ demographics by group. The age, sex, ratio of left eyes to right eyes, manifest SE value, and pupil diameter did not differ significantly between groups. The mean preoperative
Table 1. Patient characteristics. Group Parameter Mean age (y) Sex (M/F), n (%) Left/right eyes, n (%) Mean keratometric cylinder (D) Mean refractive cylinder (D) Mean MRSE (D)
Toric
High Astigmatism
Low Astigmatism
P Value
70.3 G 8.81 27/21 21/27 1.80 G 0.61 2.43 G 1.13 1.73 G 3.2
69.6 G 8.8 20/22 23/19 1.38 G 0.49 1.67 G 1.45 1.39 G 3.2
66.9 G 9.1 19/23 20/22 0.46 G 0.25 0.91 G 0.72 1.23 G 3.7
.1921 .5417 .5752 !.0001* !.0001* .2522
MRSE Z manifest refraction spherical equivalent Means G SD *Statistically significant difference between the 3 groups.
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corneal astigmatism and refractive astigmatism were highest in the toric group followed by the highastigmatism group and the low-astigmatism group (P%.0001). The toric IOL models used were SN6AT3 in 21 eyes, SN6AT4 in 18 eyes, and SN6AT5 in 9 eyes. All surgeries were uneventful, and no eye required sutures. The HOA values could be obtained with a 4.0 mm pupil in 128 eyes (97.7%) and with a 6.0 mm pupil in 58 eyes (43.9%) postoperatively. With a 4.0 mm pupil, there was no significant difference preoperatively in the mean ocular total HOAs, 3rd-order aberrations, or 4th-order aberrations between the 3 groups (PR.1408). Postoperatively, the mean ocular total HOAs were significantly greater in the toric group and highastigmatism group than in the low-astigmatism group at 3 months and 6 months (P%.0365) (Figure 1); the ocular total HOAs did not differ significantly between the toric group and the high-astigmatism group. The ocular 3rd-order aberrations were also greater in the toric and high-astigmatism groups than in the
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low-astigmatism group; the difference between the 3 groups was significant at 3 months (PZ.0403) and marginally significant at 6 months (PZ.0574). There were no significant between-group differences in ocular spherical-like 4th-order aberrations. With a 4.0 mm pupil (Figure 2) and a 6.0 mm pupil (Figure 3), there was no significant difference preoperatively in the mean corneal total HOAs, 3rd-order aberrations, or 4th-order aberrations between groups (PR.1133). Postoperatively, however, the mean corneal total HOAs were significantly greater in the toric and high-astigmatism groups than in the low-astigmatism group at 3 months and 6 months (P%.0330); the corneal total HOAs did not differ significantly between the toric group and high-astigmatism group. The corneal 3rd-order aberrations were also greater in the toric and highastigmatism groups than in the low-astigmatism group; the difference between the 3 groups was significant at 3 months (P%.0163). There was no significant difference in corneal 4th-order aberrations between groups. Regarding internal optic aberrations, no statistically
Figure 1. Comparison of the mean G SD ocular HOAs in the toric group, high-astigmatism group, and low-astigmatism group. Mean ocular total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the low-astigmatism group after cataract surgery, although there was no significant difference preoperatively. J CATARACT REFRACT SURG - VOL 38, JULY 2012
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Figure 2. Comparison of the mean G SD corneal HOAs for a 4.0 mm pupil in the toric group, high-astigmatism group, and low-astigmatism group. Mean corneal total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the lowastigmatism group after cataract surgery, although there was no significant difference preoperatively.
