Two Different Corneal Incision Designs for Correcting Corneal Astigmatism During Cataract Surgery With Multifocal Intraocular Lens Implantation

Patients And Methods

Study design

This study is a retrospective cohort study that was performed at the Eye Center of Xiangya Hospital, Central South University, Changsha, China. Patients who underwent cataract surgery in our department were consecutively included from October 2018 to October 2020. Inclusion criteria were as follows: 1) total corneal astigmatism ranging between 0.5 D and 2.0 D preoperatively; 2) implantation of ZMB00 multifocal IOLs (Abbott Medical Optics, Inc., California,USA); and 3) a single CCI or OCCI was made on the steepest meridian. Exclusion criteria were as follows: 1) corneal astigmatism greater than 2.0 D or irregular astigmatism; 2) presence of eye disease other than cataract; 3) a history of eye trauma and/or previous ocular surgery; and 4) intra-operative complications.

Eighty eyes of 80 patients, ranging in age from 37 to 81 years, were included. One eye per one patient was used in this study. If both eyes that underwent cataract surgery were eligible for this study, the first surgical eye was selected.

Corneal astigmatism was measured with Scheimpflug topography (Pentacam; Oculus, Inc, Wetzlar, Germany), and patients were divided into a CCI group and an OCCI group by pre-operative total corneal astigmatism. Patients with 0.5–1.2D pre-operative corneal astigmatism were included in the CCI group and received a single CCI on the steep meridian, and patients with 1.3–2.0 D were included in the OCCI group and received OCCI on the steep meridian. A total of 41 patients were included in the CCI group and 39 patients were included in the OCCI group. Both groups consisted of superior, temporal, and oblique subgroups on the basis of the steepest corneal meridian. The orientation of corneal astigmatism was regarded as againstthe-rule astigmatism(ATR) in the case of the steepest keratometric readings being between 0–30 and 150–180 degrees, oblique astigmatism was between 30–60 and 120–150 degrees, and with-the-rule astigmatism(WTR) was 60–120 degrees. The pre-operative clinical data of patients in the CCI and OCCI groups is described in Table 1.

Table 1

Pre-operative baseline clinical data of patients.
		CCI group	OCCI group	P
No.		41	39	/
Age (year)		64.9 ± 9.1	58.9 ± 12.4	0.09
Female/Male		21/20	20/19	0.78
Right eye/Left eye		19/22	21/18	0.57
Nuclear opalescence grade		2–4	2–4	/
Mean corneal astigmatism(D)		0.98 ± 0.22	1.63 ± 0.27	<0.001
Mean corneal power(D)		43.87 ± 1.76	43.84 ± 1.70	0.97
The orientation of corneal astigmatism	WTR	17	15	0.78
	ATR	19	19
	oblique	5	5
Corneal Total HOAs		0.092 ± 0.014	0.140 ± 0.018	<0.001
Ocular Total HOAs		0.232 ± 0.042	0.286 ± 0.023	0.62
UDVA(logMAR)		0.98 ± 0.04	1.06 ± 0.08	0.53
VF-14score		65.12 ± 1.78	67.23 ± 3.14	0.98
WTR: with-the-rule; ATR:against-the-rule; UDVA:uncorrected distance visual acuity

The study was approved by the Xiangya Hospital ethics committee and was performed in accordance with the tenets of the Declaration of Helsinki. All patients signed informed consent forms before cataract surgery, and data were collected anonymously.

Intraocular lens

The TECNIS ZMB00 is a UV-blocking, hydrophobic, acrylic, single-piece IOL. It has a C-loop haptic with near power added (+ 4.0 D) at the IOL optic plane. The IOL is designed as biconvex and consists of a wavefront-designed, anterior aspheric surface (negative spherical aberration − 0.27 µm) and posterior diffractive surface with 22 diffractive rings. The IOL power was calculated by the same technician using an IOL Master 500 optical biometer (Carl Zeiss Meditec AG, Jena, Germany) using the Haigis formula. Parameters included axial length, corneal power and anterior chamber depth.

