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Anterior and Posterior Mushroom Keratoprostheses*
ANTERIOR AND POSTERIOR MUSHROOM K E R A T O P R O S T H E S E S * A N EXPERIMENTAL STUDY H E R N A N D O CARDONA, M.D. New York
The buried keratoprosthesis was first re ported by Cardona, Castroviejo and DeVoe1 in a clinical evaluation of the Cardona implants. This team has continued its ex perimental studies with both the buried and the through-and-through keratoprostheses. A new model is herein described (fig. 1). MATERIAL AND METHODS
The new model is made of methyl methacrylate, the same plastic material used in the earlier models.2·3 It was especially polymer ized and no additives or catalyst accelerators were employed. The buried keratoprosthesis is mushroom-shaped and has no anterior projection. A similar model, made of silicon rubber, is now being tested by Brown and Dohlman4 (fig. 2). Our buried implant has two parts: A cyl inder 2.0 mm in diameter that protrudes into the anterior chamber from 1.8 to 2.0 mm, and an interlamellar plate 4.2-mm wide by 0.15-mm thick (figs. 1-A and 2 ) , which follows the curvature of the cornea. The dioptric power of the implant, combined with that of the cornea, ranges from 4- 56 to + 6 3 . It is buried beneath a total full-thick ness corneal graft and projects beyond the endothelium into the anterior chamber, or it is inserted in an interlamellar pocket. The cyclindric projection beyond the corneal en dothelium prevents the growth of mem branes behind the implant. This character istic differentiates our keratoprosthesis from similarly shaped types, including the one re ported by Tudor Thomas in 19555,e (fig. 2), * From the Department of Ophthalmology, Col lege of Physicians and Surgeons, Columbia Uni versity. This investigation was made possible by grant No. NB-04968 from the National Institutes of Health, Bethesda, Maryland, and by a Fight for Sight grant-in-aid from the National Council to Combat Blindness, Inc. New York.
which corresponds in length to the corneal thickness. Our surgical procedure also differs from that described by Tudor Thom as in that we use a full-thickness corneal graft to cover the implant while he uses a partial lamellar graft for support. In some eyes our implant is inserted in an interla mellar pocket, as described under surgical technique. This buried implant was tested in the eyes of 50 albino rabbits weighing 3.5 kg. Gener al anesthesia was induced by the injection of 1.0 cc of sodium pentothal into the marginal vein of the ear, with the addition of ether administered through a mask for one min ute. SURGICAL TECHNIQUES—BURIED IMPLANT
A 180 degree paralimbic incision is made with a razor blade knife or Castroviejo knife with depth-control mechanism (fig. 3-A), followed by lamellar dissection and preparation of an interlamellar pocket oc cupying more than one-half the corneal area. This is made either with curved scis sors or a Castroviejo spatulated dissector (fig. 3-B). A special 2.0-mm trephine is used to dissect a disc from the center of the posterior layers of the cornea (fig. 3-C). The buried mushroom implant, mounted in the forceps designed for this purpose, is then introduced into the interlamellar pocket until its posterior projection engages the opening made in the cornea (fig. 3-D). The prosthesis is then covered with the corneal flap previously dissected to prepare the pocket (fig. 3-E) and the wound is closed with 7-0 silk sutures (fig. 3-F). Recovery was uneventful for the first five months after insertion of the buried mush room implant, with very slight or no reac tion of the ocular tissues. The corneas re mained completely clear and transparent
KERATOPROSTHESES
(fig. 4-A, B, C and D ) . After six months, slight opacification appeared in the central portion of the stroma over the buried kera toprosthesis in nine of the rabbit eyes. At 14 months, 24 of the 50 rabbit eyes pre sented varying degrees of cloudiness in the epithelium over the central area of the im plant (fig. 5-A, B, C and D ) . Twelve of these 24 animals were killed and the eyes enucleated for histologie study (fig. 6 ) . The remaining 12 were kept under observation. Later a modified implant, to be described, was inserted, using a new surgical tech nique. The 26 rabbits remaining from the original 50 are still under observation with the corneas clear and no untoward reaction to date. Figure 6 shows the histologie changes in the cornea of one of the 12 rabbits killed. The eye was enucleated and fixed in 10% formalin and embedded in celloidin plus 1.0 cc of polymer of methyl methacrylate and
Fig. 1 (Cardona). (A) The anterior mushroom keratoprosthesis and measurements. (B) The posterior (buried) mushroom keratoprosthesis and measurements. (C) Thickened corneal epithelium over the central portion of the buried keratopros thesis. (D) The anterior mushroom keratoprosthe sis inserted over a buried implant.
