Multifocal intraocular lenses Richard
J. Duffey, M.D., Ralph W. Zabel, M.D., Richard
L. Lindstrom, M.D.
ABSTRACT Current multi focal intraocular lens designs incorporate refractive or diffractive optical principles to achieve increased depth of focus. Information about four basic design concepts is presented. Early clinical results with two of these, the IOLAB Nuvue two-zone refractive multifocal and the 3M diffractive multifocal, are summarized.
Key WOl'ds: accommodation, bifocal intraocular 1 ns, diffractive optic, 1l1ultifocal intraocular lens, pre byopia, ps udophakos
The normal eye is constructed so that the various refracting surfaces and ocular media focus parallel rays of light coming from a distant object upon the retina. The eye can also adjust its dioptric power through the accommodative process to bring near objects into focus. In an analysis of the Purkinje images during accommodation, Helmholtz has shown that the posterior lens surface remains fixed in position and undergoes a slight increase in curvature. The major dioptric shift during accommodation, however, results from the forward movement and marked increase in the convexity of the anterior pole of the lens. The cortex of the young lens is a soft, easily molded material contained in an elastic capsule. The traction of the zonular fibers opposes the natural tendency of the lens to assume a spherical shape. During accommodation, however, contraction of the ciliary muscles pulls the zonular attachment sites inward toward the lens equator, reducing the tension on the zonules and lens capsule which allows the lens to increase its convexity passively. The resultant
steepening of the anterior and posterior poles of the lens effects the accommodative process. The amplitude of accommodation is greatest in childhood and slowly decreases until it is lost in middle age. The loss of accommodation, although fairly uniform in the population, fluctuates with the demands of the visual task, the level of illumination , drug effects, pupillary size, and a person's general health. When the inability to carry out prolonged near vision tasks because of fatigue, headache, and other symptoms of asthenopia occurs, the condition is called presbyopia. Duane's standard curve of accommodative amplitude versus age reveals that by 60 years of age all accommodation has generally been lost; thus, although presbyopia is defined as the vision of old age, it is a poor term relative to today's life spans. Several explanations have been suggested for the development of presbyopia: (1) the lens nucleus grows and scleroses with age and the plasticity of the cortex is lost; (2) the ciliary muscle weakens and is no longer able to relax the zonules adequately; (3) the elasticity of the lens capsule
From the Department of Ophthalmology, University of Minnesota and V.A. Medical Center, 516 Delaware Street SE, Box 493, Minneapolis, Minnesota. Adaptedfrom a chapter on multifocal intraocular lenses in Colour Atlas ofIntraocular Lens Implantation, Wolfe Publishing, Ltd., London, England, 1990. Reprint requests to Richard L. Lindstrom, M.D., Department of Ophthalmology, University of Minnesota, 516 Delaware Street SE, Box 493, Minneapolis, Minnesota 55455. J CATARACT REFRACT SURG-VOL 16, JULY 1990
42.3
decreases. Experimental results support and contradict these various theories. The most common treatment of· presbyopia is bifocal spectacles. The difficulties in adapting to bifocal lenses are often considerable. As the add is increased in strength or trifocal or multifocal reading segments are required, the patient often experiences frustration and discouragement. Intraocular lens (IOL) implantation surgery has overcome the loss of visual function associated with the removal of cataracts. Since present IOLs are monofocal the loss of accommodation becomes maximal with surgery. Although the loss of accommodation is not absolute since depth of visual field and pupillary diameter provide a degree of apparent accommodation, the need to correct the resultant presbyopia is clinically apparent. In what may be considered an evolutionary step, bifocal and multifocal IOLs of several different designs have been introduced. They differ from conventional monofocal IOLs by potentially providing both distance and near vision without additional bifocal spectacle correction. At present multiple designs are being investigated and/or manufactured. We have listed those we are aware of along with information provided by the respective manufacturers. MULTIFOCAL INTRAOCULAR LENS DESIGNS Currently, multifocal IOL designs incorporate refractive and/or diffractive optical principles to achieve simultaneous distance and near visual acuity. Refractive optics can be broken down further into spheric and aspheric designs. The anterior and/ or the posterior IOL surface can be used for singular or combination designs. Information about four basic design concepts has been released by representative manufacturers. Others probably exist but remain unavailable for proprietary reasons. Some designs have already been incorporated into lenses that have been implanted clinically, while others are still in the early manufacture stage. This review will briefly discuss these different designs without critical evaluation or comment. The four designs are as follows: 1. Combination of two or more different anterior spheric refractive surfaces for distance and near correction (Pharmacia Ophthalmics multifocal and the IOLAB Nuvue multifocal IOL). The Pharmacia design (Figure 1) has a central circular distance zone surrounded by a ring-shaped near zone which is surrounded by another peripheral ring-shaped zone for distance correction. The IOLAB IOL (Figure 2) has a 2 mm diameter central optic for near vision. The remainder of the lens, which is lower in power 424
J CATARACT
Fig. 1.
