Journal of Refractive Surgery

Multifocal Effect of Against-the-Rule Myopic Astigmatism in Pseudophakic Eyes

Franco Verzella, MD; Antonio Calossi, OD

Abstract

ABSTRACT

BACKGROUND: In monofocal intraocular lens (IOL) implants we can sometimes obtain a certain degree of pseudoaccommodation. The use of a slight myopic astigmatism is proposed for postoperative refraction to achieve a significant increase in the depth of field and to reestablish a certain degree of pseudoaccommodation in Pseudophakie eyes.

METHODS: Eighty-one eyes with against-therule myopic astigmatism were evaluated in 50 patients who underwent IOL implant surgery. We selected patients with corrected monocular visual acuity greater than or equal to 20/30 and with a refraction ranging from + 0.50 to - 1 .25 diopters sph, from -0.50 to -2.75 D cyl, ax from 55° to 140°.

RESULTS: Monocular uncorrected distance visual acuity in 68% of eyes was 20/40 or better, while binocular uncorrected distance visual acuity in 84% of eyes was 20/40 or better and in 66% of eyes was 20/30 or better. Monocular uncorrected near visual acuity in 67% of eyes was J3 or better, while binocular uncorrected near visual acuity in 82% of eyes was J3 or better and in 68% was J2 or better.

Sixty-four percent of patients never wear glasses for distance, while 34% use them occasionally and only 2% always wear them.

Fifty-four percent of patients never wear glasses for near, 32% use them occasionally, while 14% always wear them.

CONCLUSION: These data show that with a low against-the-rule simple myopic astigmatism (about -1.50 D cyl x 90) we can often offer Pseudophakie patients a rewarding independence from glasses both for distant and near vision. (Refract Corneal Surg 1993;9:58-61.)

RÉSUMÉ

INTRODUCTION: Avec la lentille intraoculalre monofocal nous pouvons parfois observer un certain degré de pseudoaccommodation. Nous proposons l'utilisation d'un faible astigmatisme myopique en réfraction postopératoire afin d'augmenter le profondeur de champ et d'établir une certaine pseudoaccommodation chez les yeux pseudophakes.

MÉTHODES: Nous avons évalué 81 oeils avec astigmatisme inverse chez 50 patients qui avaient subi l'implantation d'une lentille intraoculaire (LIO). Nous avons choisi les patients avec une acuité visuelle monoculaire corrigée d'au moins 20/30 (6.7/ 10e), et avec une réfraction sphérique variant entre + 0.50 et - 1 .25 D, une réfraction cylindrique variant entre -0.50 et -2.75 D, et axiqle variant entre 55° et 140°.

RÉSULTATS: L'acuité visuelle monoculaire noncorrigée de loin dans 68% des cas fut d'au moins 20/40 (5/ 10e) tandis que l'acuité binoculaire noncorrigée de loin dans 84% des cas fut d'au moins 20/40 (5/ 10e) et dans 66% des cas fut d'au moins 20/30 (6.7/ 10e). L'acuité visuelle monoculaire de près et non-corrigée dans 67% des cas fut d'au moins J3, tandis que l'acuité visuelle binoculaire de près et non-corrigée dans 82% des cas fut d'au moins J3 et dans 68% des cas fut d'au moins J2.

64% des patients ne portent jamais des lunettes pour voir de loin, tandis que 34% en portent à l'occasion et seulement 2% en portent continuellement.

Abstract

ABSTRACT

BACKGROUND: In monofocal intraocular lens (IOL) implants we can sometimes obtain a certain degree of pseudoaccommodation. The use of a slight myopic astigmatism is proposed for postoperative refraction to achieve a significant increase in the depth of field and to reestablish a certain degree of pseudoaccommodation in Pseudophakie eyes.

METHODS: Eighty-one eyes with against-therule myopic astigmatism were evaluated in 50 patients who underwent IOL implant surgery. We selected patients with corrected monocular visual acuity greater than or equal to 20/30 and with a refraction ranging from + 0.50 to - 1 .25 diopters sph, from -0.50 to -2.75 D cyl, ax from 55° to 140°.

RESULTS: Monocular uncorrected distance visual acuity in 68% of eyes was 20/40 or better, while binocular uncorrected distance visual acuity in 84% of eyes was 20/40 or better and in 66% of eyes was 20/30 or better. Monocular uncorrected near visual acuity in 67% of eyes was J3 or better, while binocular uncorrected near visual acuity in 82% of eyes was J3 or better and in 68% was J2 or better.

Sixty-four percent of patients never wear glasses for distance, while 34% use them occasionally and only 2% always wear them.

Fifty-four percent of patients never wear glasses for near, 32% use them occasionally, while 14% always wear them.

CONCLUSION: These data show that with a low against-the-rule simple myopic astigmatism (about -1.50 D cyl x 90) we can often offer Pseudophakie patients a rewarding independence from glasses both for distant and near vision. (Refract Corneal Surg 1993;9:58-61.)