499 U = l mm
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Themas
1H2
Carl·»·
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Brtw·
tU
DMIlMl
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Fig. 2 (Cardona). Evolution of the principal models of buried keratoprostheses (Thomas, Car dona, Brown and Dohlman) and their measure ments.
1.0 cc of chloroform to soften the kerato prosthesis and facilitate cutting of the mi croscopic section. In this slide, it is possible to detect quite clearly the plastic walls of the implant by polarizing the light of the micro scope (fig. 6-D). The epithelium was slightly opaque. It in creased in thickness from the periphery in ward to the central portion of the cornea where it attained twice its normal size (fig. 6-A). In some eyes paralimbic vessels were visible. This opacification and epithelial thickening in the central area of the cornea over the prosthesis, present in approximate ly half of the rabbit eyes, is possibly due to the mechanical barrier of the interlamellar plate or, as suggested by Knowles,7 it is re lated to evaporation from the corneal sur face of the rabbit eye, or because the blink ing rate of the rabbit eye is lower than that of the human eye, as hypothesized by Brown and Dohlman.8 This phenomenon could jeopardize the purpose of the buried implant, which functioned well in about half of the rabbit eyes with no untoward reaction and no opacification. Thus it would seem to offer a good opportunity for improvement in carefully selected human eyes. But what
500
HERNANDO CARDONA
Fig. 3 (Cardona). (A) Making the paralimbic incision. (B) Preparing the interlamellar pocket. (C) Making the central corneal opening with the 2.0-mm trephine. (D) Inserting the posterior mush room keratoprosthesis in the interlamellar pocket. (E) Covering the keratoprosthesis with the corneal flap. (F) Closing the incision with 7-0 silk sutures.
about the remaining 50%? Several possible solutions have been proposed : a. Replacement of the buried keratopros thesis by the through-and-through model implant, but this might involve loss of vitre ous during performance of the various sur gical maneuvers. b. Replacement by a newly designed kera toprosthesis that can be inserted over the one already in place, with a minimum of trauma as it can be used without opening the anterior chamber. This new model, which we call the ante rior mushrpom keratoprosthesis (fig. 1-A) measures 0.65 mm in its anterior cylindric projection and the interlamellar supporting plate is 0.15-mm thick by 4.2-mm wide. The posterior curve of the plate of this implant has the same radius as that of the buried
implant and the dioptric power of the com bined prostheses, as already explained, is the same as that of a through-and-through model. INSERTION TECHNIQUE—ANTERIOR MUSHROOM IMPLANT
A special 2.0-mm trephine is used to make an opening in the center of the cornea over the buried implant (fig. 7-A). A curved paralimbic incision 9.0-mm long is made to the cleavage plane of the corneal tissue covering the buried implant (fig. 7-B). A spatula 1.5-mm wide and 10-mm long is then introduced through the pre viously trephined corneal opening and, with a circular motion, the cleavage plane is dis sected between the corneal tissue and the buried implant (fig. 7-C). The point of the
KERATOPROSTHESES
501
Fig. 4 (Cardona). (A, B, C and D) Rabbit eyes five months after insertion of a buried keratoprosthesis. The stroma and epithelium still remain clear and transparent.
Fig. S (Cardona). (A, B, C and D) Rabbit eyes with posterior (buried) mushroom keratoprosthesis after 14 months, showing opacification of the epithelium and slight vascularization over the implant.
