Generation of transgenic mice with mild and severe retinal neovascularisation

AIM

To generate a mouse model for slow progressive retinal neovascularisation through vascular endothelial growth factor (VEGF) upregulation.

METHODS

Transgenic mice were generated via microinjection of a DNA construct containing the human VEGF165 (hVEGF) gene driven by a truncated mouse rhodopsin promoter. Mouse eyes were characterised clinically and histologically and ocular hVEGF levels assayed by ELISA.

RESULTS

One transgenic line expressing low hVEGF levels showed mild clinical changes such as focal fluorescein leakage, microaneurysms, venous tortuosity, capillary non-perfusion and minor neovascularisation, which remained stable up to 3 months postnatal. Histologically, there were some disturbance and thinning of inner and outer nuclear layers, with occasional focal areas of neovascularisation. By contrast, three other lines expressing high hVEGF levels presented with concomitantly severe phenotypes. In addition to the above, clinical features included extensive neovascularisation, haemorrhage, and retinal detachment; histologically, focal to extensive areas of neovascularisation associated with retinal folds, cell loss in the inner and outer nuclear layers, and partial retinal detachment were common.

CONCLUSIONS

The authors generated four hVEGF overexpressing transgenic mouse lines with phenotypes ranging from mild to severe neovascularisation. These models are a valuable research tool to study excess VEGF related molecular and cellular changes and provide additional opportunities to test anti-angiogenic therapies.

Emergency eye care in rural Australia: role of internet

PURPOSE

Significant differences exist in the utilization of emergency eye care services in rural and urban Australia. Meanwhile, influence of internet-based technology in emergency eye care service utilization has not been established. This study aims to demonstrate, from a health provider perspective, an internet-based service's impact on emergency eye care in rural Australia.

METHODS

The teleophthalmology service was initiated in the Carnarvon Regional Hospital (CRH) of the Gascoyne region in Western Australia. A digital, slit lamp and fundus camera were used for the service. Economic data was gathered from the Department of Health of Western Australia (DOHWA), the CRH and the Lions Eye Institute.

RESULTS

During the study period (January-December, 2003) 118 persons took part in teleophthalmology consultations. Emergency cases constituted 3% of these consultations. Previous year, there were seven eye-related emergency evacuations (inter-hospital air transfers) from the Gascoyne region to City of Perth.

CONCLUSIONS

Analysis demonstrates implementation of internet-based health services has a marked impact on rural emergency eye care delivery. Internet is well suited to ophthalmology for the diagnosis and management of acute conditions in remote areas. Integration of such services to mainstream health care is recommended.

Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications

PURPOSE

Clinical assessment of outcome of corneal replacement with a synthetic cornea, AlphaCor, in patients considered at too high risk for conventional penetrating keratoplasty with donor tissue to be successful, but excluding indications such as end-stage dry eye that might be suited to traditional prosthokeratoplasty.

METHODS

All patients in the multicentre clinical trial were managed according to an approved protocol, with Ethics Committee approval in each centre. Preoperative visual acuity ranged from perception of light (PL) to 6/60 (20/200). Implantation was by means of an intralamellar technique, with a conjunctival flap in most cases. Tissues anterior to the optic were removed as a secondary procedure.

RESULTS

Up to 30 November 2001, 40 AlphaCor devices had been implanted in 38 patients, of mean age 60 years. Follow-up ranged from 0.5 months to 3 years. There had been one extrusion (2.5%) and four cases (10%) where a device had been removed due to melt-related complications. All five of these cases received a donor corneal graft after the device was removed, with these grafts remaining anatomically satisfactory and epithelialised to date. Corneal melts in AlphaCor recipients were found to be strongly associated with a history of ocular herpes simplex infection. Two further devices (5%) were removed owing to reduced optic clarity after presumed drug-related deposition, and have been successfully replaced with second devices. Mean preoperative best-corrected visual acuity was hand movements. Visual acuities after surgery ranged from PL to 6/6(-2) (20/20(-2)).

CONCLUSIONS

Early results suggest that the AlphaCor, previously known as the Chirila keratoprosthesis (Chirila KPro), has a low incidence of the complications traditionally associated with keratoprostheses and can be effective in restoring vision in patients considered untreatable by conventional corneal transplantation. Importantly, the device can be replaced with a donor graft in the event of development of a significant complication. A history of ocular herpes simplex is a contraindication to AlphaCor implantation. Ongoing monitoring of clinical outcomes in all patients will allow the indications for AlphaCor, as opposed to donor grafts, to be determined.

Potential long-term inhibition of ocular neovascularisation by recombinant adeno-associated virus-mediated secretion gene therapy

Neovascularisation (NV) within the eye often results in visual loss. Vascular endothelial growth factor (VEGF) has been implicated in the development of ocular NV. Previous studies have shown that VEGF antagonists successfully suppressed retinal and choroidal NV in animal models. However, the systemic approach and transient nature of the delivery systems used in these studies hinder therapeutic application. To achieve stable and localised ocular anti-angiogenic therapy, we explored the use of recombinant adeno-associated virus (rAAV)-mediated secretion gene therapy (SGT). In this study, we generated a rAAV vector encoding soluble VEGF receptor 1, sFlt-1 (AAV-CMV.sflt) and determined its ability to inhibit cautery-induced corneal NV and laser-induced choroidal NV. Delivery of AAV-CMV.sflt into the anterior chamber resulted in transgene expression in the iris pigment epithelium and corneal endothelium, which reduced the development of corneal NV in the stroma of cauterised rats by 36% compared with cauterised control groups (P = 0.009). Subretinal delivery of AAV-CMV.sflt near the equator of the eye also suppressed choroidal NV at the laser lesions around the optic nerve by 19% (P = 0.002), indicating that there was diffusion of the secreted anti-angiogenic protein across the retina. Both results suggest that the long-term suppression of ocular NV is possible through the use of stable rAAV-mediated SGT.

Online eye care in prisons in Western Australia

In prisons, prison medical officers provide general medical care. However, if specialist care is needed then the prisoner is transported to a specialist medical centre. This is a costly procedure and prison escapes occur during transportation. We have tested our Internet-based eye care system in prisons in Western Australia. Medical and ophthalmic history, visual acuity and intraocular pressure were stored in a browser-based multimedia database. Digital images of the retina and the external eye were recorded and transmitted to a central server. Based on the medical data and the digital images, the specialist ophthalmologist could provide a diagnosis within 24 h. Eleven patients (mean age 48, range 30-82 years) were reviewed during two separate visits to a maximum-security prison in Western Australia. Our main aim was to train prison medical officers and nurses to operate the portable ophthalmic imaging instruments and to use the Internet-based eye care system. The outcome of the pilot study indicated that considerable savings could be made in transport costs and the security risk could be reduced. The Ministry of Justice in Western Australia has decided to implement telemedicine services to provide regular ophthalmic consultation to its prisons.

Working toward a portable tele-ophthalmic system for use in maximum-security prisons: a pilot study

The medical care of prisoners is a difficult and often costly process. Basic medical needs are serviced by prison medical officers. However, specialized care often means transport to specialist centers with the attendant cost and safety. We examined portable ophthalmic equipment in a prison environment to screen 11 prisoners who were scheduled for specialist ophthalmic assessment. Medical and ophthalmic histories were documented, visual acuity was tested, digital images were taken of the external eye and retina, and intraocular pressures taken. The data were sent via modem to a specialist ophthalmologist, and the reports were dictated via e-mail at the end of each session. Of the 11 patients who were scheduled to travel for ophthalmic assessment, only 2 were still required to travel to a specialist ophthalmic center. This pilot study showed that there were considerable cost savings to be made by this screening process with the attendant increase in community safety. The prototype equipment requires refinement by further experimentation, but showed the potential as an adjunct to current examination and assessment techniques when applied to a prison population.

