Documenta Ophthalmologica 82: 89-101, 1992. 9 1992 Kluwer Academic Publishers. Printed in the Netherlands.
Mersilene (Polyester), a new suture for penetrating keratoplasty J . A . M . R A M S E L A A R , 1 W.H. B E E K H U 1 S , x W.J. R I J N E V E L D , 1 M.V. V A N A N D E L , 2 F. D I J K 2 & W.L. J O N G E B L O E D 2 1Rotterdam Eye Hospital, Rotterdam, The Netherlands; 2Laboratory Histology & Cell Biology, University of Groningen, Groningen, The Netherlands Accepted 1 September 1992 Key words: Keratometric astigmatism, Mersilene suture, Nylon suture, Penetrating keratoptas-
ty, Suture adjustment, Scanning electron microscopy Abstract. Mersilene (polyester monofilament) seems to be suitable for penetrating keratoplasty
because it is strong, shows no degradation by ultraviolet light, is insoluble, so that it can be left in situ, and offers the possibility of regulating postoperative astigmatism by suture adjustment. In 12 patients penetrating keratoplasty was performed with the combined interrupted/running suturing technique, using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture. The results were compared with those of 25 patients in whom eight interrupted nylon 10-0 sutures and one running nylon 11-0 suture were used. Six months after penetrating keratoplasty, no differences could be found between the two groups in keratometric astigmatism, visual acuity or slitlamp findings. In three patients postoperative adjustment of the running Mersilene suture reduced astigmatism by 50, 90 and 100% respectively. In an animal study the behaviour of Mersilene in the cornea was evaluated by slitlamp examination, histology and electron-microscopy. The tissue response to Mersilene was minimal. Considering the resemblance to nylon in clinical findings, minimal tissue response, lack of biodegradation and possibility of regulating postoperative astigmatism by suture adjustment, Mersilene seems to be a suitable material for penetrating keratoplasty.
Introduction
T h e role of suture materials in the d e v e l o p m e n t of inflammatory reactions has b e e n extensively investigated in general surgery. T h e study of suture materials in corneal surgery offers the o p p o r t u n i t y of in situ and microscopical evaluation [1]. In penetrating keratoplasty, i n f l a m m a t o r y reactions c a u s e d by the suture material threaten the success of the transplantation. A special factor to be considered in the evaluation of a corneal suturing t e c h n i q u e is the p o s t o p e r a t i v e astigmatism. T h e suture must be easy to handle, easy to k n o t and strong, and a d j u s t m e n t of a running suture must n o t cause it to rupture. O t h e r considerations are solubility and d e g r a d a t i o n by ultraviolet light. Because of the low healing t e n d e n c y of the cornea, rapidly absorbing sutures are contra-indicated. U n b r a i d e d (virgin) silk suture material was used in the early days, but this protein material initiates m o r e violent i n f l a m m a t o r y reactions than nylon [2], prolene and vicryl [3].
90 Wounds sutured with stainless steel sutures show only minimal tissue reaction [4-6]. Mersilene (polyester monofilament; Alcon, Fort Worth, TX) seems to be suitable for penetrating keratoplasty for several reasons: it is strong, shows no degradation by ultraviolet light, is insoluble, so that it can be left in situ, and the regulation of postoperative astigmatism by suture adjustment seems possible. Bigar, in 1990, found that the regression of surgically induced astigmatism following cataract surgery was in the same range whether nylon monofilament 10-0 or Mersilene 10-0 was used [7]. The purpose of this study was to determine whether Mersilene can be used in penetrating keratoplasty. In a clinical study we compared the results of penetrating keratoplasty using Mersilene with those obtained by our usual technique. In an animal study the behaviour of Mersilene in the cornea was evaluated and compared with the results of a previous study [6].
Material and methods
Clinical study In 12 patients we performed penetrating keratoplasty with the combined interrupted/running suturing technique using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture, 24 bites (Fig. 1). In the same
Fig. 1. Penetrating keratoplasty using 8 interrupted nylon 10-0 sutures and 1 running Mersilene 11-0 suture (2 weeks postoperatively).
91 period 25 keratoplasty patients were sutured with eight interrupted nylon 10-0 sutures and one running nylon 11-0 suture, 24 bites (Fig. 2). In 6 patients of the nylon/Mersilene group and 13 patients of the nylon/nylon group penetrating keratoplasty was combined with extracapsular cataract extraction and intraocular lens implantation. Clinical observation data (inflammatory reactions, the presence of filaments and infiltrates, keratometric astigmatism and visual acuity) were compared 1, 3, 6 and 9 months postoperatively. If necessary for the improvement of astigmatism, the interrupted sutures were selectively removed from six weeks after surgery onwards, on the basis of central keratometry readings and corneal topography (using a photokeratoscope; Nidek). In three patients in the nylon/Mersilene group suture adjustment was performed 6 to 20 weeks postoperatively according to a technique described by McNeill & Wessels [8]. Under the slitlamp the epithelial wound was opened and the running Mersilene suture was tightened in the flatter meridian of the graft and lossened in the steeper meridian. The improvement in keratometric values was evaluated.
