A GLASS INTRAOCULAR LENS K E N N E T H R. BARASCH, M.D.,
AND STANLEY POLER,
M.S.
New York, New York
Almost all intraocular lenses that have been implanted since Ridley's pioneer efforts in 1949 have polymethylmethacrylate optics and nylon, Supramid, poly propylene, or metal haptics. Almost all have been sterilized chemically with liq uid or gas. Although these devices have been useful in the visual rehabilitation of the cataract patient, they have produced complications related to design, materi als, and methods of sterilization. With some of these problems in mind, we de signed and produced an intraocular lens of autoclavable glass and polyimide as well as an insertional instrument. Glass has always been considered as a possible material for implants. Ridley 1 stated that the choice of materials for intraocular lenses is between glass and plastic and that "rather less is known about acrylic compounds." Emmrich 2 re ported a comparison of 30 glass and 108 plastic anterior chamber lenses. The glass developed less of a coating than the plas tic, and the coating that did develop was transitory. He preferred glass for its better optics, autoclavability, and resistance to degradation. Strampelli 3 implanted a se ries of quartz anterior chamber lenses and was impressed by the absence of postop erative deposits on the lenses as well as the autoclavability of these quartz im plants. In 1964 Binkhorst, Weinstein, and Troutman 4 reported on an attempt to cre ate a weightless iseikonic intraocular lens of glass using an air space within the lens
to compensate for the weight of the glass. The glass components were found to be nonreactive in rabbit eyes. The inert chemical behavior of glass as an inadvertent resident of ocular tissue has been observed by many. 5 - 1 3 Many of the toxicity tests done on potential im plant materials are carried out on tissue cultures that are grown on the walls of glass containers. Weight, rather than bioincompatibility, has limited the use of glass. Additionally, difficulty was en countered in making holes in the tiny glass optics in order to fasten supporting loops and struts. MATERIAL AND METHODS
In order to create an implant of appro priate weight within the eye, we investi gated glass with varying properties. The glass selected has a specific gravity of 2.66 and a refractive index of 1.62.14 Lenses of appropriate power ground from this glass weigh approximately 6 mg in water, depending on the power (Fig. 1). Vitreous floatation experiments carried out with intraocular lenses of varying weights showed no difference in the be havior of implants weighing from 1 to 15 mg with respect to their potential for sinking into the vitreous. 15 The greater DIOPTRIC POWER vs WEIGHT IN WATER (milligrams) of GLASS
DIOPTRIC POWER
From the Department of Ophthalmology, Mt. Sinai Medical School, (Dr. Barasch), and the Depart ment of Ophthalmology (Mr. Poler), New York Med ical College, New York, New York. Reprint requests to Kenneth R. Barasch, M.D., 115 E. 30th St., New York, NY 10016. 556
WEIGHT IN WATER (milligrams)
Fig. 1 (Barasch and Poler). Dioptric power vs weight in water (milligrams) of glass.
AMERICAN JOURNAL O F OPHTHALMOLOGY 88:556-559, 1979
VOL. 88, NO. 3, PART II
GLASS INTRAOCULAR LENS
refractive index of glass (1.62) compared with polymethylmethacrylate (1.49) al lows the formation of optics two-fifths the thickness of plastic implants (Fig. 2). Because of the greater refractive index of the glass and the larger aperture diameter, the theoretical resolving power in line pairs per millimeter is greater than that of polymethylmethacrylate lenses. 16 The problem remained, however, to de sign a method for fastening haptics to the glass optic and to find an autoclavable, biocompatible material of appropriate weight. An extensive search yielded a polyimide film with the proper physical and biologic characteristics. Its biocompatibility was evaluated in the laborato ry. 12 Both the polyimide and its extracts exhibited no toxicity for monolayers and suspensions of mouse fibroblasts (L-929) and human lung cells (Wi-38). Neither solid polyimide nor its extracts induced rabbit blood hemolysis. Intravenous in jections of extracts into mice produced no systemic toxicity. Similar extracts injected intracutaneously in rabbits produced a
GLASS
PMMA
I I
0.3 m m
557
similar reaction to that of the solvent blanks. Implantation of solid polyimide into rabbit paravertebral muscles induced no greater response than the polyethylene negative control. Extracts of polyimide dropped onto rabbit eyes resulted in no ocular irritation. The specific glass used for the implant optic underwent similar testing with similar negative results. The polyimide has an average molecular weight of 40,000 and maintains its physi cal and chemical integrity at temperatures above 400° F, allowing its sterilization in an autoclave. Its tensile strength, in ex cess of 25,000 psi at 25° C, permits its use for haptics that are 0.05 mm thick and weigh less than 0.1 mg in water. 17 This thinness creates a flexibility that cushions contact with tissue; yet the memory of the plastic allows it to retain its shape. The implants are assembled by me chanically joining two identical haptics around a glass optic (Figs. 3 and 4). The optic is held securely within a ring of polyimide that protects the iris from con tact with the thin glass edge. A single plane iris-clip intraocular lens is thus produced. The haptics are fenestrated to allow attachment to the insertional in strument and reduce mass. The thinness (0.05 mm) and flexibility of the haptic is intended to lessen the iris deformity
0.7 m m
CENTER THICKNESS Fig. 2 (Barasch and Poler). Center thickness of glass and polymethylmethacrylate (PMMA).
