Biomedical subjects

Jost Hillenkamp

Publications and source records attributed to Jost Hillenkamp.

13 recordsLinked to original sources

PubMed2006

Surgical removal of idiopathic epiretinal membrane with or without the assistance of indocyanine green: a randomised controlled clinical trial.

PURPOSE: To carry out a prospective investigation of the functional and morphological outcome of idiopathic epiretinal membrane (IEM) surgery with or without the assistance of indocyanine green (ICG) in a randomised controlled clinical trial. METHODS: Sixty patients who underwent vitrectomy with removal of IEM combined with cataract surgery were randomly allocated to two groups: 27 patients were operated on with ICG 0.1% in glucose 5%, 33 patients without ICG. Functional outcome was assessed 3-4 months postoperatively with improvement of best-corrected visual acuity (BCVA), Amsler grid test, and automated and kinetic perimetry. Postoperative residual or recurrent IEM was assessed with bio-microscopy, and macular oedema with optical coherence tomography (OCT). Improvement in BCVA was the main outcome measure. RESULTS: BCVA improved in 49 patients, remained unchanged in five and decreased in five. Improvement in BCVA and reduction of macular oedema were statistically significant within both groups (P < 0.01). Improvement in BCVA was not statistically significantly different whether ICG was used or not [0.17 (logarithm of minimum angle of resolution; logMAR) with ICG and 0.24 (logMAR) without ICG] (P = 0.59). There was no statistically significant difference in preoperative or postoperative BCVA, reduction of macular oedema, postoperative Amsler grid test, or incidence of residual or recurrent IEM between the two groups. Visual field defects were detected in two patients operated on with ICG. CONCLUSIONS: Removal of IEM with or without the assistance of ICG equally improved visual function and macular morphology.

Aged↗

PubMed2006

Correlation between optical coherence tomography and autofluorescence in acute posterior multifocal placoid pigment epitheliopathy.

PURPOSE: To report a case of bilateral acute posterior multifocal placoid pigment epitheliopathy (APMPPE) evaluated by optical coherence tomography (OCT), fundus autofluorescence (AF) and microperimetry, both in the acute phase and after resolution of symptoms. METHODS: Complete ophthalmological evaluation, including fluorescein angiography, OCT, AF, and microperimetry upon presentation and 1 month later, after lesions have subsided. An attempt to correlate the findings on presentation and changes after resolution is performed using the results of these new investigational techniques. RESULTS: APMPPE showed hyperreflectance in OCT at the level of the outer retinal layers, without increase in retinal thickness. AF revealed early decreased fluorescence due to a masking effect, and later reveals increased fluorescence after resolution of OCT findings. Function is disturbed at the lesion sites, as shown by microperimetry, and later returns to near normal values on microperimetry. CONCLUSION: APMPPE shows outer retinal layers changes on OCT, which resolve totally after subsidence of the acute phase. AF shows areas of increased fluorescence after resolution, with near normal return of function on microperimetry.

Acute Disease↗

PubMed2006

Safety testing of indocyanine green in an ex vivo porcine retina model.

PURPOSE: To assess retinal toxicity of indocyanine green (ICG) in a porcine ex vivo perfusion organ culture model, and to measure intraretinal penetration of ICG applied to the retinal surface. METHODS: The retinal surface of fresh porcine retinal tissue was exposed to ICG 0.1% and 1% dissolved in glucose 5% for 1 and 30 minutes with and without concomitant illumination. Specimens were then kept in perfusion organ culture for 24 hours before examination by light microscopy and the TUNEL technique. Tissue samples treated with DNAse served as positive controls, and samples exposed to saline served as negative controls. Fluorescence microscopy was used to localize ICG at 1 minute, 60 minutes, 2 hours, and 3 hours after a 1-minute exposure of the retinal surface to ICG 1%. RESULTS: No increase in TUNEL-positive cells was observed after exposure to ICG 0.1% for 1 minute. Moderate apoptosis was found after 1-minute exposure to ICG 1% and 30-minute exposure to ICG 0.1%, and severe apoptosis was found after 30-minute exposure to ICG 1%. Concomitant application of light did not influence the degree of apoptosis. No signs of cell necrosis were found. After 1-minute exposure of the retinal surface, ICG 1% gradually penetrated the entire retina. CONCLUSIONS: ICG induced apoptosis but not necrosis in all nuclear retinal layers in a dose-dependent manner. Brief exposure to ICG 0.1% for 1 minute and illumination for 3 minutes simulated the intraoperative use of ICG. No retinal apoptosis or necrosis was observed. ICG briefly applied to the retinal surface gradually penetrated the entire retina.

