Contrast sensitivity and depth of focus with aspheric multifocal versus conventional monofocal intraocular lens

Kamlesh, MS; Sub hash Dadeya, * MD; Sushmita Kaushik, t MS

ABSTRACT • RESUME

Background: Laboratoires Domilens, Lyon, France, has introduced a new aspheric multifocal intraocular lens (IOL), the Progress 3. The central portion, measuring 4.7 mm in diameter, has an anterior surface of progressively increasing power, such that there is a central add of +5.00 dioptres. We compared contrast sensitivity and depth of focus in patients who received the Progress 3 and in those who received a conventional monofocal IOL.

Methods: Prospective study. Forty patients with age-related cataract were randomly divided into two groups: 20 patients received the Progress 3 aspheric multifocal IOL, and 20 patients received a conventional monofocal IOL of similar design. Contrast sensitivity was measured with the Pelli-Robson letter-based chart. Depth of focus was determined by dialling a series of overcorrections over the patient's manifest refraction until the patient read 6/12 clearly. The depth of focus was defined as the range over which 6/12 or better acuity was achieved. Quality of vision was evaluated by patient questionnaire.

Results: Mean contrast sensitivity was significantly lower in the patients with a multi­focal IOL than in those with a monofocal IOL ( 1.38 vs. 1.56 log units) (p < 0.00 I). The mean depth of focus values for the two groups were 3.10 D and 1.65 D respec­tively (p < 0.00 I). The prevalence of subjective problems was similar in the two groups.

Interpretation: In our opinion, aspheric multifocal IOLs should be reserved for patients who are willing to trade increased depth offocus for reduced contrast sensitivity postoperatively.

Contexte: Le Laboratoire Domilens, de Lyon (France), a presente une nouvelle lentille intraoculaire (LIO) multifocale aspherique, Ia Progress 3. La partie centrale de Ia lentille, qui a 4,7 mm de diametre, a une surface anterieure dont Ia puissance augmente progressivement, au point d'ajouter +5,00 dioptries au centre. Nous avons compare Ia sensibilite au contraste et Ia profondeur du foyer chez des patients qui avaient rec;:u Ia Progress 3 avec celles de ceux qui avaient rec;:u des lentilles monofocales conventionnelles.

From the Guru Nanak Eye Centre, Maulana Azad Medical College, New Delhi, India

Originally received June 6, 2000 Accepted for publication Mar. 2, 2001

*Currently with Safdarjang Hospital, New Delhi, India tCurrently with the Post-Graduate Institute, Chandigarh, India

Reprint requests to: Dr. Subhash Dadeya, 197, Rouse Ave., New Delhi - 110 002, India; fax 91-11-6161013; sdadeya@freedialin.com

Presented at the 57th All India Ophthalmological Society Meeting, held in New Delhi, India, Feb. 9-11, 1997

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Methodes : Etude prospective. Quarante patients ayant une cataracte associee a l'age ont ete repartis au hasard entre deux groupes : 20 ont re~u Ia LIO multifo­cale aspherique, Progress 3, et 20, Ia lentille monofocale conventionnelle de con­ception similaire. On a mesure Ia sensibilite au contraste a l'aide de Ia charte alphabetique Pelli-Robson. On a determine Ia profondeur du foyer en appliquant une serie de surcorrections sur Ia refraction manifeste du patient et en mesurant l'etendue sur laquelle celui-ci avait une acuite de lecture de 6/12 ou meilleure. La qualite de Ia vue a ete evaluee a partir du questionnaire remis aux patients.

Resultats : La sensibilite moyenne au contraste etait de beaucoup inferieure chez les patients qui avaient une LIO multifocale a celle des patients qui avaient une LIO monofocale (I ,38 c. I ,56 unite de registre) (p < 0,00 I). La valeur moyenne de Ia profondeur du foyer etait de 3, I 0 D et de I ,65 D respectivement (p < 0,00 I). La prevalence des problemes subjectifs etait semblable dans les deux groupes.