Animal study 1. In situ preparation. Mersilene 11-0 sutures were placed in the eyes of two rabbits by a method described earlier [6]. General anesthesia was administered, using Rompun (2 ml subcutaneous) and Ketalar (1 ml intramuscular).
Fig. 2. Penetrating keratoplasty using 8 interrupted nylon 10-0 sutures and 1 running nylon 11-0 suture (4 weeks postoperatively).
92 After making a linear corneal wound, we placed four sutures in one eye in superficial layers of the cornea and three sutures in deep layers, and in the other eye four superficial sutures only. We used monofilament Mersilene 11-0 with spatula needles (Alcon, Fort Worth, TX). The Mersilene was knotted following the usual knotting technique (2-1-1). The rabbits were examined at regular weekly intervals. The tissue reactions to these sutures were evaluated, with the slitlamp and by histology and scanning electron-microscopy.
2. Preparation for light microscopy (LM) and scanning electron-microscopy (SEM). The first rabbit was killed three weeks after the operation, the other after seven weeks. The eyes were rinsed with a mixture of 0.1 M Nacacodylate buffer +6% sucrose (400 mOsm; pH 7.4) for 1 minute. After removal, the corneas were rinsed again in the sucrose/cacodylate buffer for 30 seconds and fixed in 2% glutaraldehyde in 0.1 M Na-cacodylate buffer solution (pH 7.4, 4 ~ 24 hrs) and subsequently washed with buffer solution. For SEM, pieces of the cornea including sutures were immersed in a mixture of guanidine-hydrochloride (2%), glycine (2%) and sucrose (2%) for 8 hours at 20 ~ After rinsing in the same buffer the samples were immersed again in a mixture of argine (2%) and tannic acid (2%) at 20 ~ all solutions were freshly prepared and filtered through a 0.22 ~m Millipore filter. After this procedure the samples were washed several times in distilled water and placed in an aqueous osmiumtetroxide solution (2%) for 16 hours at 20 ~ Finally the samples were dehydrated in ethanol, criticalpoint dried in liquid CO2 and examined in a ISI SEM, type DS-130 at 10-15 kV, without any external metal coating. For LM, the other pieces of the glutaraldehyde fixed corneas with sutures were washed with distilled water, dehydrated in ethanol, embedded in glycolmethacrylate (GMA) and thinly sectioned (1-2 I~m). LM-sections were stained with toluidine blue/ basic fuchsine.
Results
Surgical aspects The Mersilene (11-0) material handles like nylon (10-0) and is convenient to suture and knot. Suture adjustment of a running Mersilene suture is not difficult to perform and takes about 15 minutes.
Results of clinical study 1. Clinical observation data. In both the nylon/nylon group and the nylon/ Mersilene group, minor infiltrates (16% and 8% respectively) and filaments (20% and 25% respectively) were seen. In two cases in the nylon/nylon
93 group and one case in the nylon/Mersilene group sutures were revised because they lost tension. No difference could be found between the two groups in the subjective experience of the patients, the rate of postoperative reepitheliallisation or the clarity of the graft.
2. Visual acuity. In Table 1 the mean preoperative and 6-month postoperative visual acuities of the nylon/Mersilene and nylon/nylon groups are shown. In this table a subdivision has been made between cases with and without cataract extraction. 3. Astigmatism. Keratometric astigmatism in diopters and the standard deviation at 1, 3, 6 and 9 months postoperatively are shown for both groups in Fig. 3. An impression of the distribution of the keratometric astigmatism over the patients six months postoperatively is given in table 2. In both
Table 1. Mean preoperative and six-month postoperative visual acuity of the nylon/Mersilene and nylon/nylon groups
Visual acuity
Nylon/Mersilene group
With cataract extraction No cataract extraction Total
Nylon/Nylon group
Preop
Postop
Preop
Postop
0.21 0.13 0.18
0.41 0.31 0.36
0.19 0.43 0.30
0.54 0.55 0.54
astigmatism (diopters) 8 7
6 5 4 3 2 1 3
6
postoperative period (months) Fig. 3. Astigmatism (Diopters) and standard deviation as measured by keratometry plotted
against postoperative period (months). O: Nylon/Nylon group; [3: Nylon/Mersilene group.
94 Table 2. Distribution of keratometric astigmatism (Diopters) over patients six m o n t h s postoperatively Keratometric astigmatism
Plano
N y l o n / N y l o n group N y l o n / M e r s i l e n e group
7% 12.5%
~< 3 D 50% 50%
3-6 D
>6 D
43% 25%
none 12.5%
groups at six months only one case showed astigmatism of more than 4 diopters.
4. Suture adjustment. As shown in Table 3, in three cases of slitlamp adjustment several weeks postoperatively, we reduced astigmatism in a single session by 50, 90 and 100% respectively. The performance of this procedure took about 15 minutes.