Animals↗

PubMed2006

Human scleral hydraulic conductivity: age-related changes, topographical variation, and potential scleral outflow facility.

PURPOSE: To measure the specific hydraulic conductivity (K) of human sclera over a range of ages, to assess topographical variation, and to provide a theoretical estimate of potential scleral outflow facility. METHODS: Human donor sclera (n = 18; mean age 56.7 +/- 25.9 years; range 4-89) was clamped in a modified Ussing chamber connected to a water column set at 15.7 mm Hg. Column descent was measured over 24 hours at 20 degrees C with a digital micrometer. Scleral thickness of glutaraldehyde-fixed specimens was measured by light microscopy, taking the mean of 15 measurements per donor. Topographical variation in hydraulic conductivity (HC) was determined in an additional 10 donor eyes (mean age, 54.1 +/- 26.4 years; range 12-89), comparing anterior, equatorial, and posterior sclera. The potential transscleral outflow facility was calculated by multiplying HC by total scleral surface area and adjusting water viscosity to core body temperature. RESULTS: Mean K +/- 1SD in adults (>18 years) was 5.85 +/- 3.89 x 10(-18) m(2). K tended to be higher in pediatric donors, but there was no statistically significant age-related change. However, when all data sets were combined (n = 28), HC showed a significant decline with age. There was no significant topographical variation in HC. The potential transscleral outflow facility was 0.33 microL.min(-1).mm Hg(-1). CONCLUSIONS: Quantifying HC may help refine ocular pharmacotherapy, as transscleral water movement increases intraocular drug elimination and impedes transscleral drug delivery. The potential scleral outflow is two to three times higher than that which occurs in vivo; hence, medical or surgical interventions that fully exploit this pathway have considerable capacity to lower intraocular pressure.

Adolescent↗

PubMed2005

Effect of taurine and apical potassium concentration on electrophysiologic parameters of bovine retinal pigment epithelium.

The purpose of this study was to assess the effect of taurine and apical potassium concentration modelling in vivo light evoked changes on the transepithelial potential (TEP) and the transepithelial resistance (TER) of isolated bovine retinal pigment epithelium (RPE). Isolated specimens of bovine non-tapetal RPE-Bruch's-choroid (RPE-BC) were mounted in modified Ussing chambers. The apical and the basolateral side of the preparations were exposed to 10 mm and 10 microm concentrations of taurine in Krebs' medium with either 6.04 or 2.2 mm potassium in the apical compartment. TEP and TER were recorded over 140 min. TEP and TER decreased with exposure to taurine over the course of 1 hr followed by a stabilisation. The degree of this response did not depend on the concentration of taurine but was more pronounced when taurine was added to the apical compartment. Lowering apical potassium from 6.04 to 2.2 mm further pronounced the decrease of TEP and TER. The data show that light-induced release of taurine from the outer retina and light-induced decrease of the potassium concentration in the subretinal space synergistically lead to a temporary decrease in TEP and TER. Thereby, taurine uptake into the RPE is reduced probably by a reduction of the activity of the electrogenic Na+/taurine co-transporter of the apical RPE cell membrane. The findings suggest a mechanism whereby the sustained presence of taurine in the interphotoreceptor matrix following exposure to light may protect photoreceptor outer segments from light-induced oxidative stress.

Animals↗

PubMed2005

An experimental method for testing novel retinal vital stains.

