Multifocal versus monofocal intraocular lenses Visual and refractive comparisons Akef EI-Maghraby, M.D., Adnan Marzouky, M.D., Erfan Gazayerli, M.D., Michelle Van Der Karr, Maryclare DeLuca
While recent advances in intraocular lenses (IOLs) have led to safe, low-complication implants that provide relatively good vision for the pseudophakic patient, the current, standard lens still cannot replace the accommodative ability of the human lens. With the introduction of bifocal and multifocal IOLs, it may now be possible to provide the patient with good, unaided near vision as well as unaided distance vision. In October 1990, 3M/Vision Care reported promising results with a new multifocal IOL design based on both refractive and diffractive optics ("Clinical Study Update," 3M Health Care). Twenty to 30 concentric zones are superimposed on the posterior surface of the lens to form a diffractive structure. The difference in height between the zones, the zone steps, is less than the diameter of a red blood cell. The zones are geo-
metrically arranged to fold the majority of the incoming light into just two orders of diffraction, zero and one. The zero order allows the light to enter unimpeded.by the diffraction grating, so the refractive power of the lens determines the focus. The first order of diffraction couples the refractive power with the diffraction, splitting the light to a second focus, effectively creating an add power of +3.5 diopters (D) in the lens (approximately +2.3 D at the spectacle plane) for near vision. Forty-one percent of the light is focused at the first focal point, 41 % at the second, and 18 % at higher orders. Although preliminary results with this lens have been reported,I-3 no randomized, controlled studies have been published. We have completed a single center, randomized, prospective, controlled clinical trial in which patients were randomly as-
From El-Maghraby Eye Hospital, Jeddah, Saudi Arabia (El-Maghraby, Marzouky, Gazayerli), and the Center for Clinical Research, University of Illinois at Chicago, Department of Ophthalmology (Van Der Karr, DeLuca). Partially supported by the Saudi Eye Foundation. Analysis of data was performed by the Center for Clinical Research. Reprint requests to Akef El-Maghraby, P.O. Box 7344, Jeddah 21462, Saudi Arabia.
J CATARACT REFRACT SURG-VOL 18,
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signed to receive a 3M diffractive, multifocal IOL or a conventional, monofocal posterior chamber IOL at the time of cataract surgery. SUBJECTS AND METHODS Patients were considered eligible for this study if they were candidates for cataract extraction by phacoemulsification and the IOL to be implanted was within the range of + 17.00 to +23.00 D for emmetropia. Patients were excluded if they had evidence or history of uveitis, if they had active progressive corneal disease, if they had a history of previous intraocular surgery in the eye to be studied, if they had intraocular pressure above 23 mm Hg or were on glaucoma medications, if they had diabetic retinopathy, macular degeneration, amblyopia, or any other known disease that would decrease postoperative best corrected visual acuity to below 20/40 , if they had cataracts that were not senile in nature, or if they were blind in the contralateral eye . Randomization schedules were generated using Prodas,4 a statistical software package. Patients were randomly assigned to receive a 3M 81SLE multifocal IOL or a 3M ISLE monofocal IOL. For all IOLs used in this study, IOL power for emmetropia was calculated from axial length (measured by Sonomed E-2000 biometer) and keratome try measurements (from the KM-800 Nidek autokeratometer) using the SRK 11 5 formula with a company-recommended A-constant of 116.S for the 81SLE style and 116.0 for the ISLE style. Lens power was calculated for emmetropia for distance. All keratometry measurements were rechecked prior to power determination. Distance power selection was to the nearest O.SO D of lens power available , and proceeded to the stronger plus power if the calculation determined appropriate lens power to be exactly 0.2S D between available lens powers. Near lens add was 3.S D in the IOL plane for the 81SLE multifocal style, which corresponded to approximately 2.3 Q in the spectacle plane. All IOLs used in the study were manufactured by 3M/Vision Care and were identical in design, with the exception of the incorporation of the multi focal optic design in the 81SLE style. We felt that several factors would determine a successful multifocal IOL implantation: First, multifocal IOLs should provide equivalent uncorrected distance acuity and better uncorrected near vision. This factor depends on the quality of the multifocal IOL as well as the accuracy of implant power calculation in the multi focal group relative 148
