Pathophysiology of age-related macular degeneration

Mapping the distribution of emissive molecules in human ocular lipofuscin granules with near-field scanning optical microscopy

Several high resolution imaging techniques are utilized to probe the structure of human ocular lipofuscin granules. Atomic force microscopy reveals typical granule sizes to be about one micrometre in diameter and hundreds of nanometres in height, in agreement with previous electron microscopy results. For issues concerning the role of lipofuscin in age-related macular degeneration, recent attention has focused on the orange-emitting fluorophore, A2E. Confocal microscopy measurements are presented which reveal the presence of a highly emissive component in the granules, consistent with the presence of A2E. It is shown, however, that the interpretation of these results is complicated by the lack of structural details about the particles. To address these issues, near-field scanning optical microscopy (NSOM) measurements are presented which measure both the lipofuscin fluorescence and topography, simultaneously. These measurements reveal distinct structure in the fluorescence image which do not necessarily correlate with the topography of the granules. Moreover, direct comparison between the NSOM fluorescence and topography measurements suggests that A2E is not the major component in lipofuscin. These measurements illustrate the unique capabilities of NSOM for probing into the microstructure of lipofuscin and uncovering new insights into its phototoxicity.

Pulsatile ocular blood flow study: decreases in exudative age related macular degeneration

BACKGROUND

Pulsatile ocular blood flow (POBF) is a parameter for evaluating choroidal blood flow. POBF in the patients with non-exudative and exudative age related macular degeneration (AMD) was investigated.

METHODS

POBF, pulse amplitude (PA), systolic and diastolic blood pressures, intraocular pressure (IOP), refractive error, and axial length were compared among 10 patients with non-exudative AMD, 11 patients with exudative AMD, and 69 age matched controls. A Langham OBF computerised tonometer was used with the participants in the sitting position to measure POBF and PA.

RESULTS

No significant differences were found in age, systolic and diastolic blood pressures, IOP, or refractive error between patients with exudative and non-exudative AMD and the control subjects. In the patients with exudative AMD the POBF (median, 372.7 microl/min) and PA (median, 1.2 mm Hg) were significantly lower than in the patients with non-exudative AMD (median, 607.0 microl/min (p = 0.02) and 2.2 mm Hg (p = 0.04), respectively) and control subjects (median, 547.4 microl/min (p = 0.01) and 2.0 mm Hg (p = 0.01), respectively).

CONCLUSIONS

These data show that the POBF and PA in the patients with exudative AMD are lower than in the patients with non-exudative AMD and normal subjects. Decreased choroidal blood flow may have a role in the development of choroidal neovascularisation in AMD.

Ocular perfusion and age-related macular degeneration

PURPOSE

To review the role of ocular perfusion in the pathophysiology of age-related macular degeneration (AMD), the leading cause of irreversible blindness in the industrialized world.

METHODS

Medline search of the literature published in English or with English abstracts from 1966 to 2000 was performed using various combinations of relevant key words.

RESULTS

Vascular defects have been identified in both nonexudative and exudative AMD patients using fluorescein angiographic methods, laser Doppler flowmetry, indocyanine green angiography, and color Doppler imaging.

CONCLUSION

Although these studies lend some support to the vascular pathogenesis of AMD, it is not possible to determine if the choroidal perfusion abnormalities play a causative role in nonexudative AMD, if they are simply an association with another primary alteration, such as a primary RPE defect or a genetic defect at the photoreceptor level, or if they are more strongly associated with one particular form of this heterogeneous disease. Further study is warranted.

Molecular characterization and developmental expression of NORPEG, a novel gene induced by retinoic acid

We have characterized NORPEG, a novel gene from human retinal pigment epithelial cells (ARPE-19), in which its expression is induced by all-trans-retinoic acid. Two transcripts ( approximately 3 and approximately 5 kilobases in size) have been detected for this gene, which is localized to chromosome band 5p13.2-13.3. Placenta and testis showed the highest level of expression among various human tissues tested. Six ankyrin repeats and a long coiled-coil domain are present in the predicted sequence of the NORPEG protein, which contains 980 amino acid residues. This approximately 110-kDa protein was transiently expressed in COS-7 cells as a FLAG fusion protein and immunolocalized to the cytoplasm. Confocal microscopic analysis of the NORPEG protein in ARPE-19 cells showed threadlike projections in the cytoplasm reminiscent of the cytoskeleton. Consistent with this localization, the expressed NORPEG protein showed resistance to solubilization by Triton X-100 and KCl. An ortholog of NORPEG characterized from mouse encoded a protein that showed 91% sequence similarity to the human NORPEG protein. The expression of Norpeg mRNA was detected in mouse embryo at embryonic day 9.5 by in situ hybridization, and the expression appears to be developmentally regulated. In adult mouse, the highest level of expression was detected in the seminiferous tubules of testis.

Autosomal dominant Stargardt-like macular dystrophy segregating in a large Canadian family

BACKGROUND

Inherited macular dystrophies account for a major fraction of the cases of retinal degenerative disease that lead to permanent blindness. We describe the clinical and genetic findings in a Canadian family with a form of macular dystrophy resembling autosomal dominant Stargardt-like macular dystrophy.

METHODS

Standard ophthalmologic examinations were performed in members of a single five-generation Alberta family. Tests of visual acuity and colour vision, fundus photography, fluorescein angiography and electroretinography were performed in 15 affected people. Blood was collected from 24 family members, and DNA was extracted for genotyping. Genetic linkage analysis was performed using polymorphic short tandem repeat microsatellite markers located on chromosome 6q, a region containing loci for several macular disorders.

RESULTS

Affected family members display clinical characteristics resembling autosomal dominant Stargardt-like macular dystrophy, previously assigned to chromosome 6q (STGD3). Linkage analysis generated a peak lod score of 5.50 at an estimated recombination fraction of 0.00 for marker locus D6S300.

INTERPRETATION

The family described has an autosomal dominant macular dystrophy that resembles Stargardt-like macular dystrophy. The disease locus for this family maps to an interval on chromosome 6q that overlaps that for STGD3 and other retinal dystrophy loci. These findings provide further evidence that human chromosome 6q represents a "hot spot" for retinal disorders.

The role of oxidative stress in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blind registration in the developed world, and yet its pathogenesis remains poorly understood. Oxidative stress, which refers to cellular damage caused by reactive oxygen intermediates (ROI), has been implicated in many disease processes, especially age-related disorders. ROIs include free radicals, hydrogen peroxide, and singlet oxygen, and they are often the byproducts of oxygen metabolism. The retina is particularly susceptible to oxidative stress because of its high consumption of oxygen, its high proportion of polyunsaturated fatty acids, and its exposure to visible light. In vitro studies have consistently shown that photochemical retinal injury is attributable to oxidative stress and that the antioxidant vitamins A, C, and E protect against this type of injury. Furthermore, there is strong evidence suggesting that lipofuscin is derived, at least in part, from oxidatively damaged photoreceptor outer segments and that it is itself a photoreactive substance. However, the relationships between dietary and serum levels of the antioxidant vitamins and age-related macular disease are less clear, although a protective effect of high plasma concentrations of alpha-tocopherol has been convincingly demonstrated. Macular pigment is also believed to limit retinal oxidative damage by absorbing incoming blue light and/or quenching ROIs. Many putative risk-factors for AMD have been linked to a lack of macular pigment, including female gender, lens density, tobacco use, light iris color, and reduced visual sensitivity. Moreover, the Eye Disease Case-Control Study found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular AMD. The concept that AMD can be attributed to cumulative oxidative stress is enticing, but remains unproven. With a view to reducing oxidative damage, the effect of nutritional antioxidant supplements on the onset and natural course of age-related macular disease is currently being evaluated.

