July 2003
Volume 44, Issue 7
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Cornea  |   July 2003
Photodynamic Therapy with Verteporfin in a Rabbit Model of Corneal Neovascularization
Author Affiliations
  • Mike P. Holzer
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
  • Kerry D. Solomon
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
  • David T. Vroman
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
  • Helga P. Sandoval
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
  • Philippe Margaron
    QLT Inc., Vancouver, British Columbia, Canada.
  • Terrance J. Kasper
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
  • Craig E. Crosson
    From the Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina; and
Investigative Ophthalmology & Visual Science July 2003, Vol.44, 2954-2958. doi:10.1167/iovs.02-0572
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      Mike P. Holzer, Kerry D. Solomon, David T. Vroman, Helga P. Sandoval, Philippe Margaron, Terrance J. Kasper, Craig E. Crosson; Photodynamic Therapy with Verteporfin in a Rabbit Model of Corneal Neovascularization. Invest. Ophthalmol. Vis. Sci. 2003;44(7):2954-2958. doi: 10.1167/iovs.02-0572.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

purpose. To determine the efficacy of photodynamic therapy (PDT) with verteporfin (Visudyne; Novartis AG, Basel, Switzerland) for treatment of corneal neovascularization in a rabbit eye model.

methods. Corneal neovascularization was induced in Dutch belted rabbits by placing an intrastromal silk suture near the limbus. Verteporfin was administered by intravenous injection at a dose of 1.5 mg/kg, and the pharmacokinetics of verteporfin distribution in the anterior segment or PDT-induced (laser energy levels 17, 50, and 150 J/cm2) regression of corneal blood vessels were then determined. To assess PDT-induced toxicity of the anterior segment, corneal and iris/ciliary body histology, and IOP were evaluated after PDT.

results. Verteporfin accumulation in vascularized regions of the cornea and the iris/ciliary body tissue were time dependent and maximum levels achieved at 60 minutes after injection. In rabbits, PDT of corneal vessels using laser energy of 17 or 50 J/cm2 resulted in 30% to 50% regression of corneal neovascularization; however, in these animals, a rapid regrowth of new blood vessels occurred between 3 and 5 days. In the rabbits receiving PDT using laser energies of 150 J/cm2, the mean vessel regression was 56%. During the nine days of the laser therapy follow-up period, no vessel regrowth was observed in these rabbits. Histologic examination of the anterior segment after PDT (150 J/cm2) showed localized degeneration of the corneal blood vessels without observable change in other anterior segment structures.

conclusions. These results provide evidence that PDT can produce significant regression of neovascular corneal vessels with no observable toxicity to the anterior segments. However, the optimal laser energy necessary to induce long-term regression (150 J/cm2) was three times that used to treat choroidal neovascularization.

