Angiographic and histologic effects of fundus photodynamic therapy with a hydrophilic sensitizer (mono-L-aspartyl chlorin e6)

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

Quantitative Evaluation of Retinal Vessel Density in Central Serous Chorioretinopathy after Half-dose Photodynamic Therapy

PURPOSE

To determine vessel changes in retinochoroid with optical coherence tomographic angiography (OCT angiography) and spectral-domain OCT (SD-OCT) of patients with central serous chorioretinopathy (CSC) after half-dose photodynamic therapy (hd-PDT).

METHODS

A prospective observational study of 62 eyes of 58 patients undergoing hd-PDT was followed for 3 months. Fundus fluorescein angiography (FFA) and indocyanine green angiography (ICGA) were performed at baseline; best-corrected visual acuity (BCVA), fundus photography, OCT angiography and SD-OCT were performed at baseline, 1-month, and 3-month follow-up visits.

RESULTS

The mean vessel density of inner retina (VDIR) layer was 50.72 ± 3.17 at baseline, then decreased to 48.97 ± 4.34 at 1-month follow-up (p < .001), and partially recovered to 49.00 ± 4.28 at 3-month follow-up (p < .001); the mean area of foveal avascular zone (FAZ) was 0.303 ± 0.107 mm² at baseline, and then increased to 0.339 ± 0.121 mm² and 0.342 ± 0.125 mm² at 1-month and 3-month follow-up after hd-PDT (p < .001, p < .001). The mean diameters of choroidal big vessels (DCV) were 309.66 ± 72.24 microns at baseline, then decreased to 300.13 ± 69.38 microns at 1-month and 293.39 ± 69.92 microns at 3-month after treatment (p < .001, p < .001).

CONCLUSIONS

Currently common applied hd-PDT for patients with CSC has significantly impact on both retinal and choroidal vessels. The retinal capillary flow decreased, therefore optimizing PDT parameters for treating CSC may still be necessary in the future.

Choroidal vascularity changes in idiopathic central serous chorioretinopathy after half-fluence photodynamic therapy

PURPOSE

This study evaluated changes in choroidal vascularity after half-fluence photodynamic therapy (HF-PDT) in patients with central serous chorioretinopathy (CSC) using swept-source optical coherence tomography (SS-OCT) en face imaging.

METHODS

This retrospective comparative case series included 50 eyes of 25 patients with unilateral CSC who underwent HF-PDT and 50 age-and sex-matched normal healthy control eyes. En face SS-OCT images of the choriocapillaris, Sattler's layer, and Haller's layer were converted into binary images. The vascular proportions were defined as the percentage of the area of vascular lumen against the area of the 3.0-mm-diameter circular area. The main outcome measures were the vascular proportions before HF-PDT and at 6 weeks, 6 months, and 12 months after HF-PDT.

RESULTS

At baseline, the vascular proportions in the CSC eyes were significantly greater than those in the control eyes in all layers (choriocapillaris: 51.8% ± 15.5% vs. 41.3 ± 18.7%, P = 0.018; Sattler's: 58.6% ± 13.4% vs. 49.7% ± 15.7%, P = 0.017; Haller's: 65.3% ± 15.3% vs. 53.0% ± 13.4%, P = 0.001). In the CSC eyes, the vascular proportion in the choriocapillaris significantly decreased at 6 weeks (36.6% ± 16.9%, P < 0.001), 6 months (34.0% ± 12.3%, P < 0.001), and 12 months (34.8% ± 17.6%, P < 0.001) after HF-PDT compared with baseline. The vascular proportions in Sattler's and Haller's layers did not show a significant decrease at 6 weeks (Sattler's: 49.7% ± 17.3%, P = 0.052 and Haller's: 58.3% ± 12.9%, P = 0.558) but decreased significantly at 6 months (Sattler's: 48.9% ± 12.4%, P < 0.001 and Haller's: 57.7% ± 15.7%, P = 0.027) and 12 months after HF-PDT from the baseline values (Sattler's: 45.8% ± 10.4%, P < 0.001 and Haller's: 56.8% ± 15.7%, P < 0.001).