Overexpression of vascular endothelial growth factor (VEGF) in the retinal pigment epithelium leads to the development of choroidal neovascularization

Vascular endothelial growth factor (VEGF) has been strongly implicated in the development of choroidal neovascularization found in age-related macular degeneration. Normally expressed in low levels, this study investigates whether the overexpression of VEGF in the retinal pigment epithelium is sufficient to cause choroidal neovascularization in the rat retina. A recombinant adenovirus vector expressing the rat VEGF(164) cDNA (AdCMV.VEGF) was constructed and injected into the subretinal space. The development of neovascularization was followed by fluorescein angiography, which indicates microvascular hyperpermeability of existing and/or newly forming blood vessels, and histology. VEGF mRNA was found to be overexpressed by retinal pigment epithelial cells and resulted in leaky blood vessels at 10 days postinjection, which was maintained for up to 31 days postinjection. By 80 days postinjection, new blood vessels had originated from the choriocapillaris, grown through the Bruch's membrane to the subretinal space, and disrupted the retinal pigment epithelium. This ultimately led to the formation of choroidal neovascular membranes and the death of overlying photoreceptor cells. By controlling the amount of virus delivered to the subretinal space, we were able to influence the severity and extent of the resulting choroidal neovascularization. These results show that even temporary overexpression of VEGF in retinal pigment epithelial cells is sufficient to induce choroidal neovascularization in the rat eye.

A potential role for immune complex pathogenesis in drusen formation

Drusen are abnormal extracellular deposits that accumulate between the retinal pigmented epithelium and Bruch's membrane and are commonly associated with age-related macular degeneration. Our recent work has identified a number of plasma proteins as molecular components of drusen. Of interest is the fact that many of these drusen-associated molecules are acute phase reactant proteins and some have established roles in mediating immune responsiveness. As immune and inflammatory responses appear to play a role in the formation of other pathologic age-related deposits, we examined the distribution of immunoglobulin molecules and terminal complement complexes at sites of drusen deposition. Here, we report that concentrations of immunoglobulin G and terminal C5b-9 complement complexes are present in drusen. In addition, we observe that retinal pigmented epithelial cells overlying or directly adjacent to drusen, as well as some within apparently normal epithelia, exhibit cytoplasmic immunoreactivity for immunoglobulin and the C5 component of complement. Taken together, these results suggest that drusen biogenesis may be a byproduct of immune responsiveness, and they implicate immune complex-mediated pathogenesis involving retinal pigmented epithelial cells as an initiating event in drusen formation.

Ceramide-induced cell death in cultured rat retinal pigment epithelial cells

We investigated whether retinal pigment epithelial (RPE) responds to ceramide, a known second messenger of apoptosis. RPE cells were isolated by 6-8 day old Long Evans rat eye. We used MTS assay for viability test, and used Hoechst 33552 and propidium iodide for apoptotic cell staining. In cultured rat RPE cells, the addition of membrane-permeable ceramide induced apoptosis-like cell death rapidly. RPE cell death was dependent on C2-ceramide concentration. The effective dose (ED50) of C2-ceramide was 23.64 microM. Ceramide-induced RPE cell death was inhibited by zVAD-fmk, a CPP32-like protease inhibitor. Our findings indicated that ceramide in RPE cell death functions upstream of CPP32-like proteases.

The role of vascular endothelial growth factor (VEGF) in abnormal vascular changes in the adult rat eye

The aim of this project was to determine if the subretinal delivery of a recombinant adenovirus encoding vascular endothelial growth factor (VEGF) was sufficient to induce changes resembling choroidal neovascularisation (CNV) in a rat model. A recombinant adenovirus was produced encoding vegf164 cDNA (Ad.RSV.VEGF). Transduction of cultured RPE cells confirmed VEGF expression and ensured the absence of Ad.RSV.VEGF-related toxicity. Following subretinal injection into rat eyes, fluorescein angiography indicated that the in vivo delivery of Ad.RSV.VEGF was associated with vascular leakage. Histological analysis demonstrated that changes resembling the early signs of CNV development were also present in the Ad.RSV.VEGF injected eyes. These results suggest that while a transient VEGF expression in the RPE layer is able to induce CNV-related changes, it may be insufficient for the development of a full neovascular membrane. This study demonstrates that virus-mediated gene delivery, in addition to its clinical applications, is a potentially efficient research tool for investigating gene expression-related physiological changes in vitro and in vivo.

Effect of thalidomide, octreotide, and prednisolone on the migration and proliferation of RPE cells in vitro

PURPOSE

The retinal pigment epithelium (RPE) is involved in the pathogenesis of age-related macular degeneration. The purpose of this study was to assess the effect of thalidomide, octreotide, and prednisolone on the proliferation and migration of bovine RPE cells in vitro.

METHODS

The migration assay was performed in double-chamber-wells separated by a membrane filter with 8 microm pores. Cells were allowed to migrate vertically for 7 hr, afterwards the cells on both filtersides were fixed, stained, and the migrated cells were counted. To examine RPE proliferation, bovine RPE cells were seeded subconfluently followed by an incubation with octreotide, thalidomide or prednisolone in a concentration gradient for 24 hr. Stimulation or inhibition of DNA synthesis was measured by [(3)H]-thymidine incorporation. Statistical analysis was performed with the paired student's t-test.

RESULTS

Statistically significant (p < 0.05) inhibition of RPE cell proliferation was measured for thalidomide at a concentration of 10-50 microg/ml, for octreotide at a concentration of 5 x 10(-4) and 5 x 10(-5) M, and for prednisolone at a concentration of 250 and 500 microg/ml as compared to the negative control. RPE cell migration was significantly (p < 0.05) inhibited by thalidomide at a concentration of 10 microg/ml, by octreotide at a concentration of 5 x 10(-5) M, and also by prednisolone at a concentration of 500 microg/ml as compared to the negative control.

CONCLUSIONS

Although the main effect of thalidomide, octreotide, and prednisolone when treating patients with choroidal neovascular membranes is probably related to the inhibition of angiogenesis it should be kept in mind that these substances may additionally inhibit RPE proliferation and migration.

Changing therapeutic paradigms for exudative age-related macular degeneration: antiangiogenic agents and photodynamic therapy

Age related macular degeneration (AMD) is the leading cause of irreversible visual loss in the United States. Overall, approximately 10 - 20% of patients with AMD exhibit the exudative form, which is responsible for most of the estimated 1.2 m cases of severe visual loss from AMD. Visual loss develops in the exudative form of AMD due to abnormal choroidal neovascular membranes (CNVM) that develop under the retina, leak serous fluid and blood, and ultimately cause a blinding disciform scar in, and under, the retina. Currently, the only well-studied and widely accepted method of treatment is laser photocoagulation of the CNVM. However, only a minority of patients with exudative AMD show well-demarcated 'classic' CNVM amenable to laser treatment, and at least half of these patients suffer persistent or recurrent CNVM formation within two years. In addition, since the treatment itself causes a blinding central scotoma when the CNVM is located subfoveally, many clinicians do not treat subfoveal CNVM. With these treatment limitations, there has been a great deal of interest in alternative therapies for AMD, including anti-angiogenic agents and photodynamic therapy. Angiogenesis involves a complex interplay of cellular events involving a cascade of factors that are both inhibitory and stimulatory. Soluble growth factors have been the best-known cell modulating agents in ophthalmology, but there are a multitude of potential sites for inhibition of angiogenesis by pharmacological agents. With regard to photodynamic therapy, a photosensitising dye is injected intravascularly and low power laser light is used to activate the dye within the CNVM to cause vascular occlusion by a photochemical reaction. Closure of the CNVM is achieved without severe collateral damage to the non-vascular tissues as occurs with laser photocoagulation.

A prospective, randomized, double-masked trial on radiation therapy for neovascular age-related macular degeneration (RAD Study). Radiation Therapy for Age-related Macular Degeneration

OBJECTIVE

To determine the efficacy of external beam radiation therapy on choroidal neovascularization (CNV) secondary to age-related macular degeneration (ARMD).

DESIGN

Multicenter, parallel, randomized, double-masked clinical trial performed at nine ophthalmic and radiotherapeutic centers.

PARTICIPANTS

Two hundred five patients were randomly assigned either to treatment with 8 fractions of 2 Gy external beam irradiation (n = 101) or to control with 8 fractions of 0 Gy (sham treatment, n = 104). Both patients and ophthalmologists were masked with regard to applied treatment. Patients with subfoveal classic or occult CNV, visual acuity of 20/320 or greater on the Early Treatment Diabetic Retinopathy Study chart, lesion size of 6 disc areas or less, history of visual symptoms of 6 months or less, and absence of foveal hemorrhage were recruited.