Surgical Technique

All surgeries and corneal meridian markings were performed by the same surgeon (J.J). The steep corneal meridian was marked prior to surgery using a slit lamp. Briefly, the patient’s head was positioned on the slit lamp and the patient was asked to keep the contralateral eye open and to look forward. The slit beam was narrowed to a thin slit, centered on the pupil and aligned with the 0°–180° marks of the calibrator. Then, using a sterile 30-gauge needle, two small superficial incisions were made at the periphery of the cornea where the slit beam cut the limbus at the 0°–180° position. Care was taken to keep the slit beam on the center of the pupil for alignment. Incisions were fixated with a sterile marker pen for easier intraoperative recognition. Finally, the correct position markings were verified at the slit lamp (Fig. 1).

Surgery was performed using topical anesthesia in both groups. After the Mendez-style corneal marking ring was aligned to the two preoperative markings, dots were made using a blue pen on the planned meridian (Fig. 1). A self-sealing 3.0 mm CCI was made 1 mm anterior to the limbus on a steep meridian using a 3.0 mm keratome (Alcon Laboratories, Inc. Fort Worth, USA). There is a 2 mm marking line on the surface of the keratome so that we can ensure that the tunnel length is 2 mm. The standard phacoemulsification procedure was performed via 2 incisions. Routine phacoemulsification was performed using a standard ultrasound technique (Centurion, Alcon Laboratories, Inc. Fort Worth, USA), followed by insertion of a foldable multifocal IOL (ZMB00). The OCCI was made on the opposite steep meridian 1 mm anterior to the limbus using the same keratome prior to removal of viscoelastic material; the length of corneal tunnel was also 2 mm. Only the phacoemulsification incision was hydrated at the end of surgery. All patients received routine postoperative topical steroids for 4 weeks and antibiotic eye drops for 2 weeks.

Main Outcome Measures

Uncorrected distance visual acuity (UDVA) and uncorrected near visual acuity (UNVA) were evaluated by an optometrist; the patients and optometrists were masked during vision testing. The decimal visual acuity was then converted to a logMAR scale for statistical analysis. Corneal astigmatism was assessed using Scheimpflug topography (Pentacam ; Oculus, Inc, Wetzlar, Germany), and the root mean square (RMS) of ocular and corneal HOAs, including total HOAs, coma (Z₃ ^− 1 and Z₃ ¹), spherical aberration (Z₄ ⁰), secondary astigmatism (Z₄ ^− 2 and Z₄ ²), and trefoil (Z₃ ^− 3 and Z₃ ³), were assessed with the Zernike coefficient (iTrace, Tracey Technologies Inc., Houston, USA) in a 3.0 mm diameter central area. Astigmatic change was calculated as the difference between mean preoperative and postoperative topographic readings. Surgically induced astigmatism (SIA) was evaluated using the vector analysis on Dr. Warren Hill’s website (https:// sia-calculator.com/).To determine whether different location of CCI and OCCI can induce different corneal astigmatism, we compared SIA, corneal astigmatic change between patients with WTR and ATR astigmatism. Five patients with oblique astigmatism in CCI or OCCI group were excluded from this comparison.

The Visual Function scale-14 (VF-14) was used to evaluate postoperative visual quality. The scale included 4 items: subjective vision, visual adaptation, peripheral vision and stereoscopic vision¹². Each item was graded from 1 to 5 points, and a higher score indicated higher visual satisfaction. The final score was the average value times 20; higher scores indicated better postoperative life and visual quality.

UDVA, UNVA, total corneal astigmatism and HOAs were recorded before surgery. UDVA and UNVA were observed at 1, 4, and 12 weeks post-surgery. The HOAs were determined 12-weeks post-surgery. The VF-14 questionnaire, glare, halos, and the need for spectacles were recorded at 12 weeks post-surgery.

Statistical Analysis

Statistical analysis was performed using SPSS software (version 21.0; SPSS, Inc.). Categorical variables were compared with use of the Fisher’s exact test. A Wilcoxon Signed Ranks test was used to analyze preoperative and postoperative data. A Mann–Whitney test was used to analyze the data between the two groups. A p value less than 0.05 was considered statistically significant.

Results

Visual Acuity

UDVA and UNVA were significantly improved at 1, 4 and 12 weeks post-surgery in both groups compared to pre-operative values (P < 0.001). There was no difference in UDVA and UNVA between the two groups post-surgery (Table 2).

