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3M diffractive multifocal intraocular lens: Eight year follow-up

Slagsvold, Jon Erik MDa,*

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Journal of Cataract & Refractive Surgery: March 2000 - Volume 26 - Issue 3 - p 402-407
doi: 10.1016/S0886-3350(99)00437-X
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Abstract

In general, the primary objective of intraocular lens (IOL) implantation has been to correct aphakic vision by achieving the best distance acuity without the need for spectacle correction. However, an ideal prosthetic lens should replicate the original function of the lens at both near and distance. Trying to achieve this, 3M de-signed a multifocal IOL using the diffractive optical principle. The goal was to provide patients with “functional” distance and near acuity of 0.5 or better and a Jaeger acuity of J3 or better without spectacle correction. Many studies have shown the effectiveness of the diffractive principle.1–4 However, laboratory5–7 and clinical studies1,6,8–11 have found reduced image visual quality and contrast sensitivity and more glare with this type of IOL.

Little long-term information about the diffractive IOL is available. This study was initiated to evaluate the visual performance of the 3M diffractive lens 8 years after its implantation in human eyes.

Patients and Methods

Since 1988, 139 eyes of 112 patients were implanted with the 815 LE (3M) diffractive IOL. Thirty-five patients were lost to follow-up because of death and 5 patients because of senility or an inability to travel the long distance to the clinic. Ninety-seven eyes of 72 patients were studied. Mean age was 78.1 years ± 6.8 (SD) and mean follow-up, 7.9 ± 1.3 years.

The 3M diffractive lens is a 3-piece convex/concave poly(methyl methacrylate) (PMMA) posterior chamber IOL with a 6.0 mm optic. A concentric diffractive microstructure is superimposed on the lens' posterior surface. Forty-one percent of incident light is allocated to the distance focus, 41% to near focus, and 18% to higher orders of diffraction.

The IOLs were implanted in the bag (93 of 97 eyes) through a limbus parallel incision after capsulorhexis (86 of 97 eyes) and phacoemulsification (93 of 97 eyes). Lenses were implanted in both eyes in 34.7% of the patients. Most surgeries were outpatient and done using local anesthesia. They were all performed by the same surgeon (J.E.S.).

No patient had eye pathology (e.g., macular degeneration) other than cataract. Patients with postoperative posterior capsule opacification (PCO) limiting visual or contrast sensitivity had an early neodymium:YAG (Nd:YAG) laser capsulotomy. Distance (Snellen) and near (Jaeger) visual acuities were measured with and without correction. Vector decomposition analysis12 was used to assess astigmatic change. Senile patients unable to cooperate were excluded.

Contrast sensitivity (VisTech) was tested for distance focus with best correction for viewing at a distance of 3 meters. Patients not achieving a visual acuity of 1.0 or better were not studied with the VisTech test as macular degeneration or other causes of low vision reduce contrast sensitivity. Patients with a visual acuity of 1.0 or better were tested at 5 spatial frequencies: 1.5 to 18 cycles/degree (cpd). The VisTech system has a normal reference range which includes 90% of a normal population between the ages of 10 and 70 years.

Patients were asked about spectacle use. In addition, IOL centration was assessed using the location of the IOL rings relative to the pupil.

Results

Distance Visual Acuity

An uncorrected Snellen visual acuity of 0.5 or better was achieved in 83.9% of eyes and in 89.6% of best-case eyes (Table 1). With correction, distance visual acuity was 0.5 or better in 96.7% of eyes and in all best-case eyes (Table 2). A best corrected visual acuity of 1.0 or better was achieved in 80.4% of eyes and in 98.7% of best cases. Visual acuity was not obtainable in 3 patients (4 eyes) because of patient senility.

Table 1
Table 1:
Uncorrected distance acuity results.
Table 2
Table 2:
Corrected distance acuity results.

Refraction

Emmetropia occurred in 38.1% of the eyes; 58.8% were within ±0.25 diopter (D) and 91.8% were within ±1.00 D. Table 3 shows the results of postoperative astigmatism. Mean induced astigmatism was 0.827 ± 0.61 D. Mean against-the-rule (ATR) induced cylinder was 0.110 ± 0.20 D and mean with-the-rule cylinder, 0.717 ± 0.61 D. In 60.0% of eyes, astigmatism after 8 years was 0.50 D or less.