502
HERNANDO CARDONA
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-: _^ ' - r-^U. ..; --t-^~.» *
Fig. 6 (Cardona). Microscopic section of rabbit eye. (A) Thickened epithelium and slight opacification in the central area over the buried keratoprosthesis. (B) Normal thickness epithelium. (C) Stroma. (D) Keratoprosthesis (interlamellar plate), (a, b, c and d) Drawing showing the corresponding cross section. (Hematoxylin-eosin, χ93.4.)
spatula should penetrate to the paralimbic incision to insure that the interlamellar pocket is complete (fig. 7-D). The anterior mushroom keratoprosthesis, held in the forceps especially designed for this purpose, is introduced into the interla
mellar pocket until it engages the anterior opening made in the cornea over the buried implant (fig. 7-E). The forceps is then withdrawn and the paralimbic incision closed with 7-0 silk sutures (fig. 7-F). Ten of the rabbits that developed epitheli-
KERATOPROSTHESES
503
Fig. 7 (Cardona). (A) Corneal opening made with the special 2.0-mm trephine. (B) Making the paralimbic incision. (C) Dissecting the cleavage plane between the corneal tissue and the buried implant. (D) Penetration of the spatula to the paralimbic incision. (E) Inserting the keratoprosthesis with the special forceps. (F) Closing the incision with 7-0 silk sutures. al cloudiness over the buried implant were selected for the trial of the new anterior mushroom keratoprosthesis. The implant was inserted, using the surgical technique just described. The tolerance of the corneal tissue to this implant and the results ob tained (fig. 8-A, B. C and D) are similar to those we have already reported for the through-and-through implants.1·2 These ani mals have now been under observation for 10 to 12 months and tolerance continues to be good. The Cardona, Castroviejo and DeVoe team, encouraged by the good results ob tained in the animal study, felt that this new
keratoprosthesis offers an opportunity to improve visual acuity in carefully selected human eyes with a buried implant in place. A clinical study has been undertaken and in two patients the cloudy corneal tissue has been removed from over the buried implant and replaced by an anterior mushroom kera toprosthesis. The combined implants—the previously buried one and the anterior mushroom keratoprosthesis—have now been well tolerated by these patients for several months. However, the results of this trial in human eyes will not be reported for at least two years, the minimum time we feel the eyes should be under observation for ade-
HERNANDO CARDONA
504
Fig. 8 (Cardona). (A, B, C and D) Rabbit eyes with the anterior mushroom keratoprosthesis in place over the posterior (buried) mushroom keratoprosthesis after 12 months.
quate evalution. During this time, the study will also be extended to comprise a much greater number of patients. SUMMARY
A buried implant, in the shape of a mush room, was studied in the eyes of SO albino rabbits. The corneas remained transparent for six months when slight opacification de veloped in the central portion of the stroma over the buried implant. At 14 months, 24 of the rabbit eyes presented varying degrees of cloudiness. Twlve of the animals were killed and the eyes prepared for histologie study. Ten of the remaining 12 rabbits were reoperated and the cloudy corneal tissue over the buried implant was replaced by a new model keratoprosthesis, which is de scribed, as is the surgical technique used for its insertion. These animals have been under observation for 10 to 12 months. The sec ond mushroom implant has been well toler
ated and, with the buried implant already in place, provides dioptric power ranging from + 56 t o + 6 3 . 635 West 165th Street (10032). REFERENCES
1. Cardona, H., Castroviejo, R. and DeVoe, A. G. : The Cardona keratoprosthesis : First clinical evaluation. Acta XIX Internat. Cong. Ophth., 1962, in press. 2. Cardona, H.: Keratoprosthesis: Acrylic opti cal cylinder with supporting intralamellar plate. Am. J. Ophth., 54:284, 1962. 3. : Plastic keratoprostheses : A descrip tion of the plastic material and comparative his tologie study of the recipient cornea. Am. J. Ophth., 58:247,1964. 4. Brown, S. I. and Dohlman, C. H. : A buried corneal implant serving as a barrier to fluid. Arch. Ophth., 73:367, 1965. 5. Thomas, J. W. T. : Acrylic implant in keratoplasty. Tr. Ophth. Soc. U. Kingdom, 75:475, 1955. 6. : Prognosis in lamellar keratoplasty and possible use of buried acrylic mushroom disc in keratoplasty. An. Inst. Barraquer, 3:776, 1963. 7. Knowles, W. F. : Effect of intralamellar plastic membranes on corneal physiology. Am. J. Ophth., 51:274, 1961.
