Purpose
To examine whether long-term corneal astigmatic change with age after cataract surgery depends on patient age at the time of surgery, and to evaluate whether this change is different from that in eyes that did not undergo surgery.
Design
Retrospective cohort study.
Methods
A total of 437 eyes that underwent phacoemulsification with a 4.1-mm horizontal corneoscleral incision more than 11 years ago and 600 control eyes without surgery were divided into 4 age groups: (1) 60 years or younger, (2) 61–65 years, (3) 66–70 years, and (4) 71 years or older. The corneal astigmatic change between baseline and 5 years after baseline, between 5 and 10 years, and between baseline and 10 years, as calculated using the polar (x-y) coordinate analysis, were compared among the age groups and between eyes with and without surgery.
Results
Corneal astigmatic change, expressed as x- and y-coordinates, showed an against-the-rule change of 0.2–0.4 diopter during the 10 years in all age groups of the surgery and nonsurgery groups. Using multivariate analysis of variance, the mean x- and y-coordinates did not differ significantly among the age groups in either the surgery or nonsurgery groups ( P ≥ .4112). Furthermore, the mean x- and y-coordinates did not differ significantly between the surgery and nonsurgery groups in any age group ( P ≥ .1359).
Conclusion
Long-term corneal astigmatic change with age after cataract surgery does not differ significantly depending on patient age at the time of surgery, and is comparable to that of eyes without surgery.
Less corneal or refractive astigmatism is clearly associated with better uncorrected visual acuity (VA) after cataract surgery. To achieve sufficient uncorrected VA, recent advances in surgical techniques and devices are aimed at correcting preexisting astigmatism at the time of cataract surgery, including the toric intraocular lens (IOL), a limbal relaxing incision, or an opposite clear corneal incision. Corneal astigmatism changes toward against-the-rule astigmatism, however, with advancing age throughout life. Accordingly, surgeons should understand how corneal astigmatism continues to change after stabilization of the induced astigmatic change following cataract surgery.
Many studies with middle-term follow-up show that the surgically induced change in corneal astigmatism generally stabilizes within 1 year after sutureless cataract surgery. Long-term studies described by Rainer and associates and by Drews, however, report that corneal astigmatism continues to change toward the against-the-rule astigmatism for up to 5 years after superior incision cataract surgery, but it is possible that the later against-the-rule shift is attributable to aging. Indeed, our previous study revealed that corneal astigmatism shows an against-the-rule shift of approximately 0.2–0.4 diopter (D) within 10 years after stabilization of the induced astigmatism attributable to cataract surgery, and this change is comparable to that of eyes that did not undergo surgery. It remains unclear, however, whether this against-the-rule astigmatic change with age subsequent to the surgically induced change differed depending on the patient’s age at the time of cataract surgery.
The purpose of the present study was to investigate whether long-term changes in corneal astigmatism with advancing age after cataract surgery differ depending on age at the time of surgery, and to evaluate whether the degree of this change differs from that in healthy eyes that did not undergo surgery. The results of the present study may provide surgeons clues to determine the amount of astigmatism that should remain according to the patient’s age at the time of cataract surgery.
Methods
Patients
This was a retrospective cohort study. The medical records of all patients who had undergone sutureless phacoemulsification surgery with implantation of an IOL at the Hayashi Eye Hospital between May 2014 and August 2014 were consecutively reviewed. Only those eyes that underwent a follow-up of 11 years or longer from the time of cataract surgery were included (surgery group) in the study. Inclusion criteria for the surgery group were: (1) eyes that underwent phacoemulsification surgery with a 4.1-mm sutureless horizontal corneoscleral incision; (2) eyes that underwent at least 2 examinations by an autokeratometer at 1 year after surgery or later, and the difference between the 2 examinations was within 0.5 D in cylindrical power and within ±15 degrees in the cylindrical axis (the latter examination was defined as baseline); (3) eyes that underwent examinations by the autokeratometer at approximately 5 and 10 years after baseline; (4) first-operated eye if the patient had undergone bilateral cataract surgery; (5) eyes that had uneventful phacoemulsification surgery without sutures; (6) eyes with no comorbidity of the cornea, optic nerve, or macula; (7) eyes with no previous history of other surgery or inflammation; and (8) eyes without severe chronic eyelid disease during follow-up. Based on these criteria, a total of 437 eyes were identified, and divided into 4 age groups of (1) 60 years or younger, (2) 61–65 years, (3) 66–70 years, and (4) 71 years or older at the time of surgery. For controls for each age group, we recruited 150 eyes that did not undergo any ocular surgery during the 10 years or longer follow-up (nonsurgery group). Inclusion criteria for the nonsurgery group were (1) eyes that underwent examination by an autokeratometer at baseline, and at approximately 5 and 10 years after baseline; (2) eyes with no comorbidity of the cornea, optic nerve, or macula; (3) eyes with no history of other surgery or inflammation; and (4) eyes without severe chronic eyelid disease during follow-up. Eyes in the surgery group received a multi-piece hydrophobic acrylic IOL through a 4.1-mm straight horizontal corneoscleral incision. This research adhered to the tenets of the Declaration of Helsinki. The Institutional Review Board (IRB)/ethics committee of the Hayashi Eye Hospital, Fukuoka, Japan, at which the present study was conducted, approved the study protocol.