Results of animal study 1. Slitlamp evaluation. Three weeks after operation, the eyes sutured with only superficial sutures showed loosening of one suture with accumulation of mucus and fibrinoid material around that suture. The eyes with superficial and deep sutures showed no loss of tension or fibrinoid material. Seven weeks after operation loosening of sutures was seen in one superficial nasal suture in the eye with superficial and deep sutures and in three sutures in the other eye. The loose sutures had collected some mucus and fibrinoid material and were not broken. We did not observe absence of sutures, vascularisation or infiltrates. 2. Histological evaluation. On histological examination the reaction to Mersilene was seen to be minimal (Fig. 4). It consisted primarily of some fibroblasts in the tissue surrounding the suture. Three weeks after operation epithelial cells and endothelial cells have started to grow over the sutures (Figs. 5, 6). Suture parts not covered by the epithelium had collected some fibrinoid material.
3. Evaluation by scanning electron-microscopy. Scanning electron-microscopy showed that the epithelium of the superficially sutured rabbit corneas looked relatively smooth. Some of the sutures were evaluated above the Table 3. Keratometric astigmatism (Diopters) and vectors before and directly after suture adjustment Case
N u m b e r of weeks after operation
Astigmatism before a d j u s t m e n t
Astigmatism after adjustment
1 2 3
20 weeks 6weeks 13 weeks
6 • 165 r = 7.9 5• r=7.6 4.5 • 155 r = 7.8
3 x 180 r = 7.6 plano r = 7 . 3 0.5 • 180 r = 7.4
95
Fig. 4. Histological section of rabbit cornea 7 weeks after operation. Mersilene suture in stromal part of cornea. Minimal tissue reaction. Ep = epithelium (Toluidine basic fuchsine staining, x200).
Fig. 5. Histological section of rabbit cornea 3 weeks after operation. Mersilene suture surrounded by epithelial cells. Minimal inflammatory reaction. Arrows: polymorphonuclear granulocytes (Toluidine blue staining, x300).
epithelium; others were completely covered by the epithelium (Figs. 7, 8). No degradation of epithelial tissue was noted. Covering by endothelial cells was clearly visible (Figs. 9, 10) and was only incomplete in those cases where the suture made a wide loop outside the endothelium. At the
96
Fig. 6. Histological section of rabbit cornea 7 weeks after operation. Endothelial cells (End) have overgrown mersilene suture. Large arrow: subendothelial fibroblasts adjacent to suture (Toluidine basic fuchsine staining, x300),
Fig. 7. SEM image of rabbit cornea 3 weeks after operation. Wound and sutures are completely covered by epithelial cells ( •
97
Fig. 8. Detail of Figure 7. Arrow: Mersilene suture (x120).
Fig, 9. SEM image of rabbit cornea seven weeks after operation. Sutures are covered by endothelial cells with pronounced microvili ( x 120).
98
Fig. 10. Detail of Figure 9. Arrow: microvilli on endothelial cells (•
endothelial side active cells, with normal numbers of microvilli, were visible around the needle entrance (Figs. 9, 10).
Discussion
Clinical comparison of the slitlamp findings in two groups of penetrating keratoplasty patients operated with the combined interrupted/running suturing technique, in one group using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture and in the other group eight interrupted nylon 10-0 sutures and one funning nylon 11-0 suture, showed no differences between the groups. Six months after penetrating keratoplasty, the visual acuity and the improvement in visual acuity were in the same range in the two groups. In the postoperative period keratometric astigmatism and the standard deviation decreased in both groups in the same way. Adjustment of Mersilene Sutures under the slitlamp resulted in three cases in total or partial reduction of the corneal astigmatism. Test animals failed to demonstrate an inflammatory response when the wound was sutured with Mersilene. When we compare the results of our animal study with a previous study in which nylon and stainless steel were used [6], on slitlamp examination the stainless steel group showed less fibrinoid material and loose sutures than our group, which in turn showed less fibrinoid material and loose sutures than the nylon group. As could be seen with scanning-electron microscopy, three weeks after suturing most of the superficial sutures were well covered with epithelium, and four weeks
99 later the endothelium also covered the deep sutures. In histological sections the reaction to Mersilene was minimal. It consisted primarily of fibroblasts in the tissue surrounding the suture. In 1975 Kelly [9], who studied tissue reactions in rabbit iris and cornea to prolene and nylon sutures, described a similar slight tissue reaction. On evaluation by scanning electron-microscopy, the epithelium looks more smooth than in the earlier investigation with nylon [6], although in this case also some of the sutures and knots are elevated above the epithelium. No degradation of epithelial tissue, as was seen with nylon sutures, was observed. We noted better coverage of sutures by endothelial cells than in the previous study using nylon 10-0 material [6]. We are aware that we studied a smaller group for a shorter period, but we may conclude that Mersilene certainly does not bring about a greater tissue reaction than nylon. Stainless steel, however, seems to produce even less tissue reaction [4-6]. Considering the minimal tissue response in the animal study and the similarities to nylon when used in penetrating keratoplasty, Mersilene seems to be suitable for corneal grafting. In addition, it is strong, it shows no biodegradation, it can be left indefinitely in the cornea, thus making the corneal shape stable, and above all, it offers the possibility of suture adjustment under the slitlamp. Stainless steel sutures can not be adjusted in this way. Frequently, in keratoplasty using eight nylon 10-0 interrupted sutures and a continuous nylon 11-0 suture selective removal of interrupted sutures is indicated to reduce corneal astigmatism [10, 11]. However, when selective removal of interrupted sutures does not improve corneal astigmatism satisfactorily, suture adjustment, although a time-consuming procedure, seems to be a good alternative. Lin et al. [12] showed significant improvement in corneal astigmatism after suture adjustment of one running nylon 10-0 suture. Their study group and their control group, in which no suture adjustment took place, were sutured with one running nylon 10-0 suture only. Since the risk of suture breakage, especially during adjustment, increases with the length of time after surgery because of biodegradation of the nylon suture, Lin et al. considered the use of a suture that is resistant to biodegradation. According to these authors, polyester was unsuitable because of low elasticity and the tendency to cheese-wire through the tissue during adjustment. In our experience Mersilene 11-0 is easy to handle and easy to knot. The mechanical properties: tensile strength, Young's modulus, elongation, knot holding strength, knot pull strength and torsional flexibility, of nylon and polyester were found to be about the same [13]. Van Meter et al. [14] compared cases of postkeratoplasty astigmatism in which selective removal of sutures in the combined interrupted/running suturing technique was performed with cases in which suture adjustment of one running nylon 10-0 suture was done. They noted less postoperative
100 astigmatism, fewer manipulations, and earlier optical stability and visual rehabilitation in the suture adjustment group. No continuous sutures were broken during adjustment. Results of a long-term follow-up study by Frueh et al. [15], however, suggested that nylon 11-0 is not an ideal material for running sutures since its high rate of spontaneous rupture leads to undesired increases in postkeratoplasty astigmatism. Further, their results indicated that the selective suture removal technique can maintain decreased astigmatism only if the sutures remain intact. A long-time follow-up study will be necessary, but Mersilene, with its insolubility and lack of biodegradation or degradation by ultraviolet light, seems to be a good candidate for use in penetrating keratoplasty. Since we know now that the use of polyester sutures is feasible, our aim in the future is to use one running Mersilene 11-0 suture only, without interrupted nylon sutures.
Acknowledgements This study was supported by the Stichting Oogheelkundige Research (STORE). The authors are grateful for stimulating discussions with Professor J.G.F. Worst.
References 1. Ulin AW. The ideal suture material. Surg Gynaecol Obstet 1971; 133: 475. 2. Aronson SB, Moore TE. Suture reaction in the rabbit cornea. Arch Opthalmol 1969; 82: 531-36. 3. Gurrierrez Sant L. Histopathological reaction of the new synthetic sutures in surgery of the anterior segment. Arch Sock Esp Oftal 1985; 48: 343-49. 4. Jongebloed WL, Rijneveld WJ, Cuperus PL, van Andel P, Worst JGF. Stainless steel as suturing material in human corneas: a SEM study. Doc Ophthalmol 1988; 70: 145-54. 5. Jongebloed WL, van der Veen G, Kalicharan D~ Rijneveld WJ, Houtman WA, Worst JGF. Reaction of the rabbit corneal endothelium to nylon sutures: a SEM study. Doc Ophthalmol 1990; 75: 351-58. 6. Rijneveld WJ, Jongebloed WL, Worst JGF, Houtman WA. Comparison of the reaction of the cornea to nylon and stainless steel sutures, an animal study. Doc Ophthalmol 1989; 72: 297-307. 7. Bigar F. Astigmatismus nach Katarakt-Chirurgie: Vergleich nach Wundverschluss mit Nylonfaden und Mersilene. Klin Mbl Augenheilk 1990; 196: 314-15. 8. McNeill JL, Wessels IF, Adjustment of single continuous suture to control astigmatism after penetrating keratoplasty. Refract Corneal Surg 1989; 5: 216-23. 9. Kelly SE, Ehlers J, Llovera I, Troutman RC. Comparison of tissue reaction to nylon and prolene sutures in rabbit iris and cornea. Ophthalmic Surg 1975; 6: 105-10. 10. Binder PS. Selective suture removal can reduce postkeratoplasty astigmatism. Ophthalmology 1985; 92: 1412-16. 11. Stainer GA, Perl T, Binder PS. Controlled reduction of postkeratoplasty astigmatism. Ophthalmology 1982: 89: 668-76.
101 12. Lin DTC, Wilson SE, Reidy JJ, Klyce SD, McDonald MB, Kaufman HE, McNeill JL. An adjustable single running suture technique to reduce postkeratoplasty astigmatism. Ophthalmology 1990; 97: 934-38. 13. Cohan BC, Leenslag JW, Miles J, Pennings AJ. An evaluation of ultrastrong polyethylene fiber as an ophthalmic suture. Arch Ophthalmol 1985; 103: 1816-21. 14. van Meter WS, Gussler JR, Soloman KD, Wood TO. Postkeratoptasty Astigmatism Control. Ophthalmology 1991; 98: 177-83. 15. Frueh BE, Feldman ST, Feldman RM, Sossi NP, Frucht-Pery J, Brown SI. Running nylon suture dissolution after penetrating keratoplasty. Am J Ophthalmol 1992; 113: 406-11.
