The Retina Implant New Approach to a Visual Prosthesis / Das Retina-Implant Ein neuer Ansatz für eine Sehprothese

Currently, no treatment is available for degenerative diseases of retinal photoreceptors. The patients are faced with a high risk of blindness. Biological approaches failed to prove efficacy. A new concept for the treatment of disorders like retinitis pigmentosa is electrical stimulation at various levels of the visual system. Therefore, devices were fabricated with stimulating electrodes contacting retinal or central neurons to elicit biological activity in these cells. It became possible to fabricate even complex devices with an external power supply encapsulated within biocompatible materials. Animal experiments showed that with implanted prototypes cortical activation could be achieved and first experiments in blind human subject also suggest that vision can be restored, however at present in a very low range of simply identifying spots of light. Further developments and also the continuation of animal experiments are necessary before the clinical application will become a standard procedure.

Retinectomy for treatment of intractable glaucoma: long term results

AIM

To report long term efficacy and complications of retinectomy as an intraocular pressure lowering procedure for intractable glaucoma.

METHODS

This was a consecutive interventional case series. In 44 consecutive eyes (39 patients, 22 men and 17 women) retinectomy was performed to lower the intraocular pressure (IOP) in patients with uncontrolled IOP (>35 mm Hg for more than 4 months) despite conventional filtering surgery and drug treatment. Pars plana vitrectomy was performed and the peripheral retina was surgically excised to various degrees. The procedure was concluded by an intraocular gas tamponade of 20% C(3)F(8). Included were patients with neovascular glaucoma (12 eyes), infantile and juvenile glaucoma (three eyes), secondary glaucoma due to aphakia (13 eyes), severe ocular trauma (seven eyes), uveitis (seven eyes), and glaucoma in Ehlers-Danlos syndrome (two).

RESULTS

All patients underwent successful surgical retinectomy. All patients were followed for 5 years. Mean postoperative IOP after 4 years was 15.7 (SD 9.4) mm Hg, representing a decrease of IOP by 61% compared to the preoperative level (41.2 (9.4) mm Hg). In 52.3% of eyes long term regulation of IOP could be achieved without complications. Retinectomy was least effective in neovascular glaucoma because of central retinal vein occlusion (CRVO). Eyes with glaucoma secondary to uveitis showed a tendency towards low IOP levels with subsequent phthisis bulbi. The initial visual acuity of all patients was lower than 20/50 (mean 1.8 (0.8) logMAR) in the treated eye. Final visual acuity was 2.3 (0.6) logMAR. 21 out of 44 cases developed retinal complications (retinal detachment or proliferative vitreoretinopathy (PVR)) after surgery, requiring silicone tamponade in 11 eyes (52%) either for persistent low IOP or for PVR. Nine eyes developed phthisis, seven of which were enucleated during the follow up.

CONCLUSIONS

Long term results after retinectomy demonstrate its efficacy in otherwise intractable glaucoma. Efficacy and safety of retinectomy are dependent on the underlying disease.

Microbeam synchrotron imaging of hairs from ancient Egyptian mummies

Developments in microfocus synchrotron techniques have led to new results regarding the long-term alteration of archaeological samples of biological origin. Here, ancient hair samples from two Egyptian mummies have been analyzed using a conjunction of structural and elemental synchrotron methods. In this favored context of conservation, structural analysis revealed a remarkable preservation of keratin supramolecular organization at any observed length scale. Bulk keratin structure has therefore not been modified significantly over 2000 years. However, infrared spectroscopy indicated a partial disorganization of keratins close to the hair surface through polypeptide bond breakage. Elemental mapping showed a strongly heterogeneous distribution which can be related to mummification and cosmetic treatments.

Clinicopathological correlation of choroidal neovascularization after external beam radiotherapy in age-related macular degeneration

PURPOSE

To analyze the histopathology of choroidal neovascularization after external beam radiotherapy in age-related macular degeneration.

METHODS

A retrospective non-case-matched comparative histopathologic study. The histoarchitecture of nine surgically removed subretinal specimens from nine patients that had undergone external beam radiotherapy for exudative age-related macular degeneration was studied. Seven patients had received 20 Gy in 10 fractions and two 15 Gy in 5 fractions with an average time interval between radiotherapy and surgical extraction of 14 months (range 3-28). A consecutive series of classic, mixed and occult choroidal neovascular membranes served as controls.