Fig. 3 (Barasch and Poler). Two identical sets of polyimide haptics and a 5-mm glass optic that are the three components of the intraocular lens.
558
AMERICAN JOURNAL OF OPHTHALMOLOGY
Fig. 4 (Barasch and Poler). An assembled intra ocular lens.
produced by other single plane iris clip implants and minimize iris trauma. The 8.6 mm overall diameter and the 5 de gree deflection toward the iris plane by the four haptic loops are characteristics designed to lessen the potential for dis location (Fig. 5). A residual pupil of 4.5 mm will result with the implant in position within the eye. Total fundus visualization and easy retinoscopy should result. The flatness of the curved surface of the optic, permitted by the higher re-
SEPTEMBER, 1979
fractive index of the glass used (1.62), will reduce aberration and dazzle that might be suggested by the relatively large pupil lary aperture. Because surgical trauma is recognized as a significant factor in the complication rate with intraocular lenses, we have de signed an insertional system. The purpos es of an ideal insertional system include: (1) to hold the intraocular lens securely without damaging it; (2) to introduce the implant into the desired position without traumatizing the cornea; (3) to release the implant automatically once it is placed within the eye; and (4) to protect the vitreous and prevent it from prolapsing from the eye. It should also be simple, easy to use, and autoclavable. With these characteristics in mind, we designed a thin, hollow stainless steel insertional instrument (Fig. 6). The rounded spatula-like portion of the in strument secures the intraocular lens by passing through two opposing flexible haptic loops and behind the optic. Fluid or air is irrigated through the cannula as the implant is inserted in order to protect the endothelium. The combination of the insertional instrument and the implant gently retroplaces the vitreous as the pos terior haptics are placed behind the iris. Contact with the iris margin is sufficient to release the implant and allow with-
8.6 mm outer diameter 5 0 mm inner diameter
0.05 mm
side view
Fig. 5 (Barasch and Poler). A schematic drawing of the physical dimensions of the glass and polyimide intraocular lens.
Fig. 6 (Barasch and Poler). The glass and polyimide intraocular lens mounted on the insertional instrument.
VOL. 88, NO. 3, PART II
GLASS INTRAOCULAR LENS
drawl of the insertional instrument from the eye. SUMMARY
We designed a glass and polyimide iris-plane, iris-clip intraocular lens. It is sterilized in the autoclave and weighs approximately 6 mg in water. The optic is 0.3 mm thick for a 19-diopter lens and the flexible haptic is 0.05 mm thick. Two identical haptics and the optic are joined mechanically to form the intraocular lens. The round spatula-like portion of an in sertional instrument secures the intraocu lar lens by passing through two opposing flexible haptic loops and behind the optic. Fluid or air is irrigated through the cannula as the implant is inserted in order to protect the endothelium. REFERENCES 1. Ridley, J.: Intraocular acrylic lenses. A recent development in the surgery of cataract. Br. J. Oph thalmol. 36:113, 1952. 2. Emmrich, K.: Vorderkammerlinsen aus silikatglas. Klin. Monatsbl. Augenheilkd. 132:254, 1958. 3. Strampelli, B.: Anterior chamber lenses. Arch. Ophthalmol. 66:12, 1961. 4. Binkhorst, R. D., Weinstein, G. W., and Troutman, R. C : Weightless iseikonic intraocular lens. Am. J. Ophthalmol. 58:73, 1964.
