The IOPL after PKD treatment was compared with that obtained using sutures. Two interrupted radial sutures of black monofilament 10-0 nylon (Ethilon suture; Ethicon, Piscataway, NJ) were used to close the keratome incision. The sutures were placed in a radial fashion at approximately 90% corneal depth. Preliminary experiments produced IOPLs of approximately 230 mm Hg. This pressure is similar for the incisions closed with PKD treatment. However, it was observed that the IOP was maintained even when there was leakage around the sutures. The leaks surrounding the sutures were reversible, whereas with PKD the damage was irreversible after the opening of the incision.
This study demonstrates the feasibility of using PKD treatment to close small incisions made in the cornea of rabbit eyes ex vivo. The results show that PKD produces a significant increase in the immediate IOPL of enucleated rabbit eyes after treatment of 3.5-mm corneal incisions.
The dose–response pattern observed for the PKD treatment, using RB as a photosensitizer, is not simple. Reduced IOPL and tissue shrinkage were observed consistently at the highest irradiance of 3.82 W/cm2 and occasionally at 2.55 W/cm2 for doses between 762 and 1524 J/cm2, which suggests contributions from both photochemical and photothermal processes. The ideal conditions to produce a clinically relevant IOPL with PKD are those that balance the shortest treatment time with the highest dose; the limitation is the thermal effects produced using high irradiances. In the cornea, photothermal effects may produce collagen contraction resulting in distortion of the patient’s vision. Therefore, higher irradiances that would allow a shorter treatment time are limited by thermal effects.
Other potential photosensitizers for PKD, chosen on the basis of suitable photochemistry, were investigated. PKD treatments using R-5-P and N-HPT produced increases in the IOPL. Relative efficiencies of the photosensitizers were evaluated by comparing the IOPLs produced by optically matched solutions of the photosensitizers at the same set of irradiances and doses. However, these comparisons do not take into account considerations such as the binding efficiency of the photosensitizers, which alters the dye concentration on the incision surface. All the photosensitizers generate singlet oxygen or reactive radicals that may be toxic to cells in the cornea. Future in vivo studies are needed to determine whether this effect is relevant and, if so, to evaluate possible protective agents. Our results using R-5-P are comparable with those found by Khadem et al.4–6 who used a photoactivated adhesive consisting of fibrinogen and R-5-P irradiated with argon ion laser light (488–514 nm) to close 5-mm penetrating central corneal incisions made in human cadaveric eyes. With this method of incision closure in a smaller sample size, a mean wound-bursting pressure of 154 mm Hg was found. The maximum mean IOPL observed in our study using R-5-P was 254 mm Hg. Our results suggest that the presence of fibrinogen is not necessary to obtain a good seal. Elimination of fibrinogen from the system removes the limitations imposed by using this protein, such as the limited tensile strength and the requirement that the fibrinogen be isolated from the patient to be treated, to avoid risk of infection from donor plasma.42 Other possible suture alternatives for use in ophthalmic surgery that have been investigated include chemical glues.1–3 Glues are limited by the requirement that they be nontoxic, noncarcinogenic, and biodegradable. In addition, glues do not generally provide a permanent closure; they are sloughed off within weeks of application.
Our results show that PKD treatment of small keratome incisions in rabbit cornea ex vivo produced IOPLs comparable with those incisions closed with sutures. The leaks associated with the sutures were reversible, but after the PKD-treated incision had been opened, the seal was completely lost. However, PKD treatment can easily and effectively be repeated on the previously treated incision.
PKD offers many potential advantages over the methods currently used to attach corneal tissue and close incisions in a variety of surgical procedures such as penetrating keratoplasty, laser in situ keratomileusis (LASIK), and cataract surgery and in the treatment of corneal lacerations. The sutures currently used in corneal transplants can induce postoperative astigmatism, neovascularization, and rejection of the donor cornea. Furthermore, loose or broken sutures can leave a patient vulnerable to microbial keratitis. The suturing procedures used are skill intensive and are mainly performed by corneal specialists. PKD offers a simple procedure to close wounds, spot seal LASIK flaps and attach donor cornea, reducing the operating and rehabilitation time.