RESULTS

Clinical findings. Radiation-associated choroidal neovasculopathy was angiographically suspected in four patients: a coarse net of vessels on fluorescein angiography developing at the border of previously irradiated choroidal neovascularization was observed in three patients; blebs at the margin of a plaque on indocyanine green angiography were observed in two patients. Pathological findings. Diffuse drusen as well as intra-Bruch's fibrovascular tissue was found in all irradiated specimens. In four specimens an edematous vascularized layer was seen between diffuse drusen and normal-appearing intra-Bruch's fibrovascular tissue. This lesion was not found in the control specimens. A particular correlation for the bleb lesion was not recognized.

CONCLUSION

The appearance of an edematous subretinal pigment epithelial vascularized layer between diffuse drusen and normal-appearing fibrovascular tissue in four of nine irradiated membranes may be secondary to previous irradiation. It may correlate with the unusual exudative manifestations observed after external beam radiotherapy.

Lead-revealed lipid organization in human hair

Human hair lipids form a complex mixture of composition close to that of sebum. Part of these lipids appears in an organized state that has been studied by diffraction techniques in the literature. Nevertheless, information on the structure of these lipids remains very scarce due to their low contribution to global hair diffraction pattern. Here we show that appropriate lead treatment considerably enhances organized lipid features observed by microbeam synchrotron radiation diffraction experiments. We attribute these features to the formation of lead soaps of free fatty acids. Specific orientation of hair "lipid crystals" in planes parallel to the hair axis is clearly demonstrated. Inclusion of these lipids in the bulk of the hair shaft is shown by diffraction experiments following removal of the cuticular outermost layer of hair. Moreover, microfluorescence and diffraction experiments are consistent with part of the lipids being present as calcium soaps in native hair. We therefore consider lead fixation as a powerful tool to evaluate the lipid organization in human hair for medical, environmental and archaeological purposes, including lead poisoning.

Biocompatibility tests on the intraocular vision aid IOVA

Intraocular miniaturized image transmission systems are developed to restore vision in patients with irreversible destruction of the anterior ocular segment (i.e. chemical burns, explosion trauma, trachoma) and high risk for corneal transplantation, provided that the posterior ocular segment is intact. To ensure safety of such a device biocompatibility tests were conducted. In the present study the effects of light and temperature in various intensities and the toxicity of the implanted materials on neural function in the rabbit retina in-vivo was investigated. All tests give encouraging results concerning the feasibility of intraocular miniaturized image transmission systems.

[Medical aspects of active implants in the eye]

Due to progress in miniaturizing complex electronic systems the development of intraocular sensors and stimulators is feasible. The Retina Implant will restore vision in patients with progressive retinal degenerations by means of electrical stimulation of retinal neurons, e.g. in Retinitis pigmentosa. After severe destructions of the anterior segment with intact retina, e.g. after explosion trauma an intraocular display will restore vision. In glaucoma patients the implantation of a telemetric pressure sensor will help to optimise the management of each individual patient. Pressure profiles under everyday conditions will become available. These active implants will open new perspectives in treatment and diagnostics in ophthalmology.

X-ray-induced debromination of nucleic acids at the Br K absorption edge and implications for MAD phasing

Multi-wavelength anomalous dispersion (MAD) using brominated derivatives is considered a common and convenient technique for solving chemically synthesized nucleic acid structures. Here, it is shown that a relatively moderate X-ray dose (of the order of 5 x 10(15) photons mm(-2)) can induce sufficient debromination to prevent structure determination. The decrease in bromine occupancy with radiation dose can be accounted for by a simple exponential, with an estimated rate constant at the absorption-peak wavelength, 7.4 (0.8) MGy, that is not significantly different from its value at the absorption-edge wavelength, 9.2 (2.6) MGy (the given e.s.d.s assess the relative closeness of the two values, not their absolute accuracy, which is probably worse). Chemically, these results (and others) are consistent with bromine cleavage resulting from direct photodissociation and/or from the action of free electrons, rather than from the action of hydroxyl radicals originating from water dissociation. The free bromine species (Br(-)) diffuse too quickly, even in amorphous ice around 100 K, to allow the determination of a diffusion coefficient. From a practical point of view, it is suggested that a single data collection with a crystal consisting of iodinated instead of brominated derivatives could provide both anomalous scattering and SIR phase information by the progressive cleavage of iodine.