CONCLUSION

After HF-PDT, the choriocapillaris showed the earliest decrease in vascular proportion of en face images, Sattler's and Haller's layers showed later decreases. The temporal differences in the response of each layer may reflect the pathophysiology of CSC and the therapeutic mechanism of HF-PDT.

Chlorophyll derivatives enhance invertebrate red-light and ultraviolet phototaxis

Chlorophyll derivatives are known to enhance vision in vertebrates. They are thought to bind visual pigments (i.e., opsins apoproteins bound to retinal chromophores) directly within the retina. Consistent with previous findings in vertebrates, here we show that chlorin e₆ — a chlorophyll derivative — enhances photophobicity in a flatworm (Dugesia japonica), specifically when exposed to UV radiation (λ = 405 nm) or red light (λ = 660 nm). This is the first report of chlorophyll derivatives acting as modulators of invertebrate phototaxis, and in general the first account demonstrating that they can artificially alter animal response to light at a behavioral level. Our findings show that the interaction between chlorophyll derivatives and opsins virtually concerns the vast majority of bilaterian animals, and also occurs in visual systems based on rhabdomeric (rather than ciliary) opsins.

[Photodynamic therapy. The fields of applications and prospects for the further development in otorhinolaryngology]

This article presents a review of the modern specialized medical literature concerned with the applications of photodynamic therapy (PDT) in otorhinolaryngology and medicine at large. The necessity of such a review of the available possibilities provided by PDT is dictated by the ever increasing interest of otorhinolaryngologists and specialists of other medical disciplines in the use of this method for the treatment of tumours and inflammatory diseases as well as their pyogenic complications. The author offers the critical assessment of the experience gained with the application of the known PDT technologies for the management of various pathological conditions. Especially much attention is given to the treatment of acute and chronic inflammation in the otorhinolaryngological practice with special reference to the yet unresolved problems.

Pharmaceutical development and medical applications of porphyrin-type macrocycles

The current state of pharmaceutical development of porphyrin-type macrocycles in medicine is highlighted. Currently, several porphyrinoid-based drugs are under various stages of development as phototherapeutic agents, X-ray radiation enhancers and boron neutron capture agents. These compounds represent a burgeoning class of pharmacological agents that are potentially useful in an array of treatment areas.

Mechanisms of porphyrinoid localization in tumors

The photosensitizing and pharmacokinetic properties of porphyrin-type compounds have been investigated for nearly a century. In the last decade, two porphyrin derivatives were approved in the U.S.A. and in several other countries for the photodynamic treatment of various lesions. An overview of the different mechanisms for preferential porphyrinoid localization in malignant tumors is presented herein. Several uptake pathways are possible for each photosensitizer, which are determined by its structure, mode of delivery and tumor type. Comparisons of the different mechanisms and correlations with the structure of the sensitizer are presented. Current delivery systems for porphyrin sensitizers are described, as well as recent strategies for enhancing their tumor-specificity, including conjugation to a carrier system that selectively targets a tumor-associated receptor or antigen.

Preclinical evaluation of a novel water-soluble chlorin E6 derivative (BLC 1010) as photosensitizer for the closure of the neovessels

In the present study, photodynamic activity of a novel photosensitizer (PS), Chlorin e(6)-2.5 N-methyl-d-glucamine (BLC 1010), was evaluated using the chorioallantoic membrane (CAM) as an in vivo model. After intravenous (i.v.) injection of BLC 1010 into the CAM vasculature, the applicability of this drug for photodynamic therapy (PDT) was assessed in terms of fluorescence pharmacokinetics, i.e. leakage from the CAM vessels, and photothrombic activity. The influence of different PDT parameters including drug and light doses on the photodynamic activity of BLC 1010 has been investigated. It was found that, irrespective of drug dose, an identical continuous decrease in fluorescence contrast between the drug inside and outside the blood vessels was observed. The optimal treatment conditions leading to desired vascular damage were obtained by varying drug and light doses. Indeed, observable damage was achieved when irradiation was performed at light doses up to 5 J/cm(2) 1 min after i.v. injection of drug doses up to 0.5 mg/kg body weight(b.w.). However, when irradiation with light doses of more than 10 J/cm(2) was performed 1 min after injection of drug doses up to 2 mg/kg body weight, this led to occlusion of large blood vessels. It has been demonstrated that it is possible to obtain the desired vascular occlusion and stasis with BLC 1010 for different combinations of drug and/or light doses.