Interpretation : A notre avis, les LIO multifocales aspheriques devraient etre reservees aux patients qui preferent avoir une plus grande pro­fondeur de foyer au prix d'une sensibilite au contraste reduite apres I' operation.

The introduction of multifocal intraocular lenses (IOLs) has prompted ophthalmologists to reexam­

ine their goals of pseudophakic correction. A multi­focal IOL not only restores a patient's distance and near vision but also provides an increase in the depth of focus, in contrast to a conventional monofocal implant. 1- 3

However, several authors have reported reduced contrast sensitivity in patients with bifocal and multi­focal 10Ls.4--7 This has been attributed principally to simultaneous imaging of far and near objects by mul­tifocal IOLs, the brain selecting the image of regard and suppressing other images. However, the "out-of­focus" image may not be ignored completely, thus diminishing the contrast and resolution of the "focused" image.

Laboratoires Domilens, Lyon, France, has intro­duced a new aspheric multifocal IOL, the Progress 3 (Fig. 1). This is an all-polymethylmethacrylate single­piece biconvex lens with an optic diameter of 6.5 mm and an overall length of 12.5 mm. The peripheral zone ensures far vision. The central portion, measuring 4.7 mm in diameter, has an anterior surface of pro­gressively increasing power, such that there is a cen­tral add of +5.00 dioptres compared to the periphery in aqueous (corresponding to spectacle add of +3.00 D at 33 em). This progressive zone provides intermediate vision. There are no geometric discontinuities, such as zones or steps.

• 10

12.5mm

12.5mm

We performed a study to compare contrast sensitiv­ity and depth of focus associated with the Progress 3 and a conventional monofocal IOL.

Fig. !-Progress 3 multifocal intraocular lens (top) and Flex 65 monofocal intraocular lens (bottom).

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METHODS

In this prospective study 40 patients with age­related cataract were randomly divided into two groups. Twenty patients received the Progress 3 aspheric multifocal IOL (Laboratoires Dornilens), and 20 patients received a conventional monofocal IOL of similar design (Flex 65, Laboratoires Domilens) (Fig. 1). Patients with a known disease likely to interfere with the postoperative visual outcome were excluded, as were those with preoperative astigmatism greater than 1.50 D or axial length beyond that requiring an estimated IOL power of 18.00 D to 24.00 D for emmetropia (calculated with the Sanders-Retzlaff­Kraff II regression formula) and those who had previ­ously had eye surgery.

We obtained informed consent from each patient after explaining the nature of the surgery, the IOL to be implanted, the risks and complications, and the expected visual outcome.

All patients underwent extracapsular cataract extraction with "in-the-bag" IOL implantation. The envelope technique of capsulotomy was used in all cases. The patients were followed regularly at 1 week, 3 weeks, 6 weeks and 12 weeks postoperatively and every 3 months thereafter.

Contrast sensitivity and depth of focus were record­ed 3 months after surgery. We measured contrast sen­sitivity using the Pelli-Robson letter-based contrast

Aspheric multifocal /OL-Karnlesh et al

sensitivity chart. 8 The chart measures contrast sensi­tivity using large letters of constant size and decreas­ing contrast. The letters are organized into groups of three, with two triplets per line. The contrast decreas­es from left to right, top to bottom, with all three let­ters in each triplet having the same contrast. The chart was hung on a wall with a white background. The cen­tre of the chart was placed about 1.5 m from the ground to be approximately level with the patient's eyes. Luminance was adjusted to 90 cdlm2 with the use of two frosted 100-W bulbs mounted on stand reflectors. The stands were placed 1.2 m from the chart, ensuring no glare to the patient. When not in use, the chart was kept covered to avoid accumulation of dirt. Wearing the best distance correction and stand­ing 1 m from the chart, the patient read the chart from left to right, top to bottom, and was asked to guess when he or she thought the letters were invisible. The test was concluded when the patient guessed incor­rectly two of the three letters of the triplet concerned.