Table 3
Table 3:
Postoperative astigmatism (N = 97 eyes).

Near Acuity

Near visual acuity was tested at 25 to 40 cm. Uncorrected, 66.7% of all eyes and 73.8% of best cases had a near acuity of J3 (Table 4). With distance correction, 83.4% of all eyes and 92.1% of best cases had an acuity of J3 or better (Table 5). With distance correction and a +2.50 D reading add, near acuity was J3 or better in 94.5% of all eyes and in all best cases (Table 6). Jaeger results were not obtainable in 5 patients (7 eyes) because of senility.

Table 4
Table 4:
Uncorrected near acuity results.
Table 5
Table 5:
Near acuity results with distance correction.
Table 6
Table 6:
Near acuity with final correction (+2.50 D to distance correction).

Contrast Sensitivity

Contrast sensitivity was within the normal range at frequencies of 1.5 to 3 cpd; however, it was reduced at 6 to 18 cpd (Figure 1). Whereas 94.4% of eyes had a normal result according to the VisTech at 3 cpd, 50.7% and 63.4% were within the reference range at 6 and 18 cpd, respectively.

Figure 1.
Figure 1.:
(Slagsvold) Mean contrast sensitivity in patients with a visual acuity (VA) of 1.0 or better. The solid lines represent the upper and lower limits of a normal population (10 to 70 years old).

Spectacle Use

Fifty-four percent of the patients reported using no spectacles (Table 7). This number increased to 68.0% among those with diffractive IOLs in both eyes. Of patients who never wore spectacles, 79.5% had an uncorrected visual acuity (UCVA) of 0.8 or better. Among patients wearing spectacles for distance tasks only, some were postoperatively myopic; others blamed their “second” eye. The “second” eye was the main reason patients needed spectacles for near only, distance and near, and all the time.

Table 7
Table 7:
Multifocal efficiency measured by spectacle use (N = 72 patients).

Intraocular Lens Centration

The IOLs were centered in 85 of 97 eyes. In 11 cases with insignificant decentration, 6 had no or an incomplete capsulorhexis. One patient gradually had a sunset position of the lens after a can-opener capsulorhexis technique was used. Iris fixation of both haptics was performed 2 years postoperatively.

Capsulotomies

An Nd:YAG capsulotomy for PCO was done in 54 eyes (55.7%). Visual acuity was 0.5 or better in 60.0% of these eyes. Seven capsulotomies (9.2%) were done within 12 months. Mean time between IOL implantation and capsulotomy was 34.0 ± 23.2 months. One patient had a retinal detachment 6 months after Nd:YAG laser treatment, with a visual acuity of 1.0 postoperatively.

Discussion

In this retrospective study, all patients with the 3M diffractive IOL were invited to receive a follow-up examination. Except for those who were deceased (31.0%), the patients willingly accepted. Since their initial surgeries, no serious events had occurred and no lenses had been explanted.

Both uncorrected and corrected distance acuities were good and comparable with those in other studies of this lens2,4,13,14 and of other diffractive15,16 and refractive multifocal lenses.16–19 For near vision, eyes achieved acuity measurements similar to those in other reports of the 3M lens2,4,14 and of another diffractive IOL.15,16 However, the results were superior to those in eyes with refractive IOLs.17–20

With distance correction, most patients had an acuity of J3 or better; with a 2.50 D reading add, all the patients achieved J3. With the Pharmacia Ophthalmics diffractive lens, there was no difference in near vision when 2.75 D was added to the distance correction,15 indicating better quality of the bifocal near image. This is probably because more light is distributed to near with this lens.21 Another explanation is that the Pharmacia IOL has a higher power add (4.0 D) than the 3M lens (3.5 D). It is a problem for designers and a principal drawback of diffractive and refractive lenses that as depths of focus increases, contrast sensitivity decreases. There is a loss of contrast with multifocal lenses,3,4,10,11,14,17,20–23 and the reduction does not seem to differ between diffractive and refractive lenses.16 In general, contrast sensitivity is 1 log unit lower with multifocal than with monofocal IOLs.24