Effects of photodynamic therapy using a fractionated dosing of mono-l-aspartyl chlorin e6 in a murine tumor

One of the 'second generation' photosensitizing agents is N-acetyl chlorin e6 (NPe6). This product has a strong absorbance band at 665 nm, permitting treatment at a greater depth of tumor than earlier agents based on porphyrin structures. We examined the effects of fractionated drug administration on photodynamic efficacy. Prior studies had shown that it is the level of NPe6 in the circulation that predicts for photodynamic efficacy, indicating vascular shut-down to be the predominant mode of tumor control. Although pharmacokinetic studies revealed that >99% of NPe6 was lost from the circulation, it appears that a fractionated dosage protocol can promote photodamage to neoplastic tissue in vivo. This study also indicated the potential utility of an implantable micro array for tumor irradiation.

EVALUATION OF PHOTOPOINT PHOTOSENSITIZER MV6401, INDIUM CHLORIDE METHYL PYROPHEOPHORBIDE, AS A PHOTODYNAMIC THERAPY AGENT IN PRIMATE CHORIOCAPILLARIS AND LASER-INDUCED CHOROIDAL NEOVASCULARIZATION

PURPOSE

To assess the potential of a new photosensitizer, indium chloride methyl pyropheophorbide (PhotoPoint MV6401), for ocular photodynamic therapy (PDT) in normal choriocapillaris vessels and experimentally induced choroidal neovascularization in New-World monkeys (Saimiri sciureus).

METHODS

PhotoPoint MV6401 (Miravant Pharmaceuticals, Inc., Santa Barbara, CA) was activated at 664 nm using a DD3-0665 (Miravant Systems, Inc., Santa Barbara, CA) 0.5 W diode laser. The efficacy of MV6401 was evaluated by indirect ophthalmoscopy, fundus photography, fluorescein angiography, and histology. The drug and light doses were 0.10 micromoles/kg to 0.3 micromoles/kg and 10 J/cm to 40 J/cm, respectively, and post-injection activation times ranged from +10 minutes to +120 minutes.

RESULTS

Best closure of normal choriocapillaris was achieved at a dosage level of 0.15 micromoles/kg in primates. Histology demonstrated that increased post-injection activation times (+60 minutes to +90 minutes) and low laser light doses (10 J/cm to 20 J/cm) in the primate model resulted in selective closure of the choriocapillaris and medium sized choroidal vessels with minimal effect to the retina. Histology from neovascular lesions PDT-treated with MV6401 revealed significant diminution of vascularity, correlating with diminution of leakage observed on angiography.

CONCLUSION

PhotoPoint MV6401, indium chloride methyl pyropheophorbide, is a potent photosensitizer that demonstrates both efficacy and selectivity in primate choriocapillaris and laser-induced choroidal neovascularization occlusion. Maximum selectivity was achieved using a post infusion interval of +60 to +90 minutes.

Current and Future Treatment Options for Nonexudative and Exudative Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible visual loss in the industrialised world. Although relatively simple to diagnose through direct visualisation augmented with rapid sequence fluorescein angiography, treatment has presented a far greater challenge because the true aetiology of AMD is largely unknown. Within the past decade, researchers have introduced many new, potentially promising treatment and prevention options in an attempt to minimise the damage imparted from AMD. They capitalise on many of the theoretical and known factors contributing to AMD progression. A high-dose of an orally administered combination of the antioxidants ascorbic acid (vitamin C), tocopherol (vitamin E) and beta-carotene, in addition to copper and zinc, is the only widely accepted preventive therapy. Thermal laser photocoagulation and verteporfin photodynamic therapy are the only standard treatment options available based on large scale, randomised, prospective, placebo-controlled trials; however, efficacy is limited and only a minority of patients who present with AMD are eligible for these treatments. Many other preventive and treatment options are in all phases of clinical studies and expected to change the entire approach to AMD management in the near future. For example, alternative antioxidants, drusen ablation, apheresis and HMG-CoA reductase inhibitors have shown promise in some studies by preventing or slowing the progression of certain forms of AMD. In addition, alternative photodynamic therapies, low-intensity laser, antiangiogenic medications, radiation treatment and surgery have demonstrated the ability, albeit to differing degrees, to inhibit or possibly even reverse the severe vision loss often associated with AMD characterised by choroidal neovascularisation.