INTERVENTION

In the treatment group, external beam irradiation with 8 fractions of 2 Gy was performed, whereas in the control group, sham treatment with 8 fractions of 0 Gy was applied.

MAIN OUTCOME MEASURES

Primary outcome measure was the difference in visual acuity between baseline and after 1 year of follow-up.

RESULTS

One hundred eighty-three patients (89.3%) completed the 1-year follow-up. The mean reduction in visual acuity was 3.5 +/- 4.7 lines in 88 patients of the 8- x 2-Gy treatment group and 3.7 +/- 3.8 lines in 95 patients of the 8- x 0-Gy control group. This difference was not statistically significant (P = 0.53, Mann-Whitney U test). At 1 year, 51.1% of treated patients and 52.6% of control subjects lost three or more lines (P = 0.88). Visual acuity in the presence of classic CNV dropped by 3.7 +/- 4.4 lines in 33 patients of the treatment group versus 4.3 +/- 3.9 lines in 36 patients of the control group (P = 0.47). Visual acuity in 114 patients with occult CNV dropped by 3.4 +/- 4.9 in the treatment group (55 patients) versus 3.4 +/- 3.8 lines in the control group (59 patients) (P = 0.80).

CONCLUSIONS

In this randomized study, radiation therapy at a dose of 16 Gy applied in 8 fractions of 2 Gy provided no benefit as a treatment for subfoveal CNV secondary to ARMD at 1 year.

Polyplex-mediated gene transfer into human retinal pigment epithelial cells in vitro

The human retinal pigment epithelium (RPE) is a potential target tissue for directed transfer of candidate genes to treat age-related macular degeneration (AMD). The RPE is uniquely suited to gene therapy protocols that use liposome-mediated DNA transfer because of its high intrinsic phagocytic function in vivo. In these studies, we examined the efficacy of human RPE cell uptake and expression of the green fluorescent protein (GFP) and neomycin resistance marker genes by polyplex-mediated gene transfer in vitro. The effects of varying DNA and polyplex concentration and ratios on GFP transgene expression were examined. A narrow range of experimental conditions were found to maximize transgene expression; most important were the DNA concentration and the DNA:polyplex ratio. The transfection efficiency for human RPE cells was reproducibly 20% in vitro by this method and reached a maximum level of expression after 48 h. There was a rapid decline in gene expression over 2 weeks following polyplex-mediated gene transfer, but stable integration does occur at low frequencies with and without selection.

Progress in measurement of ocular blood flow and relevance to our understanding of glaucoma and age-related macular degeneration

New technologies have facilitated the study of the ocular circulation. These modalities and analysis techniques facilitate very precise and comprehensive study of retinal, choroidal, and retrobulbar circulations. These techniques include: 1. Vessel caliber assessment; 2. Scanning laser ophthalmoscopic fluorescein angiography and indocyanine green angiography to image and evaluate the retinal circulation and choroidal circulation respectively; 3. Laser Doppler flowmetry and confocal scanning laser Doppler flowmetry to measure blood flow in the optic nerve head and retinal capillary beds; 4. Ocular pulse measurement; and 5. color Doppler imaging to measure blood flow velocities in the central retinal artery, the ciliary arteries and the ophthalmic artery. These technique have greatly enhanced the ability to quantify ocular perfusion defects in many disorders, including glaucoma and age-related macular degeneration, two of the most prevalent causes of blindness in the industrialized world. Recently it has become clear, in animal models of glaucoma, that retinal ganglion cells die via apoptosis. The factors that initiate apoptosis in these cells remain obscure, but ischemia may play a central role. Patients with either primary open-angle glaucoma or normal-tension glaucoma experience various ocular blood flow deficits. With regard to age-related macular degeneration, the etiology remains unknown although some theories include primary retinal pigment epithelial senescence, genetic defects such as those found in the ABCR gene which is also defective in Stargardt's disease and ocular perfusion abnormalities. As the choriocapillaris supplies the metabolic needs of the retinal pigment epithelium and the outer retina, perfusion defect in the choriocapillaris could account for some of the physiologic and pathologic changes in AMD. Vascular defects have been identified in both nonexudative and exudative AMD patients using new technologies. This paper is a comprehensive update describing modalities available for the measurement of all new ocular blood flow in human and the clinical use.

Polarized vascular endothelial growth factor secretion by human retinal pigment epithelium and localization of vascular endothelial growth factor receptors on the inner choriocapillaris. Evidence for a trophic paracrine relation

The retinal pigment epithelium (RPE) maintains the choriocapillaris (CC) in the normal eye and is involved in the pathogenesis of choroidal neovascularization in age-related macular degeneration. Vascular endothelial growth factor-A (VEGF) is produced by differentiated human RPE cells in vitro and in vivo and may be involved in paracrine signaling between the RPE and the CC. We investigated whether there is a polarized secretion of VEGF by RPE cells in vitro. Also, the localization of VEGF receptors in the human retina was investigated. We observed that highly differentiated human RPE cells, cultured on transwell filters in normoxic conditions, produced two- to sevenfold more VEGF toward their basolateral side as compared to the apical side. In hypoxic conditions, VEGF-A secretion increased to the basal side only, resulting in a three- to 10-fold higher basolateral secretion. By immunohistochemistry in 30 human eyes and in two cynomolgus monkey eyes, KDR (VEGFR-2) and flt-4 (VEGFR-3) were preferentially localized at the side of the CC endothelium facing the RPE cell layer, whereas flt-1 (VEGFR-1) was found on the inner CC and on other choroidal vessels. Our results indicate that RPE secretes VEGF toward its basal side where its receptor KDR is located on the adjacent CC endothelium, suggesting a role of VEGF in a paracrine relation, possibly in cooperation with flt-4 and its ligand. This can explain the known trophic function of the RPE in the maintenance of the CC and its fenestrated permeable phenotype and points to a role for VEGF in normal eye functioning. Up-regulated basolateral VEGF secretion by RPE in hypoxia or loss of polarity of VEGF production may play a role in the pathogenesis of choroidal neovascularization.

Blue light induced apoptosis in rat retina

PURPOSE

To explore cell death in blue light induced retinal damage.

METHODS

Sprague-Dawley rats reared under cyclic light were exposed continuously to diffuse blue light (400-480 nm) at 0.64 W/m2 for 3 or 6 h after 22 h of dark adaptation. The rats were kept in darkness and killed immediately, 8, 16 and 24 h following light exposure. The retinal damage by the blue light was examined with a transmission electron microscope. The cell death was characterised by in situ terminal dUTP nick end labelling (TUNEL) and gel electrophoresis.

RESULTS

During the 24 h following light exposure, photoreceptor cell death was characterised by progressive condensation and margination of the chromatin, shrinkage or convolution and fragmentation of the nucleus, condensation of the cytoplasm, and formation of apoptotic bodies along with rapid removal of dying cells from damaged areas in the absence of inflammatory response. The TUNEL-positive nuclei were scattered individually in the outer nuclear layer just after light exposure. A wave of massive TUNEL labelling of photoreceptor nuclei peaked at 8-16 h and dropped at 24 h following light exposure. The distribution of TUNEL-positive nuclei was located predominantly at the upper temporal region of the retina, which was the most sensitive area to the damage caused by blue light. Furthermore, the multiples of internucleosomal cleavage of 180-200 base pairs were demonstrated at corresponding time points.

CONCLUSION

Photoreceptor cell apoptosis is seen early after the retina is damaged by blue light.

Dynamics of phosphorothioate oligonucleotides in normal and laser photocoagulated retina

AIMS

To investigate the distribution, persistence, and stability of fluorescently labelled phosphorothioate oligonucleotides (PS-ODNs) in normal and laser photocoagulated retina following intravitreal injection in the rat.