Surgical Procedures
A single surgeon (K.H.) performed all surgeries using essentially the same surgical procedure, as described previously. First, a continuous curvilinear capsulorrhexis measuring approximately 5.0 mm in diameter was accomplished using a 25 gauge bent needle through a side port. After continuous curvilinear capsulorrhexis, a corneoscleral incision was made horizontally at the meridian between 8 and 10 o’clock (temporally in the right eye and nasally in the left eye) for phacoemulsification. A 3.5-mm straight corneoscleral tunnel incision was made using a diamond knife (Huco, St-Blaise, Switzerland), a diamond crescent knife (Huco), and a 2.5-mm stainless steel keratome (Inami, Tokyo, Japan). After hydrodissection, endocapsular phacoemulsification of the nucleus and aspiration of the residual cortex were conducted. The wound was enlarged to 4.1 mm using a stainless keratome (Alcon Laboratories, Fort Worth, Texas, USA) for implantation of an acrylic IOL using a diamond crescent knife. The lens capsule was inflated with 1% sodium hyaluronate (Healon; AMO, Santa Ana, California, USA), after which an IOL was placed into the capsular bag using an IOL forceps (ASICO, Westmont, Illinois, USA). After the IOL was inserted, the viscoelastic material was thoroughly evacuated. No suture was placed in any case.
Outcome Measures
Data on the eyes that underwent sutureless phacoemulsification surgery with a horizontal incision (surgery group) and on the control eyes that did not undergo surgery (nonsurgery group) were recorded. These data included corneal curvature at the steeper meridian and that at 90 degrees from the steeper meridian, as well as refractive spherical and cylindrical powers as measured using an autokeratometer (ARK-700A; NIDEK, Gamagori, Japan). The type of astigmatism (with-the-rule astigmatism, against-the-rule astigmatism, or oblique astigmatism), uncorrected or distance-corrected decimal VA, time interval between surgery and examination, length and type of incision, and type of IOL implanted were also recorded. Corneal astigmatism in which the steeper meridian was between 60 degrees and 120 degrees was defined as with-the-rule astigmatism, that in which the steeper meridian was between 0 degrees and 30 degrees or between 150 degrees and 180 degrees was defined as against-the-rule astigmatism, and that in which the steeper meridian was between 30 degrees and 60 degrees or between 120 degrees and 150 degrees was defined as oblique astigmatism. Decimal VA was converted to a logMAR scale for statistical analysis.
The change in corneal astigmatism between baseline and 5 years after baseline, between 5 and 10 years after baseline, and between baseline and 10 years after baseline was analyzed using the polar (x-y) coordinate analysis, originally described by Naeser and Hjortdal. The surgically induced change in corneal astigmatism between the preoperative time point and baseline in the surgery group was also determined using the same method. The x-y coordinate analysis shows vertical (90 degrees) change in corneal astigmatism as the x-coordinate value (Rx) and torque (45 degrees) as the y-coordinate value (Ry). A positive Rx indicates a steepening of the vertical (90 degrees) corneal meridian—which is a with-the-rule change—while a negative Rx indicates a flattening of the vertical corneal meridian—which is an against-the-rule change. A positive Ry indicates a counterclockwise torque, while a negative Ry indicates a clockwise torque.