Inhibition of angiogenesis by adenovirus-mediated sFlt-1 expression in a rat model of corneal neovascularization

Pathological angiogenesis, or the production of new capillary vessels from preexisting vasculature, within the eye is a serious event that often leads to blindness. Upregulation of vascular endothelial growth factor (VEGF) has been linked to neovascularization in the eye, suggesting that it could be a suitable target to inhibit angiogenic changes. This work investigated whether the presence of a proven antiangiogenic factor, the soluble variant of the VEGF receptor, sFlt-1, in the anterior chamber is sufficient to inhibit new vessel formation in the cornea in an animal model of corneal neovascularization. A recombinant adenovirus vector that can mediate efficient in vivo gene transfer and expression in ocular cells was selected as a delivery agent. We have shown that after the injection of Ad.betagal into the anterior chamber of normal and cauterized rat eyes, corneal endothelial cells and cells of the trabecular meshwork were efficiently transduced and that beta-galactosidase (beta-Gal) expression was maintained up to 10 days postinjection. Cauterization significantly increased the amount of immunoreactive VEGF in vehicle- or Ad.null-injected animals (t test, p < 0.001 and p < 0.001, respectively). However, when cauterization was combined with Ad.sflt injection there was no statistically significant increase in the amount of immunoreactive VEGF (p = 0.12). The injection of Ad.sflt into the anterior chamber slowed or inhibited VEGF-induced angiogenic changes. After cauterization, 100% of uninjected and vehicle-injected and 82% of Ad.null-injected animals developed moderate to severe corneal angiogenesis in contrast to 18% of Ad.sflt-injected animals. These in vivo results suggest that the transient presence of antiangiogenic agents in the anterior chamber can be successfully used to inhibit the development of corneal angiogenesis.

Combined effect of cyclosporine and sirolimus on improving the longevity of recombinant adenovirus-mediated transgene expression in the retina

OBJECTIVES

To reevaluate the longevity and intraocular safety of recombinant adenovirus (rAd)-mediated gene delivery after subretinal injection, and to prolong transgene expression through the combination of 2 synergistic immunosuppressants.

METHODS

An rAd vector carrying green fluorescent protein (GFP) gene was delivered subretinally in the rat eye. The GFP expression was monitored in real time by fundus fluorescent photography. Intraocular safety was examined by observation of changes of retinal pigmentation, cell infiltration in virus-contacted area, immunophenotyping for CD4(+) and CD8(+) cytotoxic T lymphocytes, and CD68(+) macrophages, histologic findings, and dark-adapted electroretinography. Two synergistic immunosuppressants, cyclosporine and sirolimus, were used alone or in combination to prolong transgene expression by temporary immunosuppression.

RESULTS

The GFP expression peaked on day 4, dramatically decreased on day 10, and was not detectable on day 14. The decreased GFP expression was coincident with cell infiltration in virus-contacted area. Immunostaining showed that the infiltrating cells were CD4(+) and CD8(+) cytotoxic T lymphocytes and CD68(+) macrophages. Clumped retinal pigmentation and decreased b wave of dark-adapted electroretinogram were observed at 3 to 4 weeks after injection. Histologic examination confirmed rAd-induced retinal degeneration. Transient immunosuppression by cyclosporine and sirolimus, either alone or in combination, improved transgene expression, with the combination being the most efficient. The combined immunosuppression attenuated but did not retard the rAd-induced retinal damage.

CONCLUSIONS

Transgene expression mediated by rAd after subretinal delivery is short-term and toxic to the retina. Combination of cyclosporine and sirolimus may act as an immunosuppressive adjunct to prolong rAd-mediated gene transfer.

CLINICAL RELEVANCE

The intraocular safety of rAd should be carefully considered before clinical trials are performed.

Calcification of poly(2-hydroxyethyl methacrylate) hydrogel sponges implanted in the rabbit cornea: a 3-month study

Poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels have been used in the past as ocular implants. In a recent development, PHEMA sponges have shown suitable properties as materials for the peripheral component of an artificial cornea (keratoprosthesis). However, the propensity of PHEMA to calcify could threaten the long-term stability of the implanted devices. In an attempt to improve the understanding of the calcification mechanism, the dynamics, extent, and nature of calcified deposits within PHEMA sponges implanted in the cornea were investigated in this study, and the possible correlation between necrosis of cells and calcification was critically examined. Samples of a PHEMA sponge were implanted in rabbit corneas and explanted at predetermined time points (2, 4, and 12 weeks). The samples were examined by microscopy (light, transmission, scanning) and energy dispersive analysis of X-rays. Histological assessment and semiquantitative analysis of the amount of calcium deposited was performed using image analysis. An in vitro experiment was also performed by incubating sponge samples for 2 weeks in a solution of calcium and phosphate ions at a ratio similar to that in hydroxyapatite, in the absence of cells. Calcification was not seen in the 2- and 4-week explants, however, small deposits were detected in two of the 12-week explants, both within and on the sponge's constituent polymer particles. The deposit volumes represented 0.094% and 0.21%, respectively, of the total sponge volumes. Calcium deposits were present in large amounts both within the constituent polymer particles and on the surface of the sponges incubated in the abiotic calcifying solution. Cooperative mechanisms are suggested for the calcification of PHEMA sponges in vivo. The initial event may occur at a molecular level, when plasma proteins are adsorbed onto the polymer surface and bound through chelation to the calcium ions present in the medium. After their natural degradation, these structures may act as nucleation sites for calcium phosphate crystallization. Concurrently, the calcium ions can diffuse into the hydrogel particles and then the spontaneous precipitation of calcium phosphate may be caused by supersaturation due to the lower content of water in polymer, an effect which is likely predominant in vitro. The second event is the recruitment of phagocytic cells to clear calcium debris. Degeneration of these cells may then form nucleation sites for secondary calcification.

Controlled production of active cathepsin D in retinal pigment epithelial cells following adenovirus-mediated gene delivery

The transduction of a low cathepsin D-producing retinal pigment epithelial cell line with a recombinant adenovirus, Ad.proCatD, carrying a viral promoter and the precursor form of the lysosomal enzyme cathepsin D, procathepsin D, led to the upregulation of proCatD expression. However, the resultant aspartic protease activity did not exceed that observed in normal primary human retinal pigment epithelial cells. Following the injection of Ad. proCatD into rat eyes, immunohistochemistry and Western blot analysis localized the expression of procathepsin D to the retinal pigment epithelial cell layer and to the sclera/choroid/retinal epithelial cell layers, respectively. This upregulation of procathepsin D expression was accompanied by a limited increase in aspartic protease activity. The injected eyes did not demonstrate any of the retinal changes that have been associated with the overproduction and secretion of active cathepsin D. Immunoelectronmicroscopy of Ad.proCatD-transduced retinal pigment epithelial cells demonstrated the presence of cathepsin D not only in cytoplasmic vesicles and lysosomes but also in the nucleoli and, less strongly, elsewhere in euchromatic regions of some 10% of cells. In spite of the upregulated expression of procathepsin D, the production of active cathepsin D in Ad.proCatD-transduced retinal pigment epithelial cells was strictly controlled. It is proposed that active cathepsin D production is controlled at the point of posttranslational modification by an intranuclear feedback mechanism initiated by the relative excess of procathepsin D in Ad. proCatD-transduced retinal pigment epithelial cells.

Telemedicine screening of diabetic retinopathy using a hand-held fundus camera

The objective was to evaluate digital images of the retina from a handheld fundus camera (Nidek NM-100) for suitability in telemedicine screening of diabetic retinopathy. A handheld fundus camera (Nidek) and a standard fundus camera (Zeiss) were used to photograph 49 eyes from 25 consecutive patients attending our diabetic clinic. One patient had cataracts, making it impossible to get a quality image of one of the eyes (retina). The Nidek images were digitized, compressed, and stored in a Fujix DF-10M digitizer supplied with the camera. The digital images and the photographs were presented separately in a random order to three ophthalmologists. The quality of the images was ranked as good, acceptable or unacceptable for diabetic retinopathy diagnosis. The images were also evaluated for the presence of microaneurysms, blot hemorrhages, exudates, fibrous tissue, previous photocoagulation, and new vessel formation. kappa Values were computed for agreement between the photographs and digital images. Overall agreement between the photographs and digital images was poor (kappa < 0.30). On average, only 24% of the digital images were graded as being good quality and 56% as having an acceptable quality. However, 93% of the photographs were graded as good-quality images for diagnosis. The results indicate that the digital images from the handheld fundus camera may not be suitable for diagnosis of diabetic retinopathy. The images shown on the liquid crystal display (LCD) screen of the camera were of good quality. However, the images produced by the digitizer (Fujix DF-10M) attached to the camera were not as good as the images shown on the LCD screen. A better digitizing system may produce better quality images from the Nidek camera.