Table 2

Mean preoperative and postoperative UDVA and UNVA in two groups.
		OCCI group	CCI group	P
UDVA (logMar)	Pre-op	1.06 ± 0.08	0.98 ± 0.04	0.53
	Post-1 week	0.12 ± 0.02*	0.10 ± 0.02*	0.26
	Post-4 weeks	0.09 ± 0.02*	0.05 ± 0.02*	0.87
	Post-12 weeks	0.06 ± 0.02*	0.03 ± 0.01*	0.24
	Pre-op	0.92 ± 0.05	0.97 ± 0.06	0.89
UNVA (logMar)	Post-1 week	0.10 ± 0.04*	0.09 ± 0.02*	0.92
	Post-4 weeks	0.09 ± 0.01*	0.09 ± 0.02*	0.20
	Post-12 weeks	0.08 ± 0.01*	0.09 ± 0.01*	0.81
UDVA: uncorrected distance visual acuity; UNVA:uncorrected near visual acuity; OCCI:opposite clear corneal incision; CCI:clear corneal incision.
* Values are statistically significant compared with preoperative values (P < 0.001).

Residual Corneal Astigmatism

Residual corneal astigmatism at 12 weeks post-surgery is shown in Fig. 2. Residual total corneal astigmatism was 0.2–0.8 D in the CCI group and 0.2–1.1 D in the OCCI group. In the CCI group, 14 of 41 patients (34.1%) had more than 0.5 D residual astigmatism and no patients had more than 1.0 D residual astigmatism. In the OCCI group, 13 of 24 patients (54.2%) had more than 0.5 D residual astigmatism, and 3 of 24 patients (7.6%) had more than 1.0 D residual astigmatism. Among the three patients, 2 patients had ATR astigmatism and 1 patient had WTR astigmatism and their preoperative mean astigmatism was 1.9D. The mean change in corneal astigmatism was 0.52 ± 0.22 D and 1.06 ± 0.23 D in the CCI and OCCI groups, respectively (P < 0.001).

Surgically Induced Astigmatism

The mean SIA was 0.62 ± 0.16 D and 1.23 ± 0.24 D in the CCI and OCCI groups, respectively, indicating that OCCIs caused significantly greater SIA than single CCIs (P < 0.001).

The impact of CCI and OCCI on WTR and ATR astigmatism

Compared to patients with ATR astigmatism, both the SIA and corneal astigmatic change were slightly higher in patients with WTR astigmatism in both CCI group and OCCI group, but there was no statistical difference(P = 0.38,P = 0.91,P = 0.49,P = 0.08). (Table 3)

Table 3

The impact of CCI and OCCI on WTR and ATR astigmatisms
	CCI		P	OCCI		p
	WTR	ATR	P	WTR	ATR	p
Pre-operative CA	0.96 ± 0.22	1.02 ± 0.22	0.69	1.67 ± 0.26	1.56 ± 0.26	0.28
SIA	0.70 ± 0.15	0.64 ± 0.20	0.38	1.39 ± 0.21	1.37 ± 0.28	0.91
change of CA	0.52 ± 0.18	0.52 ± 0.16	0.49	1.12 ± 0.17	1.01 ± 0.28	0.08
CA:corneal astigmatism; SIA:surgically induced astigmatism; CCI:clear corneal incision; OCCI:apposite clear corneal incision; WTR:with the rule; ATR:against the rule.

Corneal and ocular HOAs

After cataract surgery, ocular HOAs were significantly decreased in both the OCCI and CCI groups (P < 0.05) 12 weeks post-surgery. Corneal HOAs, total HOAs and trefoil increased in both groups (P < 0.05). Spherical aberration and secondary astigmatism increased in the CCI group (P < 0.05), but not in the OCCI group (P > 0.05) (Table 4, Fig. 3). Compared to the CCI group, the change in trefoil was larger and the change in secondary astigmatism was smaller in the OCCI group, which demonstrated a similar change in total HOAs in the two groups(Figrue 3).