Clinicopathologic correlation in hemorrhagic age-related macular degeneration

PURPOSE

To analyze and compare the histopathology of surgically extracted membranes in hemorrhagic age-related macular degeneration (AMD) versus extracted classic, mixed and occult choroidal neovascularization (CNV) in AMD.

METHODS

Thirty consecutive membranes, surgically removed in hemorrhagic AMD, were analyzed and compared with consecutive series of 50 classic, 20 mixed and 20 occult membrane specimens in exudative AMD. The specimens were serially sectioned and stained in a stepped fashion with hematoxylin-eosin, Masson trichrome and periodic acid-Schiff stain.

RESULTS

Diffuse drusen were observed in all hemorrhagic AMD specimens, fibrovascular tissue was found in 29 of 30 specimens which was located subretinally in 11 specimens and/or in Bruch's membrane in 28 specimens. A hemorrhage was located subretinally in 21 specimens, in the stroma of the fibrovascular tissue in 17 specimens, at the choroidal side of the diffuse drusen adjacent to fibrovascular tissue in 13 specimens and at the choroidal side of the fibrovascular tissue in Bruch's membrane in 8 specimens. Grossly dilated thin-walled vessels were identified in one hemorrhagic AMD case, suggestive of polypoidal choroidal vasculopathy. Scarred tears of the retinal pigment epithelium were identified in two specimens.

CONCLUSION

A large spectrum of histo-architectural lesions is recognized in hemorrhagic maculopathy. Hemorrhages do not only characteristically appear in the subretinal space or in the stroma of the neovascular tissue but also at the choroidal side of the diffuse drusen adjacent to the neovascular complex and at the choroidal side of the intra-Bruch's fibrovascular tissue.

The signal recognition particle

The signal recognition particle (SRP) and its membrane-associated receptor (SR) catalyze targeting of nascent secretory and membrane proteins to the protein translocation apparatus of the cell. Components of the SRP pathway and salient features of the molecular mechanism of SRP-dependent protein targeting are conserved in all three kingdoms of life. Recent advances in the structure determination of a number of key components in the eukaryotic and prokaryotic SRP pathway provide new insight into the molecular basis of SRP function, and they set the stage for future work toward an integrated picture that takes into account the dynamic and contextual properties of this remarkable cellular machine.

[Macular translocation with 360 degree retinotomy in the treatment if exudative macular degeneration. Functional and angiographic results]

BACKGROUND

During surgical extraction of choroidal neovascular membranes (CNV) in age-related macular degeneration (AMD), the defective foveal retinal pigment epithelium (RPE) is removed. Subsequent translocation of the foveal neural retina to adjacent healthy RPE should result in stabilization and possibly improvement of visual acuity.

METHODS

A prospective case series was carried out using controlled surgery and examination protocols with examinations made at fixed intervals. The surgical procedures combine counterrotation of the globe, phacoemulsification and implantation of a posterior chamber lens, complete vitrectomy, induction of a total retinal detachment, 360 degrees anterior retinotomy, removal of the subfoveal neovascular complex, foveal translocation outside the RPE defect, reattachment of the retina using F6H8, peripheral laser retinopexy and temporary silicone oil tamponade.

PATIENTS

Macular translocation surgery was performed on 100 patients between December 1997 and December 1999. All patients had experienced recent visual loss due to exudative AMD and of these, 26 patients had major macular subretinal hemorrhage, 39 patients had occult and 25 patients classic subfoveal choroidal neovascularization. The preoperative findings in the remaining patients included tears in the pigment epithelium (n = 4), polypoidal choroidal vasculopathy (n = 1), recurrent subfoveal CNV following laser therapy (n = 2) and deep retinal vascular anomalous complexes (n = 3).