METHODS

Fluorescently labelled PS-ODNs were injected intravitreally into pigmented eyes at doses of 0.5-10.0 nmol in 2.0 microl solution. The dynamics of PS-ODNs was evaluated by fluorescent microscopy of cryosections and flat mounted retinal pigment epithelium (RPE)-choroid-sclera. Genescan analysis was used to assess the integrity of PS-ODNs in the retina after injection. The dynamics of PS-ODNs was also evaluated in the retina following krypton laser photocoagulation with a protocol producing choroidal neovascularisation (CNV).

RESULTS

Following intravitreal injection the PS-ODNs demonstrated dose and time dependent distribution and persistence in the retina, where they accessed all neural layers. However, they preferentially accumulated in the RPE layer, demonstrated as bright granules in the cytoplasm of the cells. Injections of 5.0 and 7.5 nmol of PS-ODNs exhibited strong fluorescence in the retina for 6 weeks after injection. Genescan analysis demonstrated that the PS-ODNs remained almost completely intact for at least 12 weeks. Following laser treatment, the PS-ODNs were concentrated in the regions of laser photocoagulation and retained high intensity for at least 8 weeks after injection, particularly localised to macrophages, RPE, and the local choroidal tissue.

CONCLUSIONS

These results indicate that PS-ODNs are stable and accessible to most neural layers of the retina, and they preferentially accumulate in the RPE layer following intravitreal injection. The successful delivery of PS-ODNs into normal and laser photocoagulated retina suggests that PS-ODNs may have potential in the development of therapy for attenuating retinal degenerations and CNV.

Color Doppler imaging discloses reduced ocular blood flow velocities in nonexudative age-related macular degeneration

PURPOSE

To study ocular perfusion defects in age-related macular degeneration.

METHODS

Twenty-five subjects with nonexudative age-related macular degeneration were compared with 25 age-matched control subjects in studies of flow velocities in several retrobulbar vessels. Color Doppler imaging, which was performed by an examiner who was masked to the subjects' assignment to the control or age-related macular degeneration group, measured peak systolic and end diastolic velocity in the ophthalmic, central retinal, and nasal and temporal posterior ciliary arteries of one eye. A resistive index was calculated from the peak systolic and end diastolic velocity.

RESULTS

Subjects with nonexudative age-related macular degeneration showed a consistent trend toward lower peak systolic and end-diastolic velocities in the posterior ciliary arteries. For example, in the nasal posterior ciliary artery, the mean end diastolic velocity measured 1.45 +/- 0.34 cm per sec in the age-related macular degeneration group compared with 1.96 +/- 0.66 cm per sec in the control group, yielding a 26% decrease in the age-related macular degeneration group, which represented the largest difference and was highly statistically significant (P = .0012). The resistive index was not significantly altered in the nasal or temporal posterior ciliary artery. Subjects with nonexudative age-related macular degeneration did not differ from control subjects in peak systolic velocity, end diastolic velocity, or resistive index in the ophthalmic artery. In the central retinal artery, the end diastolic velocity was lower (1.37 +/- 1.95 cm per sec vs 1.95 +/- 0.66 cm per sec), whereas the resistive index was higher (0.83 +/- 0.05 vs 0.76 +/- 0.06 cm per sec), in the age-related macular degeneration group; these results were highly statistically significant (P = .0007 and P < .0001, respectively).

CONCLUSIONS

Retrobulbar vascular changes in nonexudative age-related macular degeneration subjects include reduced flow velocities in the nasal and temporal posterior ciliary arteries. The reduced peak systolic velocity, combined with the reduced end diastolic velocity at a constant resistive index, seen in nonexudative age-related macular degeneration, is consistent with reduced bulk flow in these vessels, suggesting that choroidal perfusion is abnormal in this form of age-related macular degeneration. The changes in the central retinal artery suggest there may be a more generalized perfusion abnormality beyond the choroid in patients with age-related macular degeneration or that the central retinal artery exhibits a secondary autoregulatory response to a primary change elsewhere.

Do age-related macular degeneration and cardiovascular disease share common antecedents?

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss and blindness in elderly Americans. The etiology of this condition remains unknown and treatment options are limited. Some epidemiological findings point to a cardiovascular risk profile among persons with AMD. Documented risk factors for cardiovascular disease (such as age, smoking, hypertension, hypercholesterolemia, post-menopausal estrogen use, diabetes, and dietary intake of fats, alcohol and antioxidants) have also been associated with AMD in some studies. This raises the possibility that the causal pathways for cardiovascular disease and AMD may share similar risk factors. Future research on this hypothesis could lead to important insights into etiologic factors for AMD. Research could also identify modifiable risk factors and suggest new treatment options which could prevent AMD, slow its progression, or reduce visual loss. Susceptible individuals could then be targeted for improved health promotion and disease prevention measures for this disabling and highly prevalent disorder.

Radiotherapy for isolated occult subfoveal neovascularisation in age related macular degeneration: a pilot study

BACKGROUND/AIMS

Teletherapy has been proposed as a possible treatment for choroidal neovascular membranes (CNV), secondary to age related macular degeneration (AMD) not amenable to laser photocoagulation. The aim of this prospective study has been to investigate the effect of teletherapy on isolated occult choroidal neovascular membranes of subfoveal location.

METHODS

28 AMD patients presenting with retrofoveal isolated occult CNV demonstrated by fluorescein angiography were treated by external beam radiation. A complete ophthalmological examination, fluorescein angiography, and indocyanine green angiography (ICG) were performed within 15 days before treatment and repeated at follow up. A total dose of 16 Gy was applied in four sessions of 4 Gy using a 4 MeV photon beam. Follow up ranged from 6 to 9 months (mean follow up 6.4 months).

RESULTS

Visual acuity was found to be stable in 68% of the cases. The decrease in visual acuity was of 3-6 lines in 18% and of more than 6 lines in 10% of the eyes at last examination. On fluorescein angiography the size of the lesion area was found to be stable in 67%, decreased in 13%, and increased in 20% of the cases. On ICG angiography the size of the CNV was stable in 93% and increased in 7% of the cases. All the eyes experiencing a visual acuity decrease showed either no change or an increase in size of the membrane on fluorescein angiography and/or on ICG.

CONCLUSION

According to this study with strict inclusion criteria, external beam radiotherapy seems to have a beneficial effect on the evolution of isolated occult subfoveal CNV.

A new locus for autosomal dominant stargardt-like disease maps to chromosome 4

Stargardt disease (STGD) is the most common hereditary macular dystrophy and is characterized by decreased central vision, atrophy of the macula and underlying retinal-pigment epithelium, and frequent presence of prominent flecks in the posterior pole of the retina. STGD is most commonly inherited as an autosomal recessive trait, but many families have been described in which features of the disease are transmitted in an autosomal dominant manner. A recessive locus has been identified on chromosome 1p (STGD1), and dominant loci have been mapped to both chromosome 13q (STGD2) and chromosome 6q (STGD3). In this study, we describe a kindred with an autosomal dominant Stargardt-like phenotype. A genomewide search demonstrated linkage to a locus on chromosome 4p, with a maximum LOD score of 5.12 at a recombination fraction of.00, for marker D4S403. Analysis of extended haplotypes localized the disease gene to an approximately 12-cM interval between loci D4S1582 and D4S2397. Therefore, this kindred establishes a new dominant Stargardt-like locus, STGD4.

Serum vitamin E levels negatively correlate with severity of age-related macular degeneration

Age-related macular degeneration (AMD) pathogenesis has been related to UV radiation and other factors that may promote increased oxidative damage to the retina. Patients with different AMD grading (n = 25) were compared with an age-matched group of AMD-free subjects (n = 15), both groups older than 60 years. A modification of the AMD grading system is proposed that allows patient grading and not single eye grading. AMD patients showed statistically significant lower serum levels of vitamin E and Zn than AMD-free subjects. Moreover, a negative correlation (Spearman's correlation coefficient r = -0.815, P < 0.001) could be established between AMD grading of both the patients' eyes and serum vitamin E levels. Sun exposure index (SEI) was also compared and found to be significantly higher in the AMD group. The results presented establish the importance of antioxidants in AMD, and set the basis for further studies on adjuvant therapies with antioxidants for AMD. Finally, the results also confirm the pathogenic role of UV radiation in AMD.