Transpupillary thermotherapy threshold parameters: effect of indocyanine green pretreatment

PURPOSE

To evaluate the effect of combined treatment with systemic indocyanine green (ICG) on threshold fluence levels of transpupillary thermotherapy (TTT) in rabbits.

METHODS

Four pigmented rabbits and 13 nonpigmented rabbits were studied. TTT was performed on normal rabbit choriocapillaris using an 810-nm diode laser via slit-lamp biomicroscope delivery through a Goldmann macular lens. Laser spot size, power, and duration of laser exposure were varied to achieve a range of TTT fluences for threshold testing in both albino and pigmented rabbit fundi. Intravenous ICG pretreatment at doses of 0.41 to 10 mg/kg was initiated at varying times before TTT treatment. After the experiment, the eyes were enucleated under deep anesthesia, the animals were killed, and the eyes were prepared for light microscopy.

RESULTS

When intravenous ICG pretreatment was employed, there was a dose-dependent decrease in the TTT fluence threshold as compared with known threshold values. At threshold fluences, histopathologic sections revealed damage to all layers of the retina in addition to choriocapillaris damage.

CONCLUSION

Intravenous ICG pretreatment can be used to lower the TTT threshold fluence and irradiance required to create angiographically visible lesions in the normal rabbit choriocapillaris. Damage was seen in all layers of the retina and choriocapillaris at threshold levels when TTT was used alone or in combination with ICG pretreatment.

Scanning laser system for photodynamic therapy of choroidal neovascularization

BACKGROUND AND OBJECTIVES

In order to improve selectivity of photodynamic therapy (PDT) to choroidal neovascularization (CNV) associated with age-related macular degeneration, a laser scanning technique was applied to perform focal laser irradiation to the retina, and the occlusion effects of a new device to the choriocapillaris were evaluated in primate eyes.

STUDY DESIGN/MATERIALS AND METHODS

The device contains lasers for fundus observation of 785 nm and for PDT of 670 nm, matching the absorption peak of a photosensitizer, ATX-S10(Na). The laser irradiated the shape on the retina specified before treatment and shut off automatically when the predetermined treatment was achieved. The occlusion of the choriocapillaris after PDT was documented by fluorescein and indocyanine green angiography and histology.

RESULTS

The area designated for PDT was easily drawn on the touch-screen monitor, and occlusion of the choriocapillaris was achieved precisely in the area pre-selected for treatment with 5 J/cm(2) or more of radiance following administration of 8 mg/kg ATX-S10(Na).

CONCLUSIONS

This device is useful for irradiating CNV of any shape, sparing the surrounding retina. Since our previous studies suggested that selective occlusion of CNV would decrease not only the functional disturbance caused by PDT, but also the recurrence of CNV, the present device may allow more effective PDT than the slit-lamp system presently used.

Photodynamic therapy for choroidal neovascularization: a review

PURPOSE

To review the biophysical basis and current state of therapy for photodynamic closure of subfoveal choroidal neovascularization in the eye.

METHODS

A review of the literature is included, which encompasses the chemical structure, biophysical mechanism of action, range of available agents, status of clinical trials, clinical indications, results of treatments, complications, and future directions.

RESULTS

Photodynamic therapy has been shown to be effective in closing both experimental choroidal neovascularization in animal models as well as subfoveal choroidal neovascularization in humans. The therapy results in temporary closure of choroidal new vessels for a period of approximately 1 to 4 weeks. By 12 weeks, most patients have reperfusion or reproliferation of choroidal new vessels resulting in the need for retreatment to achieve continued closure and visual stabilization. Differences exist in the quantum yield, clinical efficiency, and light and sensitizer dose requirements between different classes of agents. Further clinical trials will be required to determine the optimal form of therapy, with verteporfin (Visudyne) as the only currently approved agent. Other agents, including tin etiopurpurin (Purlytin) and motexafin lutetium (Optrin), are currently undergoing phase III, and phase II trials, respectively.