The buried keratoprosthesis was first re ported by Cardona, Castroviejo and DeVoe1 in a clinical evaluation of the Cardona implants. This team has continued its ex perimental studies with both the buried and the through-and-through keratoprostheses. A new model is herein described (fig. 1). MATERIAL AND METHODS
The new model is made of methyl methacrylate, the same plastic material used in the earlier models.2·3 It was especially polymer ized and no additives or catalyst accelerators were employed. The buried keratoprosthesis is mushroom-shaped and has no anterior projection. A similar model, made of silicon rubber, is now being tested by Brown and Dohlman4 (fig. 2). Our buried implant has two parts: A cyl inder 2.0 mm in diameter that protrudes into the anterior chamber from 1.8 to 2.0 mm, and an interlamellar plate 4.2-mm wide by 0.15-mm thick (figs. 1-A and 2 ) , which follows the curvature of the cornea. The dioptric power of the implant, combined with that of the cornea, ranges from 4- 56 to + 6 3 . It is buried beneath a total full-thick ness corneal graft and projects beyond the endothelium into the anterior chamber, or it is inserted in an interlamellar pocket. The cyclindric projection beyond the corneal en dothelium prevents the growth of mem branes behind the implant. This character istic differentiates our keratoprosthesis from similarly shaped types, including the one re ported by Tudor Thomas in 19555,e (fig. 2), * From the Department of Ophthalmology, Col lege of Physicians and Surgeons, Columbia Uni versity. This investigation was made possible by grant No. NB-04968 from the National Institutes of Health, Bethesda, Maryland, and by a Fight for Sight grant-in-aid from the National Council to Combat Blindness, Inc. New York.
which corresponds in length to the corneal thickness. Our surgical procedure also differs from that described by Tudor Thom as in that we use a full-thickness corneal graft to cover the implant while he uses a partial lamellar graft for support. In some eyes our implant is inserted in an interla mellar pocket, as described under surgical technique. This buried implant was tested in the eyes of 50 albino rabbits weighing 3.5 kg. Gener al anesthesia was induced by the injection of 1.0 cc of sodium pentothal into the marginal vein of the ear, with the addition of ether administered through a mask for one min ute. SURGICAL TECHNIQUES—BURIED IMPLANT
A 180 degree paralimbic incision is made with a razor blade knife or Castroviejo knife with depth-control mechanism (fig. 3-A), followed by lamellar dissection and preparation of an interlamellar pocket oc cupying more than one-half the corneal area. This is made either with curved scis sors or a Castroviejo spatulated dissector (fig. 3-B). A special 2.0-mm trephine is used to dissect a disc from the center of the posterior layers of the cornea (fig. 3-C). The buried mushroom implant, mounted in the forceps designed for this purpose, is then introduced into the interlamellar pocket until its posterior projection engages the opening made in the cornea (fig. 3-D). The prosthesis is then covered with the corneal flap previously dissected to prepare the pocket (fig. 3-E) and the wound is closed with 7-0 silk sutures (fig. 3-F). Recovery was uneventful for the first five months after insertion of the buried mush room implant, with very slight or no reac tion of the ocular tissues. The corneas re mained completely clear and transparent
KERATOPROSTHESES
(fig. 4-A, B, C and D ) . After six months, slight opacification appeared in the central portion of the stroma over the buried kera toprosthesis in nine of the rabbit eyes. At 14 months, 24 of the 50 rabbit eyes pre sented varying degrees of cloudiness in the epithelium over the central area of the im plant (fig. 5-A, B, C and D ) . Twelve of these 24 animals were killed and the eyes enucleated for histologie study (fig. 6 ) . The remaining 12 were kept under observation. Later a modified implant, to be described, was inserted, using a new surgical tech nique. The 26 rabbits remaining from the original 50 are still under observation with the corneas clear and no untoward reaction to date. Figure 6 shows the histologie changes in the cornea of one of the 12 rabbits killed. The eye was enucleated and fixed in 10% formalin and embedded in celloidin plus 1.0 cc of polymer of methyl methacrylate and
Fig. 1 (Cardona). (A) The anterior mushroom keratoprosthesis and measurements. (B) The posterior (buried) mushroom keratoprosthesis and measurements. (C) Thickened corneal epithelium over the central portion of the buried keratopros thesis. (D) The anterior mushroom keratoprosthe sis inserted over a buried implant.