to the monofocal group. Second, the multifocal IOL should provide better near vision with distance correction in place than the monofocal IOL group. Third, best-corrected distance and near visions should be equal in the multifocal and monofocal groups, distance and near. The proportion of cases with visual acuities ofJ1 to J3 in each group was compared by chi-square analysis and the result used to compare the distribution of postoperative near vision between groups. For distance vision the proportion of cases with visual acuities of 20/40 or better were similarly compared. All patients were operated on under local anesthesia. A Honan intraocular pressure reducer was used to provide an ocular and orbital decompression. A fornix-based conjunctival flap 7 mm long was raised at the limbus. A scleral incision was made 2 mm posterior to and parallel to the superior limbus and a one half thickness scleral flap was then dissected anteriorly into clear cornea and a 3 mm entry was made into the anterior chamber for the phacoemulsification. Sodium hyaluronate (Healon®) was injected into the anterior chamber and a pear-shaped capsulotomy was fashioned using the can-opener technique by a short-angle, sharp cystotome starting at 12 0' clock. The first two incisions were made from the center to the periphery and the rest from the periphery to the center for 360 degrees. Posterior chamber phacoemulsification using a one-handed technique was performed. Following phacoemulsification of the nucleus, the ultrasound tip was withdrawn and replaced by an aspiration tip. The cortex from the 6 o'clock position was removed first, from the lateral areas next, and from the 12 o'clock position last. The wound was enlarged to 6.S mm. Healon was injected to open the capsular bag and the IOL was inserted into the bag and rotated to the 3 to 9 o'clock position. Healon was aspirated and acetylcholine (Miochol®) was injected into the anterior chamber. A 10-0 monofilament nylon suture was used in a running shoelace fashion to close the incision. RESULTS Seventy-seven patients were enrolled in the study (39 in the multifocal group and 38 in the monofocal group). Demographic information on them is presented in Table 1. Mean age was S7.4 years for the multifocal group and S6.3 years for the monofocal group. The majority of contralateral eyes in both groups were phakic with a cataract. Three of the multifocal IOLs were mildly (0 to
J CATARACT REFRACT SURG-VOL 18, MARCH
1992
Table 1. Patient characteristics.
Sex N (%) male N (%) female
Multifocal
Monofocal
16 (41 %) 39
20 (53%) 18 (47%) 38
57.4 (10.2) 45-90
56.3 (5.6) 45-70
5 27 0 7
4 30 2 2
23 (59%)
Total Age Mean (SO) Range Status of the other eye Phakic with clear lens Phakic with cataract Aphakic Pseudophakic
1 mm) to moderately (1 mm to 2 mm) decentered. At two to four months, with the distance correction in place, two of these cases had a near acuity 001 and one had J2, indicating no problem with the bifocal add function despite the decentration. One other multifocal case was well centered but the pupil was drawn up; the four month near acuity with distance correction in place was J3. Of the 77 cases in the study, four multifocal cases were excluded from analysis: two because of preexisting vision impairing maculopathies, one because of severe posterior capsule haze, and one because of high surgically induced astigmatism. N one of these problems was noted in the monofocal group. Follow-up rates for the two groups are given
Table 2. Patient follow-up. Follow-Up Rates Total number 1 day postop N (%) 2-4 weeks N (%) 2-4 months N (%) Average length of follow-up Mean (SO) Median Range
Multifocal 35
Monofocal 38
in Table 2. One multifocal and two monofocal cases were lost to follow-up immediately after surgery. Follow-up rates at two to four weeks were 97% for the multifocal group and 89% for the monofocal group. Eighty percent of multifocal cases and 87% of monofocal cases have been followed for two to four months. At the two to four month visit, the multifocal cases were, on the average, about half a diopter more myopic than the monofocal cases (Table 3). The mean spherical equivalent was -0.36 D for the multifocallens group and +0.31 D for the monofocal lens group. This difference approached statistical significance (P = .06). Although the difference was not statistically significant, a higher percentage of monofocal cases (36%) had visual acuities of 20/20-25 unaided than multifocal cases (21 %) (Table 4). Seventy-nine percent of multifocal cases and 76% of monofocal cases had acuities of 20/40 or better unaided. Two to four week and two to four month postoperative uncorrected near visual acuities are summarized for each group in Table 5 and Figures 1 and 2. At two to four weeks after surgery, a significantly (P = .03) higher proportion of multifocal
Table 3. Refractive results.