(Duffey) Pharmacia design with three different spherical refractive surfaces. The outer and inner zones are for distance and the middle zone for near.
by 4 diopters (D), is a ring-shaped zone for distance correction. Both these designs effect their dioptric changes for distance and near by refractive spheric curvature changes on the anterior surface of the IOL. 2. Combination of an anterior spheric and an anterior aspheric refractive surface for distance and near correction (Wright Medical, Inc., Nordan IOL, and IOPTEX aspheric multifocallens). The Wright Medical IOL (Figure 3) incorporates a combination spheric/aspheric anterior surface. The dioptric power between the two areas increases by a total of 3 D, the spheric portion for distance and the aspheric portion for near. The IOPTEX IOL (Figure 4) combines spherical distance vision zones with
Fig. 2.
(Duffey) IOLAB design with central zone for near and peripheral zone for distance.
REFRACT SURG-VOL 16, JULY 1990
Near Image Sharp /'
/'
/'
Near
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J. Duffey, M.D., Ralph W. Zabel, M.D., Richard
L. Lindstrom, M.D.
ABSTRACT Current multi focal intraocular lens designs incorporate refractive or diffractive optical principles to achieve increased depth of focus. Information about four basic design concepts is presented. Early clinical results with two of these, the IOLAB Nuvue two-zone refractive multifocal and the 3M diffractive multifocal, are summarized.
Key WOl'ds: accommodation, bifocal intraocular 1 ns, diffractive optic, 1l1ultifocal intraocular lens, pre byopia, ps udophakos
The normal eye is constructed so that the various refracting surfaces and ocular media focus parallel rays of light coming from a distant object upon the retina. The eye can also adjust its dioptric power through the accommodative process to bring near objects into focus. In an analysis of the Purkinje images during accommodation, Helmholtz has shown that the posterior lens surface remains fixed in position and undergoes a slight increase in curvature. The major dioptric shift during accommodation, however, results from the forward movement and marked increase in the convexity of the anterior pole of the lens. The cortex of the young lens is a soft, easily molded material contained in an elastic capsule. The traction of the zonular fibers opposes the natural tendency of the lens to assume a spherical shape. During accommodation, however, contraction of the ciliary muscles pulls the zonular attachment sites inward toward the lens equator, reducing the tension on the zonules and lens capsule which allows the lens to increase its convexity passively. The resultant
steepening of the anterior and posterior poles of the lens effects the accommodative process. The amplitude of accommodation is greatest in childhood and slowly decreases until it is lost in middle age. The loss of accommodation, although fairly uniform in the population, fluctuates with the demands of the visual task, the level of illumination , drug effects, pupillary size, and a person's general health. When the inability to carry out prolonged near vision tasks because of fatigue, headache, and other symptoms of asthenopia occurs, the condition is called presbyopia. Duane's standard curve of accommodative amplitude versus age reveals that by 60 years of age all accommodation has generally been lost; thus, although presbyopia is defined as the vision of old age, it is a poor term relative to today's life spans. Several explanations have been suggested for the development of presbyopia: (1) the lens nucleus grows and scleroses with age and the plasticity of the cortex is lost; (2) the ciliary muscle weakens and is no longer able to relax the zonules adequately; (3) the elasticity of the lens capsule