Vitronectin is a constituent of ocular drusen and the vitronectin gene is expressed in human retinal pigmented epithelial cells

Age-related macular degeneration (AMD) leads to dysfunction and degeneration of retinal photoreceptor cells. This disease is characterized, in part, by the development of extracellular deposits called drusen. The presence of drusen is correlated with the development of AMD, although little is known about drusen composition or biogenesis. Drusen form within Bruch's membrane, a stratified extracellular matrix situated between the retinal pigmented epithelium and choriocapillaris. Because of this association, we sought to determine whether drusen contain known extracellular matrix constituents. Antibodies directed against a battery of extracellular matrix molecules were screened on drusen-containing sections from human donor eyes, including donors with clinically documented AMD. Antibodies directed against vitronectin, a plasma protein and extracellular matrix component, exhibit intense and consistent reactivity with drusen; antibodies to the conformationally distinct, heparin binding form of human vitronectin are similarly immunoreactive. No differences in vitronectin immunoreactivity between hard and soft drusen, or between macular and extramacular regions, have been observed. RT-PCR analyses revealed that vitronectin mRNA is expressed in the retinal pigmented epithelium (RPE)-choroidal complex and cultured RPE cells. These data document that vitronectin is a major constituent of human ocular drusen and that vitronectin mRNA is synthesized locally. Based on these data, we propose that vitronectin may participate in the pathogenesis of AMD.

Principles of treatment of choroidal neovascularization with photodynamic therapy in age-related macular degeneration

Age-related macular degeneration (AMD) is a common cause of legal blindness in the developed countries in people older than 50 years of age. AMD complicated by choroidal neovascular membranes (CNV) accounts for 12% of AMD, but for 88% of legal blindness cases. Because of the progressive aging of the population, it is expected that AMD will be one of the greater public health problems in ophthalmology in the first half of the next century. Laser photocoagulation remains the only proven treatment for CNV in AMD, but unfortunately, is applicable only to a minority of patients presenting with CNV in AMD. Photodynamic therapy (PDT) is a new experiment treatment for CNV that combines the application of low-intensity light with a photosensitizing agent in the presence of oxygen to produce tissue effects. It uses the noninvasive potential of the laser light to cause a nonthermal localized chemotoxic reaction and obtain highly selective occlusion of the neovascular channels, with sparing of the overlying photoreceptors. Animal studies showed that PDT accounts for the effective closure of experimentally induced CNV. Phase I-II clinical studies showed that PDT using BPD can safely stabilize leakage from CNV in a majority of patients for up to 3 months. Phase III clinical studies to assess the long term prognosis of PDT-treatment of CNV in AMD are ongoing.

Near ultraviolet radiation elicits visual evoked potentials in children

OBJECTIVE

Ultraviolet radiation can be transmitted through the ocular media, as well as stimulate the retina, in some invertebrate, vertebrate and mammalian species. This study sought to determine if near ultraviolet radiation (UV-A) can elicit visual evoked potentials (VEPs) in young humans.

METHODS

VEP responses to 10 nm half-peak bandwidths of 340, 360 and 500 nm stimuli were measured in 8 children aged 7-10 years. Each VEP was based on an averaged response to 200 flashes and was recorded using a sensitivity of 250 microV (full scale) with the International 10-20 electrode placements Fz, O1, Oz, O2, and A1. Peak latencies (ms) were measured for the second negative peak, N2, third positive peak, P3, and third negative peak, N3. The amplitude (microV) between N2 and P3 was also measured.

RESULTS

Each child demonstrated a VEP response to both visible and UV-A stimuli. Most VEP parameters relative to the 340 and 360 nm stimuli (P < 0.05 to P < 0.001) were significantly different from the VEP responses to the 500 nm stimulus.

CONCLUSION

The results indicate that the near ultraviolet stimuli were indeed visible to the young human eye.

Isolation and one-step preparation of A2E and iso-A2E, fluorophores from human retinal pigment epithelium

Age-related macular degeneration, a major cause of blindness for which no satisfactory treatments exist, leads to a gradual decrease in central high acuity vision. The accumulation of fluorescent materials, called lipofuscin, in retinal pigment epithelial cells of the aging retina is most pronounced in the macula. One of the fluorophores of retinal pigment epithelial lipofuscin has been characterized as A2E, a pyridinium bis-retinoid, which is derived from two molecules of vitamin A aldehyde and one molecule of ethanolamine. An investigation aimed at optimizing the in vitro synthesis of A2E has resulted in the one-step biomimetic preparation of this pigment in 49% yield, readily producing more than 50 mg in one step. These results have allowed for the optimization of HPLC conditions so that nanogram quantities of A2E can be detected from extracts of tissue samples. By using 5% of the extract from individual aged human eyes, this protocol has led to the quantification of A2E and the characterization of iso-A2E, a new A2E double bond isomer; all-trans-retinol and 13-cis-retinol also have been identified in these HPLC chromatograms. Exposure of either A2E or iso-A2E to light gives rise to 4:1 A2E:iso-A2E equilibrium mixtures, similar to the composition of these two pigments in eye extracts. A2E and iso-A2E may exhibit surfactant properties arising from their unique wedge-shaped structures.

Increase in interphotoreceptor matrix gelatinase A (MMP-2) associated with age-related macular degeneration

Matrix metalloproteinases have increasingly been shown to be associated with diseases involving neovascularization and/or abnormal cellular migration or proliferation. A number of diseases of this type affect the retina. In this study, the activity of gelatinase A (MMP-2), the most abundant matrix metalloproteinase in IPM (interphoto receptor matrix) and vitreous, was measured with respect to age in normal human donor eyes and compared to donors with age-related macular degeneration. IPM and vitreous were obtained from a total of 88 human donors. Samples for electrophoresis were normalized for protein content and subjected to quantitative gelatin zymography. The zymograms were scanned and then digitized and quantitated using the NIH 'Image' program. There was not a statistically significant change in the level of gelatinase A in IPM or vitreous as a function of age, although a slight downward trend was found in the total gelatinase A activity within the normal population. Likewise, when comparing normal and age-related macular degeneration donors, there was not a significant difference in the gelatinase A level in vitreous or in retina-associated IPM. However, the level of gelatinase A was nearly doubled specifically in retinal pigment epithelium-associated IPM from eyes with age-related macular degeneration [0.99 +/- 0.09 U mg-1 (56) vs 1.71 +/- 0.28 U mg-1 (14) (mean +/- S.E.M. (number), P < 0.0021; 1 unit = 1.0 ng gelatin cleaved h-1). Gelatinase A may be associated with the changes that occur in age-related macular degeneration, especially the neovascularization which accompanies the exudative ('wet') form of the disease.

Retinal degeneration and transplantation in the Royal College of Surgeons rat

The Royal College of Surgeons rat provides a valuable animal model for examining the ontogeny of inherited or acquired photoreceptor degeneration and for assessing various treatment paradigms. Here we describe a sequence of events in which photoreceptor loss induces secondary changes that ultimately result in a progressive loss of retinal ganglion cells. The functional consequences of photoreceptor loss are described and compared with those observed in dystrophic animals that received grafts of pigment epithelial cells at an early stage in the degenerative process. The results of this work suggest that transplantation might slow or halt the progress of photoreceptor loss in certain human retinal degenerative conditions, provided suitable safeguards have been put in place.