We measured depth of focus by dialling a series of overcorrections from -5.00 D to +5.00 D, in 0.50-D steps, over the patient's manifest refraction until the patient read 6/12 clearly. Snellen acuities were record­ed at every step. The depth of focus (in dioptres) was defined as the range over which 6/12 or better acuity was achieved.

Quality of vision was evaluated by patient ques­tionnaire.

Table 1-Mean age, best corrected visual acuity, near addition, refrac­tion and pupil size for patients with age-related cataract who received an aspheric multifocal intraocular lens (IOL) and for those who received a conventional monofocal IOL

Group

Multifocal IOL Monofocal IOL Characteristic (n = 20) (n = 20) p value*

Mean age, yr 55.7 53.5 NS % with best corrected

distance visual acuity > 6/9 97.5 75.0 NS No. (and %) with distance-corrected near vision ::0: N9 18 (90.0) 2 (10.0) < 0.001

Mean spherical correction required for best distance correction -1.4 D -1.3 D NS

Average near addition required for near vision N6 +0.80 D +2.64 D < 0.001

Mean pupil size, mm 3.2 3.4 NS

*NS = not significant.

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Table 2-Contrast sensitivity at 3 months in the two groups

Contrast sensitivity, Group; no. (and %) of patients

log units Multifocal IOL Monofocal IOL

0.90 0 (0) 0 (0) 1.05 I (5) 0 (0) 1.20 2 ( 10) 0 (0) 1.35 I 0 (50) 2 (I 0) 1.50 5 (25) 8 (40) 1.65 2 (10) I 0 (50) 1.80 0 (0) 0 (0)

Mean 1.38 1.56

RESULTS

The patients' mean age, best corrected visual acuity, near addition, refractive error and pupil size are shown in Table 1. Contrast sensitivity results are given in Table 2. The mean contrast sensitivity was 1.38 log units for the patients with the multifocal IOL and 1.56 log units for those with the monofocal IOL, a statisti­cally significant difference (t = 5.5, p < 0.001).

There was a marked difference in depth of focus between the two groups. Eighteen patients (90%) in the aspheric multifocal IOL group focused well over a range greater than 2.50 D, compared with 3 pa­tients (15%) in the monofocal IOL group (Table 3). The mean depth of focus values for the two groups were 3.10 D and 1.65 D respectively (t = 7.8, p < 0.001).

The results for quality of vision are given in Table 4. Overall, the patients with a multifocal IOL appeared

Table 3-Depth offocus at 3 months in the two groups

Depth of Group; no. (and %) of patients focus,

dioptres MultifocaiiOL Monofocal IOL

0 0 (0) 0 (0) 0.5-1.0 0 (0) 5 (25) 1.5-2.0 2 (I 0) 12 (60) 2.5-3.0 II (55) 3 (IS) 3.5-4.0 6 (30) 0 (0) 4.5-5.0 I (5) 0 (0)

Mean 3.10 1.65

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Table 4-Quality of vision obtained after sur­gery, as assessed by patient questionnaire

Question

Rate your satisfaction with vision after surgery

Good Fair Poor

Do you need additional glasses for near work?

No Yes

Is there any difficulty with depth perception (e.g., pouring tea, lighting a match)? No Yes

Do you have problems seeing in the dark? No Yes

Glare Haloes Headache Diplopia

Group; no. (and %) of patients

Multifocal IOL Monofocal IOL

14 (70) 5 (25) I (5)

II (55) 9 (45)

16 (80) 4 (20)

10 (50) 10 (50) 9 3 6 3

16 (80) 4 (20) 0 (0)

I (5) 19 (95)

8 (40) 12 (60)

13 (65) 7 (35) 6

4

happier than those with a monofocal IOL as regards their ability to do near work and depth perception. In particular, 19 patients (95%) with the monofocal implant required additional spectacles for near work, compared with 9 patients ( 45%) with the multifocal implant. The prevalence of subjective problems was similar in the two groups.