Corneal neovascularization affects an estimated 1.4 million Americans and is a major cause of blindness worldwide. 1 Several corneal disorders including infections, chemical burns, immunologic diseases, degenerative disorders, and prior trauma can induce corneal neovascularization. In the United States, the most frequently associated etiology is long-time contact lens wear, especially that of soft hydrogel lenses. 
The primary treatment for actively proliferating corneal vessels is topical corticosteroids. 2 However, in corneas where vessels have been established for an extended period, corticosteroid treatment is often ineffective. Recently, angiogenic inhibitors have also been used to treat corneal neovascularization. 3 4 Photodynamic treatment (PDT) offers another potential treatment for corneal neovascularization. In PDT, systemically administered porphyrin derivatives accumulate in proliferating endothelial cells. Laser energy is then used to activate the porphyrin derivates 2 5 6 7 8 9 liberating cytotoxic oxygen free radicals. The ensuing cytotoxic response results in occlusion of neovascular vessels. Photodynamic treatment using verteporfin (Visudyne; Novartis AG, Basel, Switzerland), a benzoporphyrin derivative monoacid ring A, has been recently approved for the treatment of subfoveal choroidal neovascularization. 10 11 12  
The purpose of this study was to evaluate the efficacy of the FDA-approved verteporfin formulation and dose and laser treatment for corneal neovascularization. These studies examined the pharmacokinetic characteristics of verteporfin in the anterior segment of rabbit eyes with corneal neovascularization, the PDT-induced toxicity of adjacent ocular structures (e.g., the corneal endothelium and iris/ciliary body), and the optimal laser parameters for treatment of corneal neovascularization. Our results demonstrate that significant amounts of verteporfin can be found in vascularized areas of the cornea as early as 15 minutes after drug injection and that PDT is efficacious in producing and maintaining regression of corneal blood vessels up to 9 days after PDT. However, the optimal laser energy necessary to induce long-term regression (150 J/cm2) was three times that used to treat choroidal neovascularization. 
Materials and Methods
Dutch-belted rabbits, weighing 1.5 to 2 kg were maintained in a standard 12-hour light–dark cycle with free access to food and water. Corneal neovascularization was induced using a modified technique described by Schmidt-Erfurth et al. 6 Briefly, a single 7.0 silk suture was placed at midstromal depth approximately 1 mm from the limbus. For suture placement and subsequent PDT, rabbits were anesthetized with ketamine (30 mg/kg, intramuscularly [IM]) and xylazine (6 mg/kg, IM). Corneal discomfort was minimized by applying 25 μL of 0.5% proparacaine hydrochloride. All procedures were approved by the Institutional Animal Care and Use Committee at the Medical University of South Carolina, and the rabbits were treated in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. 
To determine the area of corneal neovascularization, slit-lamp photographs in a standardized magnification were taken on days 1, 4, 7, 11, 14, 18, 20, 21, 22, 25, and 29 after suture placement. Photographs were digitized, and the neovascularized area (in square millimeters) determined using NIH Image (available by ftp from zippy.nimh.nih.gov/ or from http://rsb.info.nih.gov/nih-image; developed by Wayne Rasband, National Institutes of Health, Bethesda, MD). To control for individual variation in the area of neovascularization induced by suture placement, the area on day 18 was set at 100%, and other area values were presented as the percent change from this value. All values were presented as means and standard errors. Unless noted otherwise, a minimum of four animals were used to evaluate the neovascular response at each time point. 
Assessment of Verteporfin Pharmacokinetics
Nineteen days after suture placement, rabbits were anesthetized, and verteporfin (1.5 mg/kg) was administered by intravenous injection in the marginal ear vein. At 15, 60, 120, and 240 minutes after injection, the rabbits were killed by an overdose of pentobarbital sodium. Both corneas and the ipsilateral iris/ciliary body were then isolated, and ipsilateral and contralateral aqueous samples obtained. The normal and vascularized regions of the ipsilateral cornea were separated, and the verteporfin concentration determined for each tissue and aqueous sample. Samples were analyzed for verteporfin using a spectrofluorometer (Aminco 8000 C; SLM Instruments Inc., Urbana, IL). Verteporfin concentrations were determined from standard curves and expressed as nanograms per milligram of tissue. Values were presented as means ± standard errors. A minimum of four animals were used to evaluate verteporfin concentration at each time point. 
PDT-Induced Blood Vessel Regression
Nineteen days after suture placement, rabbits were anesthetized, and verteporfin (1.5 mg/kg) was then administered by intravenous injection in the marginal ear vein. After administration of verteporfin, rabbits were exposed to laser light at 689 nm wavelength and 600 mW/cm2 (OPAL laser; Coherent Inc., Santa Clara, CA). Laser energies used were 17, 50, or 150 J/cm2. The spot size used was 4 mm in diameter and positioned on vessels as they entered the clear cornea from the limbus. Unless otherwise noted, all laser treatments were performed 15 minutes after administration of verteporfin. The area of corneal neovascularization was quantified from slit lamp photographs using NIH Image on days 20, 21, 22, 25, and 29. In selected eyes, a pneumatonometer (Classic-30; Mentor, Santa Barbara, CA) was used to measure intraocular pressure (IOP) on days 18 (pre-PDT), 20 (1 day after PDT), and 21 (2 days after PDT). 