36 (95%)
34 (97%)
34 (89%)
28 (80%)
33 (87%)
2.2 mos (1.0) 2.0 mos 2 wks-4 mos
2.5 mos (0.96) 2.5 mos 2 wks-4.25 mos
Monofocal
32 -0.64 (1.22) -3.0 to 2.5
33 +0.39 (1.10) -1.125 to 3.0
2-4 weeks· N Mean (S.D.) Range 2-4 monthst N Mean (S.D.) Range
.
32 27 -0.36 (1.62) +0.31 (1.01) -4.875 to 3.375 -1.875 to 2.5
Keratometric Cylinder
2-4 weeksi 33 (94%)
Multifocal Spherical Equivalent. (D)
".
N
Mean (S.D.) Range 2-4 monthsi N Mean (S.D.) Range
32 ·-1.29 (1.08) -5.0 to 0
33 -1.16 (1.64) -5.0 to 3.0
27 -0.95 (0.76) -2.75 to 0
32 -0.92 (1.06) -3.75 to 2.5
• P < .01 t P = .06
t Nonstatistically significant differences
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1992
149
87%
Table 4. Summary of distance visual acuity. Uncorrected and Best -Corrected Vision 20/20-25
20/30-40
Worse Than 20/40
Uncorrected 2-4 weeks Multifocal
4 (12%)
15 (44%)
15 (44%)
Monofocal
6 (18%)
17 (52%)
10 (30%)
Multifocal
6 (21 %)
16 (58%)
6 (21 %)
Monofocal
12 (36%)
13 (40%)
8 (24%)
2-4 WEEKS (p=O.03)
2-4 months
MULTIFOCAL
MONOFOCAL
Best-Corrected Fig. 1.
2-4 Weeks Multifocal
12 (35%)
17 (50%)
5 (15%)
Monofocal
14 (44%)
14 (44%)
4 (12%)
(EI-Maghraby) Proportion of cases with Jl to J3 uncorrected near vision in the monofocal and multifocal groups at two to four weeks and at two to four months.
2-4 Months Multifocal
19 (70%)
7 (26%)
1 (4%)
Monofocal
25 (78%)
6 (19%)
1 (3%)
No statistically significant differences between groups
cases (60%) had near acuities ofJ1 to J3 than monofocal cases (23%). Forty-five percent of the multifocal cases but only 18 % of monofocal cases had near acuities of J1 or J2. By two to four months, 87% of multifocal cases and 71 % of monofocal cases had near acuities ofJ1 to J3. Figure 2 shows the markedly different distribution of near vision in the multifocal and monofocal groups. Thirty percent of multifocal cases and only 4% of monofocal cases could read the J1 line. Uncorrected near vision with distance correction in place is summarized in Table 6 and Figures 3 and 4. At two to four weeks, 54% of multifocal cases and 28% of monofocal cases had uncorrected near visual acuities of J1 to J2 with distance correction
J1 Fig. 2.
J2
J3
J4-J7
>J7
(EI-Maghraby) Frequency histogram comparing near vision in the multifocal and mono focal groups.
Table 5. Uncorrected near vision; number (percentage) of cases. Postoperative Interval
Jl
J2
J3
J4-7
Multifocal
3 (15%)
6 (30%)
3 (15%)
6 (30%)
2 (10%)
Monofocal
2 (9%)
2 (9%)
1 (5%)
13 (59%)
4 (18%)
Multifocal
7 (30%)
7 (30%)
6 (26%)
2 (9%)
1 (4%)
Monofocal
1 (4%)
8 (33%)
8 (33%)
5 (21 %)
2 (8%)
Worse Than
2-4 Weeks·
2-4 Monthst
* Statistically significant difference between groups (P = .03) based on percent of cases with acuity of Jl - J3. t No statistically significant differences. 150
J CATARACT REFRACT SURG-VOL 18, MARCH 1992
J7
Table 6. Uncorrected near vision with distance correction in place; number (percentage) of cases. Postoperati ve Interval
Worse Than
Jl
J2
J3
J4-7
Multifocal
12 (36%)
6 (18%)
4 (12%)
9 (27%)
2 (6%)
Monofocal
4 (12%)
5 (16%)
6 (19%)
12 (38%)
5 (16%)
Multifocal
13 (48%)
9 (33%)
4 (15%)
0
1 (4%)
Monofocal
3 (10%)
6 (21 %)
9 (31 %)
11 (38%)
0
17
2-4 Weeks·
2-4 Monthst
'" Statistically significant difference between groups (P = .04) based on percent of cases seeing Jl - J2 . t Statistically Significant difference between groups (P < .01) based on percent of cases seeing Jl - J2.
