Rose Bengal and Green Light Versus Riboflavin-UVA Cross-Linking: Corneal Wound Repair Response.

Purpose: To study corneal wound healing after two cross-linking techniques using either rose bengal and green light (RGX) or the conventional treatment using riboflavin and UVA radiation (UVX). Methods: Corneas of New Zealand rabbits were monolaterally treated with UVX (21 eyes) or RGX (25 eyes). Treatments involved corneal de-epithelialization (8-mm diameter), soaking with photosensitizer (0.1% riboflavin in 20% dextran for 30 minutes for UVX; 0.1% rose bengal for 2 minutes for RGX), and light irradiation (370 nm, 3 mW/cm2, 30 minutes for UVX; 532 nm, 0.25 W/cm2, 7 minutes for RGX). Contralateral eyes were used as controls. Clinical follow-up included fluorescein staining, haze measurement, and pachymetry. Healing events analyzed after euthanasia at 2, 30, and 60 days included cell death (TUNEL assay), cell proliferation (BrdU [bromodeoxyuridine] immunofluorescence), and differentiation to myofibroblasts (α-SMA [alpha smooth muscle actin] immunohistochemistry). Results: Re-epithelialization and pachymetries were similar after RGX and UVX. The haze from day 1 to 15 was greater after UVX. Cell death was deeper after UVX, being localized in the anterior and middle stroma, and was superficial (anterior third) after RGX. Cell proliferation appeared after 2 days and was localized in the middle and posterior stroma in the UVX group but was superficial in the RGX group. After 60 days the number of stromal cells had not returned to the control number in either group. Conclusions: The deeper and longer-lasting cell damage caused by UVX compared to RGX may underlie the slower cell repopulation after UVX and other differences in healing. Shallower damage and a shorter treatment time suggest that RGX may be appropriate for stiffening thin corneas.

Sealing of Corneal Lacerations Using Photoactivated Rose Bengal Dye and Amniotic Membrane.

PURPOSE: Watertight closure of perforating corneoscleral lacerations is necessary to prevent epithelial ingrowth, infection, and potential loss of the eye. Complex lacerations can be difficult to treat, and repair with sutures alone is often inadequate. In this study, we evaluated a potentially sutureless technology for sealing complex corneal and scleral lacerations that bonds the amniotic membrane (AM) to the wound using only green light and rose bengal dye. METHODS: The AM was impregnated with rose bengal and then sealed over lacerations using green light to bond the AM to the deepithelialized corneal surface. This process was compared with suture repair of 3 laceration configurations in New Zealand White rabbits in 3 arms of the study. A fourth study arm assessed the side effect profile including viability of cells in the iris, damage to the blood-retinal barrier, retinal photoreceptors, retinal pigment epithelium, and choriocapillaris in Dutch Belted rabbits. RESULTS: Analyses of the first 3 arms revealed a clinically insignificant increase in polymorphonuclear inflammation. In the fourth arm, iris cells appeared unaffected and no evidence of breakdown of the blood-retinal barrier was detected. The retina from green light laser-treated eyes showed normal retinal pigment epithelium, intact outer segments, and normal outer nuclear layer thickness. CONCLUSIONS: The results of these studies established that a light-activated method to cross-link AM to the cornea can be used for sealing complex penetrating wounds in the cornea and sclera with minimal inflammation or secondary effects.

Interface Bonding With Corneal Crosslinking (CXL) After LASIK Ex Vivo.