Address for correspondence: Dr J.A.M. Ramselaar, Eye Hospital Rotterdam, 180 Schiedamse Vest, P.O.B. 70030, 3000 LM Rotterdam, The Netherlands
Mersilene (Polyester), a new suture for penetrating keratoplasty J . A . M . R A M S E L A A R , 1 W.H. B E E K H U 1 S , x W.J. R I J N E V E L D , 1 M.V. V A N A N D E L , 2 F. D I J K 2 & W.L. J O N G E B L O E D 2 1Rotterdam Eye Hospital, Rotterdam, The Netherlands; 2Laboratory Histology & Cell Biology, University of Groningen, Groningen, The Netherlands Accepted 1 September 1992 Key words: Keratometric astigmatism, Mersilene suture, Nylon suture, Penetrating keratoptas-
ty, Suture adjustment, Scanning electron microscopy Abstract. Mersilene (polyester monofilament) seems to be suitable for penetrating keratoplasty
because it is strong, shows no degradation by ultraviolet light, is insoluble, so that it can be left in situ, and offers the possibility of regulating postoperative astigmatism by suture adjustment. In 12 patients penetrating keratoplasty was performed with the combined interrupted/running suturing technique, using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture. The results were compared with those of 25 patients in whom eight interrupted nylon 10-0 sutures and one running nylon 11-0 suture were used. Six months after penetrating keratoplasty, no differences could be found between the two groups in keratometric astigmatism, visual acuity or slitlamp findings. In three patients postoperative adjustment of the running Mersilene suture reduced astigmatism by 50, 90 and 100% respectively. In an animal study the behaviour of Mersilene in the cornea was evaluated by slitlamp examination, histology and electron-microscopy. The tissue response to Mersilene was minimal. Considering the resemblance to nylon in clinical findings, minimal tissue response, lack of biodegradation and possibility of regulating postoperative astigmatism by suture adjustment, Mersilene seems to be a suitable material for penetrating keratoplasty.
Introduction
T h e role of suture materials in the d e v e l o p m e n t of inflammatory reactions has b e e n extensively investigated in general surgery. T h e study of suture materials in corneal surgery offers the o p p o r t u n i t y of in situ and microscopical evaluation [1]. In penetrating keratoplasty, i n f l a m m a t o r y reactions c a u s e d by the suture material threaten the success of the transplantation. A special factor to be considered in the evaluation of a corneal suturing t e c h n i q u e is the p o s t o p e r a t i v e astigmatism. T h e suture must be easy to handle, easy to k n o t and strong, and a d j u s t m e n t of a running suture must n o t cause it to rupture. O t h e r considerations are solubility and d e g r a d a t i o n by ultraviolet light. Because of the low healing t e n d e n c y of the cornea, rapidly absorbing sutures are contra-indicated. U n b r a i d e d (virgin) silk suture material was used in the early days, but this protein material initiates m o r e violent i n f l a m m a t o r y reactions than nylon [2], prolene and vicryl [3].
90 Wounds sutured with stainless steel sutures show only minimal tissue reaction [4-6]. Mersilene (polyester monofilament; Alcon, Fort Worth, TX) seems to be suitable for penetrating keratoplasty for several reasons: it is strong, shows no degradation by ultraviolet light, is insoluble, so that it can be left in situ, and the regulation of postoperative astigmatism by suture adjustment seems possible. Bigar, in 1990, found that the regression of surgically induced astigmatism following cataract surgery was in the same range whether nylon monofilament 10-0 or Mersilene 10-0 was used [7]. The purpose of this study was to determine whether Mersilene can be used in penetrating keratoplasty. In a clinical study we compared the results of penetrating keratoplasty using Mersilene with those obtained by our usual technique. In an animal study the behaviour of Mersilene in the cornea was evaluated and compared with the results of a previous study [6].
Material and methods
Clinical study In 12 patients we performed penetrating keratoplasty with the combined interrupted/running suturing technique using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture, 24 bites (Fig. 1). In the same
Fig. 1. Penetrating keratoplasty using 8 interrupted nylon 10-0 sutures and 1 running Mersilene 11-0 suture (2 weeks postoperatively).
91 period 25 keratoplasty patients were sutured with eight interrupted nylon 10-0 sutures and one running nylon 11-0 suture, 24 bites (Fig. 2). In 6 patients of the nylon/Mersilene group and 13 patients of the nylon/nylon group penetrating keratoplasty was combined with extracapsular cataract extraction and intraocular lens implantation. Clinical observation data (inflammatory reactions, the presence of filaments and infiltrates, keratometric astigmatism and visual acuity) were compared 1, 3, 6 and 9 months postoperatively. If necessary for the improvement of astigmatism, the interrupted sutures were selectively removed from six weeks after surgery onwards, on the basis of central keratometry readings and corneal topography (using a photokeratoscope; Nidek). In three patients in the nylon/Mersilene group suture adjustment was performed 6 to 20 weeks postoperatively according to a technique described by McNeill & Wessels [8]. Under the slitlamp the epithelial wound was opened and the running Mersilene suture was tightened in the flatter meridian of the graft and lossened in the steeper meridian. The improvement in keratometric values was evaluated.