in place (P = .04). By two to four months 81 % of multifocal cases and 31 % of monofocal cases had acuities ofJ1 to J2 (P< .01). Figure 4 demonstrates the distribution of near vision in the monofocal and multifocal groups, with improved outcome in the multifocal group. Distance vision is summarized in Table 4. Ninety-six percent of multifocal cases and 97% of monofocal cases had best-corrected visual acuities of 20/40 or better at the two to four month visit. Seventy percent of multifocal cases and 78% of monofocal cases had acuities of 20/20-25 best corrected. These differences were not significant. DISCUSSION Several IOL designs that incorporate bifocal or multifocal capabilities have recently been introduced. The simplest is the IOLAB two-zone refractive lens with an add power in the central portion of the lens dedicated to near vision. The Pharmacia bifocal IOL is also a two-zone refractive lens, but the near portion is arranged in a "donut
hole" configuration with the distance portion in the center and in the periphery. The Nordan multifocal lens uses an aspheric design to create an infinite number of focal points. 6 Theoretically, all these lens designs could compromise vision if the lens were decentered. 6 - 8 The 3M lens, however, uses all portions of the lens to create both focal points so decentration should not be a problem. In the three decentrations and the one updrawn pupil in the multifocal IOL group, near acuity did not appear to be compromised. Although our results are preliminary, the data from this study support the premise that the 3M multifocal IOL provides better near vision, both uncorrected and with distance correction in place, than a conventional single focus IOL. Problems such as astigmatism and occasional inaccuracies in power calculations may prevent the multifocal IOL from totally eliminating the need for distance glasses in all patients. The current focus on astigmatism control at the time of cataract surgery, by
48% MULl
2-4 MONTHS
81%
(P
While recent advances in intraocular lenses (IOLs) have led to safe, low-complication implants that provide relatively good vision for the pseudophakic patient, the current, standard lens still cannot replace the accommodative ability of the human lens. With the introduction of bifocal and multifocal IOLs, it may now be possible to provide the patient with good, unaided near vision as well as unaided distance vision. In October 1990, 3M/Vision Care reported promising results with a new multifocal IOL design based on both refractive and diffractive optics ("Clinical Study Update," 3M Health Care). Twenty to 30 concentric zones are superimposed on the posterior surface of the lens to form a diffractive structure. The difference in height between the zones, the zone steps, is less than the diameter of a red blood cell. The zones are geo-
metrically arranged to fold the majority of the incoming light into just two orders of diffraction, zero and one. The zero order allows the light to enter unimpeded.by the diffraction grating, so the refractive power of the lens determines the focus. The first order of diffraction couples the refractive power with the diffraction, splitting the light to a second focus, effectively creating an add power of +3.5 diopters (D) in the lens (approximately +2.3 D at the spectacle plane) for near vision. Forty-one percent of the light is focused at the first focal point, 41 % at the second, and 18 % at higher orders. Although preliminary results with this lens have been reported,I-3 no randomized, controlled studies have been published. We have completed a single center, randomized, prospective, controlled clinical trial in which patients were randomly as-
From El-Maghraby Eye Hospital, Jeddah, Saudi Arabia (El-Maghraby, Marzouky, Gazayerli), and the Center for Clinical Research, University of Illinois at Chicago, Department of Ophthalmology (Van Der Karr, DeLuca). Partially supported by the Saudi Eye Foundation. Analysis of data was performed by the Center for Clinical Research. Reprint requests to Akef El-Maghraby, P.O. Box 7344, Jeddah 21462, Saudi Arabia.