significant differences were found in total HOAs, 3rd-order aberrations, or 4th-order aberrations preoperatively or 3 or 6 months postoperatively. The mean residual refractive astigmatism in the toric and low-astigmatism groups was significantly less than in the high-astigmatism group 3 months and 6 months after surgery (P%.0001). The mean manifest SE value in the toric and low-astigmatism groups was significantly lower than in the high-astigmatism group after surgery (P%.0040). Accordingly, the mean postoperative UDVA was significantly better in the toric and low-astigmatism groups than in the high-astigmatism group at 3 months and 6 months (P%.0001). The mean postoperative CDVA was not significantly different between the 3 groups at 3 months or 6 months (PR.1466) (Table 2). The mean photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity was significantly worse in the toric and high-astigmatism groups than in the low-astigmatism group (P%.0210) (Figure 4). Statistical analysis of mesopic visual acuity at 2.5% contrast could not be obtained because it was
worse than the detection limit (1.0 logMAR) in most eyes. High- to low-contrast visual acuity in the presence of glare also tended to be worse in the toric and high-astigmatism groups than in the lowastigmatism group. Except for mesopic visual acuity with glare at 100% contrast, the difference did not reach statistical significance (Figure 5). Specifically, mesopic visual acuity with glare at 10.0%, 5.0%, and 2.5% contrast could not be analyzed because the visual acuity with glare at these contrasts was worse than the detection limit in most eyes. The mean postoperative pupil diameter was similar between the 3 groups at 3 months and 6 months (PR.2137) (Table 3). The mean corneal astigmatism at 3 months and 6 months was highest in the toric group followed by the high-astigmatism group and the low-astigmatism group (P%.0001). Using a univariate comparison test, the vector magnitude of the surgically induced corneal astigmatism tended to be greater in the toric and high-astigmatism groups than in the low-astigmatism group; the difference between the 3 groups was significant at 3 months
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Figure 3. Comparison of the mean G SD corneal HOAs for a 6.0 mm pupil in the toric group, high-astigmatism group, and low-astigmatism group. Mean corneal total HOAs and 3rd-order aberrations were greater in the toric group and high-astigmatism group than in the lowastigmatism group after cataract surgery, although there was no significant difference preoperatively.
(PZ.0156) and marginally significant at 6 months (PZ.0661). Using multivariate ANOVA, however, the mean surgically induced corneal astigmatism was not significantly different between the 3 groups (PR.6445). Using simple regression analysis, the vector magnitude of the surgically induced corneal astigmatism
Table 2. Comparison of mean logMAR CDVA between the 3 groups. Mean LogMAR CDVA G SD Exam
Toric
High Low P Astigmatism Astigmatism Value
Preop 0.61 G 0.32 0.56 G 0.33 0.64 G 0.39 .4722* 3 mo postop 0.01 G 0.61 0.01 G 0.05 0.03 G 0.04 .1467* 6 mo postop 0.02 G 0.06 0.01 G 0.06 0.03 G 0.04 .1742* CDVA Z corrected distance visual acuity *No significant difference.
correlated significantly with ocular and corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations 3 months and 6 months after cataract surgery (Table 4). In addition, the determination coefficients of corneal HOAs, 3rd-order aberrations, and 4th-order aberrations were greater than those of ocular HOAs. Furthermore, the vector magnitude of the surgically induced corneal astigmatism correlated significantly with the change in ocular and corneal total HOAs and 3rd-order aberrations (Table 5). A larger magnitude of surgically induced corneal astigmatism was significantly correlated with a greater change in corneal total HOAs (Pearson r Z 0.304, PZ.0004) (Figure 6). DISCUSSION In our study, we found that ocular total HOAs and 3rd-order coma-like aberrations were significantly greater after cataract surgery in eyes with high preexisting corneal astigmatism that had toric or nontoric
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Figure 4. Comparison of the mean G SD visual acuity at high- to low-contrast visual targets under photopic and mesopic conditions in the toric group, highastigmatism group, and lowastigmatism group. Mean photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity was worse in the toric and high-astigmatism groups than in the low-astigmatism group (P %.0210). Mesopic visual acuity at 2.5% contrast could not be analyzed, because mesopic visual acuity at this contrast was worse than the detection limit in most eyes.
IOL implantation than in eyes with low preexisting corneal astigmatism that had nontoric IOL implantation; the values were similar in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation. In addition, ocular 4th-order sphericallike aberrations did not differ significantly between the 3 groups. These results suggest that the optical quality after cataract surgery may be worse in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism.