The effects of induced acute hyperglycemia in the cat on the retinal capillary blood flow

PURPOSE

To study the effect of acute hyperglycemia on the erythrocyte flow in specific retinal capillary paths.

METHODS

A technique for fluorescent labeling of a known fraction of the erythrocyte moiety of systemic blood was combined with fluorescence viewing of the retinal capillary network in live cats. This technique was developed to enable visualization of the erythrocyte flow in the retinal capillary network and used to acquire video recording of the retinal capillary erythrocyte flow in normal feline eyes. The pattern of capillary erythrocyte flow under normal blood glucose levels and normal systemic blood pressure served as baseline. Acute hyperglycemia was induced by intravenous injection of glucose while monitoring the systemic blood pressure. Two subsets of functional capillary pathways previously defined as S (simple) and C (complex) were identified in the recorded data. The relationship between erythrocyte flux in random selections of these two pathways and the level of hyperglycemia and systemic blood pressure was determined.

RESULTS

Induction of acute hyperglycemia led to acute elevation of the systemic blood pressure that returned to baseline levels within few minutes, while blood glucose remained high. The capillary erythrocyte flux in S paths was significantly higher than in C paths at all values of systemic blood pressure. The capillary erythrocyte flux in the S paths was directly proportional to the systemic blood pressure whereas the flux in C paths was minimally affected by acute hyperglycemia for the systemic blood pressure range between 110 and 160 mm Hg.

CONCLUSIONS

The erythrocyte flux in S paths is affected by the changes of the systemic blood pressure and these paths act as 'shunt vessels' when acute elevation of the systemic blood pressure occurs. C paths maintain stable perfusion under changing conditions, most probably in an effort to minimally alter the basic metabolic needs of the retinal tissue. Hyperglycemia per se was not responsible for changes of the cell flux in these capillary paths.

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.

International transmission of tele-ophthalmology images

Tele-ophthalmic consultations were conducted between a hospital in East Java, Indonesia, and an ophthalmology centre in Perth, Western Australia. Twenty-two eyes of 14 subjects were screened for glaucoma using a hand-held fundus camera. Optic disc images comprised 267 x 234 pixels at 24 bit/pixel (187 kByte). The images were compressed and stored together with patient information on a laptop computer. The images were then transmitted to Perth using either a mobile phone or a satellite phone, taking 170 s or 240 s, respectively. Images were also compressed to five different compression levels before transmission. At a compression ratio of 1:5, the images were 36 kByte in size and took 29 s to transmit by mobile phone and 60 s by satellite phone. To measure the loss of quality, the root mean square error was calculated for each colour component, comparing the transmitted and original images. The coefficients of variation were 10% (green), 15% (blue) and 22% (red). The images received in Perth were considered to be of excellent quality and readily interpreted by ophthalmologists in terms of the likely presence of glaucoma.

Tele-ophthalmology screening for retinal and anterior segment diseases

A digital indirect ophthalmoscope (DIO) was developed and tested for use in tele-ophthalmology screening for posterior and anterior segment diseases. Using custom software, images from the DIO were digitized, compressed, stored and transmitted to a centralized eye clinic for interpretation. A total of 43 subjects were primarily screened for glaucoma using the DIO, a hand-held fundus camera and a stereo fundus camera. The photographic slides from the stereo fundus camera used as gold standards. Images (390 x 300 pixels x 3 bits) were stored using a laptop computer together with patient information. Image quality received at the central eye clinic was good and showed adequate diagnostic information. An ophthalmologist estimated cup-disc ratios and graded the quality of the images. The sensitivity and specificity of each instrument was calculated. A high sensitivity and specificity was found when using the DIO, indicating that it could be used in tele-ophthalmic screenings. Further modifications are needed to make the instrument more user-friendly and to enable it to be used with undilated pupils, so that it can be easily operated by health-care personnel in remote areas. The camera can also be used to image gross external eye pathology.

Fred Hollows lecture: digital screening for eye disease

The purpose of this study was to explore progress, in the adaptation to community screening for blinding eye disease, of digital imaging devices and technology for storage and transmission. Available imaging systems were compared to gold standard clinical photography in terms of sensitivity and specificity for diagnosis of common blinding eye conditions. Since the use of expensive non-portable imaging devices is likely to be limited for widespread community screening purposes, a portable fundus camera (Nidek, Chiyoda-ku, Japan) and a prototype monocular digital indirect ophthalmoscope constructed at the Lions Eye Institute (LEI) were selected for comparative trials for the screening of optic disc cupping, glaucoma and clinical signs of diabetic retinopathy. Fifty-one eyes of 27 consecutive patients being assessed at the LEI clinic for glaucoma were dilated and photographed with a Zeiss retinal camera, and digital images were taken with the portable Nidek NM100 fundus camera (Carl Zeiss, Oberkochen, Germany) or with a prototype digital monocular indirect ophthalmoscope. Vertical cup: disc ratios (VCDR) were measured on the disc photographs by one ophthalmologist while three other clinicians were presented with compressed digital images in random order to estimate VCDR. Field trials were also carried out to demonstrate the practicality of compression, local storage and then transmission by mobile telephone ISDN lines and satellite, of optic discs and fundus images of patients with diabetes in either rural Western Australia or Surabaya, Indonesia. Kappa values of correlations of measurement of agreement between measured and estimated VCDR were 0.87, 0.45 and 0.84, respectively, for the three observers, corresponding to a specificity of 79-97% and a sensitivity of 70-95%. The portable Nidek fundus camera was also assessed for specificity and sensitivity in the diagnosis of diabetic retinopathy in comparison to standard Zeiss fundus camera photographs. Of 49 eyes in 25 consecutive patients attending the LEI clinic for assessment of diabetic retinopathy, three ophthalmologists assessed photographs and images in random order. When used for screening diabetic retinopathy, the digital images of the Nidek camera were graded as adequate quality in only 56% of eyes compared to 93% of the photographs. The kappa value of agreement in analysis of diabetic retinopathy was only 0.30. The prototype digital monocular indirect ophthalmoscope compared favourably with the Nidek camera. At 1:5 compression, images of size 36 kB transmitted from Surabaya to Perth took 29 s on the mobile telephone, while uncompressed images took 170 s. Images compressed 1:5 were transmitted in 60 s using the satellite telephone, while the uncompressed images took 240 s. Satellite transmission was more expensive but the lines were more stable than telephone connections from Indonesia. Digital imaging is becoming a powerful tool for ophthalmology in clinical records, teaching and research, and interoffice diagnostic opinions. It also has enormous potential for community screening for blinding eye diseases, such as glaucoma and diabetic retinopathy. Inexpensive portable imaging devices that are easy to use, and on which local health workers might be trained, must be developed and validated in terms of sensitivity and specificity of performance. The technology of image capture, image compression, transmission, data base storage and analysis is rapidly evolving and becoming less expensive.

A novel immunoassay for the evaluation of rod outer segment digestion in cultured retinal pigment epithelial cells

In this work a novel enzyme-linked immunoabsorbent assay quantifying residual rod outer segments in the medium of rod outer segment-challenged retinal pigment epithelial cells is described. A retinal pigment epithelial cell line (D407) that produces low level of cathepsin D, and a primary human retinal pigment epithelial cell culture (HRPE51) that has normal cathepsin D levels, were challenged with bovine rod outer segments. At 3 days post-challenge, the amount of undigested or residual bovine rod outer segments left in the culture medium was quantified by an enzyme-linked immunoabsorbent assay. An antibody raised against bovine rod outer segments, which had been purified and labelled with nitroiodophenyl haptens, was used in the assay. The sensitivity of the immunoassay was less than 10(2) bovine rod outer segments per mL and the signal followed a linear curve, saturating around 10(6) bovine rod outer segments per mL. HRPE51 cells had no residual bovine rod outer segments present in the medium following a challenge with 10(4) bovine rod outer segments per mL. In the medium of D407 cells, residual bovine rod outer segment levels were higher at all bovine rod outer segment concentrations when compared to the residual bovine rod outer segment levels in HRPE51 cells, suggesting that D407 cells have a lower digestive capacity. These results demonstrated that the immunoassay for detecting bovine rod outer segments is a sensitive and reliable technique that can be used to quantify the amount of residual bovine rod outer segments, following bovine rod outer segment challenge of retinal pigment epithelial cells.

