Journal of Refractive Surgery

Original Article 

Effect of Spherical Equivalent Error on Visual Acuity at Various Distances in Eyes With a Trifocal Intraocular Lens

Ken Hayashi, MD; Tatshuhiko Sato, MD; Chizuka Igarashi, MD; Motoaki Yoshida, MD

Abstract

PURPOSE:

To examine the effect of manifest refraction spherical equivalent error on visual acuity at various distances in eyes that received a trifocal intraocular lens (IOL).

METHODS:

Sixty eyes of 30 patients who underwent bilateral implantation of a trifocal IOL (Alcon PanOptix TFNT00; Alcon Laboratories, Inc., Fort Worth, TX) were enrolled. Corrected visual acuity from far to near distances was measured using an all-distance vision tester after simulating the spherical equivalent error by adding spherical lenses with refractive powers of +1.00, +0.50, 0.00, −0.50, and −1.00 diopters (D); addition of a plus lens simulates myopia, whereas addition of a minus lens simulates hyperopia.

RESULTS:

Mean visual acuity at all distances differed significantly among the spherical lens added groups (P ≤ .0374). Mean distance visual acuity at infinity, 5, and 3 m was significantly worse in all lens added groups (+1.00, +0.50, −0.50, and −1.00 D) than in the no lens group (P < .0001). Mean intermediate visual acuity at 1 and 0.7 m did not differ significantly between each of the lens added groups and the no lens group. Mean near visual acuity at 0.3 m was significantly better in the +1.00 and +0.50 D groups and significantly worse in the −0.50 and −1.00 D groups than in the no lens group (P ≤ .0044).

CONCLUSIONS:

A manifest spherical equivalent error of slight myopia significantly improved near visual acuity but worsened distance visual acuity, whereas that of slight hyperopia worsened both distance and near visual acuity in eyes with trifocal IOLs, suggesting that slight myopia is a better target refraction than slight hyperopia, although emmetropia is the optimum target.

[J Refract Surg. 2019;35(5):274–279.]

Abstract

PURPOSE:

To examine the effect of manifest refraction spherical equivalent error on visual acuity at various distances in eyes that received a trifocal intraocular lens (IOL).

METHODS:

Sixty eyes of 30 patients who underwent bilateral implantation of a trifocal IOL (Alcon PanOptix TFNT00; Alcon Laboratories, Inc., Fort Worth, TX) were enrolled. Corrected visual acuity from far to near distances was measured using an all-distance vision tester after simulating the spherical equivalent error by adding spherical lenses with refractive powers of +1.00, +0.50, 0.00, −0.50, and −1.00 diopters (D); addition of a plus lens simulates myopia, whereas addition of a minus lens simulates hyperopia.

RESULTS:

Mean visual acuity at all distances differed significantly among the spherical lens added groups (P ≤ .0374). Mean distance visual acuity at infinity, 5, and 3 m was significantly worse in all lens added groups (+1.00, +0.50, −0.50, and −1.00 D) than in the no lens group (P < .0001). Mean intermediate visual acuity at 1 and 0.7 m did not differ significantly between each of the lens added groups and the no lens group. Mean near visual acuity at 0.3 m was significantly better in the +1.00 and +0.50 D groups and significantly worse in the −0.50 and −1.00 D groups than in the no lens group (P ≤ .0044).

CONCLUSIONS:

A manifest spherical equivalent error of slight myopia significantly improved near visual acuity but worsened distance visual acuity, whereas that of slight hyperopia worsened both distance and near visual acuity in eyes with trifocal IOLs, suggesting that slight myopia is a better target refraction than slight hyperopia, although emmetropia is the optimum target.

[J Refract Surg. 2019;35(5):274–279.]

Many types of new multifocal intraocular lenses (IOLs) were recently developed and became commercially available. Of these IOLs, trifocal IOLs and extended depth-of-focus IOLs are two major improvements in multifocal IOLs.1–9 Trifocal IOLs provide useful uncorrected distance, intermediate, and near visual acuity with a high rate of patient satisfaction.1–6 Particularly, a new type of the trifocal IOL with quadrifocal diffractive technology (AcrySof PanOptix TFNT00; Alcon Laboratories, Inc., Fort Worth, TX) provides an excellent wide range of vision without compromising contrast sensitivity.10,11

Residual astigmatism after cataract surgery impairs uncorrected visual acuity in eyes implanted with multifocal IOLs.12–15 Specifically, refractive astigmatism of approximately 1.00 diopter (D) or more significantly decreases uncorrected visual acuity from far to near distances in eyes with both refractive and diffractive bifocal IOLs.14,15 The manifest refraction spherical equivalent error also must worsen visual function without spectacles in eyes with a multifocal IOL. Based on the experience of monofocal IOL implantation, surgeons currently tend to target myopia when selecting the power of the multifocal IOLs. However, it has not been shown to date how uncorrected visual acuity impairs according to the degree of the manifest refraction spherical equivalent error in eyes with multifocal IOLs.