Table 4

Mean preoperative and 3-month postoperative corneal and ocular HOAs in the CCI and OCCI groups.
	Cornea		Ocular
	OCCI	CCI	OCCI	CCI
Total HOA
preoperative	0.140 ± 0.018	0.092 ± 0.014	0.286 ± 0.023	0.232 ± 0.042
postoperative	0.176 ± 0.018*	0.127 ± 0.016*	0.167 ± 0.018*	0.128 ± 0.020*
P	<0.001	<0.001	<0.001	<0.001
Coma
preoperative	0.065 ± 0.011	0.052 ± 0.011	0.124 ± 0.021	0.140 ± 0.032
postoperative	0.063 ± 0.012*	0.050 ± 0.010	0.065 ± 0.010*	0.071 ± 0.012*
P	<0.001	0.182	<0.001	<0.001
Spherical Aberration
preoperative	0.023 ± 0.008	0.027 ± 0.006	0.049 ± 0.012	0.062 ± 0.014
postoperative	0.024 ± 0.007	0.031 ± 0.006*	0.028 ± 0.006*	0.038 ± 0.006*
P	0.226	<0.001	<0.001	<0.001
Secondary Astigmatism
preoperative	0.023 ± 0.007	0.022 ± 0.005	0.029 ± 0.008	0.032 ± 0.006
postoperative	0.023 ± 0.006	0.025 ± 0.005*	0.023 ± 0.005*	0.028 ± 0.011*
P	0.797	<0.001	<0.001	<0.001
Trefoil
preoperative	0.038 ± 0.008	0.041 ± 0.009	0.070 ± 0.011	0.618 ± 0.009
postoperative	0.065 ± 0.010*	0.059 ± 0.010*	0.058 ± 0.010*	0.056 ± 0.010*
P	<0.001	<0.001	<0.001	<0.001
HOA: total higher-order aberrations; CCI: clear corneal incision; OCCI: opposite clear corneal incision
* Values are statistically significant compared with preoperative examinations (P < 0.05).

Visual quality

The VF-14 scores were significantly higher in both groups at 12-weeks post-surgery (both P < 0.001, Table 5). All patients reported that they were not wearing spectacles most of the time; although 10 patients (12.5%) needed spectacles when reading for long periods of time. A total of 12 patients (15%) reported glare and 9(11.2%) reported halos, but only 3 (3.8%) patients reported being bothered by these phenomena when driving at night.

Table 5

Mean preoperative and 3-month postoperative VF-14 scores in the two groups.
	Preoperative	Postoperative	P
CCI group	65.12 ± 1.78	88.87 ± 2.13	< 0.001*
OCCI group	67.23 ± 3.14	86.47 ± 4.25	< 0.001*
CCI: clear corneal incision; OCCI: opposite clear corneal incision

Discussion

In this study, two different corneal incisions (CCI and OCCI) made at the steepest meridian were used to reduce corneal astigmatism during cataract surgery. Because the corrective effect of a single CCI made at the steepest meridian is limited, and astigmatism has not been fully corrected after CCI in eyes with more than 1.2 D of astigmatism prior to surgery, ¹³ CCI at the steepest meridian was only used in patients with astigmatisms between 0.5 and 1.2 D, and OCCI was used in patients with astigmatisms between 1.3 and 2.0 D. It has been reported that the mean astigmatism correction with CCI is about 0.5 D,^9,11,14,15 and the mean astigmatism correction with OCCI varies from 0.50 to 2.06 D, depending on the preoperative corneal astigmatism, as well as the location and length of the incisions. ^10,11,15 In the current study, a 3.0 mm OCCI on the steep corneal meridian reduced astigmatism by 1.06 D, and single CCI reduced astigmatism by 0.52 D. The results obtained herein are within the range reported previously.^{9–11, 14,15,16}