Methods and limits of digital image compression of retinal images for telemedicine

PURPOSE

To investigate image compression of digital retinal images and the effect of various levels of compression on the quality of the images.

METHODS

JPEG (Joint Photographic Experts Group) and Wavelet image compression techniques were applied in five different levels to 11 eyes with subtle retinal abnormalities and to 4 normal eyes. Image quality was assessed by four different methods: calculation of the root mean square (RMS) error between the original and compressed image, determining the level of arteriole branching, identification of retinal abnormalities by experienced observers, and a subjective assessment of overall image quality. To verify the techniques used and findings, a second set of retinal images was assessed by calculation of RMS error and overall image quality.

RESULTS

Plots and tabulations of the data as a function of the final image size showed that when the original image size of 1.5 MB was reduced to 29 KB using JPEG compression, there was no serious degradation in quality. The smallest Wavelet compressed images in this study (15 KB) were generally still of acceptable quality.

CONCLUSIONS

For situations where digital image transmission time and costs should be minimized, Wavelet image compression to 15 KB is recommended, although there is a slight cost of computational time. Where computational time should be minimized, and to remain compatible with other imaging systems, the use of JPEG compression to 29 KB is an excellent alternative.

Inhibition of diclofenac formulated in hyaluronan on angiogenesis in vitro and its intraocular tolerance in the rabbit eye

PURPOSE

To investigate the effect of diclofenac, a potent nonsteroidal anti-inflammatory drug, formulated in hyaluronan (diclofenac/HA) on angiogenesis in vitro and its intraocular toxicity in vivo.

METHODS

The effect of diclofenac/HA on angiogenesis was determined by choriocapillary endothelial cells on Matrigel stimulated by vascular endothelial growth factor (VEGF). The tube areas were quantified by image digital analysis. For toxicity study, diclofenac/HA was injected intravitreally with a dose range from 100 to 1080 microg in 26 rabbits following gas compression vitrectomy. Potential toxicity was assessed by indirect ophthalmoscopy and by histological studies (light and electron microscopy). Retinal function was monitored by electroretinography (ERG) in six rabbits that received 400 microg of diclofenac/HA.

RESULTS

Diclofenac/HA, 180, 90 microg/ml, inhibited tube formation to 24% and 55% of the standard group (Media Ham's F12 plus 5% fetal calf serum and 50 ng/ml VEGF) respectively (P<0.01). Intravitreal injection of 540 microg or higher doses of diclofenac/HA resulted in ocular toxicity in the rabbit, demonstrated as cataract, vitreous haze and retinal damage observed by indirect ophthalmoscopy and light- and electron-microscopic examinations. No toxicity was observed in the eyes that received 400 microg or less diclofenac/HA, which was further supported by the normal ERG examined at 4 and 25 days post injection.

CONCLUSIONS

Diclofenac/HA inhibits tube formation in vitro and is non-toxic to the rabbit retina at concentrations that are inhibitory to tube formation. Our results suggest diclofenac/HA may be an effective candidate to inhibit ocular neovascularisation related to granulomatous reaction in the eye.

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.

Synthesis, physical characterization, and biological performance of sequential homointerpenetrating polymer network sponges based on poly(2-hydroxyethyl methacrylate)

A limitation in the use of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) sponges as implantable devices is their inherently poor mechanical strength. This precludes proper surgical manipulation, especially in the eye where the size of the implant is usually small. In this study a new method was developed to produce mechanically stronger PHEMA sponges. Sequential homointerpenetrating polymer network (homo-IPN) sponges were made by using HEMA as the precursor for generating both the first network and the successive interpenetrated networks. Following the formation of network I, the sponge was squeezed to remove the interstitial water, soaked in the second monomer (also HEMA), and squeezed again to remove the excess monomer from the pores before being subjected to the second polymerization leading to the formation of network II. Two two-component IPN sponges (K2 and K4) with increasing HEMA content in the network II and a three-component IPN sponge (K3) were produced, and their properties were compared to those of a homopolymer PHEMA sponge (control). Apart from elongation, the tensile properties were all significantly enhanced in the IPN sponges; the water content was the same as in the control sponge, except for sponge K4, which was lower. Light microscopy revealed similar pore morphologies of the control and IPN sponges K2 and K3, and the majority of the pores were around 25 microm. Sponge K4 displayed smaller pores of around 10 microm. Cellular invasion into the sponges was examined in vitro (incubation with 3T3 fibroblasts) and in vivo (implantation in rabbit corneas). Although the in vitro assay detected a change in the cell behavior in the early stage of invasion, which was probably due to the formation of IPNs, such changes were not reflected in the longer term in vivo experiment. There was a proper integration of sponges K2 and K3 with the corneal stroma, but much less cellular invasion and no neovascularization in sponge K4. We concluded that IPN formation is a valid method to enhance the strength of PHEMA sponges, provided that the content of HEMA in the successive networks is not too high.

Preferential adenovirus-mediated transduction of cells at the sites of laser photocoagulation in the rat eye

PURPOSE

This study aimed to investigate the feasibility of recombinant adenovirus-mediated gene transfer into cells implicated in the development of choroidal neovascularization (CNV).

METHODS

A rat model of CNV which used laser photocoagulation was developed. Gene delivery into the laser spots was investigated following subretinal injection of recombinant adenoviruses, AdRSVlacZ, AdCMVlacZ or AdCMVgfp. Immunohistochemical analysis was performed using a proliferating cell nuclear antigen antibody and a cytokeratin-specific antibody to identify the cell types transduced by the recombinant adenoviruses.

RESULTS

At 7 days post-injection, lacZ expression was detected in 51.6 +/- 13.2% and 71.2 +/- 19.3% of laser spots in AdRSVlacZ- and AdCMVlacZ-injected eyes, respectively. By 28 days post-injection, lacZ expression was only present in AdCMVlacZ-injected eyes. In vivo fundus fluorescent photography of AdCMVgfp-injected eyes detected gfp expression in 79.9 +/- 12.7% and 35.6% +/- 19.7% of laser spots at 4 and 7 days post-injection, respectively. Although fundus fluorescent photography did not detect the gfp signal at 10 days post-injection, fluorescent microscopy revealed a gfp signal in 81.3 +/- 6.0% of laser spots. Immunohistochemical analysis detected retinal pigment epithelial (RPE) cells as the most predominant proliferating cell type in the laser spots, although several other proliferating cell types were also identified. X-gal staining showed that the majority of transduced cells were those present in the laser spots.

CONCLUSIONS

It is proposed that following laser photocoagulation, proliferating RPE cells are susceptible to adenovirus-mediated gene delivery and that they may be suitable targets for the delivery of antiangiogenic factors by recombinant adenoviruses in order to inhibit developing CNV membranes.

Evaluation of a portable fundus camera for use in the teleophthalmologic diagnosis of glaucoma

PURPOSE

The digital images of the optic disk from a portable fundus camera were evaluated for suitability in teleophthalmologic screening for glaucoma.

METHODS

Fifty-one eyes of 27 consecutive patients from our glaucoma clinic were dilated and photographed with a Zeiss FF retinal camera (Carl Zeiss, Oberkochen, Germany) and a portable Nidek NM-100 (Nidek, Tokyo, Japan) fundus camera. Digital images from the portable fundus camera were digitized, compressed and stored in a Fujix DF-10M (Fuji, Tokyo, Japan) digitizer. Lossy compressed digital images and photographs from the Zeiss camera were presented separately in random order to three ophthalmologists for estimation of vertical cup:disk ratios (VCDR) and to evaluate image quality as good, acceptable, or unacceptable for screening glaucoma. Gold standard VCDRs were measured from monoscopic photographic slides obtained using the Zeiss camera by a fourth ophthalmologist.