On days 20, 21, and 26, selected animals were killed by an overdose of pentobarbital sodium. The eyes were enucleated and fixed in 4% paraformaldehyde. Anterior segments were then isolated and embedded in paraffin and parasagittal sections cut and stained with hematoxylin and eosin for histologic evaluation. For endothelial flatmounts, corneas were isolated, the endothelium stained with 0.5% alizarin red, and the cell number and morphology evaluated. Both, flatmounts and cross sections were observed with photographs using a fluorescence microscope (Axioplan-2; Carl Zeiss, Oberkochen, Germany). 
Results
Figure 1 shows the accumulation of verteporfin as a function of time, in the neovascularized regions of the ipsilateral cornea and iris/ciliary body of rabbits after drug administration. In the neovascularized regions of the cornea and iris/ciliary body, verteporfin was measurable at 15 minutes after intravenous drug injection. At 60 minutes after injection, verteporfin levels increased to approximately 0.07 ng/mg of tissue in the neovascularized regions of the cornea, and 0.24 ng/mg of tissue in the iris/ciliary body. In the cornea, these levels remained relatively stable through 240 minutes after injection. However, in the iris/ciliary body, verteporfin levels exhibited an exponential decline with a half-life of 263 minutes. No verteporfin was detected in the contralateral corneas, nor in ipsilateral corneal samples 180° opposite the neovascularized region. No detectable levels of verteporfin were measured in the ipsilateral or contralateral aqueous humor. 
Figure 2 shows slit lamp photographs of the neovascularized cornea 1 day before and 3 and 6 days after PDT. Corneal edema was observed around the suture; however, corneal transparency remained unchanged in other regions exposed to laser treatment. Vascular hemorrhages were observed from 1 to 3 days after PDT, but the presence of these hemorrhages decreased over time. No changes in iris shape or response to light were observed in any animal after PDT. 
In Figure 3 , the effects of laser treatment (50 J/cm2) on the neovascularized area at 5 or 15 minutes after the intravenous injection of verteporfin are presented. Laser treatments starting 5 minutes after administration of verteporfin produced a mean decrease in the vascularized area of 33%, when measured 2 days after laser treatment. In rabbits receiving laser treatment 15 minutes after verteporfin, the mean decrease in the neovascularized area was 68% at 2 days after laser treatment. In both groups, there was a progressive return of the corneal vessels. However, at each time point, laser treatment 15 minutes after administration of verteporfin showed a greater reduction in the neovascularized area when compared with laser treatment 5 minutes after verteporfin. 
In Figure 4 , regression of corneal neovascularization after PDT with laser energies of 17, 50, and 150 J/cm2 are presented. For each group, laser treatment was applied 15 minutes after the administration of verteporfin. As shown in this figure, there was an energy-related decrease in the neovascularized area with increasing laser energies. Rabbits treated with laser energies of 17 J/cm2 exhibited a 25% to 35% regression in neovascularized area, and these vessels showed rapid regrowth into the cornea. Rabbits treated with 50 or 150 J/cm2, exhibited an initial regression of 50% to 60% in mean neovascularized area. In the rabbits receiving 50 J/cm2, a progressive regrowth of the corneal vessels was measured from 3 to 9 days after laser treatment. However, in rabbits receiving 150 J/cm2, no regrowth in corneal vessels was measured throughout the course of the study (9 days after laser treatment). 
To evaluate whether PDT produces any acute side effects that could contribute to a long-term decrease in visual acuity, the effect of PDT on IOP, anterior segment histology and corneal endothelial cell number and morphology were examined. For these studies, rabbits with suture-induced neovascularization underwent PDT at a laser dose of 150 J/cm2 15 minutes after administration of verteporfin. In five animals, IOP was measured the day before (day 18) and 1 and 2 days after PDT (days 20 and 21). Mean IOP on day 18 was 29 ± 1.2 mm Hg. One day after PDT, the mean IOP was decreased by 7.6 ± 1.9 mm Hg when compared with pretreatment levels. This decrease in IOP was short in duration with IOPs returning to pre-PDT levels by day 2 after treatment. Evaluation of animals at later time points revealed no significant change in IOP from pretreatment values. 
For histologic evaluation, rabbits were killed 2 and 6 days (days 21 and 25) after PDT (150 J/cm2; 15 minutes after administration of verteporfin). Figure 5 shows light photomicrographs of the neovascularized rabbit cornea 2 days after PDT. In these, extravascular red blood cells were observed in the corneal stroma, and the endothelial lining of the neovascular vessels was disrupted. Except for the presence of red blood cells in the corneal stroma, the epithelium and endothelium were normal in appearance with no signs of cell death in any layer. By 6 days after PDT, only dispersed remnants of vessels were present in the cornea, and, except for the presence of activated keratocytes around the suture, the corneas were normal in appearance (data not shown). Evaluation of the iris/ciliary body stroma demonstrated no signs of vascular hemorrhage, and the endothelial cells lining the iris/ciliary body vessels were normal in appearance (Fig. 5) . In addition, the iris/ciliary body stroma was normal in appearance with no sign of degeneration. At 6 days after PDT, no signs of iris/ciliary body degeneration or other abnormalities were observed (data not shown). 
Corneal flatmounts were used to evaluate endothelial change associated with PDT. When compared with control corneas (untreated), endothelial regions exposed to laser energies of 150 J/cm2 showed no change in endothelial cell shape or number (data not shown) 2 days after PDT. 
Discussion