CONCLUSIONS

Photodynamic therapy is a promising treatment modality shown to be effective in achieving closure and stabilization of vision loss compared with placebo control in eyes with subfoveal choroidal neovascularization.

Clinicopathologic studies of age-related macular degeneration with classic subfoveal choroidal neovascularization treated with photodynamic therapy

BACKGROUND

Photodynamic therapy (PDT) is a relatively new modality that is currently under clinical and experimental evaluation for treatment of subfoveal choroidal neovascularization (CNV). The authors report the case of an 82-year-old woman who underwent verteporfin-mediated PDT for classic subfoveal CNV. Fluorescein angiography performed 2 weeks after treatment disclosed reduction of the initial area of neovascularization and leakage by approximately 60%. Three weeks after PDT, however, the area of leakage was almost the same size as that before treatment. The patient underwent submacular membranectomy almost 4 weeks after treatment. The authors describe the ultrastructural vascular changes after PDT and a clinicopathologic study of classic CNV.

METHODS

The submacular membrane was studied by light and electron microscopy and immunohistochemical techniques.

RESULTS

Ultrastructural examination of the peripheral vessels showed evidence of endothelial cell degeneration with platelet aggregation and thrombus formation. Occasional occluded vessels were surrounded by macrophages, a phenomenon previously reported to describe the process of resorption of such blood vessels. The vessels in the center of the membrane were unremarkable.

CONCLUSION

Photodynamic therapy causes endothelial cell damage, thrombus formation, and vascular occlusion of classic CNV in age-related macular degeneration.

Photodynamic therapy of experimental choroidal neovascularization with a hydrophilic photosensitizer: mono-L-aspartyl chlorin e6

PURPOSE

To demonstrate the selective localization of the hydrophilic photosensitizer mono-L-aspartyl chlorin e6 (NPe6) in experimental choroidal neovascularization in nonhuman primate eyes.

METHODS

Sixty-seven experimental choroidal neovascular lesions (CNV) were created in the fundi of Macaca monkeys using the modified Ryan's model and documented by fluorescein and indocyanine green angiography. To determine the biodistribution of NPe6 and the optimal timing of laser irradiation after dye administration, NPe6 angiography and fluorescence microscopy with NPe6 were performed. Photodynamic therapy (PDT) was performed at various dye doses (0.5-10.0 mg/kg) and laser fluences (7.5-225.0 J/cm2) on the CNV and on 10 areas of normal retina and choroid. Treatment outcomes were assessed by fluorescein and indocyanine green angiography and confirmed by light and electron microscopy.

RESULTS

NPe6 fluorescence microscopy demonstrated intense fluorescence of CNV and retinal pigment epithelial cells. Choroidal vessel walls and outer retina adjacent to CNV fluoresced moderately; retinal vessel walls and microcapillaries had trace fluorescence. The fluorescence of CNV lesions on fluorescein angiography became stronger than that of retinal vessels 20-60 minutes after dye injection. Choroidal neovascular lesion closure was achieved with NPe6 PDT without significant damage to the sensory retina. Histology demonstrated necrosis of CNV endothelial cells with minimal damage to surrounding tissues.

CONCLUSIONS

NPe6 PDT selectively localizes to experimental CNV in nonhuman primates, resulting in occlusion of CNV with sparing of the neurosensory retina.

Retreatment effect of NPe6 photodynamic therapy on the normal primate macula

PURPOSE

To evaluate the safety and efficacy of repeated photodynamic therapy (PDT) with mono-L-aspartyl chlorin e6 (NPe6) on normal primate fovea and choroid.