RESULTS

Measurement of agreement (Kappa values) between estimated VCDR of digital images and photographs by the three ophthalmologists were 0.52, 0.38, and 0.50 respectively. Agreement between gold standard and estimated VCDR from photographs were 0.87, 0.45, and 0.84 respectively (specificity between 79% and 97%, sensitivity between 70% and 95%). Kappa values obtained between gold standard and estimated VCDR from digital images were 0.52, 0.49, and 0.49, respectively (specificity between 68% and 79%, sensitivity between 67% and 87%.

CONCLUSION

Moderate to good agreement indicates that the digital images from the portable fundus camera may be suitable for optic disk assessment in the current configuration. This easy to use Nidek hand-held camera could be a viable instrument for teleophthalmology if a better digitizing system is incorporated to improve the quality of the images.

Distribution of cathepsin D in human eyes with or without age-related maculopathy

Cathepsin D is a ubiquitous enzyme which plays an important role in the catabolism of proteins. Enzymatic studies showed that cathepsin D is the most important lysosomal enzyme in the proteolysis of opsin. The importance of cathepsin D in the lysosomal digestion of phagocytosed photoreceptor outer segments by the retinal pigment epithelium suggests that a decrease in cathepsin D activity might contribute to the development of hyalinized drusen and to the development of age-related maculopathy. The aim of this project was to study the immunohistochemical localization of cathepsin D in human eyes and particularly to compare the immunoreactivity of cathepsin D normal retinal pigment epithelial cells and in cells surrounding hyalinized drusen or lesions of age-related maculopathy. Following clinicopathological examinations the eyes were fixed, paraffin embedded and individual sections were subjected to Picro-Mallory staining for histopathological examination. Bleaching was performed then immunohistochemistry was carried out using a monoclonal mouse anti-human cathepsin D antibody. On the basis of the appearance of basal laminar deposit the eyes were divided into five groups corresponding to levels of progression in age-related maculopathy development. Following optimization of bleaching cathepsin D immunostaining was clearly visible in the iris epithelium, ciliary body and the retinal pigment epithelial layer of all eyes with the highest immunoreactivity present in the RPE cells. Within the neural retina the ganglion cells demonstrated a weak signal. Retinal pigment epithelial cathepsin D immunoreactivity was not impaired by age, geographical location or by age-related maculopathy status. There was a small increase in cathepsin D immunoreactivity around hyalinized drusen. The maintenance of cathepsin D immunoreactivity in eyes with hyalinized drusen or in samples with age-related maculopathy suggest that down-regulation of cathepsin D expression in the affected locations does not precede the development of these conditions. However, further studies are required to establish if the immunoreactive cathepsin D represents the fully processed biologically active enzyme.

Development of a poly(2-hydroxyethyl methacrylate) orbital implant allowing direct muscle attachment and tissue ingrowth

PURPOSE

To develop a poly(2-hydroxyethyl methacrylate) orbital implant that allows tissue ingrowth and direct muscle attachment to minimize the risk of extrusion and to enhance cosmesis.

METHODS

Assessment of clinical outcomes and histologic findings after implantation of 18 prototype prostheses into rabbits. The implants were not wrapped with other tissues or materials.

RESULTS

One case of infection was observed but there were no extrusions, with up to 21 months follow-up. Biocolonization was confirmed histologically. Good movement was observed when a cosmetic shell was fitted.

CONCLUSIONS

The prototype prosthesis appears promising, with particular advantages being the direct attachment of extraocular muscles, good cosmesis and movement, and a low complication rate in this pilot study.

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.

Generation and characterization of a recombinant adenovirus expressing vascular endothelial growth factor for studies of neovascularization in the eye

There is accumulating evidence that an increased expression of vascular endothelial growth factor from retinal pigment epithelial cells may be important in choroidal neovascularization. In vivo studies have demonstrated that subretinal injection of recombinant adenovirus vectors produces long-term transgene expression specifically within retinal pigment epithelial cells. A recombinant adenovirus encoding of vascular endothelial growth factor (Ad.RSV.VEGF) was therefore produced and characterized in order to determine whether an upregulation of vascular endothelial growth factor expression is sufficient to induce choroidal neovascularization. Ad.RSV.VEGF was produced by homologous recombination and its identity confirmed by restriction enzyme analysis. Ad.RSV.VEGF was characterized in vitro by the transduction of cultured retinal pigment epithelial cells. The in vitro characterization confirmed vascular endothelial growth factor mRNA and protein expression from Ad.RSV.VEGF and demonstrated the biological activity of the vascular endothelial growth factor protein. A preliminary in vivo study suggested that the subretinal injection of Ad.RSV.VEGF induced vascular leakage.

Correlation of histological findings with gadolinium enhanced MRI scans during healing of a PHEMA orbital implant in rabbits

BACKGROUND/AIMS

To investigate a poly(2-hydroxyethyl methacrylate) (PHEMA) orbital implant with a spongy anterior hemisphere and a smooth gel posterior hemisphere, by histology correlated with magnetic resonance images.

METHODS

Following enucleation, eight rabbits received PHEMA implants to which the muscles were directly sutured, and underwent gadolinium enhanced magnetic resonance imaging (MRI) from 3 to 52 weeks. After the rabbits were killed, the implants were removed, cut in a plane corresponding to the scan, and processed for light and electron microscopy.

RESULTS

All eight rabbits retained their implant to the end of the study period without complications. The scans demonstrated muscle attachment to the anterior half of the implant, and enhancement was seen on injection of gadolinium chelate. Histology confirmed muscle attachment, and cellular and vascular ingrowth. Over time, a transformation from reactive inflammatory to relatively non-vascular scar tissue was seen within the implant. Calcium deposits in one implant were detected by imaging and histology.

CONCLUSION

The implants are readily visualised on MRI. Muscle attachment and fibrovascular ingrowth into the anterior hemisphere are seen, while encapsulation of the posterior hemisphere is minimal. Histological findings confirm the progress of the healing response, with initial inflammation and marked vascularisation, developing later into quiescent scar tissue predominantly of fibroblasts.

Localization of IgG in the normal and dystrophic rat retina after laser lesions

PURPOSE

To test the hypothesis that access to extravasated plasma protein IgG may influence photoreceptor survival following laser photocoagulation and to determine whether this correlates with the retinal glial reaction.

METHODS

A total of 45 rats (18 Royal College of Surgeons (RCS) dystrophic and 18 RCS-rdy+ congenic control) were used for this experiment. Nine non-lasered littermates of same age were used as controls. The superior retinas of postnatal day 23 rats were irradiated with a grid pattern of 40 argon green laser lesions of 50 microm in diameter and two powers (150 and 300 mW) for 0.2 s. At various times after laser lesions (up to 14 days), animals were perfused, the retinas snap frozen and sectioned on a cryostat. A one-step immunohistochemical technique was used by incubating with rabbit anti-rat IgG conjugated directly to horseradish peroxidase. Adjacent sections were processed using an antibody to glial fibrillary acidic protein (GFAP) by the standard avidin-biotin complex method.

RESULTS

The labelling pattern for extravasated IgG after laser lesion was very similar in both RCS and RCS-rdy+ rat retinas. At 6, 12 and 24 h after lesions, IgG immunoreactivity (IR) was very intense in the lesion core and flanks. The outer plexiform layer (OPL) and photoreceptor inner segments provided a ready pathway for lateral spread of IgG. However, in the outer nuclear layer (ONL), IgG localization was much more restricted. Despite very intense IgG IR in the ONL of the coagulated lesion core, there was always a very sharply delineated boundary where the label abruptly halted. The GFAP labelling in both RCS dystrophic and RCS-rdy+ congenic control rat retinas showed that this boundary was between normal and necrotic cells because there was a core where GFAP was not produced by Müller cells. By 2 days after lesions, the coagulated cells in the lesion core were being removed by phagocytic cells that were IgG IR. Labelled phagocytic cells were also found among the inner and outer segment region on the lesion flanks. There was still IgG IR in the lesion, but the label was faint. No IgG IR was found in the retina at 3, 4, 7 and 14 days after lesions. Absorption control with pure rat IgG showed the label to be specific.