J CATARACT REFRACT SURG-VOL 18,
MARCH 1992
147
signed to receive a 3M diffractive, multifocal IOL or a conventional, monofocal posterior chamber IOL at the time of cataract surgery. SUBJECTS AND METHODS Patients were considered eligible for this study if they were candidates for cataract extraction by phacoemulsification and the IOL to be implanted was within the range of + 17.00 to +23.00 D for emmetropia. Patients were excluded if they had evidence or history of uveitis, if they had active progressive corneal disease, if they had a history of previous intraocular surgery in the eye to be studied, if they had intraocular pressure above 23 mm Hg or were on glaucoma medications, if they had diabetic retinopathy, macular degeneration, amblyopia, or any other known disease that would decrease postoperative best corrected visual acuity to below 20/40 , if they had cataracts that were not senile in nature, or if they were blind in the contralateral eye . Randomization schedules were generated using Prodas,4 a statistical software package. Patients were randomly assigned to receive a 3M 81SLE multifocal IOL or a 3M ISLE monofocal IOL. For all IOLs used in this study, IOL power for emmetropia was calculated from axial length (measured by Sonomed E-2000 biometer) and keratome try measurements (from the KM-800 Nidek autokeratometer) using the SRK 11 5 formula with a company-recommended A-constant of 116.S for the 81SLE style and 116.0 for the ISLE style. Lens power was calculated for emmetropia for distance. All keratometry measurements were rechecked prior to power determination. Distance power selection was to the nearest O.SO D of lens power available , and proceeded to the stronger plus power if the calculation determined appropriate lens power to be exactly 0.2S D between available lens powers. Near lens add was 3.S D in the IOL plane for the 81SLE multifocal style, which corresponded to approximately 2.3 Q in the spectacle plane. All IOLs used in the study were manufactured by 3M/Vision Care and were identical in design, with the exception of the incorporation of the multi focal optic design in the 81SLE style. We felt that several factors would determine a successful multifocal IOL implantation: First, multifocal IOLs should provide equivalent uncorrected distance acuity and better uncorrected near vision. This factor depends on the quality of the multifocal IOL as well as the accuracy of implant power calculation in the multi focal group relative 148
to the monofocal group. Second, the multifocal IOL should provide better near vision with distance correction in place than the monofocal IOL group. Third, best-corrected distance and near visions should be equal in the multifocal and monofocal groups, distance and near. The proportion of cases with visual acuities ofJ1 to J3 in each group was compared by chi-square analysis and the result used to compare the distribution of postoperative near vision between groups. For distance vision the proportion of cases with visual acuities of 20/40 or better were similarly compared. All patients were operated on under local anesthesia. A Honan intraocular pressure reducer was used to provide an ocular and orbital decompression. A fornix-based conjunctival flap 7 mm long was raised at the limbus. A scleral incision was made 2 mm posterior to and parallel to the superior limbus and a one half thickness scleral flap was then dissected anteriorly into clear cornea and a 3 mm entry was made into the anterior chamber for the phacoemulsification. Sodium hyaluronate (Healon®) was injected into the anterior chamber and a pear-shaped capsulotomy was fashioned using the can-opener technique by a short-angle, sharp cystotome starting at 12 0' clock. The first two incisions were made from the center to the periphery and the rest from the periphery to the center for 360 degrees. Posterior chamber phacoemulsification using a one-handed technique was performed. Following phacoemulsification of the nucleus, the ultrasound tip was withdrawn and replaced by an aspiration tip. The cortex from the 6 o'clock position was removed first, from the lateral areas next, and from the 12 o'clock position last. The wound was enlarged to 6.S mm. Healon was injected to open the capsular bag and the IOL was inserted into the bag and rotated to the 3 to 9 o'clock position. Healon was aspirated and acetylcholine (Miochol®) was injected into the anterior chamber. A 10-0 monofilament nylon suture was used in a running shoelace fashion to close the incision. RESULTS Seventy-seven patients were enrolled in the study (39 in the multifocal group and 38 in the monofocal group). Demographic information on them is presented in Table 1. Mean age was S7.4 years for the multifocal group and S6.3 years for the monofocal group. The majority of contralateral eyes in both groups were phakic with a cataract. Three of the multifocal IOLs were mildly (0 to
J CATARACT REFRACT SURG-VOL 18, MARCH
1992
Table 1. Patient characteristics.