Purpose: Interface bonding with corneal crosslinking (CXL) after LASIK using two different photosensitizers was studied ex vivo. Methods: A LASIK flap was created in enucleated rabbit eyes using a femtosecond laser. After the dissection, CXL was performed to seal the interface. In one group interface CXL was performed using rose bengal and green light, whereas in a second group riboflavin and UV-A light was used. In both groups irradiance, radiant exposure, dye concentration, and imbibition time was varied. In a control group, LASIK only was performed. After the procedures, the maximal shear-force required to separate the flap from the stroma was measured. Additionally, corneal transmission spectra were recorded. Results: Optimized parameters for rose bengal/green-light bonding lead to a 2.1-fold increase in shear-force compared with untreated control eyes (P < 0.01). The optimal parameter combination was: irradiance of 180 mW/cm2 for 14 minutes (total radiant exposure 150 J/cm2), rose bengal concentration 0.1%, and an imbibition time of 2 minutes. Optimized riboflavin/UV-A light parameters were 0.5% for 2 minutes with a radiant exposure of 8.1 J/cm2 obtained by an irradiance of 30 mW/cm2 for 4.5 minutes. These optimized parameters lead to a 2-fold increase compared with untreated control eyes (P < 0.01). Optical transmission experiments suggest safety for more posterior structures. Conclusions: Based on ex-vivo results, interface bonding after LASIK using crosslinking with either rose bengal or riboflavin increases the adhesion between flap and stromal bed. In vivo trials are needed to evaluate the temporal evolution of the effect.

Antimicrobial Blue Light Therapy for Infectious Keratitis: Ex Vivo and In Vivo Studies.

Purpose: To investigate the effectiveness of antimicrobial blue light (aBL) as an alternative or adjunctive therapeutic for infectious keratitis. Methods: We developed an ex vivo rabbit model and an in vivo mouse model of infectious keratitis. A bioluminescent strain of Pseudomonas aeruginosa was used as the causative pathogen, allowing noninvasive monitoring of the extent of infection in real time via bioluminescence imaging. Quantitation of bacterial luminescence was correlated to colony-forming units (CFU). Using the ex vivo and in vivo models, the effectiveness of aBL (415 nm) for the treatment of keratitis was evaluated as a function of radiant exposure when aBL was delivered at 6 or 24 hours after bacterial inoculation. The aBL exposures calculated to reach the retina were compared to the American National Standards Institute standards to estimate aBL retinal safety. Results: Pseudomonas aeruginosa keratitis fully developed in both the ex vivo and in vivo models at 24 hours post inoculation. Bacterial luminescence in the infected corneas correlated linearly to CFU (R2 = 0.921). Bacterial burden in the infected corneas was rapidly and significantly reduced (>2-log10) both ex vivo and in vivo after a single exposure of aBL. Recurrence of infection was observed in the aBL-treated mice at 24 hours after aBL exposure. The aBL toxicity to the retina is largely dependent on the aBL transmission of the cornea. Conclusions: Antimicrobial blue light is a potential alternative or adjunctive therapeutic for infectious keratitis. Further studies of corneal and retinal safety using large animal models, in which the ocular anatomies are similar to that of humans, are warranted.

Corneal Biomechanical Response Following Collagen Cross-Linking With Rose Bengal-Green Light and Riboflavin-UVA.

PURPOSE: To compare the biomechanical corneal response of two different corneal cross-linking (CXL) treatments, rose bengal-green light (RGX) and riboflavin-UVA (UVX), using noninvasive imaging. METHODS: A total of 12 enucleated rabbit eyes were treated with RGX and 12 with UVX. Corneal dynamic deformation to an air puff was measured by high speed Scheimpflug imaging (Corvis ST) before and after treatment. The spatial and temporal deformation profiles were evaluated at constant intraocular pressure of 15 mm Hg, and several deformation parameters were estimated. The deformation profiles were modeled numerically using finite element analysis, and the hyperelastic corneal material parameters were obtained by inverse modeling technique. RESULTS: The corneal deformation amplitude decreased significantly after both CXL methods. The material parameters obtained from inverse modeling were consistent with corneal stiffening after both RGX and UVX. Within the treated corneal volume, we found that the elasticity decreased by a factor of 11 after RGX and by a factor of 6.25 after UVX. CONCLUSIONS: The deformation of UVX-treated corneas was smaller than the RGX-treated corneas. However, the reconstructed corneal mechanical parameters reveal that RGX produced in fact larger stiffening of the treated region (100-µm depth) than UVX (137-µm depth). Rose bengal-green light stiffens the cornea effectively, with shorter treatment times and shallower treated areas. Dynamic air puff deformation imaging coupled with mechanical simulations is a useful tool to characterize corneal biomechanical properties, assess different treatments, and possibly help optimize the treatment protocols.