CONCLUSIONS

The extravasated IgG was derived from the choroidal circulation because at no stage was IgG localized around the retinal vasculature. The IgG labelling was surprisingly widespread and, therefore, did not correlate with photoreceptor sparing, although it preceded the widespread Müller cell expression of GFAP and may, therefore, trigger glial reaction.

Conservative management of documented neuroretinitis in cat scratch disease associated with Bartonella henselae infection

BACKGROUND

Bartonella henselae has been identified as the causative agent of the neuroretinitis associated with cat scratch disease (CSD). Immunofluorescent antibody tests with good sensitivity and specificity are available to aid in diagnosis. Despite diagnostic advances, optimal management remains controversial. We present a case of documented B. henselae macular neuroretinitis managed without antibiotics and discuss antibiotic use in this condition.

METHODS

We examined a young woman with macular neuroretinitis and established a diagnosis of CSD. Management consisted of a review of the literature, followed by educating her about the condition and close observation. We documented the course of her disease.

RESULTS

We diagnosed neuroretinitis associated with B. henselae infection based on immunofluorescent antibody titres and clinical presentation. Our patient's neuroretinitis resolved promptly without antibiotic therapy.

CONCLUSIONS

Macular neuroretinitis in CSD can be satisfactorily diagnosed with the use of fluorescent antibodies in the appropriate clinical setting. Optimal treatment for the disease has not been established and observation combined with patient education remains an appropriate option. The self-limited nature of the disease implies that treatment studies not using controls must be interpreted with great caution. Adverse drug reactions and other iatrogenic complications can be reduced by limiting antibiotic use in settings where a meaningful treatment benefit has not been established.

Progression of myelinated retinal nerve fibers

PURPOSE

To present a case demonstrating progression of retinal nerve fiber myelin and to suggest that myelinated retinal nerve fibers be considered among the peripapillary choristomas.

METHOD

Case report. A 46-year-old woman demonstrated progression of myelinated retinal nerve fibers and associated retinal vascular anomalies.

RESULTS

Myelinated retinal nerve fibers can be progressive. We confirm earlier reports of vascular anomalies associated with retinal nerve fiber myelin and show that they can also be progressive.

CONCLUSIONS

The rarely progressive nature of myelinated retinal nerve fibers and the histopathologic studies published to date suggest that myelinated retinal nerve fibers represent a striking ophthalmoscopic feature resulting from ectopic oligodendrocytes; thus, the entity may be described as an oligodendrocytic choristoma.

A case for electronic manipulation of medical images?

Two ophthalmic case histories requiring differing techniques to document the long-term outcomes of ocular tumours are presented. In the first case, after documenting a treated choroidal melanoma it was necessary to intervene with digital manipulation to enhance the images for clinical interpretation. Conversely, after documenting an iris tumour over an eight-year period, it was considered that the original images were suitable for interpretation without intervention. This raises the issue of images presented as legal evidence when digital technology is used to manipulate and enhance the images. Are these images admissible as evidence in court, and should the original data also be archived to prevent conflicting interpretations by the legal system? In light of The House of Lords recommendations on digital images as evidence, it is suggested that both the manipulated and original images are archived to avoid debate on the extent to which an image has been altered.

Cell viability and inflammatory response in hydrogel sponges implanted in the rabbit cornea

In the quest for the development of a functional keratoprosthesis, the biocompatibility of the porous skirt material in the Chirila keratoprosthesis (KPro) was investigated. The population of live and dead cells within, and the inflammatory response to, a tissue-integrating poly(2-hydroxyethyl methacrylate) (PHEMA) sponge were studied. Samples of the hydrogel sponge were implanted in rabbit corneas and explanted at predetermined time points up to 12 weeks. The explanted sponges were subjected to cell viability assay using two types of fluoroprobes, 5-chloromethylfluorescein diacetate and ethidium homodimer-1. A semiquantitative analysis was performed to assess the number of dead cells within the sponge and in the area of corneal stroma proximal to the sponge. Five rabbits were used for each end point (2, 4 and 12 weeks). To investigate the inflammatory response to the sponge, immunocytochemistry, using specific antibodies to rabbit macrophages, enzyme histochemistry of chloroacetate esterase (to detect neutrophils) and transmission electron microscopy (TEM) were also employed at 24 h, 2, 4 and 12 weeks after implantation. Four weeks after implantation, fewer viable cells were observed in the sponge when compared to the 2-week implant. However, the proportion of viable cells increased dramatically by 12 weeks. The proportion of nonviable cells decreased gradually with time; central sponge contained 34+/-11 % dead cells after 2 weeks, and 15+/-4.3% after 12 weeks. The staining of inflammatory cells demonstrated the presence of macrophages and neutrophils up to 12 weeks after implantation. TEM confirmed the presence of these cell types and others. including eosinophils and myofibroblasts, as well as blood capillaries. The presence of a significant number of viable cells at each time point and the uniform reduction of the nonviable cell proportion with time suggests that the sponge is a conducive environment supporting a prolific, viable cellular colonization. Dead cells observed in the first instance indicate a normal injury pattern. However, the presence of a small but significant proportion of invading inflammatory cells 12 weeks after implantation confirms a characteristic pattern of wound healing within the sponges.

Expression of cathepsin S antisense transcripts by adenovirus in retinal pigment epithelial cells

PURPOSE

To show the production of sense or antisense transcripts by recombinant adenoviruses, to investigate whether the transcripts produced were suitable for downregulating the expression of the targeted gene, cathepsin S (CatS), and to examine the effect of antisense transcript production on the biologic function of retinal pigment epithelial (RPE) cells, including the regulation of endogenous aspartic protease expression.

METHODS

Ad.MLP.CatSAS, Ad.RSV.CatSAS, and Ad.MLP.CatSS recombinant viruses were produced by homologous recombination. The recombinant viruses were tested by restriction enzyme digestion to confirm the orientation of the inserts. The expression of antisense transcripts was tested by northern blot analysis. Western blot analysis was used to study the regulation of the endogenous CatS protein in ARPE19 cells. The biologic effect of CatS downregulation in ARPE19 cells was tested by proliferation and phagocytosis assays, de novo cathepsin D (CatD) synthesis, and measurement of aspartic protease activity.

RESULTS

After characterization of the recombinant adenovirus constructs, the production of antisense and sense CatS transcripts was shown in ARPE19 cells. The transcripts appeared at approximately 1.9 kb 48 hours after transduction, and the expression of the antisense transcripts was similar in constructs carrying either the MLP or the RSV promoter. Western blot analysis showed that ARPE19 cells transduced with Ad.MLP.CatSAS and Ad.RSV.CatSAS had no detectable CatS. In contrast, there was a strong signal appearing at 24 kDa in ARPE19 cells transduced with Ad.MLP.CatSS. ARPE19 cells were transduced to a high level. The transduction of ARPE19 cells with the recombinant adenoviruses did not affect the morphologic appearance of the cells, their proliferation, or their phagocytosing ability. However, ARPE19 cells transduced by Ad.MLP.CatSAS recombinant adenovirus showed a significant downregulation of de novo CatD synthesis and a twofold decrease in aspartic protease activity.

CONCLUSIONS

Recombinant adenoviruses were shown to be suitable for producing antisense CatS transcripts to modulate endogenous CatS expression in RPE cells. It is proposed that CatS may play an important role, directly or indirectly, in the lysosomal digestion of outer segments through the regulation of other lysosomal enzyme activity, such as the expression of CatD.

Expression of cell adhesion molecules and vascular endothelial growth factor in experimental choroidal neovascularisation in the rat

AIMS

To investigate the longevity and reproducibility of choroidal neovascularisation (CNV) induced by krypton laser photocoagulation in the rat. The presence of cell adhesion molecules (CAMs) and vascular endothelial growth factor (VEGF) during the development of CNV was also studied.

METHODS

67 pigmented rats underwent retinal photocoagulation by krypton laser. The eyes were examined by either single or serial fluorescein angiography at 3 days, 1, 2-3, 4-5, 7-8, and 12 weeks post photocoagulation. The expression of CAMs (ICAM-1, E-selectin, and CD44) and VEGF post photocoagulation was studied by immunohistochemistry.