Since vision can be affected by as little as a 0.5 D residual astigmatism with multifocal IOL implantation, patients with more than 1.0 D residual astigmatism are not recommended for multifocal IOL implantations ^1,2. In this study, patients with more than 0.5 D or 1.0 D residual corneal astigmatism were counted post-surgery. Half of the patients had less than 0.5 D residual astigmatism and almost all patients had less than 1.0 D residual astigmatism postoperatively, resulting in most patients reporting satisfaction with UDVA and UNVA after multifocal IOL implantation. At 12 weeks post-surgery, UDVA was 0.06 and 0.03 logMAR, and UNVA was 0.08 and 0.09 logMAR in the CCI and OCCI groups, respectively. This finding is consistent with the visual improvement reported by others using multifocal IOLs in patients with less than 1.0 D preoperative corneal astigmatism. ^17–19 However, there were still three patients in OCCI group had more than 1.0D residual astigmatism at 12 weeks post-surgery. We thought the reason why postoperative residual astigmatism was still high was the high preoperative corneal astigmatism (mean 1.9D) in these three patients, so multifocal toric IOLs may be more suitable for these patients.

The location of the corneal incisions was a factor that affect the corneal astigmatism after cataract surgery. Many studies have demonstrated that a temporally located incision induces less astigmatism than other types of incisions^20,21. But such alterations have not been reported in CCI or OCCI which was made on the steep meridian. In previous studies, the rate of SIA showed no statistical difference between superior, temporal, and oblique OCCI^22,23. Similar to previous studies, the rate of SIA in our study was detected slightly higher in the case of superior incisions, but the difference was not statistically significant. Further investigations should be carried out to explain the similarity in the rates of SIA detected in superior and temporal OCCI incisions.

Wavefront analysis is an objective measurement of visual quality and may predict visual complaints. Although approximately 93% of the aberration in a normal eye is known to be attributable to lower-order aberrations, HOAs are important for achieving the best optical quality in pseudophakic eyes. ^24–26 In this study, the ocular HOAs decreased significantly after surgery, which indicated an increase of visual quality with mulitifocal IOL implantation.

It has been shown that corneal incisions can increase the values of the root mean square (RMS) of corneal HOAs ^27–30; thus, we assessed the changes in corneal aberrations after surgery. The wavefront parameters of total HOAs, trefoil, coma, spherical aberrations, and secondary astigmatism were compared, since these aberrations constitute the major components of HOAs. In this study, both CCI and OCCI caused an increase in postoperative corneal HOAs, which is consistent with results of previous research.^27–30 The change in the trefoil aberration increases significantly the larger the corneal incision. ^30,31 The current study found that the change of trefoil aberration was larger in the OCCI group than in the CCI group, which may be related to the additional surgical incision. However, the change in secondary astigmatism was smaller in the OCCI group than in the CCI group; thus, the change in total HOA was similar between the two groups. These findings show that compared with CCI, OCCI can increase astigmatism correction, but it does not increase the total corneal HOA.

Subjective vision quality is also an essential component for assessing visual performance. In this study, subjective vision quality was assessed using the VF-14 questionnaire. The questionnaire was used to evaluate near and far vision after cataract surgery. The findings showed that quality of life was significantly improved in both groups. Patients in our study who selected multifocal IOLs do not want to wear reading glasses after surgery. Since all patients in the current study had good UCNV and were spectacle-free most of the time after surgery, our procedure met the expectations of these patients. Glare and halo are common optical side effects after cataract surgery, especially when multifocal IOLs are inserted, and can significantly affect the visual performance and satisfaction of patients. Overall, 10patients (12.5%) reported glare and 9 (11.2%) reported halos, while only 3 (3.8%) patients reported being bothered by these phenomena when driving at night.

This study had some limitations. First, this was a retrospective study and did not compare different methods for correcting corneal astigmatism.Second Moreover, the 12 weeks follow-up time was relatively short; therefore, research into long-term outcomes is necessary. Furthermore, the limited number of patients enrolled reduced the statistical power of the analysis.

In conclusion, patients in this study had satisfactory vision quality after surgery. As for the correction of corneal astigmatism, CCI/OCCI requires no additional skill or instrumentation when 3.0 mm phacoemulsification incisions are used. Therefore, for patients with mild-to-moderate corneal astigmatism who elect to undergo implantation of a multifocal IOL during cataract surgery, CCI/OCCI is a recommended method for correcting corneal astigmatism

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Two Different Corneal Incision Designs for Correcting Corneal Astigmatism During Cataract Surgery With Multifocal Intraocular Lens Implantation

Abstract

Introduction

Patients And Methods

Results

Discussion

Declarations

References