INTERPRETATION

We found a loss of contrast sensitivity with the aspheric multifocal IOL. Similar results have been reported with other multifocal 10Ls.7•9- 11 A marked increase in depth of focus has been observed with mul­tifocal 10Ls.1- 3•12 Holladay and colleagues 12 reported a two- to threefold increase in depth of focus for all

multifocal IOLs as compared to monofocal IOLs. Our results are in agreement with these findings. The increased depth of focus may be even more apparent with the aspheric multifocal IOL that we studied. The central portion of the lens, measuring 4.7 mm in diam­eter, has an anterior surface of progressively increasing power, such that there is a central add of +5.00 D, thereby increasing the depth of focus. Other multifocal IOLs are essentially bifocal, having two foci, one for distance and one for near. Comparative analyses of dif­ferent types of multifocal IOL are needed to investi­gate this possibility.

No multifocal IOL can give a perfect result in all cases. The human brain, while adapting to the pro­cess of simultaneous imaging, may not ignore the out-of-focus image completely. Resolution is usual­ly compromised, because the performance of these lenses is determined by the degree to which contrast at the focused image is reduced by the out-of-focus image.

Patient selection is another important factor. Owing to the reduction in contrast sensitivity, multifocal IOLs ideally should not be advised for those who wish to read quickly and for professionals such as airline pilots. In our study the responses to the patient ques­tionnaire regarding satisfaction with the lens did not reveal any perceived major drawback attributable to the multifocal IOL per se. The quality of corrected distance and near vision in the two groups was com­parable, as were the reported difficulties with glare, haloes, headache and diplopia as well as overall satis­faction. However, significantly more patients in the monofocal lens group than in the multifocal lens group reported needing spectacles for near work. Our findings clearly tip the scales slightly in favour of multifocal IOLs for people who would prefer not wear spectacles after cataract surgery. Furthermore, to ben­efit from the properties of multifocal IOLs, accurate biometric measurements and proper centration of the IOL are advisable. Finally, the surgeon factor must not be overlooked.

In conclusion, the inherent trade-off with multifocal lenses between increased depth of focus and de­creased contrast sensitivity appears to be accepted by most patients. Larger studies employing standardized measurements of patient satisfaction are needed to

Aspheric multifocal /OL-Kamlesh et al

determine whether this trade-off is as desirable as it seems at present.

The authors do not have any financial interest in any of the products mentioned in this article.

REFERENCES

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2. Post CT. Comparison of depth of focus and low contrast acuities for monofocal and multifocal patients at 1 year. Ophthalmology 1992;99:1658-64.

3. Ravalico G, Baccara F, Isola V. [Functional evaluation of a new type of intraocular lens: Domilens type PROGRESS 1.] J Fr Ophtalmol1994;17(3):175-81.

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5. Olsen T, Corydon L. Contrast sensitivity as a function of focus in patients with a diffractive multifocal intraocular lens. J Cataract Refract Surg 1990;16(11):703-6.

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8. Pelli DG, Robson JG, Wilkins AI. Design of a new letter chart for measuring contrast sensitivity. Clin Vision Sci 1978;2(3): 187-99.

9. Steinert RF, Post CT Jr, Brint SF, Fritch CD, Hall DL, Wilder LW, et a!. A prospective, randomized, double­masked comparison of a zonal-progressive multifocal in­traocular lens and a monofocal intraocular lens. Ophthal­mology 1992;99:853-61.

10. Williamson W, Poirier L, Coulon P, Verin P. Compared optical performances of multifocal and monofocal intraoc­ular lenses (contrast sensitivity and dynamic visual acuity). Br J Ophthalmol1994;78:249-51.

11. Winther-Nielson A, Corydon L, Olsen T. Contrast sensi­tivity and glare in patients with a diffractive multifocal intraocular lens. J Cataract Refract Surg 1993;19(3): 254-7.

12. Holladay JT, Van Dijk H, Lang A, Portney V, Willis TR, Sun R, et a!. Optical performance of multifocal intraocular lenses. J Cataract Refract Surg 1990;16(4):413-22.

Key words: monofocal intraocular lens, aspheric multifocal intraocular lens, contrast sensitivity, depth of focus

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