Influence of nicotine and cotinine on retinal phospholipase A2 and its significance to macular function

The macula is a constituent of the sensory retina that is necessary for sharp contrast and color vision. A significant relationship has been found between tobacco smoking and age-related macular degeneration. Opsin, rhodopsin and phospholipase A2 (PLA2) are located in excitable membranes of retina which are enriched with polyunsaturated fatty acids (PUFA). A question may arise as to whether nicotine and its major metabolite cotinine influence PLA2 so that arachidonic acid (AA) and proinflammatory prostaglandins (PG) are produced in the retina. Therefore, the effects of nicotine and cotinine on the retinal PLA2 were studied. PLA2 activity of rat retinal sonicates was assayed using 1-palmitoyl-2[1-14C]arachidonyl-Phosphatidylethanolamine (PE, 2.2 nmol) as a substrate in Tris buffer (10 mM, pH 7.4) at 37 degrees C with and without nicotine or cotinine in the assay medium. These studies gave the following results: (1) Rat retinal PLA2 activity was 4.2+/-0.8 pmol PE hydrolyzed/100 ng protein/hr. (2) Nicotine in low concentrations (1-150 nM) activated PLA2 (EC50 5 nM). (3) Cotinine also activated PLA2 (EC50 300 nM). (4) Only high concentrations of nicotine (> 1.0 microM) and cotinine (> 25 microM) exhibit inhibition of PLA2. (5) All three known PLA2 inhibitors, mepacrine, 4-bromophenacyl bromide and bromoacetylcholine bromide (IC50: 0.5mM, 88 microM, 30 mM, respectively) inhibited retinal PLA2 activity. These observations suggest that polyunsaturated fatty acids are cleaved, and arachidonic acid, the precursor for prostaglandins and related pro-inflammatory mediators, is liberated by nicotine and cotinine. Oxidative stress (reduced levels of antioxidants), vascular insufficiency, as well as activation of PLA2 by nicotine and cotinine may contribute for retinal degeneration in smokers during aging.

Case-control study of the risk factors for age related macular degeneration. France-DMLA Study Group

AIM

A case-control study was initiated to determine the risk factors for the development of age related macular degeneration (AMD).

METHODS

Study participants, who were all white, aged 50-85 years, and were recruited from private ophthalmology practices. Each practitioner enrolled patients with bilateral AMD, who were then matched with controls for sex and age. Environmental factors and systemic and ocular histories were screened. All patients had bilateral red-free fundus photographs and fluorescein angiography. Photographs were classified into pigment epithelium alterations, drusen, geographic atrophy, and exudative AMD. Statistical analysis included the identification of risk factors for AMD. A multivariate analysis was performed at the end of the study. Analysis included the entire study population and was carried out for each stage of AMD.

RESULTS

1844 controls were compared with 1844 patients with AMD. Mean age was 71 years for controls and 72 for cases. Logistic regression identified six major risk factors for AMD (whole population): arterial hypertension (odds ratio (OR) = 1.28), coronary disease (OR = 1.31), hyperopia (OR = 1.33), light coloured irises (OR = 1.22), and lens opacities or previous cataract surgery (OR = 1.55). The significance of vascular risk factors was increased for late stages of AMD, especially the atrophic forms (coronary disease, OR = 3.19).

CONCLUSIONS

This large case-control study confirms some of the risk factors previously identified and may contribute to the determination of methods for prevention of AMD.

Age-related macular degeneration: a review of experimental treatments

Age-related macular degeneration (AMD) is the leading cause of irreversible visual loss in the USA. Laser photocoagulation of choroidal neovascular membranes (CNVMs) in exudative AMD is currently the only well-studied and widely accepted treatment modality. It is beneficial for only a small minority of patients who show well-demarcated "classic" CNVMs, and it destroys normal retinal tissue, creates a scotoma, and is associated with an unacceptably high CNVM persistence and recurrence rate. Consequently, investigators have attempted to develop new modalities for treatment of CNVMs. These treatment modalities can be grouped into four major categories: photodynamic therapy; pharmacologic inhibition of CNVM formation with antiangiogenic agents; surgical intervention, including excision of subfoveal CNVMs; and radiation therapy. All of these experimental treatment modalities are directed toward destroyiing CNVMs, the end result of the exudative process, and all have limitations. The ideal treatment of the future must be based on the pathogenesis of the disease at a stage well before CNVMs develop. Investigations in nonexudative AMD are currently focusing on several major areas. Epidemiologic factors, such as genetics, sunlight, and nutrition, are being evaluated in several large studies, including the Age-Related Eye Disease Study, with the possibility of ultimately limiting the risk of AMD through behavior modification. Laser treatment of drusen is being evaluated as a means of limiting the risk of CNVM formation, although mixed results have been reported in the small number of studies to date. Choroidal perfusion abnormalities have been described in AMD, and some investigators postulate that altering blood flow may limit the risk of CNVM formation. No perfusion-treatment trials have been completed to date.

Visual field loss in RCS rats and the effect of RPE cell transplantation

The consequences of progressive retinal degeneration on central visual function were studied by recording single and multiunit receptive fields (RFs) across the surface of the superior colliculus (SC) of pigmented dystrophic RCS rats. Retinal morphology was used to provide a correlation between function and histological appearance. In addition, the potential protective effect of retinal pigment epithelium (RPE) transplantation was studied in a similar manner in dystrophic animals in which RPE cells were injected into the subretinal space, or the vitreous humor, at between 21 and 28 days of age. The visual responsiveness of SC units in dystrophic rats differed markedly from those in nondystrophics. Dystrophic rats developed a relative scotoma beginning in the central visual field by 42-45 days of age and expanding to include 50% of the visual field by 97-107 days. In contrast, following subretinal RPE transplantation, there was photoreceptor rescue correlated with a partial to complete preservation of RF representation when examined at 85 to 108 days of age. The majority of photoreceptor rescue occurred in the region of graft placement with possible low level rescue across the central retina. Dystrophic animals that had received intravitreal RPE transplants showed poor photoreceptor survival as well as minimal functional preservation. Our results indicate that there is a progressive central to peripheral loss of visual responsiveness in the SC of dystrophic RCS rats which can be limited by subretinal injections of healthy RPE cells.

Serum-free media for culturing and serial-passaging of adult human retinal pigment epithelium

The ability of a chemically-defined serum-free culture medium to support the attachment, growth and serial passaging of primary adult human retinal pigment epithelial (RPE) cells was studied. Primary cultures of adult human RPE were established in a chemically-defined serum-free culture medium on both bare or bovine corneal endothelial extracellular matrix-coated tissue-culture plastic. Confluent cells were serially passaged in chemically-defined serum-free culture medium three times by trypsinization, and trypsin activity was quenched with aprotinin. First passage RPE cells were plated onto tissue-culture plastic precoated with bovine corneal endothelial extracellular matrix or uncoated tissue-culture plastic in 24 well plates at a density of 50 viable cells mm-2. Cells were maintained either in chemically-defined serum-free culture medium, DMEM without serum, or DMEM with 15% fetal bovine serum. For each medium plating, efficiencies were determined 24 hours after plating, and growth rates were determined on the first, third and seventh days after plating. Morphometric image analysis was performed on cells cultured for up to 6 weeks and three serial passages. Seeding efficiency on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and treated tissue-culture plastic were higher for chemically-defined serum-free culture medium (88.9+/-2.7% and 47.1+/-4.1%, respectively) and DMEM with serum (87.2+/-5.6% and 52.9+/-10.5%, respectively) than DMEM without serum (59.2+/-5.6% and 33.1+/-6.9%, respectively; P<0.01). The RPE proliferation rate in chemically-defined serum-free culture medium was comparable to DMEM with serum on both substrates within the first 3 days, although cells in DMEM with serum had a higher proliferation rate on day 7. Cells cultured in DMEM without serum, eventually decreased in number. RPE maintained in chemically-defined serum-free culture medium maintained a consistent proliferation rate, reached confluence, and retained an epitheloid morphology on either extracellular matrix or tissue-culture plastic for up to 6 weeks and three serial passages. Primary RPE reached confluence at 12+/-3 days on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and 21+/-5 days on treated tissue-culture plastic. Confluent cultures were composed of small hexagonal cells with epitheloid morphology on both substrates. We concluded that primary adult human RPE can be cultured in this chemically-defined serum-free culture medium. RPE will proliferate, reach confluence, retain their epitheloid morphology and can be serially passaged in the absence of serum.