METHODS

Macaca fuscata monkeys were used as experimental subjects. Mono-L-aspartyl chlorin e6 at a dose of 2 mg/kg was administered by intravenous infusion. Laser irradiation was applied within 5 minutes using a 664-nm diode laser at a power output of 5.9 mW (750 mW/cm2), spot size of 1,000 microm, and time of 10 seconds. This resulted in a fluence of 7.5 J/cm2. Three consecutive PDT treatments at 2-week intervals were applied over the center of the fovea and posterior fundus near the arcade vessels of each eye. The animals were killed and the eyes were enucleated for histologic study 2 weeks after the last treatment.

RESULTS

Limited changes could be observed in the sensory retina under light microscopy. Photoreceptor cells and outer segments were not damaged, even after repeated PDT. Proliferation and duplication of the retinal pigment epithelial cells were common findings. A plaque of fibrous tissue was present, interwoven with retinal pigment epithelial cells in eyes that received repeated PDT. The retinal vessels remained patent even after three sessions of PDT. However, occlusion of the choriocapillaris and the large choroidal vessels was observed after repeated PDT treatment.

CONCLUSION

Repeated PDT of healthy nonhuman primate fundi using a hydrophilic photosensitizer (NPe6) shows preservation of the neurosensory retina components and architecture with damage confined to the retinal pigment epithelium and choriocapillaris.

Localization of rose bengal, aluminum phthalocyanine tetrasulfonate, and chlorin e6 in the rabbit eye

PURPOSE

The localization and site of action of photosensitizers in the eye may be important for photodynamic therapy for fundus disorders but remain poorly understood for most agents. We investigated the intraocular localization of xanthene, phthalocyanine, and chlorin photosensitizers by using fluorescence microscopy and digital fundus fluorescence angiography.

METHODS

Rose bengal (40 mg/kg), aluminum phthalocyanine tetrasulfonate (CASPc) (5 mg/kg), or chlorin e6 (2 mg/kg) was intravenously administered to albino rabbits. The eyes were enucleated and examined by means of fluorescence microscopy 5, 20, 60, and 120 minutes and 24 hours after dye injection. In vivo digital fundus fluorescence angiography with use of rose bengal (2-4 mg/kg), CASPc (2 mg/kg), and chlorin e6 (2 mg/kg) was performed.

RESULTS

For all agents studied pathologically, there was moderate fluorescence from the choroid and retinal pigment epithelium 5 minutes after dye injection. Mild fluorescence detected from the photoreceptor outer segments at 5 minutes was increased at 20 minutes. Angiographic studies with use of rose bengal, CASPc, and chlorin e6 revealed differences in the pattern and rate of photosensitizer accumulation.

CONCLUSIONS

Rose bengal, CASPc, and chlorin e6 accumulate rapidly in the choroid and retinal pigment epithelium and less rapidly in the outer retina. Differences in ocular localization of these photosensitizers were demonstrated. The significance of these findings for potential photodynamic therapy with these agents requires further investigation.

Dynamic observation of selective accumulation of a photosensitizer and its photodynamic effects in rat experimental choroidal neovascularization

PURPOSE

The authors investigated the selective accumulation of a photosensitizer, ATX-S10(Na), in experimental choroidal neovascularization (CNV) in rats using a highly sensitive colorchromatic charge coupled device (CCD) camera.

METHODS

To detect the development of experimental CNV in 30 rats, the animals were followed weekly with simultaneous fluorescein and indocyanine green angiography. After injecting ATX-S10(Na), the authors detected fluorescence from the photosensitizer using a highly sensitive color CCD camera. The camera was connected to a surgical microscope, under which rat fundi were observed through a coverglass in contact with the cornea. The retinas were excited with 405-435 nm light, and the light emitted from the photosensitizer passed through a 680-nm bandpass filter before being detected by the CCD camera.

RESULTS

Immediately after injection, fluorescence appeared in the retinal vessels and then the entire retina. Thirty minutes postinjection, the intensity of the fluorescence was still strong from the whole retina, and the CNV was not detected. One hour after injection, retinal fluorescence was weak but still observable; 1.5 hours postinjection, retinal fluorescence was undetectable but fluorescence was strong from the CNV. Under the optimum therapeutic conditions, CNV was effectively occluded.

CONCLUSION

ATX-S10(Na) selectively accumulates in the CNV in rats. The optimum therapeutic timing is approximately 1.5 hours postinjection of the dye in this CNV model.