The purpose of the current study was to investigate the effect of manifest refraction spherical equivalent error on visual acuity from far to near distances in eyes that received a trifocal IOL. Manifest refraction spherical equivalent error was simulated by adding various diopters of spherical lenses to eyes with a trifocal IOL.

Patients and Methods

Study Design

This was an experimental exploratory study to examine the effect of the manifest refraction spherical equivalent error on distance visual acuity in eyes with a trifocal IOL. The study was conducted at the Hayashi Eye Hospital in Fukuoka, Japan, between June 1 and November 9, 2018. Patients were sequentially enrolled between June 13 and September 27, 2018. The study adhered to the tenets of the Declaration of Helsinki. The institutional review board of the Hayashi Eye Hospital approved the study design, and informed consent was obtained from all patients. The study was registered in the University Hospital Medical Information Network (UMIN000034862).

Participants

Sixty eyes of 30 patients who underwent bilateral implantation of the PanOptix trifocal IOL were enrolled in the current study. Preoperative exclusion criteria were any pathology of the cornea, macula, or optic nerve; opaque media other than cataract; history of ocular inflammation or surgery; corneal astigmatism of +1.00 D or greater; marked irregular corneal astigmatism; amblyopia; and any difficulties with examinations or follow-up. Intraoperative exclusion criteria were a small pupillary diameter requiring pupil expansion procedures and eventful surgery.

Surgical Techniques

A single surgeon (KH) performed the surgeries using the previously described surgical procedures.16 Cataract surgery on the second eye was performed approximately 2 days after surgery on the first eye. For phacoemulsification, the surgeon performed a 2.4-mm clear corneal incision. First, two side ports were made with a 0.6-mm slit knife at 90° away from the main incision. A continuous curvilinear capsulorrhexis measuring approximately 5 mm in diameter was created using a bent needle. The surgeon then made a 2.4-mm single-plane clear corneal incision using a steel keratome horizontally for eyes having against-the-rule or oblique corneal astigmatism, and superiorly for eyes having with-the-rule astigmatism. After hydrodissection, phacoemulsification of the nucleus and aspiration of the residual cortex were conducted. The lens capsule was inflated with 1% sodium hyaluronate (Hyaguard; Nitten Co. Ltd, Tokyo, Japan), after which the IOL was placed into the capsular bag using a Monarch II injector with a D cartridge (Alcon Laboratories, Inc.). After IOL insertion, the ophthalmic viscoelastic material was evacuated. In this series, all surgeries were uneventful, and all IOLs were implanted in the capsular bag.

Simulation of Manifest Refraction Spherical Equivalent Error

A manifest refraction spherical equivalent error of various degrees was simulated by adding a spherical lens after full distance correction in eyes with a trifocal IOL. Addition of a plus lens simulates myopia, whereas addition of a minus lens simulates hyperopia. The powers of the spherical lenses were +1.00 (−1.00 D myopia), +0.50 (−0.50 D myopia), 0.00 (emmetropia), −0.50 (+0.50 D hyperopia), and −1.00 (+1.00 D hyperopia) D.

Outcome Measures

Both eyes of 30 patients underwent examinations at 6 months after surgery and later. The logarithm of the minimum angle of resolution (logMAR) visual acuity at infinity, 5, 3, 2, 1, 0.7, 0.5, and 0.3 m was measured using an all-distance vision tester (AS-15; Kowa, Tokyo, Japan) after simulating various degrees of manifest refraction spherical equivalent error. The AS-15 measures equivalent logMAR visual acuity from far to near distances by the examiner placing a spherical lens and various visual targets at proper distances along the visual axis. In the current study, we defined visual acuity at infinity and 5 m to be distance visual acuity, that at 1.0, 0.7, and 0.5 m to be intermediate visual acuity, and that at 0.3 m to be near visual acuity.

The refractive spherical and cylindrical powers were objectively measured using autorefractometers (TONOREF II version 1.17 and III version 1.05.01; Nidek, Gamagori, Japan). The objective manifest refraction spherical equivalent value was determined as the spherical power plus half the cylindrical power. Keratometric astigmatism was measured using an autokeratometer (Nidek). All examinations were performed by experienced ophthalmic technicians not aware of the objectives of the study.