Sex N (%) male N (%) female
Multifocal
Monofocal
16 (41 %) 39
20 (53%) 18 (47%) 38
57.4 (10.2) 45-90
56.3 (5.6) 45-70
5 27 0 7
4 30 2 2
23 (59%)
Total Age Mean (SO) Range Status of the other eye Phakic with clear lens Phakic with cataract Aphakic Pseudophakic
1 mm) to moderately (1 mm to 2 mm) decentered. At two to four months, with the distance correction in place, two of these cases had a near acuity 001 and one had J2, indicating no problem with the bifocal add function despite the decentration. One other multifocal case was well centered but the pupil was drawn up; the four month near acuity with distance correction in place was J3. Of the 77 cases in the study, four multifocal cases were excluded from analysis: two because of preexisting vision impairing maculopathies, one because of severe posterior capsule haze, and one because of high surgically induced astigmatism. N one of these problems was noted in the monofocal group. Follow-up rates for the two groups are given
Table 2. Patient follow-up. Follow-Up Rates Total number 1 day postop N (%) 2-4 weeks N (%) 2-4 months N (%) Average length of follow-up Mean (SO) Median Range
Multifocal 35
Monofocal 38
in Table 2. One multifocal and two monofocal cases were lost to follow-up immediately after surgery. Follow-up rates at two to four weeks were 97% for the multifocal group and 89% for the monofocal group. Eighty percent of multifocal cases and 87% of monofocal cases have been followed for two to four months. At the two to four month visit, the multifocal cases were, on the average, about half a diopter more myopic than the monofocal cases (Table 3). The mean spherical equivalent was -0.36 D for the multifocallens group and +0.31 D for the monofocal lens group. This difference approached statistical significance (P = .06). Although the difference was not statistically significant, a higher percentage of monofocal cases (36%) had visual acuities of 20/20-25 unaided than multifocal cases (21 %) (Table 4). Seventy-nine percent of multifocal cases and 76% of monofocal cases had acuities of 20/40 or better unaided. Two to four week and two to four month postoperative uncorrected near visual acuities are summarized for each group in Table 5 and Figures 1 and 2. At two to four weeks after surgery, a significantly (P = .03) higher proportion of multifocal
Table 3. Refractive results.
36 (95%)
34 (97%)
34 (89%)
28 (80%)
33 (87%)
2.2 mos (1.0) 2.0 mos 2 wks-4 mos
2.5 mos (0.96) 2.5 mos 2 wks-4.25 mos
Monofocal
32 -0.64 (1.22) -3.0 to 2.5
33 +0.39 (1.10) -1.125 to 3.0
2-4 weeks· N Mean (S.D.) Range 2-4 monthst N Mean (S.D.) Range
.
32 27 -0.36 (1.62) +0.31 (1.01) -4.875 to 3.375 -1.875 to 2.5
Keratometric Cylinder
2-4 weeksi 33 (94%)
Multifocal Spherical Equivalent. (D)
".
N
Mean (S.D.) Range 2-4 monthsi N Mean (S.D.) Range
32 ·-1.29 (1.08) -5.0 to 0
33 -1.16 (1.64) -5.0 to 3.0
27 -0.95 (0.76) -2.75 to 0
32 -0.92 (1.06) -3.75 to 2.5
• P < .01 t P = .06
t Nonstatistically significant differences
J CATARACf REFRACf SURG-VOL 18, MARCH
1992
149
87%
Table 4. Summary of distance visual acuity. Uncorrected and Best -Corrected Vision 20/20-25
20/30-40
Worse Than 20/40
Uncorrected 2-4 weeks Multifocal
4 (12%)
15 (44%)
15 (44%)
Monofocal
6 (18%)
17 (52%)
10 (30%)
Multifocal
6 (21 %)
16 (58%)
6 (21 %)
Monofocal
12 (36%)
13 (40%)
8 (24%)
2-4 WEEKS (p=O.03)
2-4 months
MULTIFOCAL
MONOFOCAL
Best-Corrected Fig. 1.
2-4 Weeks Multifocal
12 (35%)
17 (50%)
5 (15%)
Monofocal
14 (44%)
14 (44%)
4 (12%)
(EI-Maghraby) Proportion of cases with Jl to J3 uncorrected near vision in the monofocal and multifocal groups at two to four weeks and at two to four months.