Glutathione in human plasma: decline in association with aging, age-related macular degeneration, and diabetes

Blood samples were analyzed for GSH and GSH redox state in 40 age-related macular degeneration (ARMD) patients (> 60 y), 33 non-ARMD diabetic patients (> 60 years), 27 similarly aged non-ARMD and nondiabetic individuals (> 60 years), and 19 younger individuals (< 60 years) without ARMD or diabetes. Results showed a significantly lower plasma GSH in older individuals (ARMD, diabetes, and controls) than in younger individuals (p < .01). Total GSH (GSHt) obtained following treatment with dithiothreitol was significantly lower only in diabetic cases (p < .05) but also approached significance for ARMD cases (p = .089). Estimation of redox potential indicated that the plasma GSH pool is considerably more oxidized in all of the older groups. Analyses of whole blood GSH showed that GSH was significantly lower in diabetic cases compared to the other groups, but did not reveal any difference associated with age or ARMD. In contrast, GSSG in whole blood was significantly higher in the older groups compared to the younger controls. The results suggest that in studies of age-related pathologies, oxidation of GSH may be a more important parameter than a decline in pool size, while in specific pathologies such as diabetes, both oxidation and a decline in pool size may be important.

Development of exudative age-related macular degeneration after cataract surgery

The macular status of patients with findings consistent with early dry age-related macular degeneration (AMD) who underwent an extracapsular cataract extraction with intraocular lens implantation was evaluated by fundoscopy and fluorescein angiography pre-operatively and during the first post-operative year. Five patients who developed the exudative form of AMD, and who represent the problems arising when treating patients with AMD and cataract, are described. Patients who received laser photocoagulation responded with recurrent choroidal neovascularisation. We suggest that patients with signs of age-related changes scheduled for cataract surgery should undergo a thorough pre- and post-operative assessment of their retinal status.

Presumed macular choroidal watershed vascular filling, choroidal neovascularization, and systemic vascular disease in patients with age-related macular degeneration

PURPOSE

To investigate the possible association of presumed macular choroidal watershed vascular filling (PMWF), choroidal neovascularization, and systemic vascular disease in patients with age-related macular degeneration.

METHODS

In a retrospective study, we evaluated 74 randomly selected indocyanine green videoangiograms of 74 patients with age-related macular degeneration. We also reviewed the charts of 20 randomly selected, age-matched control patients without age-related macular degeneration, initially referred for uniocular conditions, and subsequently performed indocyanine green videoangiography on their normal fellow eyes. We evaluated these videoangiograms for the presence of PMWF, manifesting as characteristic early choroidal hypofluorescence and its relation to choroidal neovascularization when present. Additionally, the incidence of hypertension, coronary artery disease, peripheral vascular disease, and diabetes mellitus was determined.

RESULTS

Forty-one (55.4%) of 74 patients with age-related macular degeneration vs three (15.0%) of 20 normal control patients exhibited PMWF on indocyanine green videoangiography (P = .0014). Of the 61 patients with age-related macular degeneration and choroidal neovascularization, 36 (59.0%) exhibited PMWF on videoangiography. Associated choroidal neovascularization arose from the PMWF zone in 33 (91.7%) of these cases. Hypertension was observed in 24 (58.5%) of 41 patients with age-related macular degeneration and PMWF vs nine (27.3%) of 33 patients with age-related macular degeneration who did not exhibit PMWF (P = .007).

CONCLUSIONS

An increased incidence of PMWF occurs in patients with age-related macular degeneration with a possible predisposition for the development of associated choroidal neovascularization. Additionally, PMWF may be accentuated by associated hypertensive choroidal microvascular insult.

Radiation therapy for macular degeneration: technical considerations and preliminary results

PURPOSE

This study was undertaken to assess the toxicity and possible benefits from the administration of low-dose external-beam irradiation for Age-Related Macular Degeneration (ARMD). The premise of the treatment is that radiation induces regression and/or promotes inactivation of the subretinal neo-vasculature, resulting in reabsorption of fluid and blood thus reducing the risk for further leakage or bleeding, as well as subretinal fibrosis. Clinically, the beneficial effect could be translated into stabilization of visual acuity and prevention of progression of the wet type of ARMD with the possibility for some visual improvement.

METHODS AND MATERIALS

Allegheny University Hospitals, Hahnemann, Department of Radiation Oncology, treated 278 patients prospectively beginning in January 1995 with low-dose irradiation for wet-type macular degeneration. Two hundred forty-nine patients were treated with a total dose of 14.40 Gy in eight fractions of 1.80 Gy over 10-13 elapsed days, and 27 patients with 20 Gy at 2 Gy per fraction over 12-15 days. The first two patients were treated to a total dose of 10.00 Gy in five fractions of 2.00 Gy. Patients were evaluated at 2-3 weeks and 2-3 months. A percentage (36.7%) of the patients had previously received laser treatments in the study eye, 21.9% once, 5% twice, 9.7% three or more. Subjective visual acuity and toxicity data was collected on all patients.

RESULTS

At 2-3 weeks after treatment 195 patients (70%) retained their visual acuity without change, 68 patients (24.5%) stated they had improved vision, and 15 patients (4.8%) stated their vision continued to decrease. Two to 3 months after treatment, 183 patients (65.8%) had no change in their vision, 75 patients (27%) had an improvement in their vision, and 20 patients (7.2%) had a decrease in visual acuity. Transient acute reactions occurred in 14 of the 278 patients treated.

CONCLUSION

Our observations in this group of 278 patients support the conclusion that many patients will have improved or stable vision after treatment with low-dose irradiation for age related wet type macular degeneration.

Pathophysiology and management of subretinal hemorrhage

Subretinal hemorrhage can arise from the retinal and/or choroidal circulation. Significant subretinal hemorrhage occurs in several conditions, but most commonly is associated with age-related macular degeneration, presumed ocular histoplasmosis, high myopia, retinal arterial macroaneurysm, and trauma. Released toxins, outer retinal shear forces, and a diffusion barrier created by subretinal hemorrhage all contribute to photoreceptor damage and visual loss. The use of tissue plasminogen activator and improvements in surgical instrumentation have facilitated surgical drainage and have made it a useful option in the management of selected cases. Mechanisms of subretinal hemorrhage formation, underlying etiologies, diagnostic evaluation, and the histopathology of damage are summarized. Published surgical series are reviewed and surgical advances are summarized. The value of surgically removing subretinal hemorrhages to improve visual outcome remains unestablished, because definitive studies have not been performed. Guidelines for selecting candidates for surgical intervention are proposed.

A hemodynamic model of the pathogenesis of age-related macular degeneration

The clinical message of this editorial is that age-related macular degeneration may be a vascular disorder. It may be a manifestation of the hemodynamic consequence of the process of lipoid infiltration that, when it involves other organs such as those of the cardiovascular or cerebrovascular systems, is called atherosclerosis. The hemodynamic model presented here postulates that in age-related macular degeneration, the increase in resistance to the flow of blood in the choroid is caused by an age-related and diet-related decrease in the compliance of the sclera. It proposes that the form of age-related macular degeneration produced may depend on the relative resistances of the ophthalmic and cerebral circulations. A decrease in perfusion, leading to the atrophic form of age-related macular degeneration, is the outcome if the resistance of the cerebral circulation is relatively lower than that of choroid. Conversely, a relatively greater increase in the increase in the hydrostatic pressure in the choroidal vessels, leading to the exudative form of the disorder.

Harvest and storage of adult human retinal pigment epithelial sheets

PURPOSE

To describe a method for the harvesting and storing of intact viable sheets of adult human retinal pigment epithelial (RPE) cells.

METHODS

Adult human RPE cells were harvested as intact sheets from 21 cadaver eyes, using the enzyme Dispase. The sheets were embedded in 50% gelatin containing 300 mM sucrose and stored at 4 degrees C. The viability of the cells, as well as their ability to proliferate in vitro, was studied for 96 hours after harvesting. Light microscopy (LM), transmission (TEM) and scanning electron microscopy (SEM) were performed to determine the integrity and ultrastructural features of the cells. Microbiologic culture of the harvested sheets was performed to exclude contamination.

RESULTS

LM, TEM and SEM showed intact RPE cells with well-developed microvilli, basal infoldings and intercellular connections. The initial viability of intact RPE sheets was 86%, with a progressive decline in viability with increased storage time. Cells harvested within 24 hours after death maintained greater viability than those harvested after 24 hours (p < 0.05). Harvested RPE cells were free of microbial contamination and rapidly proliferated when cultured in vitro.