RESULTS

A total of 97 patients completed the 12-month examination. Visual acuity increased by 15 or more ETDRS chart letters in 24 patients, remained stable in 42 patients and deteriorated by 15 or more EDTRS chart letters in 34 patients 12 months postoperatively. The silicone oil tamponade was removed in 97 patients, in 10 patients, silicone oil had to be reinjected because of severe complications. A secondary procedure was necessary in 25 patients, primary PVR was observed in 9 eyes, secondary PVR developed in 10 eyes, a macular pucker in 5 eyes and a macular hole in 1 patient. Other postoperative complications included persistent hypotonia, macular edema, IOL dislocation, keratopathy and recurrent CNV (n = 3).

CONCLUSIONS

Macular translocation is a technically demanding operation, which requires a considerable learning curve. Although the procedure has a high rate of surgical and postoperative complications, the functional and anatomical results appear to be promising for selected patients with subfoveal CNV secondary to AMD.

[Surgical procedures in the treatment of age-related macular degeneration]

The surgical techniques for removal of a subretinal membrane associated with age-related macular degeneration will be discussed and compared on the basis of published data. The so-called simple subretinal membrane extraction will be compared with pigment epithelium cell transplantation and with the various techniques for macular translocation. The pars plana gas injection with tissue plasminogen activator procedure will also be mentioned. Because a controlled trial with a sufficient number of patients and follow-up has not been carried out for any of these techniques, the results of published case series will be used for this review.

Cystic meningioma: challenges in the diagnosis

A patient with an unusual cystic meningioma is described. The pathophysiology of cyst formation is discussed.

The emergence of different resistance mechanisms toward nucleoside inhibitors is explained by the properties of the wild type HIV-1 reverse transcriptase

Nucleoside reverse transcriptase inhibitors (NRTIs) represent one of the main drug families used against AIDS. Once incorporated in DNA, they act as chain terminators, due to the lack of a 3'-hydroxyl group. As for the other anti-human immunodeficiency virus type 1 drugs, their efficiency is limited by the emergence of resistant viral strains. Unexpectedly, previous studies indicated that resistance toward NRTIs is achieved via two distinct and generally exclusive mechanisms. Resistance mutations either decrease the efficiency of NRTIs incorporation or increase their excision from the extended primer. To understand the emergence of different resistance mechanisms toward a single inhibitor class, we compared the incorporation and the pyrophosphorolysis of several NRTIs using wild type reverse transcriptase (WT RT). We found that the efficiency of discrimination or excision by pyrophosphorolysis in the presence of nucleotides of a given NRTI is a key determinant in the emergence of one or the other resistance pathway. Indeed, our results suggest that the pathway by which RT become resistant toward a given NRTI can be predicted by studying the inhibition of WT RT, because the resistance mutations do not confer new properties to the mutant enzyme, but rather exacerbate pre-existing properties of the WT enzyme. They also help to understand the low cross-resistance toward d4T observed with the 3'-azido-3'-deoxythymidine (AZT or zidovudine)-resistant RT.

Role of SRP RNA in the GTPase cycles of Ffh and FtsY

The bacterial homologues of the signal recognition particle (SRP) and its receptor, the Ffh*4.5S RNA ribonucleoprotein complex and the FtsY protein, respectively, form a unique complex in which both Ffh and FtsY act as GTPase activating proteins for one another, resulting in the mutual stimulation of GTP hydrolysis by both proteins. Previous work showed that 4.5S RNA enhances the GTPase activity in the presence of both Ffh and FtsY, but it was not clear how this was accomplished. In this work, kinetic and thermodynamic analyses of the GTPase reactions of Ffh and FtsY have provided insights into the role of 4.5S RNA in the GTPase cycles of Ffh and FtsY. We found that 4.5S RNA accelerates the association between Ffh and FtsY 400-fold in their GTP-bound form, analogous to its 200-fold catalytic effect on Ffh*FtsY association previously observed with the GppNHp-bound form [Peluso, P., et al. (2000) Science 288, 1640-1643]. Further, Ffh-FtsY association is rate-limiting for the observed GTPase reaction with subsaturating Ffh and FtsY, thereby accounting for the apparent stimulatory effect of 4.5S RNA on the GTPase activity observed previously. An additional step, GTP hydrolysis from the Ffh*FtsY complex, is also moderately facilitated by 4.5S RNA. These results suggest that 4.5S RNA modulates the conformation of the Ffh*FtsY complex and may, in turn, regulate its GTPase activity during the SRP functional cycle.