Animal study 1. In situ preparation. Mersilene 11-0 sutures were placed in the eyes of two rabbits by a method described earlier [6]. General anesthesia was administered, using Rompun (2 ml subcutaneous) and Ketalar (1 ml intramuscular).
Fig. 2. Penetrating keratoplasty using 8 interrupted nylon 10-0 sutures and 1 running nylon 11-0 suture (4 weeks postoperatively).
92 After making a linear corneal wound, we placed four sutures in one eye in superficial layers of the cornea and three sutures in deep layers, and in the other eye four superficial sutures only. We used monofilament Mersilene 11-0 with spatula needles (Alcon, Fort Worth, TX). The Mersilene was knotted following the usual knotting technique (2-1-1). The rabbits were examined at regular weekly intervals. The tissue reactions to these sutures were evaluated, with the slitlamp and by histology and scanning electron-microscopy.
2. Preparation for light microscopy (LM) and scanning electron-microscopy (SEM). The first rabbit was killed three weeks after the operation, the other after seven weeks. The eyes were rinsed with a mixture of 0.1 M Nacacodylate buffer +6% sucrose (400 mOsm; pH 7.4) for 1 minute. After removal, the corneas were rinsed again in the sucrose/cacodylate buffer for 30 seconds and fixed in 2% glutaraldehyde in 0.1 M Na-cacodylate buffer solution (pH 7.4, 4 ~ 24 hrs) and subsequently washed with buffer solution. For SEM, pieces of the cornea including sutures were immersed in a mixture of guanidine-hydrochloride (2%), glycine (2%) and sucrose (2%) for 8 hours at 20 ~ After rinsing in the same buffer the samples were immersed again in a mixture of argine (2%) and tannic acid (2%) at 20 ~ all solutions were freshly prepared and filtered through a 0.22 ~m Millipore filter. After this procedure the samples were washed several times in distilled water and placed in an aqueous osmiumtetroxide solution (2%) for 16 hours at 20 ~ Finally the samples were dehydrated in ethanol, criticalpoint dried in liquid CO2 and examined in a ISI SEM, type DS-130 at 10-15 kV, without any external metal coating. For LM, the other pieces of the glutaraldehyde fixed corneas with sutures were washed with distilled water, dehydrated in ethanol, embedded in glycolmethacrylate (GMA) and thinly sectioned (1-2 I~m). LM-sections were stained with toluidine blue/ basic fuchsine.
Results
Surgical aspects The Mersilene (11-0) material handles like nylon (10-0) and is convenient to suture and knot. Suture adjustment of a running Mersilene suture is not difficult to perform and takes about 15 minutes.
Results of clinical study 1. Clinical observation data. In both the nylon/nylon group and the nylon/ Mersilene group, minor infiltrates (16% and 8% respectively) and filaments (20% and 25% respectively) were seen. In two cases in the nylon/nylon
93 group and one case in the nylon/Mersilene group sutures were revised because they lost tension. No difference could be found between the two groups in the subjective experience of the patients, the rate of postoperative reepitheliallisation or the clarity of the graft.
2. Visual acuity. In Table 1 the mean preoperative and 6-month postoperative visual acuities of the nylon/Mersilene and nylon/nylon groups are shown. In this table a subdivision has been made between cases with and without cataract extraction. 3. Astigmatism. Keratometric astigmatism in diopters and the standard deviation at 1, 3, 6 and 9 months postoperatively are shown for both groups in Fig. 3. An impression of the distribution of the keratometric astigmatism over the patients six months postoperatively is given in table 2. In both
Table 1. Mean preoperative and six-month postoperative visual acuity of the nylon/Mersilene and nylon/nylon groups
Visual acuity
Nylon/Mersilene group
With cataract extraction No cataract extraction Total
Nylon/Nylon group
Preop
Postop
Preop
Postop
0.21 0.13 0.18
0.41 0.31 0.36
0.19 0.43 0.30
0.54 0.55 0.54
astigmatism (diopters) 8 7
6 5 4 3 2 1 3
6
postoperative period (months) Fig. 3. Astigmatism (Diopters) and standard deviation as measured by keratometry plotted
against postoperative period (months). O: Nylon/Nylon group; [3: Nylon/Mersilene group.
94 Table 2. Distribution of keratometric astigmatism (Diopters) over patients six m o n t h s postoperatively Keratometric astigmatism
Plano
N y l o n / N y l o n group N y l o n / M e r s i l e n e group
7% 12.5%
~< 3 D 50% 50%
3-6 D
>6 D
43% 25%
none 12.5%
groups at six months only one case showed astigmatism of more than 4 diopters.
4. Suture adjustment. As shown in Table 3, in three cases of slitlamp adjustment several weeks postoperatively, we reduced astigmatism in a single session by 50, 90 and 100% respectively. The performance of this procedure took about 15 minutes.