RESULTS

CNV related fluorescein leakage appeared in 46.4% of 766 laser spots delivered to the 58 eyes that were tested at 2-3 weeks post treatment. The ratio of hyperfluorescent laser sites did not change significantly at 8 weeks post laser. The number of leaky spots was independent of the total number of lesions delivered to each eye (at 2-3 weeks post laser 10-15 spots/eye: 44% and 25-30 spots/eye: 49%; t = 0.7673; p = 0.3903). Nine eyes were followed by serial angiography between 2 and 12 weeks. The laser spots with fluorescein leakage at 2 weeks (51.5%) remained leaky at 12 weeks (51.5%). Histopathologically, macrophage accumulation peaked at 5 days and CNV was firstly observed at 1 week post photocoagulation. ICAM-1, E-selectin, CD44, and VEGF were maximally induced at 3-5 days post laser photocoagulation, and were localised to RPE, choroidal vascular endothelial, and inflammatory cells. VEGF was also detected in intravascular leucocytes at the sites of laser lesions.

CONCLUSIONS

These studies demonstrated that krypton laser photocoagulation can be successfully used to produce lesions similar to those of human CNV. The response induced remained present for an extended period of time (12 weeks), thus offering a potential model to screen candidate CNV inhibitory agents. In addition, it is proposed that the expression of ICAM-1, E-selectin, CD44, and VEGF before new vessel formation might be linked to the initiation of CNV.

Laser-induced chorioretinal venous anastomosis for nonischemic central retinal vein occlusion: evaluation of the complications and their risk factors

PURPOSE

To evaluate the complications of laser-induced chorioretinal venous anastomosis in nonischemic central retinal vein occlusion (CRVO) and to identify the associated risks.

METHODS

A retrospective consecutive series of 91 eyes (91 patients) with nonischemic CRVO with a mean +/- SD duration of 15.0 +/- 15.2 weeks (range, 3 to 72 weeks )and corrected visual acuity reduced to 20/100 or less because of perfused macular edema were reviewed. All eyes had one or more anastomotic attempts using argon laser (combined with Nd-YAG laser in 46 eyes) and a minimum of 12 months of follow-up.

RESULTS

Successful chorioretinal venous anastomoses were created in 49 eyes (54%). Eighteen eyes (20%) had neovascular complications. These consisted of intravitreal, intraretinal, and subretinal neovascular membranes and were significantly associated with retinal ischemia (P < .001). There was avascular fibrous tissue proliferation at the anastomotic site in eight eyes (9%), and it was not associated with retinal ischemia (P = .727). No eye developed further capillary nonperfusion once an anastomosis became functional. A chorioretinal venous anastomosis was associated with improved vision (P < .001); 84% of eyes had an average +/- SD improvement of 4.3 +/- 3.8 lines (range, 2 to 20 lines), with the remaining 16% having no improvement or reduced vision.

CONCLUSION

The major vision-threatening complication of laser-induced chorioretinal venous anastomosis for nonischemic CRVO is neovascular membranes occurring at the anastomotic site; these are associated with retinal ischemia. Prompt laser photocoagulation to areas of retinal ischemia that develop after the anastomotic attempt has been made may reduce the risk and severity of this complication.

The correlation between cerebrospinal fluid pressure and retrolaminar tissue pressure

PURPOSE

To measure the effects of cerebrospinal fluid pressure (CSFp) on retrolaminar tissue pressure (RLTp) and the translaminar pressure gradient (TLPG), particularly at low CSFp, which is the normal situation in erect posture.

METHODS

Micropipettes coupled to a servonull pressure system were passed into eyes of anesthetized dogs to the optic disc and advanced in steps through the lamina cribrosa to the optic nerve subarachnoid space (ONSAS), while pressure measurements were taken. Cerebrospinal fluid pressure and intraocular pressure (IOP) were monitored and controlled. The TLPG was measured at varying IOPs and CSFps. The RLTp and ONSAS pressure (ONSASp) were measured at varying CSFps. In separate experiments, the optic nerve dura was incised, and pressure measurements were taken across the pia mater.

RESULTS

The TLPG was strongly correlated to the difference between IOP and CSFp (r=0.93; n=18) when CSFp was more than zero. Mean RLTp was 3.7+/-0.2 mm Hg (SEM; n=15) when CSFp was 0 mm Hg. The ONSASp and RLTp were largely dependent on the presence of CSFp higher than break point pressures of -0.5 mm Hg and 1.33 mm Hg, respectively. However, below these break points, RLTp (slope 0.07) and ONSASp (slope 0.18) were little influenced by CSFp. Separate measurements across the pia mater revealed that 95% of the pressure drop occurred within 100 microm of the pial surface.

CONCLUSIONS

The TLPG and RLTp are dependent on CSFp when CSFp is more than -0.5 mm Hg. Below this level, there is no hydrostatic continuity between the intracranial and optic nerve subarachnoid space. In this range, RLTp is stable and is little influenced by CSFp changes.

Relation between pressure determined by ophthalmodynamometry and aortic pressure in the dog

AIMS

Ophthalmodynamometry has been used extensively since the last century; however, controversy surrounds what it actually measures. This study was set up to determine the relation between ophthalmodynamometric (ODP) and systemic blood pressures.

METHODS

Aortic pressure was continuously monitored and altered by phlebotomy in six anaesthetised dogs, while ophthalmodynamometry was performed, by directly altering intraocular pressure. Maxillary artery pressure was monitored in two animals. All pressure transducers were zeroed at eye level.

RESULTS

Mean ODP was 96.6% (1.6%) (95% confidence interval, n = 49) of aortic pressure. Mean maxillary artery pressure was 95.7% (5.5%) (95% CI, n = 16) of aortic pressure. ODP was 1.9 (0.6) mm Hg (95% CI, n = 33) higher than maxillary artery pressures.

CONCLUSION

ODP was only slightly below aortic pressure and not significantly different from maxillary artery pressure, the analogue of the internal carotid artery in humans. These results also suggest a retinal artery collapse pressure of at least 1.9 mm Hg.

Cell polarity, phagocytosis and viral gene transfer in cultured human retinal pigment epithelial cells

PURPOSE

To investigate whether there is a difference in the expression of adenovirus transgenes in human retinal pigment epithelial cells when the vector was exposed to the apical or basal surface, the effect of transgene expression on rod outer segment (ROS) phagocytosis and finally, the role of phagocytosis in gene transfer to RPE cells, using the Royal College of Surgeons (RCS) rat.

METHODS

Monolayers of human retinal pigment epithelium (HRPE) or an RPE cell line (A407) had the apical or basal surfaces exposed to 10(7) pfu/ml of replication deficient adenovirus (Ad.RSV.betagal) carrying the beta-galactosidase marker gene, and the numbers of expressing cells were compared. Parallel cultures were infected and challenged with fluorescein-labelled bovine rod outer segments (FBROS). The fluorescence of infected versus uninfected cells was recorded for both challenged and unchallenged states, using fluorophotometric flow cytometry. Primary cultures of RCS rat RPE were established and the transgene uptake dynamics compared to control Long Evans rat RPE cells.

RESULTS

The expression of transgene in HRPE and A407 cell cultures was an order of magnitude greater when the vector was exposed apically (analysis of variance p < 0.05). There was no difference in the phagocytic capacity of Ad.RSV.betagal-infected and -noninfected cells when challenged with FBROS. There was also no difference in the number of cells expressing transgene, when compared to the RCS or Long Evans control rat RPE.

CONCLUSIONS

The surface of exposure in polarized retinal pigment epithelial cells affects the rate of uptake and expression of adenovirus. The defective ROS phagocytosis in RCS rat RPE cells did not lead to a decrease in transgene expression relative to the Long Evans control cells. Finally we have found that phagocytosis is not significantly altered with adenoviral transgene expression in this in vitro model.

Tele-ophthalmic screening using digital imaging devices

BACKGROUND

Digital imaging systems provide immediate, magnified images that can easily be analysed, enhanced, archived, printed on near photographic-quality paper and transferred electronically to remote computers. We have assembled a digital ophthalmic system and tested it on patients with some common causes of blindness: corneal scarring and cataract, diabetic retinopathy, macular degeneration and glaucoma.