There is uncertainty surrounding the safety of the vital stains currently used to assist macular surgery, and there may be other agents that are more suitable. This study aimed to validate a method of screening retinal vital stains for their potential surgical utility. Bovine retina was exposed to test agents at a range of concentrations. Masked observers determined the minimum dye concentration that reliably stained the retina, defined as the minimum visible concentration (MVC). Computer image analysis (CIE94 colour difference equation) was used to estimate the magnitude of the colour difference between stained and unstained retina. Agents that had favourable staining characteristics underwent safety testing using a retinal pigment epithelium and glial cell culture model. Cells were exposed to each agent and viability was assessed with a mitochondrial enzyme (MTT) assay, and fluorescent live-dead probe (ethidium homodimer-1/calcein-AM). Frozen sections were used to determine which retinal layers were stained. Techniques were tested on the following agents: alcian blue; diethyloxadicarbocyanine; Evan's blue; fast green; fluorescein; Janus green; methylene blue; naphthol green; neutral red; procian (reactive) yellow; rose bengal; and trypan blue. For most dyes, the results of image analysis showed that colour differences increased linearly with dye concentration, although some displayed a more exponential relationship. Five agents showed favourable staining characteristics: Evan's blue, rose bengal, naphthol green, neutral red, and trypan blue (MVC 0.02, 0.01, 0.1, 0.002, 0.01%, respectively). Safety testing of these five agents did not show toxicity, except in glial cells exposed to rose bengal. Relative to the negative control (saline), these showed a 48% reduction in viability using the MTT assay (p<0.001; t=4.71; CI 30-75%), and qualitative damage on fluorescence microscopy. Frozen sections showed that some agents produced diffuse staining of all retinal layers, others produced selective inner retinal staining. There are thousands of biological stains available and many of these may be more effective or safer than those currently used for retinal surgery. This study provides a means of screening potentially useful vital stains.

Animals↗

PubMed2004

The influence of path length and matrix components on ageing characteristics of transport between the choroid and the outer retina.

PURPOSE: To determine the relative influence of path length and matrix components on the movement of small solutes and water between the choroid and the outer retina. METHODS: Human and bovine Bruch's membrane-choroid (BC) tissue samples were mounted in modified Ussing chambers, and the diffusion of taurine and hydraulic conductivity (Lp) was determined. In humans, diffusion of taurine was determined as a function of age of the donor. The relative contribution of Bruch's membrane in the BC complex to transport processes was measured after its removal by laser ablation. Similarly, the effect of choroidal path length was determined. In humans, tracking the trend of age-related thinning provided samples of various path lengths. In young bovine animals (< or =2 years old), choroidal thickness was adjusted by laser ablation. RESULTS: Diffusion of taurine across human BC decreased linearly from 162.7 to 105.9 nanomoles/h per 3 mm between 10 and 90 years of age (P < 0.05). Ablation of Bruch's membrane increased diffusion of taurine from 129 to 287.9 nanomoles/h per 4 mm in human (donor age 55, 74, and 82 years; P < 0.005) but caused no statistically significant change in bovine BC. Diffusion of taurine across bovine BC was greater in samples with partially ablated choroid (218 nanomoles/h per 4 mm) than in normal control samples (128.75 nanomoles/h per 4 mm). Lp was not measurable in bovine samples after complete ablation of Bruch's membrane, but did not change significantly as the choroid thinned. CONCLUSIONS: The data suggest that both path length and matrix components contribute to the decline of diffusion of small solutes across BC with age. The importance of matrix components was also demonstrated in restricting the movement of water while choroidal thickness played little if any role.

Adolescent↗

PubMed2004

Safety testing of indocyanine green and trypan blue using retinal pigment epithelium and glial cell cultures.

PURPOSE: Indocyanine green (ICG) and trypan blue have been advocated as vital stains for use during macular surgery. The safety of these agents was tested using a cell culture model. METHODS: Human retinal pigment epithelium (RPE) and Müller cell lines were exposed to ICG over a range of concentrations up to 0.5%, and trypan blue up to 0.2%. Cells were exposed to each dye for 5, 15, or 30 minutes, rinsed, and incubated 24 hours. Cell viability was measured using a mitochondrial dehydrogenase-assay and fluorescent live-dead probe. Experiments were repeated using 0.5% and 1% ICG and 0.06% and 0.12% trypan blue, with follow-up at 0, 1, 5, and 15 days. ICG experiments were repeated in the presence of illumination from a xenon light-source channeled through a surgical endolight, and using reduced osmolarity solutions of 0.1%, 0.5%, and 1% (185 vs. 275 mOsM). RESULTS: There was no clear relationship between cell viability and the concentration of the agent or duration of follow-up, except in RPE cells exposed to 1% ICG. These showed a linear (R(2) 0.9952) decline in viability with time, with a significant reduction by day 15 (P = 0.016). RPE cells exposed to ICG and illumination were not significantly different from the negative control, but when illumination was combined with low osmolarity, viability was reduced (P = 0.0016). ICG and illumination reduced Müller cell viability (P < 0.0001 for both 185 and 275 mOsM). Müller cells incubated with 185 mOsM 1% ICG showed a significant reduction in viability (P < 0.0001) not seen with the 185 mOsM 0.5% or 0.1% solutions or in the low-osmolarity RPE groups. CONCLUSIONS: The combination of exposure to 0.5% ICG and the newer endoillumination light-sources can damage cultured Müller cells. Although the preparations of ICG most commonly used clinically did not produce significant damage, relatively small changes in ICG osmolarity and concentration did. This suggests that safety margins are not large. Trypan blue is safe in a cell culture model.