559
5. Archer, D. B., Davies, M. S., and Kanski, J. J.: Non-metallic foreign bodies in the anterior cham ber. Br. J. Ophthalmol. 53:453, 1969. 6. Bickerton, T. H.: Successful extraction of a piece of glass from an eye where it had lodged for more than ten years. Br. Med. J. 1:896, 1888. 7. Claiborne, J. H.: Piece of glass removed from the interior of the eye after thirteen years. Am. ] . Surg. 36:228, 1922. 8. Cohen, M.: Iris cyst following traumatic im plantation of glass splinter. Arch. Ophthalmol. 45: 413, 1951. 9. Doherty, W. B.: Case of splinter of glass in the anterior chamber of four years' duration. Am. J. Ophthalmol. 30:177, 1947. 10. Duke-Elder, S., and MacFaul, P. A.: Injuries. Mechanical Injuries. In Duke-Elder, S. (ed.): System of Ophthalmology, vol. 14, pt. 1. St. Louis, C. V. Mosby, 1972, p . 503. 11. Hudomel, J.: On Foreign bodies in the cham ber angle. Szemeszet. 98:82, 1961. 12. McDonald, P. R., and Ashodian, M. J.: Re tained glass foreign bodies in the anterior chamber. Am. J. Ophthalmol. 48:747, 1959. 13. Stallard, H. B.: Intraocular foreign body (a series of 72 cases in the B. L. A.). Br. J. Ophthalmol. 31:13, 1947. 14. Lynell Medical Technology, Inc.: Lynell In traocular Lens Investigator's Manual. New York, 1978, p . 7. 15. Barasch, K. R., and Poler, S.: Intraocular lens weight and the vitreous. Ophthalmic Surg. 10:65, 1979. 16. Dunn, M. J.: The resolving power of intraocu lar lens implants. Am. IOL Implant Soc. J. 4:126, 1978. 17. Wallach, M. L.: Structure-property relations of polyimide films. J. Polymer Sci. 6 (part A-2): 953, 1968.
AND STANLEY POLER,
M.S.
New York, New York
Almost all intraocular lenses that have been implanted since Ridley's pioneer efforts in 1949 have polymethylmethacrylate optics and nylon, Supramid, poly propylene, or metal haptics. Almost all have been sterilized chemically with liq uid or gas. Although these devices have been useful in the visual rehabilitation of the cataract patient, they have produced complications related to design, materi als, and methods of sterilization. With some of these problems in mind, we de signed and produced an intraocular lens of autoclavable glass and polyimide as well as an insertional instrument. Glass has always been considered as a possible material for implants. Ridley 1 stated that the choice of materials for intraocular lenses is between glass and plastic and that "rather less is known about acrylic compounds." Emmrich 2 re ported a comparison of 30 glass and 108 plastic anterior chamber lenses. The glass developed less of a coating than the plas tic, and the coating that did develop was transitory. He preferred glass for its better optics, autoclavability, and resistance to degradation. Strampelli 3 implanted a se ries of quartz anterior chamber lenses and was impressed by the absence of postop erative deposits on the lenses as well as the autoclavability of these quartz im plants. In 1964 Binkhorst, Weinstein, and Troutman 4 reported on an attempt to cre ate a weightless iseikonic intraocular lens of glass using an air space within the lens
to compensate for the weight of the glass. The glass components were found to be nonreactive in rabbit eyes. The inert chemical behavior of glass as an inadvertent resident of ocular tissue has been observed by many. 5 - 1 3 Many of the toxicity tests done on potential im plant materials are carried out on tissue cultures that are grown on the walls of glass containers. Weight, rather than bioincompatibility, has limited the use of glass. Additionally, difficulty was en countered in making holes in the tiny glass optics in order to fasten supporting loops and struts. MATERIAL AND METHODS
In order to create an implant of appro priate weight within the eye, we investi gated glass with varying properties. The glass selected has a specific gravity of 2.66 and a refractive index of 1.62.14 Lenses of appropriate power ground from this glass weigh approximately 6 mg in water, depending on the power (Fig. 1). Vitreous floatation experiments carried out with intraocular lenses of varying weights showed no difference in the be havior of implants weighing from 1 to 15 mg with respect to their potential for sinking into the vitreous. 15 The greater DIOPTRIC POWER vs WEIGHT IN WATER (milligrams) of GLASS
DIOPTRIC POWER
From the Department of Ophthalmology, Mt. Sinai Medical School, (Dr. Barasch), and the Depart ment of Ophthalmology (Mr. Poler), New York Med ical College, New York, New York. Reprint requests to Kenneth R. Barasch, M.D., 115 E. 30th St., New York, NY 10016. 556
WEIGHT IN WATER (milligrams)
Fig. 1 (Barasch and Poler). Dioptric power vs weight in water (milligrams) of glass.