METHODS

Digital images were obtained using a variety of ophthalmic imaging devices ranging from slit-lamp, fundus camera, indirect ophthalmoscope and scanning laser ophthalmoscope. These images were compressed in order to concentrate image information (image size reduced by 90-95%) and minimize transmission time (reduced by 97-98%). Standard or mobile telephone lines were used to transmit images to remote terminals.

RESULTS/DISCUSSION

Transmission time was reduced from 15-20min to 20-30s and the image size was reduced from 1.3 MB to 20-30 kB by compressing the images before transmission. Image quality is still excellent.

Non-mydriatic fundus photography: a viable alternative to fundoscopy for identification of diabetic retinopathy in an Aboriginal population in rural Western Australia?

PURPOSE

To evaluate the Canon CR5-45NM non-mydriatic fundus camera (Canon, Kanagawa, Japan) for identifying retinopathy and the need for laser treatment in a population of Aboriginal patients with diabetes mellitus in rural Western Australia.

METHODS

Diabetic Aboriginal patients were photographed through undilated pupils using a Canon CR5-45NM non-mydriatic fundus camera, after which ophthalmoscopy was performed using indirect ophthalmoscopy through dilated pupils. The examining ophthalmologist recorded the presence of retinopathy and the need for laser treatment. A proportion of patients were rephotographed through dilated pupils. Photographs were reviewed by a second ophthalmologist who evaluated the quality of the image, the presence of retinopathy and the need for laser treatment. Results of fundus photographs and ophthalmoscopy were compared.

RESULTS

Three hundred and twenty-eight eyes in 164 Aboriginal patients were examined. The mean patient age was 48.2 years (range 16-81 years) and the mean duration of diabetes was 7.5 years (range 1-35 years). Seventy-four eyes (22.6%) were diagnosed with retinopathy using combined examination techniques, 44 (59.5%) of which were identified by ophthalmoscopy and 55 (74.3%) by photography. Thirty-five eyes were deemed to need treatment, 18 (51.4%) of which were identified by ophthalmoscopy and 30 (85.7%) by photography. Kappa coefficient measurement for agreement for presence of retinopathy and need for referral was 0.41 and 0.53, respectively. Photograph quality was significantly improved following pupil dilation.

CONCLUSIONS

The Canon CR5-45NM non-mydriatic fundus camera was relatively good at identifying diabetic retinopathy and could usefully be applied within a screening programme for treatable disease within this population.

Robotic ocular ultramicrosurgery

BACKGROUND

There is an increasing need for improved microsurgical techniques in the eye. Delivery of small quantities of chemicals or cells into specific retinal locations, for example, cannot be achieved with hand-held instruments. The present paper describes the design principles used in the development of a robotic ocular ultramicrosurgical system and the results from preliminary animal trials.

METHODS

We have developed a robotic ocular ultramicrosurgical system and a range of instruments for specific intraocular applications.

RESULTS

We have successfully used the system for intravascular (< 70 microm) drug delivery, implantation of microdrainage devices and the intraretinal manipulation of microelectrodes with minimal damage.

CONCLUSION

A clinically usable system using the same principles appears feasible.

Recombinant adenovirus-mediated gene delivery into the rat retinal pigment epithelium in vivo

PURPOSE

The present paper describes changes following the subretinal injection of a recombinant replication-deficient adenovirus carrying the beta-galactosidase reporter gene construct into the rat retina.

METHODS

Ad.RSV.betagal-mediated transduction of rat retinal pigment epithelium (RPE) cells in vitro and in vivo was examined following X-gal staining.

RESULTS

There was a low level of beta-galactosidase expression in the RPE cells at 4 days postinjection. At 7 days postinjection, a strong transgene expression was present in RPE cells and the expression was maintained at 14 days postinjection. Except for the accumulation of cells at the site of the injection, the morphology of the rest of the retina remained normal.

CONCLUSION

These results demonstrate that the RPE layer can be successfully targeted for gene delivery in the rat.

Implantation of PHEMA keratoprostheses after alkali burns in rabbit eyes

PURPOSE

We have previously examined histologically the healing of a PHEMA core-and-skirt keratoprosthesis (the Chirila KPro) as a full-thickness implant in healthy animal corneas. The present study was carried out to determine whether a diseased cornea could also generate biocolonization of the skirt region of a KPro.

METHODS

Ten KPros were placed as full-thickness corneal implants under conjunctival flaps in 10 alkali-burned rabbit corneas. Histological findings at intervals from 2 weeks to 6 months postoperatively were compared with earlier findings in 10 rabbits that had received identical KPros without prior alkali injury.

RESULTS

Despite severe corneal injury and the reduced keratocyte population present, there were no clinically detected complications in 60%. Histological findings established that, compared with healthy host tissue, skirt biocolonization and KPro-cornea healing after an alkali burn were impaired, with evidence of epithelial downgrowth in 40%. One animal required euthanasia earlier than the planned end point, but no KPro extrusions occurred.

CONCLUSION

Biocolonization of a KPro skirt is reduced but not prevented in an alkali-induced corneal inflammation model. Although no extrusions occurred, close follow-up and anticollagenolytic medication would be required to minimize the complication rate.

Chorioretinal venous anastomoses: effect of different laser methods and energy in human eyes without vein occlusion

BACKGROUND

This study was performed to determine the laser energy required to rupture both Bruch's membrane and retinal veins reliably in order to create a venous chorioretinal anastomosis.

METHODS

A histological examination was conducted of argon green and YAG laser applications to the retina made prior to enucleation in eight eyes with large intraocular melanomas.

RESULTS

Argon laser application of 50 microns in size and 0.1 s duration to intervascular areas of the retina will reliably rupture Bruch's membrane at a power level of at least 1.5 W. If the argon laser spot is placed overlying a retinal vein, a power level of up to 2.5-3.0 W will rupture Bruch's membrane in 60%, with only 34% of the retinal veins showing evidence of rupture. The YAG laser with power levels of 3-4 mJ will reliably rupture the retinal vein in cases where it has not previously been ruptured by the argon laser.

CONCLUSION

When attempting to create a chorioretinal venous anastomosis in an eye with a non-ischaemic central retinal vein occlusion, Bruch's membrane should be ruptured first by placing the argon laser application at the side of the retinal vein before an attempt to rupture the retinal vein itself is made in case haemorrhage from the ruptured vein obscures the view. A power level of at least 2.5 W should be used. If the argon laser is unsuccessful in rupturing the retinal vein, a YAG laser (3-4 mJ) is effective.

The distribution of angioarchitectural changes within the vicinity of the arteriovenous crossing in branch retinal vein occlusion

OBJECTIVE

Branch retinal vein occlusions (BRVOs) are known to occur most commonly in the vicinity of arteriovenous (A/V) crossings. The authors aimed to identify types of venous wall abnormalities in BRVO and document their position in relation to the A/V crossing.

DESIGN

A retrospective review of the color photographs and fluorescein angiograms from the most recent 110 patients with first- or second-order BRVO was performed.

MAIN OUTCOME MEASURES

The films were examined for the presence of angioarchitectural changes of specified type within one-quarter disk diameter of the A/V crossing involved in the BRVO. The specific changes noted were fluorescein leakage, presumed thrombi, and flow abnormalities, which were recorded along with their position in relation to the A/V crossing.

RESULTS

Of the 110 patients diagnosed with BRVO, 59 had photography of satisfactory quality. Forty-one (70%) of these 59 patients had venous lesions, of which significantly more (chi-square -5.74, P < 0.02) were downstream (56%) than upstream (12%) from the A/V crossing. Thirty-two percent were upstream and downstream. Of the hemodynamic changes seen, 49% had late venous phase leakage of fluorescein, 85% had abnormal flow, and 7% had presumed thrombi. All thrombi seen were downstream.

CONCLUSIONS

Venous lesions in the vicinity of the A/V crossing commonly are seen in BRVO, most of which occur downstream. This suggests that the venous narrowing at the crossing may induce downstream hemodynamic changes predisposing to endothelial damage and thrombus generation.