Cell Line↗

PubMed2004

Compartmental analysis of taurine transport to the outer retina in the bovine eye.

PURPOSE: To assess the relative resistance presented individually by Bruch's membrane-choroid (BC) and the retinal pigment epithelium (RPE) to movement of taurine between the choroidal circulation and the outer retina. To quantify the effect of light-evoked changes in subretinal potassium concentration on the transepithelial transport of taurine across bovine RPE. METHODS: Transport studies were performed in Ussing chambers with intact and RPE-denuded specimens of BC. RPE viability was monitored by recording transepithelial potential (TEP) and transepithelial resistance (TER). Taurine transport with substrate concentrations in the micro- and millimolar range, reflecting physiological taurine concentrations in plasma, retina, and subretinal space was quantified by high-performance liquid chromatography (HPLC) and radiotracer techniques. Taurine transport was also assessed after apical potassium concentration was lowered from 6.0 to 2.2 mM to mimic the effects of light. RESULTS: Transport of taurine across RPE-BC at a 10-mM substrate concentration increased from 32.92 before to 111.72 nanomoles/4 mm per hour after removal of the RPE. Similarly, at 50 microM taurine, transport rates increased from 0.158 to 0.439 nanomoles/4 mm per hour after removal of the RPE. At both high (10 mM) and low (50 microM) substrate concentrations, lowering of apical potassium was associated with decreased transport of taurine across the RPE. For taurine concentrations greater than 42 microM, the rate-limiting compartment for transport of taurine to the outer retina was the RPE monolayer. Similar rates were observed across each compartment for concentrations <42 microM. CONCLUSIONS: The magnitude and directionality of taurine transport across the RPE is determined solely by the driving taurine concentration gradient and is modulated by subretinal levels of potassium. Such modulation may provide a mechanism for conserving retinal taurine. Processes that increase the resistance to diffusion across Bruch's membrane such as human ageing and increased thickening and deposition of debris associated with age-related macular degeneration (AMD) are likely to affect transport across the RPE, culminating in a secondary retinal taurine deficiency.

Animals↗

PubMed2004

Taurine uptake by human retinal pigment epithelium: implications for the transport of small solutes between the choroid and the outer retina.

PURPOSE: To characterize the Michaelis-Menten kinetics of the taurine transporter (TT) in retinal pigment epithelium (RPE) freshly isolated from human donor eyes. To identify the rate limiting compartment in the pathway of taurine delivery from the choroidal blood supply to the outer retina composed by Bruch's-choroid (BC) and the RPE in the human older age group. METHODS: In human donor samples (4 melanoma-affected eyes, and 14 control eyes; age range, 62-93 years), radiochemical techniques were used to determine the RPE taurine accumulation at various exogenous concentrations. The transport capability of human RPE was obtained from a kinetic analysis of the high-affinity carrier over a substrate concentration of 1 to 60 microM taurine. RESULTS: Uptake of taurine into human RPE at a taurine concentration of 1 microM was independent of donor age (P > 0.05) and averaged at 2.83 +/- 0.27 (SEM) pmol/10 minutes per 6-mm trephine. Taurine transport by human RPE was mediated by a high-affinity carrier of K(m) 50 microM and V(max) of 267 pmol/10 minutes per 5-mm disc. CONCLUSIONS: In human donor RPE, uptake of taurine remained viable in the age range 62 to 93 years. Taurine transport rates in the RPE were lower than across the isolated BC complex, and thus the data suggest that the former compartment houses the rate-limiting step in the delivery of taurine to the outer retina.

Aged↗

PubMed2003

Human retinal molecular weight exclusion limit and estimate of species variation.