499 U = l mm
1S»
Themas
1H2
Carl·»·
«--2.011-·->
Brtw·
tU
DMIlMl
ISM
Fig. 2 (Cardona). Evolution of the principal models of buried keratoprostheses (Thomas, Car dona, Brown and Dohlman) and their measure ments.
1.0 cc of chloroform to soften the kerato prosthesis and facilitate cutting of the mi croscopic section. In this slide, it is possible to detect quite clearly the plastic walls of the implant by polarizing the light of the micro scope (fig. 6-D). The epithelium was slightly opaque. It in creased in thickness from the periphery in ward to the central portion of the cornea where it attained twice its normal size (fig. 6-A). In some eyes paralimbic vessels were visible. This opacification and epithelial thickening in the central area of the cornea over the prosthesis, present in approximate ly half of the rabbit eyes, is possibly due to the mechanical barrier of the interlamellar plate or, as suggested by Knowles,7 it is re lated to evaporation from the corneal sur face of the rabbit eye, or because the blink ing rate of the rabbit eye is lower than that of the human eye, as hypothesized by Brown and Dohlman.8 This phenomenon could jeopardize the purpose of the buried implant, which functioned well in about half of the rabbit eyes with no untoward reaction and no opacification. Thus it would seem to offer a good opportunity for improvement in carefully selected human eyes. But what
500
HERNANDO CARDONA
Fig. 3 (Cardona). (A) Making the paralimbic incision. (B) Preparing the interlamellar pocket. (C) Making the central corneal opening with the 2.0-mm trephine. (D) Inserting the posterior mush room keratoprosthesis in the interlamellar pocket. (E) Covering the keratoprosthesis with the corneal flap. (F) Closing the incision with 7-0 silk sutures.
about the remaining 50%? Several possible solutions have been proposed : a. Replacement of the buried keratopros thesis by the through-and-through model implant, but this might involve loss of vitre ous during performance of the various sur gical maneuvers. b. Replacement by a newly designed kera toprosthesis that can be inserted over the one already in place, with a minimum of trauma as it can be used without opening the anterior chamber. This new model, which we call the ante rior mushrpom keratoprosthesis (fig. 1-A) measures 0.65 mm in its anterior cylindric projection and the interlamellar supporting plate is 0.15-mm thick by 4.2-mm wide. The posterior curve of the plate of this implant has the same radius as that of the buried
implant and the dioptric power of the com bined prostheses, as already explained, is the same as that of a through-and-through model. INSERTION TECHNIQUE—ANTERIOR MUSHROOM IMPLANT
A special 2.0-mm trephine is used to make an opening in the center of the cornea over the buried implant (fig. 7-A). A curved paralimbic incision 9.0-mm long is made to the cleavage plane of the corneal tissue covering the buried implant (fig. 7-B). A spatula 1.5-mm wide and 10-mm long is then introduced through the pre viously trephined corneal opening and, with a circular motion, the cleavage plane is dis sected between the corneal tissue and the buried implant (fig. 7-C). The point of the
KERATOPROSTHESES
501
Fig. 4 (Cardona). (A, B, C and D) Rabbit eyes five months after insertion of a buried keratoprosthesis. The stroma and epithelium still remain clear and transparent.
Fig. S (Cardona). (A, B, C and D) Rabbit eyes with posterior (buried) mushroom keratoprosthesis after 14 months, showing opacification of the epithelium and slight vascularization over the implant.