Statistical Analysis
The normality of the data distribution was tested using the Kolmogorov-Smirnov test. Because Rx and Ry had normal distribution, the differences in Rx and Ry among the 4 age groups, between the surgery and nonsurgery groups, and between the left and right eyes were compared using multivariate analysis of variance (MANOVA). When a statistically significant difference was detected among the age groups, the difference between each group pair was compared using MANOVA for continuous variables and the χ 2 or Fisher exact test for categorical variables with Bonferroni adjustment for multiple comparisons. Simple correlations between baseline age and the Rx or Ry were examined using Pearson correlation analysis. Because portions of the data regarding corneal astigmatism, and some of the other variables, were not normally distributed, corneal astigmatism, visual acuity, and the other continuous variables among the age groups were compared using the Kruskal-Wallis test, and between the surgery and nonsurgery groups using the Mann-Whitney U test. The number of eyes that had a with-the-rule, against-the-rule, or oblique corneal astigmatism and the other discrete variables were compared between the surgery and nonsurgery groups using the χ 2 or Fisher exact test, and among the 4 age groups using the χ 2 goodness-of-fit test. Differences with a P value of less than .05 were considered statistically significant.
Results
A total of 437 eyes that underwent a 4.1-mm horizontal corneoscleral incision were enrolled in the surgery group, while 600 eyes were enrolled in the nonsurgery group. Patient characteristics of the surgery group and the nonsurgery group in the 4 age groups are shown in Table 1 . Age, sex, and the ratio of the left to right eyes did not differ significantly between the surgery and nonsurgery groups.
| Characteristic | Surgery Group | Nonsurgery Group | P Value |
|---|---|---|---|
| 60 years or younger | |||
| Age (y) | 57.2 ± 2.3 | 57.0 ± 2.1 | .1580 |
| Sex (M/F) | 47/66 | 61/89 | .9800 |
| Left/right | 55/58 | 73/77 | >.9999 |
| 61–65 years | |||
| Age (y) | 63.8 ± 1.4 | 63.9 ± 1.0 | .9787 |
| Sex (M/F) | 35/72 | 56/94 | .5273 |
| Left/right | 50/57 | 74/76 | .7751 |
| 66–70 years | |||
| Age (y) | 68.9 ± 1.2 | 68.7 ± 0.8 | .0655 |
| Sex (M/F) | 36/79 | 62/88 | .1216 |
| Left/right | 60/55 | 73/77 | .6582 |
| 71 years and older | |||
| Age (y) | 75.0 ± 2.8 | 74.3 ± 2.1 | .0514 |
| Sex (M/F) | 25/77 | 55/95 | .0578 |
| Left/right | 51/51 | 81/69 | .6202 |
Surgically Induced Corneal Astigmatism in the Surgery Group
The mean interval between surgery and baseline was 13.4 ± 2.3 months, ranging between 12 and 23 months. The length and type of incision were identical in all age groups. The surgically induced corneal astigmatism expressed in Rx and Ry between preoperative astigmatism and that at baseline is shown in Table 2 . The mean Rx between preoperative corneal astigmatism and that at baseline was 0.30 ± 0.70 D, while the mean Ry was 0.03 ± 0.42 D, which indicates that, on average, a with-the-rule astigmatic change and very small torque was induced by the cataract surgery. The mean Rx and Ry did not differ significantly among the 4 age groups ( P = .4598).
| X-Coordinate Value (D) | Y-Coordinate Value (D) | |
|---|---|---|
| 60 years or younger | 0.26 ± 0.57 | 0.00 ± 0.42 |
| 61–65 years | 0.21 ± 0.70 | 0.00 ± 0.34 |
| 66–70 years | 0.38 ± 0.82 | 0.04 ± 0.48 |
| 71 years or older | 0.35 ± 0.70 | 0.08 ± 0.42 |
| P value | .4598 a | |
a No statistically significant difference using the multivariate analysis of variance.
Corneal Astigmatism at Baseline, 5 Years After Baseline, and 10 Years After Baseline
In the surgery group, the mean corneal astigmatism did not differ significantly among the 4 age groups preoperatively, at baseline, or at 5 and 10 years after baseline ( P ≥ .3395). In the nonsurgery group, the mean corneal astigmatism differed significantly among the age groups at baseline and at 5 and 10 years after baseline ( P ≤ .0465). The mean corneal astigmatism at baseline and at 5 years and 10 years after baseline was significantly greater in the surgery group than in the nonsurgery group in the 60 years or younger, 61–65 years, and 66–70 years age groups ( P ≤ .0493; Table 3 ), except in the 60 years or younger group at 5 years after baseline ( P = .1410), but did not differ significantly in the 71 years or older age group ( P ≥ .6369).