The authors thank Norman Michaud and Thomas Flotte for collecting the confocal images and for useful discussion, Hans-Christian Luedemann and Dominic Bua for technical help, and Be�atrice M. Aveline for preparation of N-HPT.
1. Henrick A, Gaster RN, Silverstone PJ. Organic tissue glue in the closure of cataract incisions. J Cataract Refract Surg. 1987;13: 551–553.
2. Henrick A, Kalpakian B, Gaster RN, et al. Organic tissue glue in the closure of cataract incisions in rabbit eyes. J Cataract Refract Surg. 1991;17:551–555.
3. Shigemitsu T, Majima Y. The utilization of a biological adhesive for wound treatment: comparison of suture, self-sealing sutureless and cyanoacrylate closure in the tensile strength test. Int Ophthalmol. 1997;20:323–328.
4. Goins KM, Khadem J, Majmudar PA, et al. Photodynamic biological tissue glue to enhance corneal wound healing after radial keratotomy. J Cataract Refract Surg. 1997;23:1331–1338.
5. Goins KM, Khadem J, Majmudar PA. Relative strength of photodynamic biological tissue glue in penetrating keratoplasty in cadaver eyes. J Cataract Refract Surg. 1998;24:1566–1570.
6. Khadem J, Truong T, Ernest JT. Photodynamic biological tissue glue. Cornea. 1994;13:406–410.
7. Barak A, Eyal O, Rosner M, et al. Temperature controlled CO2 laser tissue welding of ocular tissues. Surv Ophthalmol. 1997; 42(suppl):S77– 81.
8. Bass LS, Treat MR. Laser tissue welding: a comprehensive review of current and future applications. Lasers Surg Med. 1995;17:315– 349.
9. Jain KK, Gorisch W. Repair of small blood vessels with the neodynium-YAG: a preliminary report. Surgery. 1979;85:684–688.
10. Oz MC, Bass LS, Popp HW, et al. In vitro comparison of thuliumholium- chromium: YAG and argon ion lasers for welding of biliary tissue. Lasers Surg Med. 1989;9:248 –253. IOVS, October 2000, Vol. 41, No. 11 Photochemical Keratodesmos for Corneal Incision Repair 3339
11. Poppas DP, Schlossberg SM. Laser tissue welding in urological surgery. Urology. 1994;43:143–148.
12. Sauer JS, Hinshaw JR, McGuire KP. The first sutureless, laser welded, end to end bowel anastomosis. Lasers Surg Med. 1989;9: 70–73.
13. Schober RF, Ulrich F, Sander T, et al. Laser-induced alteration of collagen substructure allows microsurgical tissue welding. Science. 1986;232:1421–1422.
14. Dubbleman TMAR, Goeij AFPMD, Stevenick JV. Photodynamic effects of protoporphyrin on human erythrocytes: nature of crosslinking of membrane proteins. Biochim Biophys Acta. 1981;511: 141–151.
15. Verweij H, Dubbelman TMAR, Steveninck JV. Photodynamic protein crosslinking. Photochem Photobiol. 1981;28:87–94.
16. Shen H, Spikes JD, Kopeckova P, et al. Photodynamic crosslinking of proteins, II: photocrosslinking of a model protein-ribonuclease. J Photochem Photobiol B. 1978;35:213–219.
17. Girotti AW. Photosensitized crosslinking of erythrocyte membrane proteins: evidence against participation of amino groups in the reaction. Biochim. Biophys Acta. 1980;602:45–56.
18. Judy MM, Matthews JL, Boriack RL, et al. Photochemical crosslinking of proteins with visible-light absorbing 1,8-naphthalimides. Proc SPIE Int Soc Opt Eng. 1993;1882:221–224.
19. Ramshaw JAM, Stephens LJ, Tulloch PA. Methylene blue sensitized photo-oxidation of collagen fibrils. Biochim Biophys Acta. 1994; 1206:225–230.
20. Spoerl E, Huhle M, Seiler T. Induction of cross-links in corneal tissue. Exp Eye Res. 1998;66:97–103.
21. Judy MM, Fuh L, Matthews JL, et al. Gel electrophoretic studies of photochemical cross-linking of type I collagen with brominated 1,8-naphthalimide dyes and visible light. Proc SPIE Int Soc Opt Eng. 1994;2128:506–509.