Results of animal study 1. Slitlamp evaluation. Three weeks after operation, the eyes sutured with only superficial sutures showed loosening of one suture with accumulation of mucus and fibrinoid material around that suture. The eyes with superficial and deep sutures showed no loss of tension or fibrinoid material. Seven weeks after operation loosening of sutures was seen in one superficial nasal suture in the eye with superficial and deep sutures and in three sutures in the other eye. The loose sutures had collected some mucus and fibrinoid material and were not broken. We did not observe absence of sutures, vascularisation or infiltrates. 2. Histological evaluation. On histological examination the reaction to Mersilene was seen to be minimal (Fig. 4). It consisted primarily of some fibroblasts in the tissue surrounding the suture. Three weeks after operation epithelial cells and endothelial cells have started to grow over the sutures (Figs. 5, 6). Suture parts not covered by the epithelium had collected some fibrinoid material.
3. Evaluation by scanning electron-microscopy. Scanning electron-microscopy showed that the epithelium of the superficially sutured rabbit corneas looked relatively smooth. Some of the sutures were evaluated above the Table 3. Keratometric astigmatism (Diopters) and vectors before and directly after suture adjustment Case
N u m b e r of weeks after operation
Astigmatism before a d j u s t m e n t
Astigmatism after adjustment
1 2 3
20 weeks 6weeks 13 weeks
6 • 165 r = 7.9 5• r=7.6 4.5 • 155 r = 7.8
3 x 180 r = 7.6 plano r = 7 . 3 0.5 • 180 r = 7.4
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Fig. 4. Histological section of rabbit cornea 7 weeks after operation. Mersilene suture in stromal part of cornea. Minimal tissue reaction. Ep = epithelium (Toluidine basic fuchsine staining, x200).
Fig. 5. Histological section of rabbit cornea 3 weeks after operation. Mersilene suture surrounded by epithelial cells. Minimal inflammatory reaction. Arrows: polymorphonuclear granulocytes (Toluidine blue staining, x300).
epithelium; others were completely covered by the epithelium (Figs. 7, 8). No degradation of epithelial tissue was noted. Covering by endothelial cells was clearly visible (Figs. 9, 10) and was only incomplete in those cases where the suture made a wide loop outside the endothelium. At the
96
Fig. 6. Histological section of rabbit cornea 7 weeks after operation. Endothelial cells (End) have overgrown mersilene suture. Large arrow: subendothelial fibroblasts adjacent to suture (Toluidine basic fuchsine staining, x300),
Fig. 7. SEM image of rabbit cornea 3 weeks after operation. Wound and sutures are completely covered by epithelial cells ( •
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Fig. 8. Detail of Figure 7. Arrow: Mersilene suture (x120).
Fig, 9. SEM image of rabbit cornea seven weeks after operation. Sutures are covered by endothelial cells with pronounced microvili ( x 120).
98
Fig. 10. Detail of Figure 9. Arrow: microvilli on endothelial cells (•
endothelial side active cells, with normal numbers of microvilli, were visible around the needle entrance (Figs. 9, 10).
Discussion
Clinical comparison of the slitlamp findings in two groups of penetrating keratoplasty patients operated with the combined interrupted/running suturing technique, in one group using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture and in the other group eight interrupted nylon 10-0 sutures and one funning nylon 11-0 suture, showed no differences between the groups. Six months after penetrating keratoplasty, the visual acuity and the improvement in visual acuity were in the same range in the two groups. In the postoperative period keratometric astigmatism and the standard deviation decreased in both groups in the same way. Adjustment of Mersilene Sutures under the slitlamp resulted in three cases in total or partial reduction of the corneal astigmatism. Test animals failed to demonstrate an inflammatory response when the wound was sutured with Mersilene. When we compare the results of our animal study with a previous study in which nylon and stainless steel were used [6], on slitlamp examination the stainless steel group showed less fibrinoid material and loose sutures than our group, which in turn showed less fibrinoid material and loose sutures than the nylon group. As could be seen with scanning-electron microscopy, three weeks after suturing most of the superficial sutures were well covered with epithelium, and four weeks
99 later the endothelium also covered the deep sutures. In histological sections the reaction to Mersilene was minimal. It consisted primarily of fibroblasts in the tissue surrounding the suture. In 1975 Kelly [9], who studied tissue reactions in rabbit iris and cornea to prolene and nylon sutures, described a similar slight tissue reaction. On evaluation by scanning electron-microscopy, the epithelium looks more smooth than in the earlier investigation with nylon [6], although in this case also some of the sutures and knots are elevated above the epithelium. No degradation of epithelial tissue, as was seen with nylon sutures, was observed. We noted better coverage of sutures by endothelial cells than in the previous study using nylon 10-0 material [6]. We are aware that we studied a smaller group for a shorter period, but we may conclude that Mersilene certainly does not bring about a greater tissue reaction than nylon. Stainless steel, however, seems to produce even less tissue reaction [4-6]. Considering the