AMERICAN JOURNAL O F OPHTHALMOLOGY 88:556-559, 1979
VOL. 88, NO. 3, PART II
GLASS INTRAOCULAR LENS
refractive index of glass (1.62) compared with polymethylmethacrylate (1.49) al lows the formation of optics two-fifths the thickness of plastic implants (Fig. 2). Because of the greater refractive index of the glass and the larger aperture diameter, the theoretical resolving power in line pairs per millimeter is greater than that of polymethylmethacrylate lenses. 16 The problem remained, however, to de sign a method for fastening haptics to the glass optic and to find an autoclavable, biocompatible material of appropriate weight. An extensive search yielded a polyimide film with the proper physical and biologic characteristics. Its biocompatibility was evaluated in the laborato ry. 12 Both the polyimide and its extracts exhibited no toxicity for monolayers and suspensions of mouse fibroblasts (L-929) and human lung cells (Wi-38). Neither solid polyimide nor its extracts induced rabbit blood hemolysis. Intravenous in jections of extracts into mice produced no systemic toxicity. Similar extracts injected intracutaneously in rabbits produced a
GLASS
PMMA
I I
0.3 m m
557
similar reaction to that of the solvent blanks. Implantation of solid polyimide into rabbit paravertebral muscles induced no greater response than the polyethylene negative control. Extracts of polyimide dropped onto rabbit eyes resulted in no ocular irritation. The specific glass used for the implant optic underwent similar testing with similar negative results. The polyimide has an average molecular weight of 40,000 and maintains its physi cal and chemical integrity at temperatures above 400° F, allowing its sterilization in an autoclave. Its tensile strength, in ex cess of 25,000 psi at 25° C, permits its use for haptics that are 0.05 mm thick and weigh less than 0.1 mg in water. 17 This thinness creates a flexibility that cushions contact with tissue; yet the memory of the plastic allows it to retain its shape. The implants are assembled by me chanically joining two identical haptics around a glass optic (Figs. 3 and 4). The optic is held securely within a ring of polyimide that protects the iris from con tact with the thin glass edge. A single plane iris-clip intraocular lens is thus produced. The haptics are fenestrated to allow attachment to the insertional in strument and reduce mass. The thinness (0.05 mm) and flexibility of the haptic is intended to lessen the iris deformity
0.7 m m
CENTER THICKNESS Fig. 2 (Barasch and Poler). Center thickness of glass and polymethylmethacrylate (PMMA).
Fig. 3 (Barasch and Poler). Two identical sets of polyimide haptics and a 5-mm glass optic that are the three components of the intraocular lens.
558
AMERICAN JOURNAL OF OPHTHALMOLOGY
Fig. 4 (Barasch and Poler). An assembled intra ocular lens.