Light-activated sealing of skin wounds.

BACKGROUND AND OBJECTIVES: We have developed a light-activated technology for rapidly sealing skin surgical wounds called photochemical tissue bonding (PTB). The goals of this study were to evaluate parameters influencing PTB in order to optimize its clinical efficacy and to determine whether PTB can be used to seal wounds in moderately to highly pigmented skin. STUDY DESIGN/MATERIALS AND METHODS: Application of Rose Bengal (RB) followed by exposure to 532 nm was used to seal linear incisions (1.5 mm deep, 2 cm long) in lightly pigmented (Yorkshire) and darkly pigmented (Yucatan) swine skin. The force required to open the seal (the bonding strength) was measured by in situ tensiometry. Reflectance spectra, epidermal transmission spectra, and histology were used to characterize the skin. The relationships of RB concentration and fluence to bonding strength were established in Yorkshire skin. Surface temperature was measured during irradiations and cooling was used while sealing incisions in Yucatan skin. Monte Carlo simulations were carried out to estimate the effect of epidermal melanin on the power absorbed in the dermis at the incision interface. RESULTS: The lowest fluence, 25 J/cm(2), delivered at an irradiance of 0.5 W/cm(2) substantially increased the bonding strength (∼ 10-fold) compared to controls in Yorkshire swine skin. Increasing the fluence to 100 J/cm(2) enhanced bonding strength by a further 1.5-fold. Application of 0.1% RB for 2 minutes produced the greatest bonding strength using 100 J/cm(2) and limited the penetration of RB to an ∼ 50 µm band on the dermal incision wall. Reflectance spectra indicated that Yorkshire skin had minimal melanin and that Yucatan skin was a good model for highly pigmented human skin. In Yucatan skin, the bonding strength increased 1.7-fold using 0.1% RB and 200 J/cm(2) at 1.5 W/cm(2) with cooling and epinephrine. Monte Carlo simulation indicated that absorption of 532 nm light by epidermal melanin in dark skin decreased the power absorbed along the incision in the dermis by a factor of 2.7. CONCLUSIONS: These results suggest that in lightly pigmented skin the PTB treatment time can be shortened without compromising the bonding strength. Sealing incisions using PTB in moderately and highly pigmented skin will require a careful balance of irradiance and cooling.

Light-activated sutureless closure of wounds in thin skin.

BACKGROUND AND OBJECTIVES: Closing lacerations in thin eyelid and periorbital skin is time consuming and requires high skill for optimal results. In this study we evaluate the outcomes after single layer closure of wounds in thin skin with a sutureless, light-activated photochemical technique called PTB. STUDY DESIGN/MATERIALS AND METHODS: Dorsal skin of the SKH-1 hairless mouse was used as a model for eyelid skin. Incisions (1.2 cm) were treated with 0.1% Rose Bengal dye followed by exposure to 532 nm radiation (25, 50, or 100 J/cm(2); 0.25 W/cm(2)) for PTB. Other incisions were sutured (five 10-0 monofilament), exposed only to 532 nm (100 J/cm(2)), or not treated. Outcomes were immediate seal strength (pressure causing leakage through incision of saline infused under wound), skin strength at 1, 3, and 7 days (measured by tensiometry), inflammatory infiltrate at 1, 3, and 7 days (histological assessment), and procedure time. RESULTS: The immediate seal strength, as measured by leak pressure, was equivalent for all PTB fluences and for sutures (27-32 mmHg); these pressures were significantly greater than for the controls (untreated incisions or laser only treatment; P < 0.001). The ultimate strength of PTB-sealed incisions was greater than the controls at day 1 (P < 0.05) and day 3 (P < 0.025) and all groups were equivalent at day 7. Sutures produced greater inflammatory infiltrate at day 1 than observed in other groups (P = 0.019). The average procedure time for sutured closure (311 seconds) was longer than for the PTB group treated with 25 J/cm(2) (160 seconds) but shorter than the group treated with 100 J/cm(2) (460 seconds). CONCLUSION: PTB produces an immediate seal of incisions in thin, delicate skin that heals well, is more rapid than suturing, does not require painful suture removal and is easy to apply.