| Surgery Group | Nonsurgery Group | P Value | |
|---|---|---|---|
| 60 years and younger | |||
| Baseline (D) | 1.04 ± 0.64 | 0.84 ± 0.60 | .0461 a |
| 5 years after baseline (D) | 1.03 ± 0.77 | 0.87 ± 0.60 | .1410 |
| 10 years after baseline (D) | 1.01 ± 0.73 | 0.81 ± 0.58 | .0116 a |
| 60–65 years | |||
| Baseline (D) | 1.00 ± 0.76 | 0.68 ± 0.34 | .0044 a |
| 5 years after baseline (D) | 0.96 ± 0.66 | 0.72 ± 0.38 | .0120 a |
| 10 years after baseline (D) | 1.02 ± 0.76 | 0.76 ± 0.44 | .0493 a |
| 66–70 years | |||
| Baseline (D) | 1.03 ± 0.73 | 0.72 ± 0.50 | <.0001 a |
| 5 years after baseline (D) | 1.02 ± 0.63 | 0.72 ± 0.51 | <.0001 a |
| 10 years after baseline (D) | 1.02 ± 0.70 | 0.84 ± 0.59 | .0235 a |
| 71 years or older | |||
| Baseline (D) | 0.87 ± 0.58 | 0.87 ± 0.58 | .7419 |
| 5 years after baseline (D) | 0.97 ± 0.61 | 0.95 ± 0.65 | .6369 |
| 10 years after baseline (D) | 0.98 ± 0.64 | 1.01 ± 0.71 | .8848 |
Changes in Corneal Astigmatism During 5 Years and 10 Years After Baseline
In both the surgery and nonsurgery groups, the mean Rx was a negative value of approximately −0.1 to −0.2 D between baseline and 5 years after baseline and between 5 and 10 years after baseline, and approximately −0.2 to −0.4 D between baseline and 10 years after baseline in the 4 age groups, which indicates an against-the-rule change in all age groups. The mean Ry was small in all age groups of the surgery and nonsurgery groups, which indicates a slight torque. In both the surgery ( Figure 1 ) and nonsurgery groups ( Figure 2 ), no significant differences were detected among the 4 age groups in the mean Rx and Ry between baseline and 5 years after baseline, between 5 and 10 years, and between baseline and 10 years ( P ≥ .4112). Comparison of the surgery and nonsurgery groups revealed that the mean Rx and Ry did not differ significantly between baseline and 5 years after baseline, between 5 and 10 years, or between baseline and 10 years in any age group ( P ≥ .1359).
Correlation Between Age and Long-Term Change in Corneal Astigmatism
In both the surgery and nonsurgery groups, no significant correlation was found between age and the Rx or Ry between baseline and 5 years after baseline, between 5 and 10 years after baseline, or between baseline and 10 years after baseline ( Table 4 ).
| Surgery Group | Nonsurgery Group | |||
|---|---|---|---|---|
| Pearson r | P Value | Pearson r | P Value | |
| X-coordinate value (Rx) | ||||
| Baseline–5 years | −0.062 | .1954 a | −0.040 | .3247 a |
| 5–10 years | −0.041 | .3976 a | −0.015 | .7145 a |
| Baseline–10 years | −0.022 | .6456 a | −0.051 | .2136 a |
| Y-coordinate Value (Ry) | ||||
| Baseline–5 years | −0.051 | .2840 a | −0.019 | .6345 a |
| 5–10 years | −0.010 | .8304 a | −0.048 | .2389 a |
| Baseline–10 years | −0.032 | .4989 a | −0.030 | .4591 a |
Distribution of Eyes With With-the-Rule Astigmatism, Against-the-Rule Astigmatism, and Oblique Astigmatism at Baseline and 10 Years After Baseline
In both the surgery ( Figure 3 ) and nonsurgery groups ( Figure 4 ), the number of eyes having against-the-rule and oblique astigmatism increased during the 10 years after baseline in the 4 age groups, while that of eyes having with-the-rule astigmatism decreased; the difference between baseline and 10 years after baseline was significantly different in all age groups ( P < .0001). The number of eyes having with-the-rule astigmatism was greater and that of against-the-rule or oblique astigmatism was less in the surgery group than in the nonsurgery group in the age group of 61–65 years, 66–70 years, and 71 years and older at baseline ( P ≤ .0483), while the number of eyes having with-the-rule astigmatism, against-the-rule astigmatism, or oblique astigmatism did not differ significantly between the surgery and nonsurgery groups in the age groups of 60 years or younger and 61–65 years at 10 years after baseline ( P ≥ .1528).