Mechanisms of action of photodynamic therapy with verteporfin for the treatment of age-related macular degeneration

Age-related macular degeneration, especially the neovascular form of the disease, is the leading cause of blindness in elderly people in developed countries. Thermal photocoagulation is still the preferred treatment for choroidal neovascularization that does not involve the fovea, but it is suitable for only a small number of patients and it can lead to immediate loss of visual acuity. Photodynamic therapy with use of photochemical light activation of verteporfin as a photosensitizer (verteporfin therapy) has been shown to be effective in treating vascularized tumors, and its potential to treat other conditions involving neovascularization has also been suggested. Preclinical and clinical studies have indicated that verteporfin therapy can be used to treat choroidal neovascularization secondary to age-related macular degeneration effectively and safely. Selective occlusion of choroidal neovasculature by this therapy causes minimal damage to the neurosensory retina and, therefore, does not induce loss of visual acuity. This benefit allows verteporfin therapy to be used in the large proportion of patients who are not eligible for treatment by laser photocoagulation. The mechanistic aspects of the mode of action of light-activated verteporfin are described in this review.

Update on photodynamic therapy

Photodynamic therapy is a relatively selective form of treatment for choroidal neovascularization. Unlike standard laser photocoagulation, photodynamic therapy can close choroidal neovascularization with minimal or no detectable damage to surrounding tissues. Therefore, it allows the clinician to treat subfoveal choroidal neovascularization without immediately adversely affecting central visual function. Several dyes for photodynamic therapy have been under various stages of formal clinical investigation. There is now mounting evidence that shows that photodynamic therapy with at least one of these dyes can significantly reduce the risk of visual loss in eyes with subfoveal choroidal neovascularization from age-related macular degeneration. This form of treatment promises to have a major, favorable impact on public health in areas of the world in which age-related macular degeneration is common.

Problems with and pitfalls of photodynamic therapy

OBJECTIVE

To delineate the various factors that may influence the outcome of photodynamic therapy of the retina and choroid.

DESIGN

Experimental animal study.

ANIMALS

Pigmented and nonpigmented rabbits; rhesus monkeys.

INTERVENTION

The hydrophilic photosensitizer, mono-L-aspartyl chlorin e6, which is maximally activated at 664 nm, was studied after intravenous injection into pigmented and nonpigmented rabbits and rhesus monkeys. Laser light was supplied by a red diode laser coupled to a modified slit-lamp biomicroscope and delivered to the ocular fundus after passing through a standard fundus contact lens. Standard photodynamic parameters were used. The effects of fundus pigmentation, intraocular pressure, spot focus and defocus, region of fundus treated, equivalent fluence, and retreatment were observed in the different animal species.

MAIN OUTCOME MEASURES

Slit-lamp biomicroscopy, fluorescein angiography, light and transmission electron microscopy.

RESULTS

Fundus pigmentation appeared to be a factor only at the lowest fluence level tested, where only 4 of 12 lesions attempted in pigmented fundi were noted on fluorescein angiography, compared with 12 of 12 lesions in albino rabbits. At normal intraocular pressures and a given fluence, 10 of 10 lesions were fully manifested on fluorescein angiography, compared with 4 of 10 at 30 mmHg and 0 of 10 at pressures sufficient to blanch the optic nerve (>60 mmHg). For laser spots either focused or defocused, there were 6 of 6 lesions that were fully manifested on fluorescein angiography for each of the parameters. Lesions treated in the fovea resulted in larger spots on fluorescein angiography. The fluence of 5 mW for 10 seconds resulted in a larger lesion on angiography than the equivalent fluence of 10 mW for 5 seconds. Areas of retreatment in rabbits demonstrated more thinning of the neurosensory retina and loss of photoreceptor outer segments and nuclei than corresponding areas receiving one treatment.

CONCLUSIONS

Photodynamic therapy results varied, depending on intraocular pressure, region of fundus treated, ocular pigmentation, and the total time of exposure to the photosensitizer. Retreatment resulted in progressive thinning of the neurosensory retina with loss of photoreceptor outer segments and nuclei in the rabbit eye.