minimal tissue response in the animal study and the similarities to nylon when used in penetrating keratoplasty, Mersilene seems to be suitable for corneal grafting. In addition, it is strong, it shows no biodegradation, it can be left indefinitely in the cornea, thus making the corneal shape stable, and above all, it offers the possibility of suture adjustment under the slitlamp. Stainless steel sutures can not be adjusted in this way. Frequently, in keratoplasty using eight nylon 10-0 interrupted sutures and a continuous nylon 11-0 suture selective removal of interrupted sutures is indicated to reduce corneal astigmatism [10, 11]. However, when selective removal of interrupted sutures does not improve corneal astigmatism satisfactorily, suture adjustment, although a time-consuming procedure, seems to be a good alternative. Lin et al. [12] showed significant improvement in corneal astigmatism after suture adjustment of one running nylon 10-0 suture. Their study group and their control group, in which no suture adjustment took place, were sutured with one running nylon 10-0 suture only. Since the risk of suture breakage, especially during adjustment, increases with the length of time after surgery because of biodegradation of the nylon suture, Lin et al. considered the use of a suture that is resistant to biodegradation. According to these authors, polyester was unsuitable because of low elasticity and the tendency to cheese-wire through the tissue during adjustment. In our experience Mersilene 11-0 is easy to handle and easy to knot. The mechanical properties: tensile strength, Young's modulus, elongation, knot holding strength, knot pull strength and torsional flexibility, of nylon and polyester were found to be about the same [13]. Van Meter et al. [14] compared cases of postkeratoplasty astigmatism in which selective removal of sutures in the combined interrupted/running suturing technique was performed with cases in which suture adjustment of one running nylon 10-0 suture was done. They noted less postoperative
100 astigmatism, fewer manipulations, and earlier optical stability and visual rehabilitation in the suture adjustment group. No continuous sutures were broken during adjustment. Results of a long-term follow-up study by Frueh et al. [15], however, suggested that nylon 11-0 is not an ideal material for running sutures since its high rate of spontaneous rupture leads to undesired increases in postkeratoplasty astigmatism. Further, their results indicated that the selective suture removal technique can maintain decreased astigmatism only if the sutures remain intact. A long-time follow-up study will be necessary, but Mersilene, with its insolubility and lack of biodegradation or degradation by ultraviolet light, seems to be a good candidate for use in penetrating keratoplasty. Since we know now that the use of polyester sutures is feasible, our aim in the future is to use one running Mersilene 11-0 suture only, without interrupted nylon sutures.
Acknowledgements This study was supported by the Stichting Oogheelkundige Research (STORE). The authors are grateful for stimulating discussions with Professor J.G.F. Worst.
References 1. Ulin AW. The ideal suture material. Surg Gynaecol Obstet 1971; 133: 475. 2. Aronson SB, Moore TE. Suture reaction in the rabbit cornea. Arch Opthalmol 1969; 82: 531-36. 3. Gurrierrez Sant L. Histopathological reaction of the new synthetic sutures in surgery of the anterior segment. Arch Sock Esp Oftal 1985; 48: 343-49. 4. Jongebloed WL, Rijneveld WJ, Cuperus PL, van Andel P, Worst JGF. Stainless steel as suturing material in human corneas: a SEM study. Doc Ophthalmol 1988; 70: 145-54. 5. Jongebloed WL, van der Veen G, Kalicharan D~ Rijneveld WJ, Houtman WA, Worst JGF. Reaction of the rabbit corneal endothelium to nylon sutures: a SEM study. Doc Ophthalmol 1990; 75: 351-58. 6. Rijneveld WJ, Jongebloed WL, Worst JGF, Houtman WA. Comparison of the reaction of the cornea to nylon and stainless steel sutures, an animal study. Doc Ophthalmol 1989; 72: 297-307. 7. Bigar F. Astigmatismus nach Katarakt-Chirurgie: Vergleich nach Wundverschluss mit Nylonfaden und Mersilene. Klin Mbl Augenheilk 1990; 196: 314-15. 8. McNeill JL, Wessels IF, Adjustment of single continuous suture to control astigmatism after penetrating keratoplasty. Refract Corneal Surg 1989; 5: 216-23. 9. Kelly SE, Ehlers J, Llovera I, Troutman RC. Comparison of tissue reaction to nylon and prolene sutures in rabbit iris and cornea. Ophthalmic Surg 1975; 6: 105-10. 10. Binder PS. Selective suture removal can reduce postkeratoplasty astigmatism. Ophthalmology 1985; 92: 1412-16. 11. Stainer GA, Perl T, Binder PS. Controlled reduction of postkeratoplasty astigmatism. Ophthalmology 1982: 89: 668-76.
101 12. Lin DTC, Wilson SE, Reidy JJ, Klyce SD, McDonald MB, Kaufman HE, McNeill JL. An adjustable single running suture technique to reduce postkeratoplasty astigmatism. Ophthalmology 1990; 97: 934-38. 13. Cohan BC, Leenslag JW, Miles J, Pennings AJ. An evaluation of ultrastrong polyethylene fiber as an ophthalmic suture. Arch Ophthalmol 1985; 103: 1816-21. 14. van Meter WS, Gussler JR, Soloman KD, Wood TO. Postkeratoptasty Astigmatism Control. Ophthalmology 1991; 98: 177-83. 15. Frueh BE, Feldman ST, Feldman RM, Sossi NP, Frucht-Pery J, Brown SI. Running nylon suture dissolution after penetrating keratoplasty. Am J Ophthalmol 1992; 113: 406-11.
Address for correspondence: Dr J.A.M. Ramselaar, Eye Hospital Rotterdam, 180 Schiedamse Vest, P.O.B. 70030, 3000 LM Rotterdam, The Netherlands