22. Judy MM, Matthews JL, Boriack RL, et al. Heat-free photochemical tissue welding with 1,8-naphthalimide dyes using visible (420 nm) light. Proc SPIE Int Soc Opt Eng. 1993;1876:175–179.
23. Gollnick K, Schenck GO. Mechanism and stereoselectivity of photosensitized oxygen transfer reactions. Pure Appl Chem. 1964;9: 507–525.
24. Gandin E, Lion Y, Van de Worst A. Quantum yield of singlet oxygen production by xanthene derivatives. Photochem Photobiol. 1983;37:271–278.
25. Kato Y, Uchida K, Kawakishi S. Aggregation of collagen exposed to UVA in the presence of riboflavin: plausible role of tyrosine modification. Photochem Photobiol. 1994;59:343–349.
26. Hill T, Redmond RW, Kochevar IE. Photosensitized crosslinking of collagen: mechanistic approaches to improved tissue welding. In: First Internet Conference Photochemistry and Photobiology. 1997.
27. Aveline BM, Kochevar IE, Redmond RW. Photochemistry of the nonspecific hydroxyl radical generator, N-hydoxypyridine-2(1H)- thione. J Am Chem Soc. 1996;118:10113–10123.
28. Barton DHR, Jaszberenyi JC, Morrell AI. The generation and reactivity of oxygen centered radicals from the photolysis of derivatives of N-hydroxy-2-thiopyridone. Tetrahedron Lett. 1991;32: 311–314.
29. Boivin J, Crepon E, Zard SZ. N-hydroxy-2-pyridinethione: a mild and convenient source of hydroxyl radicals. Tetrahedron Lett. 1990;31:6869–6872.
30. Hess KM, Dix TA. Evaluation of N-hydroxy-2-thiopridone as a non-metal dependent source of the hydroxyradical in non-aqueous systems. Anal Biochem. 1992;206:309–314.
31. Abergel RP, Lyons RF, White RA. Skin closure by Nd: YAG laser welding. J Am Acad Dermatol. 1986;14:810–814.
32. Cilesiz I, Thomsen S, Welch AJ. Controlled temperature tissue fusion: argon laser welding of rat intestine in vivo. Parts 1 and 2. Lasers Surg Med. 1997;21:269–286.
33. Massicotte JM, Stewart RB, Poppas DP. Effects of endogenous absorption in human albumin solder for acute laser wound closure. Lasers Surg Med. 1998;23:18 –24.
34. Oz M, Johnson JP, Parangi S, et al. Tissue soldering by use of indocyanine green dye-enhanced fibrinogen with the near infrared diode laser. J Vasc Surg. 1990;11:718–725.
35. Poppas D, Stewart RB, Massicotte M, et al. Temperature-controlled laser photocoagulation of soft tissue: in vivo evaluation using a tissue welding model. Lasers Surg Med. 1996;18:335–344.
36. Poppas D, Massicotte JM, Stewart RB, et al. Human albumin solder supplemented with TGF-B1 accelerates healing following laser welded wound closure. Lasers Surg Med. 1996;19:360–368.
37. Stewart R, Benbrahim A, LaMuraglia GM, et al. Laser assisted vascular welding with real time temperature control. Lasers Surg Med. 1996;19:9 –16.
38. Wider T, Libutti SK, Greenwald DP, et al. Skin closure with dyeenhanced laser welding and fibrinogen. Plastic Reconstructr Surg. 1991;88:1018–1025.
39. Chuck R, Oz MC, Delohery TM, et al. Dye-enhanced laser tissue welding. Lasers Surg Med. 1989;9:471–477.
40. Lessing HE, Richardt D, Von Jena A. Quantitative triplet photophysics by picosecond photometry. J Mol Struct. 1982;84:281– 292.
41. Fleming GR, Knight AWE, Morris JM, et al. Picosecond fluorescence studies of xanthene dyes. J Am Chem Soc. 1977;99:4306– 4311.
42. Khodadoust A. Tissue adhesives in ophthalmology. In: Sears ML, Tarkkanen A, eds. Surgical Pharmacology of the Eye. New York: Raven Press; 1985:223–234. 3340 Mulroy et al. IOVS, October 2000, Vol. 41, No. 11