The most significant loss of contrast sensitivity with the diffractive IOL is found under twilight conditions.10 In our study, patients were not specifically asked about visual problems under subnormal light conditions (e.g., driving at night). On the other hand, they did not report visual disturbances during the follow-up examination. These aspects with the lens were considered preoperatively during patient selection. The results of contrast sensitivity testing with the 3M IOL were fairly good considering that the study's patients had a mean age of 78 years and that the normal reference range (10 to 70 years old) probably did not pertain to them. The reduced contrast with this IOL did not always seem to affect the patients on a day-to-day basis.

As not needing to wear spectacles is a major concern for many patients, postoperative UCVA is important. In our study, 79.5% of patients not wearing glasses had a UCVA of 0.8 or better in contrast to 69.9% in the total group. With the diffractive lens in both eyes, 2 of 3 patients never wore glasses, a finding similar to13 or better than that in most reports.18,24,25

Patients with refractive multifocal IOLs tend to use spectacles more often. Possibly, the refractive design stresses distance and intermediate vision to the detriment of near vision.16 For near tasks, 2 of 3 patients never wore glasses, in contrast to 52% found by Percival25 and 46% with a Pharmacia diffractive IOL.15 A few patients were dissatisfied because they were disturbed by their second eye or had to wear spectacles because postoperative astigmatism resulted in relatively poor UCVA. When patients could function without spectacles, many did not seem to find halos or glare bothersome.

Another factor in good functional results is postoperative emmetropia. We targeted for emmetropia, and our results are comparable to those of other studies.4,13,26,27 With time, many eyes had a shift toward ATR, probably resulting from weakness of the 12 o'clock incision area caused by the 6.0 mm optic PMMA IOL. New folding lenses and different incision sites depending on preoperative corneal configuration will reduce the problem of postoperative astigmatism.

Good centration is important to the success of all IOL implantations, although the function of the 3M diffractive lens is less sensitive to decentration than most refractive multifocal IOLs. With its ring structure, the degree of decentration of the 3M lens was easy to assess. In nearly all cases, the IOLs were well centered. An envelope capsulotomy is known to decentrate the lens upward, as was the case in a few eyes in this study in which this technique was used.

Posterior capsule opacification is the most common complication of modern cataract surgery, with an incidence of up to 50% by 2 years postoperatively.28 It has been speculated that as multifocal IOLs distribute light to 2 foci, even minor PCO might trouble patients. With the 3M posterior concave IOL, the Elschnig pearl type of PCO occurred more frequently than the fibrotic type. The Elschnig type requires an Nd:YAG capsulotomy be performed earlier than with the fibrotic type. There was no difficulty focusing on the capsule; however, laser pits on the optic of this injection-molded lens were somewhat more distinct and irregular than those on other types of PMMA IOLs. Newer lens materials and designs (e.g., acrylic polymers) may decrease the need for laser capsulotomy.29 Data from a U.S. Food and Drug Administration study showed the occurrence of Nd:YAG capsulotomy in eyes with the 3M diffractive lens to be 10% at 4 to 6 months.14 Half the eyes in the current study were treated with a laser during the 8 year follow-up. At the time of capsulotomy, 2 of 3 eyes had a usable acuity of 0.5 or better. One may conclude that patients with the 3M lens do not need earlier capsulotomies than patients receiving monofocal convex/concave PMMA lenses.

The results of this study proved the 3M diffractive lens to be safe and effective, which may be the result of careful patient selection. As when considering implanting more modern multifocal lenses, the surgeon must spend time with patients preoperatively and postoperatively to determine whether they are good candidates for these lenses. Motivated patients and those with a profession or lifestyle suitable for this lens were encouraged. Good candidates were those with bilateral implantation. Worried, impatient, and demanding patients were avoided, and no occupational drivers were included as the phenomenon of disturbing glare has been reported with these types of lenses.

New diffractive and refractive multifocal lenses have been developed. They are promising; however, they will not replace the monofocal IOL. As in this study, they will provide a valuable alternative in selected cases.

References

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