Statistical Analysis

Data of both eyes were averaged and analyzed as a representative value in each patient. The normality of the data distribution was tested by inspecting a histogram. Because corrected logMAR visual acuity at most distances did not follow a normal distribution, nonparametric tests were used for the analyses. Differences in the mean logMAR visual acuity at various distances and continuous variables among the added spherical lens power groups were compared using the Kruskal–Wallis test. Categorical variables were compared among the groups using the chi-square goodness of fit test. When a statistically significant difference was detected among groups, the differences in the logMAR visual acuity between each of the lens added groups and the no lens group were compared using the Wilcoxon signed-rank test with Bonferroni's adjustment for multiple comparisons, and the differences in categorical variables was compared using the chi-square test with the Bonferroni's adjustment. Any differences with a P value less than .05 were considered statistically significant.

Results

The 30 enrolled patients (8 men, 22 women) underwent all of the scheduled examinations. The mean ± standard deviation age of the patients was 67.4 ± 5.1 years, with a range of 53 to 76 years. Patient characteristics on the day of examination are shown in Table 1.

Characteristics of Patients With a Trifocal IOL at the Time of Examination

Table 1:

Characteristics of Patients With a Trifocal IOL at the Time of Examination

Figure 1 shows the curve of mean logMAR visual acuity in each group. In the no lens (emmetropia) group, mean logMAR visual acuity reached 0 at all distances (infinity, 5, 3, 2, 1, 0.7, and 0.5 m) except for near distance at 0.3 m; mean near logMAR visual acuity at 0.3 m was 0.01 ± 0.09, and did not reach 0. In the +1.00 D (−1.00 D myopia) group, mean logMAR visual acuity reached 0 at near and intermediate distances (1, 0.7, 0.5, and 0.3 m). In the +0.50 D (−0.50 D myopia) group, mean logMAR visual acuity of 0 was achieved at far, intermediate, and near distances (5, 3, 2, 1, 0.7, 0.5, and 0.3 m), except for far visual acuity at infinity. In the −0.50 D (+0.50 D hyperopia) group, mean logMAR visual acuity reached 0 at far and intermediate distances (infinity, 5, 3, 1, 0.7, and 0.5 m). In the −1.00 D (+1.00 D hyperopia) group, mean logMAR visual acuity of 0 was achieved only at intermediate distance (1 m).

Mean logarithm of the minimum angle of resolution (logMAR) visual acuity (VA) at far to near distances in eyes to which a spherical lens of (A) +1.00, (B) +0.50, (C) 0.00, (D) −0.50, and (E) −1.00 diopters (D) was added. In the no lens (0D) group simulating emmetropia, mean logMAR VA reached 0 at most distances except for near distance at 0.3 m. Dotted line indicates logMAR VA of 0.

Figure 1.

Mean logarithm of the minimum angle of resolution (logMAR) visual acuity (VA) at far to near distances in eyes to which a spherical lens of (A) +1.00, (B) +0.50, (C) 0.00, (D) −0.50, and (E) −1.00 diopters (D) was added. In the no lens (0D) group simulating emmetropia, mean logMAR VA reached 0 at most distances except for near distance at 0.3 m. Dotted line indicates logMAR VA of 0.

Mean logMAR visual acuity at all distances differed significantly among the +1.00, +0.50, 0.00, −0.50, and −1.00 D groups (P ≤ .0374). Comparisons of the mean logMAR visual acuity at various distances between each of the lens added groups and the no lens group are shown in Figure 2. Mean distance logMAR visual acuity at infinity, 5, and 3 m in the no lens group was −0.07 ± 0.03, −0.07 ± 0.03, and −0.07 ± 0.03, respectively, whereas mean logMAR visual acuity at infinity, 5, and 3 m in the +0.50 D group was 0.04 ± 0.10, −0.02 ± 0.07, and −0.04 ± 0.07, respectively. Mean distance visual acuity at infinity, 5, and 3 m was significantly worse in all lens added groups compared with the no lens group (P < .0001). Mean visual acuity at 2 m was significantly worse in the +1.00, −0.50, and −1.00 D groups than in the no lens group (P ≤ .0002), whereas mean visual acuity was not significantly different between the +0.50 D group and the no lens group. Mean intermediate visual acuity at 1 and 0.7 m did not differ significantly between any of the lens added groups and the no lens group. Mean intermediate visual acuity at 0.5 m was significantly worse in the +1.00, −0.50, and −1.00 D groups than in the no lens group (P ≤ .0118), whereas mean intermediate visual acuity at 0.5 m did not differ significantly between the +0.50 D group and the no lens group. Mean near visual acuity at 0.3 m was significantly better in the +1.00 and +0.50 D groups than in the no lens group (P ≤ .0044), whereas mean near visual acuity was significantly worse in the −0.50 and −1.00 D groups than in the no lens group (P < .0001).

Comparison of mean logarithm of the minimum angle of resolution (logMAR) visual acuity (VA) between eyes to which spherical lens of +1.00, +0.50, −0.50, and −1.00 diopters (D) was added and eyes to which no spherical lens (0D) was added. *P value indicates a significant difference in mean VA between each of the lens added groups and no lens group.