Photochemical tissue bonding: a potential strategy for treating limbal stem cell deficiency.

BACKGROUND AND OBJECTIVE: To determine the feasibility of attaching human amniotic membrane (HAM), pre-cultured with limbal stem cells (LSCs), to cornea using a novel, light-activated tissue bonding method. MATERIALS AND METHODS: LSCs were isolated from rabbit eyes, and then cultured on de-epithelialized HAM to create grafts (HAM/LSC). These were then transplanted onto rabbit eyes with surgically created limbal stem cell deficiency (LSCD). The grafts were secured either by sutures or by a light-activated method called photochemical tissue bonding (PTB). Outcomes included corneal opacity, inflammation, neovascularization, and collagen alignment. RESULTS: The isolated and cultured cells were verified to be LSCs based on their K19+/intergrin ß1+/P63+/K3 profile. Securing the HAM/LSC graft with PTB provided better outcomes. At 28 days post-surgery, the corneal opacity scores were significantly lower after securing the graft with PTB compared with suture attachment (0.8 ± 0.5 vs. 1.8 ± 0.5, P < 0.01). Similarly, neovascularization scores were lower after PTB (0.8 ± 0.5 vs. 1.5 ± 0.6, P < 0.01). Quantification of MPO and CD31 levels from immunofluorecent staining indicated that PTB stimulated less neutrophil infiltration (5.3 ± 2.2 vs. 13.3 ± 3.1, P < 0.01) and less new blood vessels formation (2.0 ± 0.8 vs. 6.3 ± 1.3, P < 0.01) at the wound site. The collagen alignment in PTB-treated corneas, as shown by immunofluorescence and second harmonic generation image, was better organized in the PTB-treated group than in the suture group. CONCLUSION: Bonding LSC grafts with PTB produced improved outcomes compared to suture attachment. This light-activated method is a promising modality for treating patients with LSCD.

Phototoxicity is not associated with photochemical tissue bonding of skin.

BACKGROUND AND OBJECTIVE: We have developed a light-activated method called photochemical tissue bonding (PTB) for closing wounds using green light and a photosensitizing dye (Rose Bengal-RB) to initiate photochemical crosslinking of wound surface proteins. These studies were designed to determine whether RB causes phototoxicity during closure of skin incisions with PTB. STUDY DESIGN/MATERIALS AND METHODS: RB phototoxicity was evaluated after sealing incisions in porcine skin ex vivo and rabbit skin in vivo using PTB (1 mM RB, 100 J/cm(2), 532 nm, 0.3 or 0.5 W/cm(2).) Dead cells were identified by pyknotic nuclei and eosinophilic cytoplasm on H&E-stained sections. The influence on RB phototoxicity of penetration of RB into the wound wall (by confocal microscopy), RB concentration in the tissue (by extraction), and fluence of 532 nm reaching depths in skin (calculated from skin optical properties) were investigated. RESULTS: No significant differences were found in the percent dead cells in PTB-treated and control incisions in porcine skin at 24 hours or in rabbit skin at 2 hours and 3 and 7 days after surgery. RB was retained in a approximately 100 microm wide band next to the wound wall. The mean RB concentration within this band was 0.42+/-0.03 mM. Monte Carlo modeling of light distribution indicated that the fluence rate decreased from the subsurface peak to 0.5 W/cm(2) in the mid-dermis (approximately 350 microm.) In vitro RB phototoxicity to dermal fibroblasts yielded an LD(50) of 0.50+/-0.09 J/cm(2) when the cells contained 0.46 mM RB. CONCLUSIONS: PTB does not cause phototoxicity when used to repair skin wounds even though the RB concentration and 532 nm fluence in the mid-dermis during PTB are much greater than the LD(50) for RB phototoxicity in vitro. These results indicate that phototoxicity is not a concern when using PTB for tissue repair.