CONCLUSION

Intact sheets of adult human RPE can be isolated using the enzyme Dispase. The cells appeared suitable for retinal transplantation if harvested within 24 hours of death and maintained 82% viability for as long as 48 hours if stored at 4 degrees C.

Extracellular matrix of retinal pigment epithelium regulates choriocapillaris endothelial survival in vitro

The role of extracellular matrix of retinal pigment epithelial cells (RPE-ECM) in the regulation of the survival of choriocapillaris endothelial cells (CCE) was investigated in vitro. The CCE survival was evaluated by trypan blue staining, neutral red uptake, and the counting of viable cells. Results showed that CCE cells survived on RPE-ECM. Pre-treatment of RPE-ECM individually with neutralizing antibodies to acidic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, or transforming growth factor beta(pan specific to TGFbeta1, TGFbeta1.2, TGFbeta2 and TGFbeta5), did not alter the survival rate of CCE cells on RPE-ECM, as compared to that of the control (CCE survival rates on RPE-ECM pretreated with normal rabbit IgG). However, the treatment of RPE-ECM with neutralizing antibody to basic fibroblast growth factor (bFGF) caused CCE death by 77.1+/-15.7%. The CCE death was defined as apoptosis based on the morphological markers (shrinkage in cell size with blebbing of plasma membranes, condensation and fragmentation of nuclei, and DNA fragmentation in multiples of approximately 200 bp). The addition of phorbol 12-myristate 13-acetate (PMA) (2 nM) to the culture medium was effective for complete prevention of CCE apoptosis; the protecting effect of PMA on CCE apoptosis can be abolished by H7 (25 microM), but not HA1004 (50 microM), suggesting the involvement of PKC in protecting CCE from apoptosis. The inhibition of protein synthesis of CCE cells by cycloheximide (0.1 microM) did not affect the apoptotic process of the cells. In a separate experiment, when CCE cells were cultured in a medium saturated with bFGF (5 ng ml-1) without RPE-ECM, the cells also died by apoptosis. However, this apoptotic process was not affected by PMA. Cycloheximide also failed to affect the apoptotic process. These results suggest that both RPE-ECM insoluble molecules and RPE-ECM-bound bFGF modulate choriocapillaris survival by suppressing CCE apoptosis.

Matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-1 in the retinal pigment epithelium and interphotoreceptor matrix: vectorial secretion and regulation

Matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) play an essential role in both normal and pathological extracellular matrix degradation, and a TIMP has been associated with at least one type of retinal degeneration. We have studied expression of MMP-2 and TIMP-1 by zymography, immunocytochemistry, and immunoblotting in the retinal pigment epithelium (RPE) from normal, aged and diseased retinas. MMPs and TIMPs were found in the rat RPE, interphotoreceptor matrix (IPM), and in media conditioned by human and rat RPE in culture. In other polarized cells. MMPs and TIMP-2 are secreted vectorially towards the basal lamina. In the RPE, however, MMP-2 and TIMP-1 were secreted preferentially from the apical surface, the surface bordering the IPM. These findings provide new evidence that MMPs and TIMPs could play a role in the turnover of IPM components. Cell homogenates and conditioned media from RPE isolated from mutant Royal College of Surgeons (RCS) rats with inherited retinal dystrophy had similar amounts of MMP-2 and TIMP-1 as those from congenic control rats. The secretion of MMP-2 and TIMP-1 from RPE cell cultures isolated from young and aged human donors varied widely. However, with increasing cell passage number, secretion of MMPs and TIMPs from human RPE increased dramatically. Also, growing human RPE on bovine corneal endothelial cell-generated extracellular matrix instead of plastic reduced the secretion of both MMPs and TIMPs. These data suggest that the integrity of Bruch's membrane may serve to regulate RPE functions in MMP and TIMP secretion and that extracellular matrices contain signals that regulate MMP and TIMP synthesis and/or secretion by the RPE.

Transplantation of RPE in age-related macular degeneration: observations in disciform lesions and dry RPE atrophy

A study was carried out to investigate whether human RPE allografts are tolerated or rejected in the subretinal space and to determine the feasibility of RPE transplantation in subjects with age-related macular degeneration (AMD).

METHODS

Patches of human fetal RPE (13-20 weeks of gestational age) were transplanted into the subretinal space of five patients after surgical removal of subfoveal fibrovascular membranes, and to four subjects with dry geographic atrophy. Suspensions of RPE cells were transplanted to four other patients with nonexudative AMD. Results were evaluated with clinical ophthalmological examination, SLO microperimetry and fluorescein angiography over 8-20 months.

RESULTS

In disciform lesions, RPE transplants developed macular edema and fluorescein leakage concomitant with gradual reduction of visual acuity, implying host-graft rejection, over 1-6 months. In geographic atrophy, three of four transplants showed little change in shape and size after 12 months (one transplant was slowly rejected). In non-exudative AMD, RPE suspension transplants showed no evidence of rejection and were associated with the disappearance of drusen; visual acuity remained stable and SLO microperimetry confirmed retinal function over the transplanted area.

CONCLUSION

Human RPE allografts are not invariably rejected in the subretinal space without immunosuppression. The rejection rate is lower in nonexudative than in neovascular AMD. An intact blood-retinal barrier is likely to protect against rejection. It is technically feasible to transplant human RPE into the submacular space without adversely affecting visual function in nonexudative AMD over relatively long periods of time.

Monocular optokinetic nystagmus in humans with age-related maculopathy

AIM

To investigate full field monocular optokinetic nystagmus (OKN) in patients with age-related maculopathy (ARM) and relative central scotoma.

METHODS

Six patients aged 59-88 years with bilateral ARM and an aged-matched control group of six patients aged 54-83 years were examined. Visual fields were assessed with a Humphrey field analyser using the threshold 30-1 routine. Monocular full field horizontal optokinetic stimuli were presented on a hemicylindrical screen subtending 172 degrees horizontally and 50 degrees vertically. The stimulus was a projected random dot pattern and three stimulus velocities were used, 30, 50, and 70 degrees/s in both nasalward and temporalward directions. Each trial lasted between 30 and 40 seconds and eye movements were monitored using infrared oculography.

RESULTS

The ARM patients had relative central scotomas with an average depth of 10 dB. Neither the ARM nor the age-matched groups displayed any directional preponderance or a buildup of the slow phase eye velocity with time. No statistically significant difference in the gain was found between the two groups (p > 0.05).

CONCLUSIONS

Marked central field loss in ARM does not significantly impair OKN gain. This supports the view that complete central retinal integrity is by no means essential and that the peripheral retina provides an important input to the generation of OKN.

Full characterization of the maculopathy associated with an Arg-172-Trp mutation in the RDS/peripherin gene

The objective of this study was to fully characterize the macular dystrophy phenotype and genotype in a large family of the Zermatt area of Switzerland. Clinical and molecular studies of the family included a comprehensive eye examination and a mutational analysis of the RDS, rhodopsin, and TIMP-3 genes. In selected cases, fluorescein angiography, perimetry, and electroretinography were performed. Forty-two family members at risk of expressing the maculopathy were studied. Of these, 24 were found to be clinically affected. The severity of macular disease in these patients was clearly age-related and different stages of progression were identified. Central pigmentary alterations were seen in adolescent patients, while patients in their late teens and twenties exhibited drusen-like deposits. Later, these defects formed focal areas of atrophy which eventually led to central geographic atrophy with severe visual loss by the fifth decade and cone-rod dysfunction. The transmission of this condition is autosomal dominant with complete penetrance. The underlying genetic defect is a mutation in codon 172 of the RDS/peripherin gene, a gene expressed in both rods and cones, which results in the substitution of tryptophan for an arginine residue at that position. 'Zermatt macular dystrophy' is a dominant, age-related, progressive macular dystrophy which in later stages resembles atrophic age-related macular degeneration. The size of the family studied allowed definition of the clinical spectrum of this condition and identification of the related genetic defect which allows more precise diagnosis and counseling.