Corneal neovascularization is a sight-threatening condition that is associated with several eye disorders and long-term contact lenses wear. 1 Photodynamic therapy has been shown to be efficacious for the treatment of subfoveal choroidal neovascularization. 10 11 12 The successful treatment of choroidal neovascularization by PDT opens the possibility of treating other neovascular diseases of the eye in a similar manner. The potential of using PDT for corneal neovascularization has been previously investigated. 5 6 7 8 9 However, these studies evaluated photosensitive substances, dosages, or procedures that have not received U.S. Food and Drug Administration (FDA) approval. The present study was designed to investigate the FDA-approved verteporfin formulation and dosage and laser energies for the treatment of corneal neovascularization. 
In our study, suture-induced corneal neovascularization was measurable by day 3 and increased in area to involve approximately 20% of the cornea by 14 to 18 days. In vascularized corneal regions, verteporfin was detectable by 15 minutes after intravenous injection and continued to increase up to 60 minutes after injection. From 60 to 240 minutes, verteporfin levels remained steady in vascularized corneal regions. Verteporfin was not detectable in nonvascularized areas of the ipsilateral corneas, the contralateral (control) corneas, or aqueous humor. The localization of verteporfin to the neovascularized region supports the idea that potential side effects in adjacent normal corneal structures should be minimal. The prolonged residence time of verteporfin in vascularized regions probably relates to leakage out of the neovascularized vessels, and the accumulation of verteporfin in the corneal stroma around the vessels. Previous studies have shown neovascular corneal vessels have a high leakage potential. 13 Prior studies by Schmidt-Erfurth et al., 6 also demonstrated that, after administration of verteporfin, corneal uptake peaked at 60 minutes. However, at times beyond 60 minutes, verteporfin declined exponentially over the next 12 hours. This difference in corneal washout of verteporfin may be related to the difference in detection methods between these two studies. 
Pharmacokinetic data provided evidence that verteporfin can accumulate in the corneal stroma around neovascular vessels. Hence, initial studies evaluating the efficacy of PDT for corneal neovascularization tested laser treatment at 5 and 15 minutes after administration of verteporfin. The hope for these studies was that the early 5-minute time would be effective, thus limiting potential damage to extravascular corneal structures. As shown in Figure 3 , laser treatments at 5 minutes after verteporfin was administered were less effective than 15 minutes after injection. The requirement for laser treatments to begin no earlier than 15 minutes after injection is similar to that determined for the treatment of subfoveal choroidal neovascularization and probably relates to the need for endothelial uptake of verteporfin for full efficacy. 14 Increasing laser application times beyond 15 minutes after verteporfin could increase the chance of PDT-induced corneal side effects, as the concentration of verteporfin increases in the corneal stroma. 
Results from the laser dosimetry study demonstrated that in PDT treatment of corneal neovascularization, there is an energy-dependent increase in the regression of neovascular vessels with increasing laser energy from 17 or 50 J/cm2. In this study, the maximum effective laser energy was 150 J/cm2. This energy is three times that needed to create significant long-lasting clinical regression of choroidal neovascularization. 12 This increase in laser energy required to induce a long-term regression of corneal vessels may be related to the lower vascular density in the cornea compared with the choriocapillaris. Schmidt-Erfurth et al., 6 found that PDT using laser energy of 10 J/cm2 was effective in occluding neovascular vessels in the cornea for up to 3 days. However, these studies did not evaluate vessel regrowth beyond 3 days after treatment. In our study, we also found acute regression of corneal vessels at energy levels of 17 and 50 J/ cm2. However, vessels treated at these lower energy levels showed complete regrowth by 9 days after laser treatment. 
Cellular uptake of verteporfin is by means of low-density lipoprotein receptors 14 ; and this uptake is required for the expression of the cytotoxic response to PDT. As trabecular meshwork 15 and corneal endothelial 16 cells express low-density lipoprotein receptors, these tissues are potential targets for the cytotoxic effects of PDT. Slit lamp and histologic evaluation of corneal neovascular vessels after PDT showed substantial degeneration of these vessels at 1 and 2 days after laser treatment, similar to previous reports. However, the corneal epithelium, surrounding stroma and endothelium were not visibly altered by PDT. In addition, no significant changes in endothelial cell shape or number or in IOP were observed in these animals. Although anterior segment structures express low-density lipoprotein receptors, our data support the idea that PDT is relatively selective for corneal neovascular vessels when laser treatment occurs 15 minutes after verteporfin is administered. 
Although substantial verteporfin concentrations were observed in the iris, no changes in iris/ciliary body histology, pupil size, or regularity were noted in these animals. These results support the notion that PDT interaction with the iris/ciliary body should be limited in pigmented individuals. 
In conclusion, our studies provide evidence that PDT using the FDA-approved formulation and dosage of verteporfin is efficacious for the treatment of corneal neovascularization. Long-term follow-up and the efficacy of PDT retreatment should be evaluated in additional studies. The primary difference observed in the treatment of corneal neovascularization compared with the treatment of subfoveal choroidal neovascularization is the increased energy required to produce maximal and sustained regression of the neovascular vessels in the cornea. The optimal time point to start laser treatment after administration of verteporfin was 15 minutes. This timing is similar to that identified for PDT in the treatment of subfoveal neovascularization. Overall, these studies provide evidence that PDT using verteporfin as the photosensitive drug, can provide an efficacious treatment for the regression of corneal neovascular vessels. 
 