RÉSUMÉ

INTRODUCTION: Avec la lentille intraoculalre monofocal nous pouvons parfois observer un certain degré de pseudoaccommodation. Nous proposons l'utilisation d'un faible astigmatisme myopique en réfraction postopératoire afin d'augmenter le profondeur de champ et d'établir une certaine pseudoaccommodation chez les yeux pseudophakes.

MÉTHODES: Nous avons évalué 81 oeils avec astigmatisme inverse chez 50 patients qui avaient subi l'implantation d'une lentille intraoculaire (LIO). Nous avons choisi les patients avec une acuité visuelle monoculaire corrigée d'au moins 20/30 (6.7/ 10e), et avec une réfraction sphérique variant entre + 0.50 et - 1 .25 D, une réfraction cylindrique variant entre -0.50 et -2.75 D, et axiqle variant entre 55° et 140°.

RÉSULTATS: L'acuité visuelle monoculaire noncorrigée de loin dans 68% des cas fut d'au moins 20/40 (5/ 10e) tandis que l'acuité binoculaire noncorrigée de loin dans 84% des cas fut d'au moins 20/40 (5/ 10e) et dans 66% des cas fut d'au moins 20/30 (6.7/ 10e). L'acuité visuelle monoculaire de près et non-corrigée dans 67% des cas fut d'au moins J3, tandis que l'acuité visuelle binoculaire de près et non-corrigée dans 82% des cas fut d'au moins J3 et dans 68% des cas fut d'au moins J2.

64% des patients ne portent jamais des lunettes pour voir de loin, tandis que 34% en portent à l'occasion et seulement 2% en portent continuellement.

Some authors16 have observed that in monofocal IOL implantation, we can sometimes obtain a certain degree of pseudoaccommodation. Nakazawa and Ohtsuki3 measured pseudoaccommodation in 42 Pseudophakie eyes with posterior chamber monofocal implants. Reported average accommodation was 2.03 ± 1.03 diopters.

The results of Nakazawa and Ohtsuki suggest that apparent accommodation in Pseudophakie eyes is strongly influenced by pupil diameter, which in turn affects the depth of focus and, consequently, the depth of field. If the total refractory power of an eye is constant, as is the case with the Pseudophakie eye, the depth of field is inversely proportional to pupil diameter. Nakazawa and Ohtsuki report that apparent accommodation is inversely proportional to pupil diameter according to the following linear regression equation:

Ace = (4.97 -i- 0) + 0.12 (r = 0.45)

From the data reported by Holladay and colleagues7 we can deduce that, in the physiologic range of the pupil diameter (about 1.5 ** 6 mm), there is a good correlation among refractive error (defocus equivalent), minimal angle of resolution (1/AV), and pupil size.

It is obvious that pupil diameter cannot be controlled and if myotic drugs are used, these paralyze the photomotor mechanism that permits an increase in retinal illumination at low illumination levels, thus hindering good sight under poor light conditions.

Huber4,5 proposed the use of a slight myopic astigmatism for postoperative refraction to achieve a significant increase in the depth of focus and to reestablish a certain degree of pseudoaccommodation in Pseudophakie eyes.

Sawusch and Guyton8 developed a mathematical model and calculated for a schematic eye the optimum astigmatism required to obtain the maximum depth of focus and the minimum of blurring for objects at a distance of between 0.5 and 6 m. The ideal refraction reported is - 0.25 sph - 0.75 cyl.

If a slight simple myopic astigmatism is present, a focal line may give images that are not very blurred for distant objects and the other one images not too blurred for near objects. If the myopic astigmatism is against the rule, the focal line closest to the retina for near vision is the vertical one, and since print characters have more vertical components than those in other directions, a slight against-the-rule myopic astigmatism, although having little effect on the visual acuity at a distance, will aid reading with the naked eye in the case of presbyopia. Taking up these ideas, we have noticed that Pseudophakie patients with a slight simple against-the-rule myopic astigmatism are generally remarkably independent from glasses for distant and near sight.

MATERIALS AND METHODS

We examined 50 patients (32 males and 18 females) undergoing cataract extraction and implantation of posterior chamber intraocular lenses (IOLs). Forty-five of the patients examined were Pseudophakie in both eyes, the other five were monocular. The patients ages ranged from 36 to 83 years (mean, 63 years). All were examined at least 6 months after the operation. We selected patients with a corrected binocular visual acuity greater than or equal to 20/30 and with a refraction within the following range: sphere between + 0.50 and - 1.25 D, cylinder between -0.50 and -2.75 D, axis between 55° and 140°. All the eyes had round and reactive pupils.

Table

Table 1Summary of Refraction (D) and Visual AcuityTable 2Uncorrected Monocular and Binocular Distance Visual Acuity (81 Eyes, 50 Patients)

Table 1

Summary of Refraction (D) and Visual Acuity

Table 2

Uncorrected Monocular and Binocular Distance Visual Acuity (81 Eyes, 50 Patients)

The following parameters were measured in the various patients: corrected distant monocular visual acuity, uncorrected distant monocular and binocular visual acuity, corrected near monocular visual acuity, uncorrected near monocular and binocular visual acuity.