Similarly, the corneal total HOAs and 3rd-order aberrations in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL were significantly greater than in eyes with low preexisting corneal astigmatism that received a nontoric IOL. In addition, there was no significant difference in the HOAs of the internal optics. Furthermore, in most eyes, the corneal total HOAs and 3rd-order aberrations increased postoperatively, while the ocular HOAs decreased. These findings suggest that corneal
Figure 5. Comparison of the mean G SD visual acuity at high- to lowcontrasts in the presence of a glare under photopic and mesopic conditions in the toric group, highastigmatism group, and lowastigmatism group. Mean high- to low-contrast visual acuity with glare tended to be worse in the toric and high-astigmatism groups than in the low-astigmatism group, but the difference did not reach statistical significance except for mesopic visual acuity with glare at 100% contrast. Mean mesopic visual acuity with glare at 10%, 5%, and 2.5% contrast could not be analyzed, because the mesopic visual acuity at these contrasts was worse than the detection limit in most eyes.
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Table 3. Comparison of the mean pupil diameter in the 3 groups. Mean Pupil Diameter (mm) G SD Parameter
Toric
High LowP Astigmatism Astigmatism Value
†
Far (mm) Preop 3 mo postop 6 mo postop Near (mm)z Preop 3 mo postop 6 mo postop
3.6 G 0.6 3.4 G 0.5 3.5 G 0.5
3.5 G 0.8 3.4 G 0.6 3.3 G 0.5
3.6 G 0.5 3.5 G 0.6 3.5 G 0.5
.7663 .4906* .2137*
3.1 G 0.6 2.9 G 0.5 3.0 G 0.5
3.1 G 0.6 2.9 G 0.5 2.9 G 0.5
3.1 G 0.5 3.0 G 0.5 3.0 G 0.5
.9476 .4022* .2794
*No significant difference † Pupil diameter at far distance z Pupil diameter at near distance
HOAs, specifically 3rd-order aberrations, are induced more after cataract surgery in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism. The mean CDVA did not differ significantly between the 3 groups. Photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity, however, were significantly worse in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation than in eyes with low preexisting corneal astigmatism that had nontoric IOL implantation. Furthermore, high- to low-contrast visual acuity in the presence of a glare source tended to be worse in eyes with high preexisting astigmatism that had toric or nontoric IOL implantation. These results indicate that visual function in eyes with high preexisting
Table 4. Simple regression analysis between the vector magnitude of surgically induced corneal astigmatism and ocular total HOAs and 3rd-order aberrations and between the vector magnitude of surgically induced corneal astigmatism and corneal total HOAs and 3rd-order aberrations. Analysis
R2*
P Value
Between ocular HOAs and vector magnitude of SIA 3 months Total HOAs 0.148 !.0001† 3rd-order aberrations 0.126 !.0001† 6 months Total HOAs 0.137 !.0001† 3rd-order aberrations 0.075 .0045† Between corneal HOAs and vector magnitude of SIA 3 months Total HOAs 0.188 !.0001† 3rd-order aberrations 0.154 !.0001† 6 months Total HOAs 0.194 !.0001† 3rd-order aberrations 0.141 !.0001† HOAs Z higher-order aberrations; SIA Z surgically induced astigmatism *Determination coefficient † Statistically significant correlation
corneal astigmatism that received a toric or nontoric IOL was worse than that in eyes with low preexisting corneal astigmatism that received a nontoric IOL. Thus, the visual function outcomes were consistent with the ocular HOAs and optical quality results. Previous studies14–16 found that implantation of a posterior chamber or iris-supported toric phakic IOL improved CDVA or contrast sensitivity. This finding might be the result of the precise correction of a moderate to high degree of myopic astigmatism
Table 5. Simple regression analysis between the vector magnitude of surgically induced corneal astigmatism and changes in corneal total HOAs, 3rd-order aberrations, and 4th-order aberrations 3 months after surgery. Analysis
R 2*
P Value
Between ocular HOAs and vector magnitude of SIA Total HOAs 0.061 .0126† 3rd-order aberrations 0.085 .0042† 4th-order aberrations 0.018 .1966 Between corneal HOAs and vector magnitude of SIA Total HOAs 0.092 .0004 3rd-order aberrations 0.092 .0006 4th-order aberrations 0.022 .1023 HOAs Z higher-order aberrations; SIA Z surgically induced astigmatism *Determination coefficient † Statistically significant correlation
Figure 6. Correlation between the vector magnitude of surgically induced astigmatism (SIA) and change in corneal total HOAs from baseline at 3 months after cataract surgery. A larger vector magnitude of the SIA correlated significantly with a greater change in corneal total HOAs (Pearson r Z 0.304, PZ.0004).