Crystal structures of coaxially stacked kissing complexes of the HIV-1 RNA dimerization initiation site

We describe the crystal structures of the RNA dimerization initiation sites (DIS) of HIV-1 subtypes A and B. Both molecules adopt a hairpin conformation, with loop sequences consisting of 272-AGGUGCACA-280 and 272-AAGCGCGCA-280, respectively. This includes a six-base self-complementary stretch (underlined) that allows homodimerization through the formation of a loop-loop, or 'kissing-loop', complex. The DISs for the two sequences have identical conformations, and the two interacting hairpins show a perfect coaxial alignment. The conserved purines, A272 and R273, are stacked in a bulged-out conformation and symmetrically join the upward and downward strands of each hairpin by crossing the helix major groove. There is good agreement between these structures and previous results from chemical probing in solution, as well as with differences in magnesium dependence for dimerization. The overall shape of the kissing-loop complex is very similar to that of the previously determined subtype A DIS duplex form. Unexpectedly, the purine R273 is the only base seen at a different position and is responsible for the difference in topology between the two forms. We propose that the transition from kissing-loop duplex could occur by a recombination mechanism based on symmetrical chain cleavage at R273 of each hairpin and subsequent cross-religation, rather than by base-pair melting and subsequent reannealing.

[Chemistry of cosmetics in antiquity]

Several texts, statues and paintings denote the importance of make up and eye medicines since the earliest periods of Egyptian history. We have investigated cosmetic powders that were preserved in original alabaster and reed containers. Quantitative crystallographic and chemical analysis of the mineral and organic components revealed surprising facts. In addition to the well known galena PbS and cerussite PbCO3, two unexpected constituents have been identified: laurionite PbOHCl and phosgenite Pb2 (CO3) Cl2, which are rare halide minerals found in lead slag only in certain places where the sea water has weathered lead debris left over from silver mining operations in Antiquity. Alteration of natural lead minerals is also unlikely, given the excellent state of conservation of the reed vessels. This evidence indicates that laurionite and phosgenite were synthesised artificially. Support for this statement comes from recipes of medicinal products to be "used in ophthalmology" reported by Greco-Roman authors such as Dioscorides and Pline (1st Century B.C.): silver foam PbO is crushed and mixed with rock salt and sometimes with natron (Na2CO3). The reaction seems to be straightforward. However, our experiments in the laboratory have shown a major difficulty, arising from the concomitant production of alkali, which raises the pH and leads to different products. It follows that the Egyptians very early mastered this kind of chemical synthesis and technology, a fact of great importance in the History of Sciences. Fire-based technology had been mastered to manufacture Egyptian Blue pigments since the third millennium B.C. The present results now suggest that wet chemistry was already known 4000 years ago. This key finding provides a new insight into the chemical technology of far greater antiquity than has previously been believed. Yet, an important question remains relative to the ultimate motivation for these technological developments. If the Egyptians initially only aimed at different nuances of grey, they could use cerussite, an easily accessible mineral, crushed and mixed with galena. Thus, one should seek other motivations; we shall propose to consider a religious-ritual context, ultimately linked to a pharmaceutical aspect.

High-throughput evaluation of olefin copolymer composition by means of attenuated total reflection Fourier tranform infrared spectroscopy

As a consequence of developing fully automated reactors for organic and organometallic synthesis and polymerizations combined with rapid on-line analysis, databases, and data mining, the analysis of polymers with respect to composition and properties has been speeded up. High-throughput evaluation of olefin copolymers requires fast measurements and high accuracy without tedious sample preparation such as pressing KBr pellets. This has been achieved by using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR spectroscopy) in conjunction with multivariate calibration in order to determine the composition of olefin copolymers such as ethene/propene, ethene/1-hexene and ethene/1-octene copolymers.