PURPOSE: To determine the maximum size of molecule capable of freely diffusing across human retina, referred to as the retinal exclusion limit (REL), and the location of any sites of high resistance to diffusion. To assess the degree of interspecies variation in the REL of three animals commonly used to model human disease. METHODS: Trephines of human neuroretina were mounted in a modified Ussing chamber. FITC-dextrans of various molecular weights (MWT) were dissolved in phosphate-buffered saline, and the rate of transretinal diffusion was determined over 24 hours with a spectrophotometer. The theoretical REL was calculated by extrapolating the linear relationship between the rate of diffusion and log(MWT). In separate experiments to determine the sites of barrier to diffusion, FITC-dextrans with a MWT greater than the calculated REL were applied to either the inner or outer retinal surface, processed as frozen sections, and viewed with a fluorescence microscope. Experiments to determine the REL were repeated in bovine, porcine, and rabbit retina. RESULTS: The REL in human tissue was 76.5+/-1.5 kDa (6.11+/-0.04 nm). The inner and outer plexiform layers formed the sites of highest resistance to diffusion. The REL in pigs, cattle, and rabbits were 60 +/- 11.5, 78.5 +/- 20.5, and 86 +/- 30 kDa, respectively (5.68 +/- 0.45, 6.18 +/- 0.61, and 6.38 +/- 0.88 nm). CONCLUSIONS: In humans, the inner and outer plexiform layers are sites of high resistance to the diffusion of large molecules, resulting in an REL of 76.5 kDa. There was only moderate interspecies variation in the REL of the animals studied, suggesting that they provide adequate models for the study of human transretinal macromolecular diffusion.

Aged↗

PubMed2003

An experimental model of rhegmatogenous retinal detachment: surgical results and glial cell response.

PURPOSE: To modify existing experimental models to simulate the typical clinical presentation of human rhegmatogenous retinal detachment (RRD), namely an RD caused by a retinal break, in a phakic eye, with a posterior vitreous detachment (PVD); to model RRD in a species that is anatomically similar to humans; and to characterize the glial cell response to RRD. METHODS: Mixed-breed pigs underwent vitrectomy, PVD, subretinal injection of viscoelastic, and creation of a break at the apex of the RD. The crystalline lens was not removed. Follow-up was for 0, 1, and 7 days. Tissue was processed for light and electron microscopy. The glial cell response was characterized using antibodies to glial fibrillary acidic protein (GFAP). RESULTS: Of 11 RRDs created in seven pigs, 10 increased in size and 1 decreased. Light and electron microscopy demonstrated typical features of RD. There was constitutive expression of GFAP in astrocytes and Müller cells with increased immunoreactivity from day 1. CONCLUSIONS: This study provided a model of RRD that simulates the typical clinical presentation in humans. It used techniques that most vitreoretinal surgeons are familiar with, and an animal that is widely available and anatomically similar to humans. Anatomic success was high, and the glial cell response established comparability with other species.

Animals↗

PubMed2002

The effects of cidofovir 1% with and without cyclosporin a 1% as a topical treatment of acute adenoviral keratoconjunctivitis: a controlled clinical pilot study.

OBJECTIVE: To evaluate the efficacy of cidofovir 1% eyedrops with and without cyclosporin A 1% eyedrops as a treatment of acute adenoviral keratoconjunctivitis (AKC). DESIGN: Randomized, controlled trial. PARTICIPANTS: Thirty-four patients with acute adenoviral keratoconjunctivitis of recent onset. METHODS: Patients were divided into 4 treatment groups: 1) cidofovir four times daily, 2) cidofovir 10 times daily, 3) cidofovir four times daily and cyclosporin A four times daily, and 4) sodium chloride four times daily (control). The diagnosis was confirmed by adenoviral polymerase chain reaction from conjunctival swabs. Duration of treatment was 21 days. MAIN OUTCOME MEASURES: Severity of conjunctival injection, conjunctival chemosis, punctate epithelial keratitis during the course of treatment, and presence and severity of corneal subepithelial infiltrates were evaluated by a clinical score. Duration until subjective improvement of symptoms was recorded. RESULTS: The frequency of severe corneal opacities was lower with cidofovir (P = 0.048). Cidofovir was toxic locally to the skin of the eyelids and the conjunctiva in a dose-dependent manner. Symptoms of local toxicity were clinically similar to the signs of the initial viral inflammation. They first appeared 8 to 12 days after beginning of treatment and completely subsided 7 to 28 days after discontinuation of cidofovir. The outcome measures of local inflammation did not differ between the four treatment groups. Cyclosporin A did not alter the course of the infection. CONCLUSIONS: Cidofovir lowers the frequency of severe corneal opacities, but its clinical use 4 to 10 times daily at a 1% concentration is limited by local toxicity. Further clinical studies to find an efficacious yet tolerable dosage regimen of cidofovir, possibly using an improved pharmaceutical preparation, are required.

Acute Disease↗