From the Department of Ophthalmology, University of Minnesota and V.A. Medical Center, 516 Delaware Street SE, Box 493, Minneapolis, Minnesota. Adaptedfrom a chapter on multifocal intraocular lenses in Colour Atlas ofIntraocular Lens Implantation, Wolfe Publishing, Ltd., London, England, 1990. Reprint requests to Richard L. Lindstrom, M.D., Department of Ophthalmology, University of Minnesota, 516 Delaware Street SE, Box 493, Minneapolis, Minnesota 55455. J CATARACT REFRACT SURG-VOL 16, JULY 1990
42.3
decreases. Experimental results support and contradict these various theories. The most common treatment of· presbyopia is bifocal spectacles. The difficulties in adapting to bifocal lenses are often considerable. As the add is increased in strength or trifocal or multifocal reading segments are required, the patient often experiences frustration and discouragement. Intraocular lens (IOL) implantation surgery has overcome the loss of visual function associated with the removal of cataracts. Since present IOLs are monofocal the loss of accommodation becomes maximal with surgery. Although the loss of accommodation is not absolute since depth of visual field and pupillary diameter provide a degree of apparent accommodation, the need to correct the resultant presbyopia is clinically apparent. In what may be considered an evolutionary step, bifocal and multifocal IOLs of several different designs have been introduced. They differ from conventional monofocal IOLs by potentially providing both distance and near vision without additional bifocal spectacle correction. At present multiple designs are being investigated and/or manufactured. We have listed those we are aware of along with information provided by the respective manufacturers. MULTIFOCAL INTRAOCULAR LENS DESIGNS Currently, multifocal IOL designs incorporate refractive and/or diffractive optical principles to achieve simultaneous distance and near visual acuity. Refractive optics can be broken down further into spheric and aspheric designs. The anterior and/ or the posterior IOL surface can be used for singular or combination designs. Information about four basic design concepts has been released by representative manufacturers. Others probably exist but remain unavailable for proprietary reasons. Some designs have already been incorporated into lenses that have been implanted clinically, while others are still in the early manufacture stage. This review will briefly discuss these different designs without critical evaluation or comment. The four designs are as follows: 1. Combination of two or more different anterior spheric refractive surfaces for distance and near correction (Pharmacia Ophthalmics multifocal and the IOLAB Nuvue multifocal IOL). The Pharmacia design (Figure 1) has a central circular distance zone surrounded by a ring-shaped near zone which is surrounded by another peripheral ring-shaped zone for distance correction. The IOLAB IOL (Figure 2) has a 2 mm diameter central optic for near vision. The remainder of the lens, which is lower in power 424
J CATARACT
Fig. 1.
(Duffey) Pharmacia design with three different spherical refractive surfaces. The outer and inner zones are for distance and the middle zone for near.
by 4 diopters (D), is a ring-shaped zone for distance correction. Both these designs effect their dioptric changes for distance and near by refractive spheric curvature changes on the anterior surface of the IOL. 2. Combination of an anterior spheric and an anterior aspheric refractive surface for distance and near correction (Wright Medical, Inc., Nordan IOL, and IOPTEX aspheric multifocallens). The Wright Medical IOL (Figure 3) incorporates a combination spheric/aspheric anterior surface. The dioptric power between the two areas increases by a total of 3 D, the spheric portion for distance and the aspheric portion for near. The IOPTEX IOL (Figure 4) combines spherical distance vision zones with
Fig. 2.
(Duffey) IOLAB design with central zone for near and peripheral zone for distance.
REFRACT SURG-VOL 16, JULY 1990
Near Image Sharp /'
/'
/'
Near
/'
~~/'~~~=---_--"'''-