Figure 1.
 
Changes in cornea and iris/ciliary body verteporfin concentration traced during the 4 hours after treatment. Verteporfin (1.5 mg/kg) was administered intravenously to rabbits. Results are expressed as the mean ± SE; n = 4.
Figure 1.
 
Changes in cornea and iris/ciliary body verteporfin concentration traced during the 4 hours after treatment. Verteporfin (1.5 mg/kg) was administered intravenously to rabbits. Results are expressed as the mean ± SE; n = 4.
Figure 2.
 
Effect of PDT (150 J/cm2; 15 minutes after administration of verteporfin) on corneal neovascular vessels induced by suture placement. (A) Cornea, 1 day before PDT (day 18). (B) Same cornea, 3 days after PDT (day 22). (C) Same cornea, 6 days after PDT (day 25). Note new vessels growing from the limbus.
Figure 2.
 
Effect of PDT (150 J/cm2; 15 minutes after administration of verteporfin) on corneal neovascular vessels induced by suture placement. (A) Cornea, 1 day before PDT (day 18). (B) Same cornea, 3 days after PDT (day 22). (C) Same cornea, 6 days after PDT (day 25). Note new vessels growing from the limbus.
Figure 3.
 
Effect of verteporfin administration timing, on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) at 5 or 15 minutes before laser treatment (50 J/cm2). Results are expressed as the mean ± SE; n = 4 (day 29, n = 2).
Figure 3.
 
Effect of verteporfin administration timing, on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) at 5 or 15 minutes before laser treatment (50 J/cm2). Results are expressed as the mean ± SE; n = 4 (day 29, n = 2).
Figure 4.
 