produced by other single plane iris clip implants and minimize iris trauma. The 8.6 mm overall diameter and the 5 de gree deflection toward the iris plane by the four haptic loops are characteristics designed to lessen the potential for dis location (Fig. 5). A residual pupil of 4.5 mm will result with the implant in position within the eye. Total fundus visualization and easy retinoscopy should result. The flatness of the curved surface of the optic, permitted by the higher re-
SEPTEMBER, 1979
fractive index of the glass used (1.62), will reduce aberration and dazzle that might be suggested by the relatively large pupil lary aperture. Because surgical trauma is recognized as a significant factor in the complication rate with intraocular lenses, we have de signed an insertional system. The purpos es of an ideal insertional system include: (1) to hold the intraocular lens securely without damaging it; (2) to introduce the implant into the desired position without traumatizing the cornea; (3) to release the implant automatically once it is placed within the eye; and (4) to protect the vitreous and prevent it from prolapsing from the eye. It should also be simple, easy to use, and autoclavable. With these characteristics in mind, we designed a thin, hollow stainless steel insertional instrument (Fig. 6). The rounded spatula-like portion of the in strument secures the intraocular lens by passing through two opposing flexible haptic loops and behind the optic. Fluid or air is irrigated through the cannula as the implant is inserted in order to protect the endothelium. The combination of the insertional instrument and the implant gently retroplaces the vitreous as the pos terior haptics are placed behind the iris. Contact with the iris margin is sufficient to release the implant and allow with-
8.6 mm outer diameter 5 0 mm inner diameter
0.05 mm
side view
Fig. 5 (Barasch and Poler). A schematic drawing of the physical dimensions of the glass and polyimide intraocular lens.
Fig. 6 (Barasch and Poler). The glass and polyimide intraocular lens mounted on the insertional instrument.
VOL. 88, NO. 3, PART II
GLASS INTRAOCULAR LENS
drawl of the insertional instrument from the eye. SUMMARY
We designed a glass and polyimide iris-plane, iris-clip intraocular lens. It is sterilized in the autoclave and weighs approximately 6 mg in water. The optic is 0.3 mm thick for a 19-diopter lens and the flexible haptic is 0.05 mm thick. Two identical haptics and the optic are joined mechanically to form the intraocular lens. The round spatula-like portion of an in sertional instrument secures the intraocu lar lens by passing through two opposing flexible haptic loops and behind the optic. Fluid or air is irrigated through the cannula as the implant is inserted in order to protect the endothelium. REFERENCES 1. Ridley, J.: Intraocular acrylic lenses. A recent development in the surgery of cataract. Br. J. Oph thalmol. 36:113, 1952. 2. Emmrich, K.: Vorderkammerlinsen aus silikatglas. Klin. Monatsbl. Augenheilkd. 132:254, 1958. 3. Strampelli, B.: Anterior chamber lenses. Arch. Ophthalmol. 66:12, 1961. 4. Binkhorst, R. D., Weinstein, G. W., and Troutman, R. C : Weightless iseikonic intraocular lens. Am. J. Ophthalmol. 58:73, 1964.
559
5. Archer, D. B., Davies, M. S., and Kanski, J. J.: Non-metallic foreign bodies in the anterior cham ber. Br. J. Ophthalmol. 53:453, 1969. 6. Bickerton, T. H.: Successful extraction of a piece of glass from an eye where it had lodged for more than ten years. Br. Med. J. 1:896, 1888. 7. Claiborne, J. H.: Piece of glass removed from the interior of the eye after thirteen years. Am. ] . Surg. 36:228, 1922. 8. Cohen, M.: Iris cyst following traumatic im plantation of glass splinter. Arch. Ophthalmol. 45: 413, 1951. 9. Doherty, W. B.: Case of splinter of glass in the anterior chamber of four years' duration. Am. J. Ophthalmol. 30:177, 1947. 10. Duke-Elder, S., and MacFaul, P. A.: Injuries. Mechanical Injuries. In Duke-Elder, S. (ed.): System of Ophthalmology, vol. 14, pt. 1. St. Louis, C. V. Mosby, 1972, p . 503. 11. Hudomel, J.: On Foreign bodies in the cham ber angle. Szemeszet. 98:82, 1961. 12. McDonald, P. R., and Ashodian, M. J.: Re tained glass foreign bodies in the anterior chamber. Am. J. Ophthalmol. 48:747, 1959. 13. Stallard, H. B.: Intraocular foreign body (a series of 72 cases in the B. L. A.). Br. J. Ophthalmol. 31:13, 1947. 14. Lynell Medical Technology, Inc.: Lynell In traocular Lens Investigator's Manual. New York, 1978, p . 7. 15. Barasch, K. R., and Poler, S.: Intraocular lens weight and the vitreous. Ophthalmic Surg. 10:65, 1979. 16. Dunn, M. J.: The resolving power of intraocu lar lens implants. Am. IOL Implant Soc. J. 4:126, 1978. 17. Wallach, M. L.: Structure-property relations of polyimide films. J. Polymer Sci. 6 (part A-2): 953, 1968.