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and that a young crystalline lens might preclude the deterioration of the optical quality of the eye. Accordingly, this does not likely hold true for pseudophakic eyes that have implantation of a toric IOL for aphakia. We believe that our study is the first to show that ocular HOAs are greater and visual function is worse after cataract surgery in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL than in eyes with low preexisting astigmatism that received a nontoric IOL. The difference in ocular and corneal total HOAs and 3rd-order aberrations after cataract surgery is predominantly attributed to the difference in induced irregular corneal astigmatism caused by CCIs. The vector magnitude of the surgically induced corneal astigmatism was greater in the toric group and highastigmatism group than in the low-astigmatism group based on univariate analysis, although no significant difference was found using multivariate analysis. Furthermore, the vector magnitude of the surgically induced corneal astigmatism was significantly correlated with ocular and corneal HOAs, which represent irregular astigmatism, as well as with changes in corneal HOAs resulting from the cataract surgery. Based on these results, we believe that the cataract incision induces more irregular astigmatism and regular astigmatism in eyes with high preexisting corneal astigmatism than in eyes with low preexisting corneal astigmatism. In contrast, because there was no significant between-group difference in the HOAs of the internal optics, which are derived mainly from the IOL,18–20 the toric IOL component may not markedly influence HOAs or optical quality. In conclusion, after cataract surgery, ocular and corneal HOAs, specifically 3rd-order coma-like aberrations, were greater in eyes with high preexisting corneal astigmatism that received a toric or nontoric IOL than in eyes with low preexisting corneal astigmatism that received a nontoric IOL, which led to the impairment in photopic low-contrast visual acuity and mesopic high- to low-contrast visual acuity in eyes with high preexisting astigmatism that received a toric or nontoric IOL. Based on the results in the present study, we believe that corneal HOAs are induced more in eyes with high preexisting corneal astigmatism than in eyes with low preexisting astigmatism and that a greater degree of HOAs does not derive mainly from the toric IOL component. It is conceivable, however, that ocular wavefront aberrations are markedly induced when there is marked axis misalignment of the toric IOL. Further study is needed to examine the effect of the toric component of the IOL on ocular HOAs, particularly when there is marked axis misalignment of the toric IOL.
WHAT WAS KNOWN Previous studies show that implantation of a toric IOL improves CDVA or contrast sensitivity. To date, however, optical quality such as HOAs and visual function have not been studied in pseudophakic eyes that had toric IOL implantation. WHAT THIS PAPER ADDS After cataract surgery, corneal HOAs, specifically thirdorder aberrations, were induced more in eyes with high preexisting corneal astigmatism that received a toric IOL or nontoric IOL than in eyes with low preexisting corneal astigmatism that received a nontoric IOL. This increase in corneal HOAs led to the impairment of contrast sensitivity in eyes with high preexisting astigmatism that received a toric IOL or a nontoric IOL.
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OTHER CITED MATERIAL
A. Alcon, Inc. AcrySofÒ Toric IOL Web Based Calculators. Available at: http://www.acrysoftoriccalculator.com. Accessed March 9, 2012
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First author: Ken Hayashi, MD Hayashi Eye Hospital, Fukuoka, Japan