2-4 Months Multifocal
19 (70%)
7 (26%)
1 (4%)
Monofocal
25 (78%)
6 (19%)
1 (3%)
No statistically significant differences between groups
cases (60%) had near acuities ofJ1 to J3 than monofocal cases (23%). Forty-five percent of the multifocal cases but only 18 % of monofocal cases had near acuities of J1 or J2. By two to four months, 87% of multifocal cases and 71 % of monofocal cases had near acuities ofJ1 to J3. Figure 2 shows the markedly different distribution of near vision in the multifocal and monofocal groups. Thirty percent of multifocal cases and only 4% of monofocal cases could read the J1 line. Uncorrected near vision with distance correction in place is summarized in Table 6 and Figures 3 and 4. At two to four weeks, 54% of multifocal cases and 28% of monofocal cases had uncorrected near visual acuities of J1 to J2 with distance correction
J1 Fig. 2.
J2
J3
J4-J7
>J7
(EI-Maghraby) Frequency histogram comparing near vision in the multifocal and mono focal groups.
Table 5. Uncorrected near vision; number (percentage) of cases. Postoperative Interval
Jl
J2
J3
J4-7
Multifocal
3 (15%)
6 (30%)
3 (15%)
6 (30%)
2 (10%)
Monofocal
2 (9%)
2 (9%)
1 (5%)
13 (59%)
4 (18%)
Multifocal
7 (30%)
7 (30%)
6 (26%)
2 (9%)
1 (4%)
Monofocal
1 (4%)
8 (33%)
8 (33%)
5 (21 %)
2 (8%)
Worse Than
2-4 Weeks·
2-4 Monthst
* Statistically significant difference between groups (P = .03) based on percent of cases with acuity of Jl - J3. t No statistically significant differences. 150
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J7
Table 6. Uncorrected near vision with distance correction in place; number (percentage) of cases. Postoperati ve Interval
Worse Than
Jl
J2
J3
J4-7
Multifocal
12 (36%)
6 (18%)
4 (12%)
9 (27%)
2 (6%)
Monofocal
4 (12%)
5 (16%)
6 (19%)
12 (38%)
5 (16%)
Multifocal
13 (48%)
9 (33%)
4 (15%)
0
1 (4%)
Monofocal
3 (10%)
6 (21 %)
9 (31 %)
11 (38%)
0
17
2-4 Weeks·
2-4 Monthst
'" Statistically significant difference between groups (P = .04) based on percent of cases seeing Jl - J2 . t Statistically Significant difference between groups (P < .01) based on percent of cases seeing Jl - J2.
in place (P = .04). By two to four months 81 % of multifocal cases and 31 % of monofocal cases had acuities ofJ1 to J2 (P< .01). Figure 4 demonstrates the distribution of near vision in the monofocal and multifocal groups, with improved outcome in the multifocal group. Distance vision is summarized in Table 4. Ninety-six percent of multifocal cases and 97% of monofocal cases had best-corrected visual acuities of 20/40 or better at the two to four month visit. Seventy percent of multifocal cases and 78% of monofocal cases had acuities of 20/20-25 best corrected. These differences were not significant. DISCUSSION Several IOL designs that incorporate bifocal or multifocal capabilities have recently been introduced. The simplest is the IOLAB two-zone refractive lens with an add power in the central portion of the lens dedicated to near vision. The Pharmacia bifocal IOL is also a two-zone refractive lens, but the near portion is arranged in a "donut
hole" configuration with the distance portion in the center and in the periphery. The Nordan multifocal lens uses an aspheric design to create an infinite number of focal points. 6 Theoretically, all these lens designs could compromise vision if the lens were decentered. 6 - 8 The 3M lens, however, uses all portions of the lens to create both focal points so decentration should not be a problem. In the three decentrations and the one updrawn pupil in the multifocal IOL group, near acuity did not appear to be compromised. Although our results are preliminary, the data from this study support the premise that the 3M multifocal IOL provides better near vision, both uncorrected and with distance correction in place, than a conventional single focus IOL. Problems such as astigmatism and occasional inaccuracies in power calculations may prevent the multifocal IOL from totally eliminating the need for distance glasses in all patients. The current focus on astigmatism control at the time of cataract surgery, by
48% MULl
2-4 MONTHS
81%
(P