Low level light effects on inflammatory cytokine production by rheumatoid arthritis synoviocytes.

BACKGROUND AND OBJECTIVE: Low level light therapy (LLLT) is being evaluated for treating chronic and acute pain associated with rheumatoid arthritis (RA) and other inflammatory diseases. The mechanisms underlying the effectiveness of LLLT for pain relief in RA are not clear. The objectives of this study were to determine whether LLLT decreased production of pro-inflammatory cytokines by cells from RA joints, and, if so, to identify cellular mechanisms. STUDY DESIGN/MATERIALS AND METHODS: Synoviocytes from RA patients were treated with 810 nm radiation before or after addition of tumor necrosis factor-alpha (TNF-alpha). mRNA for TNF-alpha, interleukin (IL)-1beta, IL-6, and IL-8 was measured after 30, 60, and 180 minutes using RT-PCR. Intracellular and extracellular protein levels for 12 cytokines/chemokines were measured at 4, 8, and 24 hours using multiplexed ELISA. NF-kappaB activation was detected using Western blotting to follow degradation of IkappaBalpha and nuclear localization of the p65 subunit of NF-kappaB. RESULTS: Radiation at 810 nm (5 J/cm(2)) given before or after TNF-alpha decreases the mRNA level of TNF-alpha and IL-1beta in RA synoviocytes. This treatment using 25 J/cm(2) also decreases the intracellular levels of TNF-alpha, IL-1beta, and IL-8 protein but did not affect the levels of seven other cytokines/chemokines. TNF-alpha-induced activation of NF-kappaB is not altered by 810 nm radiation using 25 J/cm(2). CONCLUSIONS: The mechanism for relieving joint pain in RA by LLLT may involve reducing the level of pro-inflammatory cytokines/chemokines produced by synoviocytes. This mechanism may be more general and underlie the beneficial effects of LLLT on other inflammatory conditions.

Evaluation of photochemical tissue bonding for closure of skin incisions and excisions.

BACKGROUND AND OBJECTIVES: Photochemical tissue bonding (PTB) is a new non-thermal technique for tissue repair involving application of a photochemically active dye and irradiation with visible light. The objective was to compare PTB with standard sutures and the tissue adhesive, octyl cyanoacrylate, for closure of skin incisions and excisions. STUDY DESIGN/MATERIALS AND METHODS: Incisions and excisions made on the flanks of a Hanford mini-pig were secured with subcutaneous sutures. Superficial closure methods were 3-0 monofilament sutures, PTB (Rose Bengal and green light), tissue adhesive and the combination of tissue adhesive then PTB. Wounds were evaluated 2, 4, and 6 weeks postoperatively for cosmetic outcomes and histology. RESULTS: Cosmetic outcomes and histological scar width of incisions and excisions did not differ among the treatment groups at 2, 4, and 6 weeks. CONCLUSION: PTB is as effective as standard sutures for wound closure in porcine skin in terms of cosmetic outcomes and safety.

Photochemical keratodesmos as an adjunct to sutures for bonding penetrating keratoplasty corneal incisions.