Figure 2.

Comparison of mean logarithm of the minimum angle of resolution (logMAR) visual acuity (VA) between eyes to which spherical lens of +1.00, +0.50, −0.50, and −1.00 diopters (D) was added and eyes to which no spherical lens (0D) was added. *P value indicates a significant difference in mean VA between each of the lens added groups and no lens group.

Discussion

The findings of the current study revealed that a mean logMAR visual acuity of 0 was achieved at most distances except for 0.3 m in the no lens group, simulating emmetropia in eyes with the PanOptix trifocal IOL. Mean logMAR visual acuity of the +1.00 D group simulating −1.00 D myopia reached 0 at near and intermediate distances, whereas that of the +0.50 D group simulating −0.50 D myopia reached 0 extensively from far to near distances. In contrast, mean logMAR visual acuity of the −1.00 D group simulating +1.00 D hyperopia reached 0 only at intermediate distance at 1 m, whereas that of the −0.50 D group simulating +0.50 D hyperopia reached 0 from far to intermediate distances. These findings suggest that the peak curve of mean visual acuity shifts toward near distance with a decrease in the spherical equivalent error toward myopia, and that eyes with slight myopia can obtain a wide region of excellent visual acuity.

Mean near visual acuity was significantly better in the +0.50 and +1.00 D groups than in the no lens group, whereas mean near visual acuity was significantly worse in the −0.50 and −1.00 D groups than in the no lens group. However, mean distance visual acuity was significantly worse in all of the lens added groups than in the no lens group, and mean intermediate visual acuity did not differ significantly between each of the lens added groups and the no lens group. These findings suggest that slight myopia provides a wider region of vision than does slight hyperopia.

Refractive error after cataract surgery decreases uncorrected visual acuity in eyes with multifocal IOLs. Previous studies showed that residual astigmatism impairs uncorrected visual acuity in eyes with multifocal IOLs.12–15 However, it was not clear how the manifest refraction spherical equivalent error worsens uncorrected VA at various distances in eyes with multifocal IOLs. The current study revealed that the mean visual acuity curve shifts toward near distance when the spherical equivalent error is reduced toward myopia, and that slight myopia provides a wider region of excellent uncorrected visual acuity than does slight hyperopia in eyes with a trifocal IOL. Based on these findings, surgeons should target emmetropia to slight myopia when selecting the power of the trifocal IOL.

The current study has several limitations. First, the study was conducted as an experimental study to simulate the manifest refraction spherical equivalent error. Examination of the effect of the actual postoperative spherical equivalent error on uncorrected visual acuity may be more suitable. However, the findings of the current study were clear and likely hold true in the actual clinical situation. Second, the effect of spherical equivalent error in eyes with bifocal IOLs was not examined. The effect of spherical equivalent error may differ between eyes with bifocal and trifocal IOLs. Visual outcomes of trifocal IOLs are better than those of bifocal IOLs,4–6,11,17,18 so we consider that trifocal IOLs will become the more preferred multifocal IOL compared with bifocal IOLs.

A manifest refraction spherical equivalent error of slight myopia significantly improved near visual acuity but worsened distance visual acuity in eyes with a trifocal IOL. In contrast, a spherical equivalent error of slight hyperopia significantly worsened both distance and near VAs. Thus, slight myopia can provide a wider region of useful uncorrected visual acuity than does slight hyperopia. Accordingly, when selecting the power of the trifocal IOL, slight myopia is a better target refraction than slight hyperopia, although emmetropia is the optimum target. Further studies to assess the effect of the manifest refraction spherical equivalent error in eyes with bifocal IOLs are necessary.

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Characteristics of Patients With a Trifocal IOL at the Time of Examination

CharacteristicMean ± SD
Age (y)67.4 ± 5.08
Sex (M/F) (n)8/22
Corneal astigmatism (D)0.49 ± 0.33
MRSE (D)−0.11 ± 0.31
Pupillary diameter (mm)3.43 ± 0.68
Uncorrected logMAR visual acuity0.01 ± 0.09
Corrected logMAR visual acuity−0.10 ± 0.06
Authors

From the Hayashi Eye Hospital, Fukuoka, Japan.

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (KH); data collection (KH, TS, CI, MY); interpretation and analysis of data (KH); writing the manuscript (KH); critical revision of the manuscript (TS, CI, MY); statistical expertise (KH)

Correspondence: Ken Hayashi, MD, Hayashi Eye Hospital, 4-23-35 Hakataekimae, Hakata-Ku, Fukuoka 812-0011, Japan. E-mail: hayashi-ken@hayashi.or.jp

Received: January 16, 2019
Accepted: April 03, 2019

10.3928/1081597X-20190404-01

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