Effect of laser energy on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) 15 minutes before laser therapy. Results are expressed as the mean ± SE; n = 4.
Figure 4.
 
Effect of laser energy on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) 15 minutes before laser therapy. Results are expressed as the mean ± SE; n = 4.
Figure 5.
 
Photomicrographs of rabbit cornea and iris/ciliary body cross sections collected 2 days (day 21) after PDT (150 J/cm2). In the cornea (A, B) there was evidence of vascular hemorrhage and disruption of the endothelial lining of neovascular vessels (open arrows). However, the corneal epithelium, stroma, and endothelium were normal in appearance. The iris/ciliary body stroma and vascular endothelium were normal in appearance, and there was no evidence of vascular hemorrhage (C, D).
Figure 5.
 
Photomicrographs of rabbit cornea and iris/ciliary body cross sections collected 2 days (day 21) after PDT (150 J/cm2). In the cornea (A, B) there was evidence of vascular hemorrhage and disruption of the endothelial lining of neovascular vessels (open arrows). However, the corneal epithelium, stroma, and endothelium were normal in appearance. The iris/ciliary body stroma and vascular endothelium were normal in appearance, and there was no evidence of vascular hemorrhage (C, D).
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Figure 1.
 
Changes in cornea and iris/ciliary body verteporfin concentration traced during the 4 hours after treatment. Verteporfin (1.5 mg/kg) was administered intravenously to rabbits. Results are expressed as the mean ± SE; n = 4.
Figure 1.
 
Changes in cornea and iris/ciliary body verteporfin concentration traced during the 4 hours after treatment. Verteporfin (1.5 mg/kg) was administered intravenously to rabbits. Results are expressed as the mean ± SE; n = 4.
Figure 2.
 
Effect of PDT (150 J/cm2; 15 minutes after administration of verteporfin) on corneal neovascular vessels induced by suture placement. (A) Cornea, 1 day before PDT (day 18). (B) Same cornea, 3 days after PDT (day 22). (C) Same cornea, 6 days after PDT (day 25). Note new vessels growing from the limbus.
Figure 2.
 
Effect of PDT (150 J/cm2; 15 minutes after administration of verteporfin) on corneal neovascular vessels induced by suture placement. (A) Cornea, 1 day before PDT (day 18). (B) Same cornea, 3 days after PDT (day 22). (C) Same cornea, 6 days after PDT (day 25). Note new vessels growing from the limbus.
Figure 3.
 
Effect of verteporfin administration timing, on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) at 5 or 15 minutes before laser treatment (50 J/cm2). Results are expressed as the mean ± SE; n = 4 (day 29, n = 2).
Figure 3.
 
Effect of verteporfin administration timing, on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) at 5 or 15 minutes before laser treatment (50 J/cm2). Results are expressed as the mean ± SE; n = 4 (day 29, n = 2).
Figure 4.
 
Effect of laser energy on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) 15 minutes before laser therapy. Results are expressed as the mean ± SE; n = 4.
Figure 4.
 
Effect of laser energy on PDT-induced corneal neovascular vessel regression. On day 19, rabbits were treated with verteporfin (1.5 mg/kg) 15 minutes before laser therapy. Results are expressed as the mean ± SE; n = 4.
Figure 5.
 
Photomicrographs of rabbit cornea and iris/ciliary body cross sections collected 2 days (day 21) after PDT (150 J/cm2). In the cornea (A, B) there was evidence of vascular hemorrhage and disruption of the endothelial lining of neovascular vessels (open arrows). However, the corneal epithelium, stroma, and endothelium were normal in appearance. The iris/ciliary body stroma and vascular endothelium were normal in appearance, and there was no evidence of vascular hemorrhage (C, D).
Figure 5.
 
Photomicrographs of rabbit cornea and iris/ciliary body cross sections collected 2 days (day 21) after PDT (150 J/cm2). In the cornea (A, B) there was evidence of vascular hemorrhage and disruption of the endothelial lining of neovascular vessels (open arrows). However, the corneal epithelium, stroma, and endothelium were normal in appearance. The iris/ciliary body stroma and vascular endothelium were normal in appearance, and there was no evidence of vascular hemorrhage (C, D).
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