PURPOSE: To evaluate the benefit of photochemical keratodesmos (PKD) in acute wound closure of penetrating keratoplasty (PKP) corneal incisions in vivo. SETTING: Massachusetts General Hospital and Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. METHODS: Penetrating keratoplasty incisions were performed in both eyes of 6 New Zealand white rabbits, followed by application of 1.5 mM rose bengal dye at the wound edges. The incision in 1 eye of each rabbit was irradiated with neodymium:YAG laser light at 532 nm and fluence of 40 J/cm2; the contralateral control eye was untreated. Intraocular pressure at which fluid leaked at the edges (IOPL) was determined immediately after surgery. RESULTS: The mean IOPL was 410 mm Hg +/- 70 (SD) in the PKD-treated eyes and 250 +/- 150 mm Hg in the unirradiated eyes. The difference was statistically significant by paired t test (P<.05). CONCLUSIONS: Photochemical keratodesmos may be a useful adjunct to sutures for approximating PKP corneal incisions in the immediate postoperative period. This process does not induce high temperature, and thus denaturation can be avoided and structural integrity restored.

Photochemical keratodesmos for bonding corneal incisions.

PURPOSE: To evaluate the immediate and long-term effectiveness of a dye-plus-laser irradiation treatment (photochemical keratodesmos [PKD]) for sealing corneal incisions. METHODS: Incisions (3.5 mm) in rabbit corneas were treated on the incision walls with rose bengal dye followed by exposure to 514-nm laser radiation. PKD was evaluated in three groups (n = 3-6) using laser fluences of 115, 153, or 192 J/cm(2) (180-, 240-, and 300- second exposures, respectively) compared with an untreated group (n = 8). The intraocular pressure at which leakage occurred (IOP(L)) during infusion of saline into the anterior chamber was determined. In a long-term study, treated and control corneas were observed weekly for 10 weeks for the appearance of neovascularization, anterior chamber inflammation, iridocorneal adhesion, corneal melting, and scarring. RESULTS: Immediately after treatment, the IOP(L) increased with increasing laser fluence, producing IOPs of 230 +/- 90, 370 +/- 120, and more than 500 mm Hg at 115, 153, and 192 J/cm(2), respectively, compared with 40 +/- 20 mm Hg in control eyes (P < 0.005). No reduction in the IOP(L) was observed up to 14 days after surgery. Corneal melting in PKD-treated or control eyes was not observed in the 10-week healing study. Neovascularization, which peaked at 4 weeks but resolved by 8 weeks, was detected around the incision in both PKD-treated and control eyes. CONCLUSIONS: Immediate and lasting sealing of corneal incisions was obtained in eyes treated with PKD, using short irradiation times. These results suggest that PKD has potential for improved corneal tissue bonding.

Ultraviolet A radiation induces rapid apoptosis of human leukemia cells by Fas ligand-independent activation of the Fas death pathways.

Endogenous cellular chromophores absorb ultraviolet A radiation (UVA, 290-320 nm), the major UV component of terrestrial solar radiation, leading to the formation of reactive oxidizing species that initiate apoptosis, gene expression and mutagenesis. UVA-induced apoptosis of T helper cells is believed to underlie the UVA phototherapy for atopic dermatitis and other T cell-mediated inflammatory skin diseases. We have evaluated the involvement of the Fas-Fas ligand (FasL) pathway in rapid UVA-induced apoptosis in human leukemia HL-60 cells. UVA-induced apoptosis was not inhibited by pretreatment with a neutralizing anti-Fas antibody, although the same UVA treatment initiated cleavage of caspase-8 and subsequent processing of Bid and caspase-3-like proteases. Inhibition of caspase-8 by Lle-Glu (OMe)-Thr-Asp(OMe)-fluoromethyl ketone completely blocked caspase-3 cleavage and apoptosis in UVA-treated cells, suggesting that apoptosis was initiated by the Fas pathway. This inference was supported by demonstrating that immunoprecipitates obtained from UVA-treated cells using anti-Fas antibody contained caspase-8 and Fas-associating protein with death domain (FADD). In addition, Fas clustering in response to UVA treatment was observed by immunofluorescence microscopy. These data support a mechanism for rapid, UVA-induced apoptosis in HL-60 cells involving initial formation of the Fas-FADD-caspase-8 death complex in an FasL-independent manner.