502
HERNANDO CARDONA
-IS** •'S-» - ϊ * ν
~*'~---^Γ·":
s---*.-^sar
-: _^ ' - r-^U. ..; --t-^~.» *
Fig. 6 (Cardona). Microscopic section of rabbit eye. (A) Thickened epithelium and slight opacification in the central area over the buried keratoprosthesis. (B) Normal thickness epithelium. (C) Stroma. (D) Keratoprosthesis (interlamellar plate), (a, b, c and d) Drawing showing the corresponding cross section. (Hematoxylin-eosin, χ93.4.)
spatula should penetrate to the paralimbic incision to insure that the interlamellar pocket is complete (fig. 7-D). The anterior mushroom keratoprosthesis, held in the forceps especially designed for this purpose, is introduced into the interla
mellar pocket until it engages the anterior opening made in the cornea over the buried implant (fig. 7-E). The forceps is then withdrawn and the paralimbic incision closed with 7-0 silk sutures (fig. 7-F). Ten of the rabbits that developed epitheli-
KERATOPROSTHESES
503
Fig. 7 (Cardona). (A) Corneal opening made with the special 2.0-mm trephine. (B) Making the paralimbic incision. (C) Dissecting the cleavage plane between the corneal tissue and the buried implant. (D) Penetration of the spatula to the paralimbic incision. (E) Inserting the keratoprosthesis with the special forceps. (F) Closing the incision with 7-0 silk sutures. al cloudiness over the buried implant were selected for the trial of the new anterior mushroom keratoprosthesis. The implant was inserted, using the surgical technique just described. The tolerance of the corneal tissue to this implant and the results ob tained (fig. 8-A, B. C and D) are similar to those we have already reported for the through-and-through implants.1·2 These ani mals have now been under observation for 10 to 12 months and tolerance continues to be good. The Cardona, Castroviejo and DeVoe team, encouraged by the good results ob tained in the animal study, felt that this new
keratoprosthesis offers an opportunity to improve visual acuity in carefully selected human eyes with a buried implant in place. A clinical study has been undertaken and in two patients the cloudy corneal tissue has been removed from over the buried implant and replaced by an anterior mushroom kera toprosthesis. The combined implants—the previously buried one and the anterior mushroom keratoprosthesis—have now been well tolerated by these patients for several months. However, the results of this trial in human eyes will not be reported for at least two years, the minimum time we feel the eyes should be under observation for ade-
HERNANDO CARDONA
504
Fig. 8 (Cardona). (A, B, C and D) Rabbit eyes with the anterior mushroom keratoprosthesis in place over the posterior (buried) mushroom keratoprosthesis after 12 months.
quate evalution. During this time, the study will also be extended to comprise a much greater number of patients. SUMMARY
A buried implant, in the shape of a mush room, was studied in the eyes of SO albino rabbits. The corneas remained transparent for six months when slight opacification de veloped in the central portion of the stroma over the buried implant. At 14 months, 24 of the rabbit eyes presented varying degrees of cloudiness. Twlve of the animals were killed and the eyes prepared for histologie study. Ten of the remaining 12 rabbits were reoperated and the cloudy corneal tissue over the buried implant was replaced by a new model keratoprosthesis, which is de scribed, as is the surgical technique used for its insertion. These animals have been under observation for 10 to 12 months. The sec ond mushroom implant has been well toler
ated and, with the buried implant already in place, provides dioptric power ranging from + 56 t o + 6 3 . 635 West 165th Street (10032). REFERENCES
1. Cardona, H., Castroviejo, R. and DeVoe, A. G. : The Cardona keratoprosthesis : First clinical evaluation. Acta XIX Internat. Cong. Ophth., 1962, in press. 2. Cardona, H.: Keratoprosthesis: Acrylic opti cal cylinder with supporting intralamellar plate. Am. J. Ophth., 54:284, 1962. 3. : Plastic keratoprostheses : A descrip tion of the plastic material and comparative his tologie study of the recipient cornea. Am. J. Ophth., 58:247,1964. 4. Brown, S. I. and Dohlman, C. H. : A buried corneal implant serving as a barrier to fluid. Arch. Ophth., 73:367, 1965. 5. Thomas, J. W. T. : Acrylic implant in keratoplasty. Tr. Ophth. Soc. U. Kingdom, 75:475, 1955. 6. : Prognosis in lamellar keratoplasty and possible use of buried acrylic mushroom disc in keratoplasty. An. Inst. Barraquer, 3:776, 1963. 7. Knowles, W. F. : Effect of intralamellar plastic membranes on corneal physiology. Am. J. Ophth., 51:274, 1961.