Monocular visual acuity was considered in 81 eyes, since 19 eyes with a best spectacle corrected visual acuity of less than 20/40 were excluded. Binocular visual acuity was tested in all patients.

When visual acuity in one eye was less than 20/40, (19 patients), binocular visual acuity did not improve over the best eye. Visual acuity for distance (6 m) was measured with a Rodenstock Rodomat projector.

For near, a Ronsenbaum pocket vision screener was held in the hand of the patient at a distance of 35 cm with 200 lux.

Spectacles for distance and near were prescribed for all patients.

An interview regarding the independence from glasses was performed in all patients, at least 3 months after prescription.

Patients' answers were placed in four categories:

* "I always wear my glasses."

* "I wear my glasses only at times."

* "I never wear my glasses, because I do not need them."

* "I wear my glasses, out of habit."

RESULTS

Our results are summarized in Tables 1-4.

In 68% of eyes, an uncorrected distant monocular visual acuity greater than or equal to 20/40 was found, whereas binocular visual acuity in 84% was greater than or equal to 20/40 and in 66% of eyes greater than or equal to 20/30. In 67% of eyes an uncorrected near monocular visual acuity greater than or equal to J3 was found, whereas binocular visual acuity in 82% of eyes was greater than or equal to J3, in 68%, greater than or equal to J2.

Fifty-six percent of all patients never wear glasses for distance, 8% out of habit, 34% occasionally, whereas 2% wear them all the time.

Fifty-four percent of patients never wear glasses for near, 32% use them occasionally, while 14% always wear them.

Table

Table 3Uncorrected Monocular and Binocular Near Visual Acuity (81 Eyes, 50 Patients)Table 4Use of Glasses for Distance and Near (Percentage of Patients)

Table 3

Uncorrected Monocular and Binocular Near Visual Acuity (81 Eyes, 50 Patients)

Table 4

Use of Glasses for Distance and Near (Percentage of Patients)

Best visual acuities and depth of focus were found in patients with myopic astigmatism from - 1.00 to -2.00D × 90°.

DISCUSSION

Our results confirm that a slight against-the-rule simple myopic astigmatism for postoperative refraction can often render Pseudophakie patients independent from glasses. The ideal refraction is sphere 0.00, cylinder -1.50, axis 90°. The majority of patients with this type of refraction have good uncorrected distant visual acuity and at the same time have quite good near vision without correction. Although this does not permit good vision of finer details, it frequently permits reading without glasses and almost total independence from distance correction. These patients do not wear glasses for many of their activities. Many of them only need correction for reading for long periods or for driving.

For good visual acuity, both distant and near, to be obtained without correction, good macular functioning is necessary and complete transparency of the ocular media. In binocular vision, the benefits of the refractive condition suggested here are undoubtedly greater.

We think that this type of refractive solution is a valid alternative to multifocal IOLs, the greatest advantage being that, when naked eye vision is not satisfactory, this can easily be corrected with glasses, which is not always the case with multifocal IOLs.

REFERENCES

1. Sugitani Y, Komori T, Kitoh R, Hayano S. Apparent accommodation (pseudoaccommodation) in pseudofakia. Folia Ophthalmol Jpn. 1979;30:326-330.

2. Hoshi H, Kamegasawa A, Chikuda M, et al. Visual functions of the intraocular lens implanted eye (Pseudophakie eye) with special reference to pseudoaccommodation. Folia Ophthalmol Jpn. 1980;31;1409-1419.

3. Nakazawa M, Ohteuki K. Apparent accommodation in Pseudophakie eyes after implantation of posterior chamber intraocular lenses. Am J Ophthalmol. 1983;96:435-438.

4. Huber C. Planned myopic astigmatism as a substitute for accommodation in pseudophakia. American Intraocular Implant Society Journal. 1981;7:244-248.

5. Huber C. Myopic astigmatism as a substitute for accommodation in pseudophakia. Doc Ophthalmol. 1981;52:123-178.

6. Datiles MB, Gacayco T. Low myopia with low astigmatic correction gives cataract surgery patients good depth offocm. Ophthalmology. 1990;97:922-926.

7. Holladay JT, Lynn MJ, Waring GO, Gemmili M, Keehn GC, Fielding B. The relationship of visual acuity, refractive error and pupil size after radial keratotomy. Arch Ophthalmol. 1991;109:70-76.

8. Sawusch MR, Guyton DL. Optimal astigmatism to enhance depth of focus after cataract surgery. Ophthalmology. 1991;98:1026-1029.

Table 1

Summary of Refraction (D) and Visual Acuity

Table 2

Uncorrected Monocular and Binocular Distance Visual Acuity (81 Eyes, 50 Patients)

Table 3

Uncorrected Monocular and Binocular Near Visual Acuity (81 Eyes, 50 Patients)

Table 4

Use of Glasses for Distance and Near (Percentage of Patients)

10.3928/1081-597X-19930101-12

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