Referral for rehabilitation in case of permanent visual handicap:guideline of the Dutch Society of Ophthalmology

The Dutch Society of Ophthalmology (NOG) has developed an evidence-based guideline for the referral of visually impaired people for rehabilitation and support. Referral for rehabilitation and support must be preceded by diagnosis and treatment. Consultation of an ophthalmologist is essential. Information about the disease should be given to the patient orally as well as in writing. The ophthalmologist brings up the possibility of rehabilitation in the presence of a visual acuity &lt; 0.5 and/or visual field of &lt; 30 degrees in the better eye and a well-defined request for help. Visually impaired patients with a relatively simple request for help are referred to a specialised optometrist whenever possible. Visually impaired patients with more complex requests for help are referred to a multidisciplinary (regional or national) rehabilitation centre for people with a visual handicap. Visually impaired and blind patients are informed about the existence of patient organisations. Referral for rehabilitation is done by means of a structured letter with all relevant information. A copy of this letter should be sent to the family physician and all other attending physicians.</p

Visuele beperkingen bij ouderen in Nederland – risicogroepen en mogelijkheden tot interventie

Doel Het in kaart brengen van het aantal ouderen met een visuele beperking in Nederland, nu en in de toekomst. Mogelijkheden tot interventie worden aangegeven. Methode en materiaal De schattingen zijn gebaseerd op een recent onderzoek in opdracht van Stichting InZicht, ZonMw, waarin literatuur gegevens over prevalentie van blindheid en slechtziendheid en de oorzaken daarvan uit bevolkingsonderzoeken in Nederland, West Europa, de Verenigde Staten en Australië zijn gerelateerd aan de laatste demografische gegevens voor Nederland. Resultaten Van de 16,4 miljoen Nederlanders in 2008 zijn er 2,4 miljoen (14,7%) 65 jaar of ouder. Van deze laatste groep wonen 155.000 mensen in een verpleeg of verzorgingshuis, de rest woont zelfstandig. In 2008 zijn naar schatting 77.000 Nederlanders blind en 234.000 slechtziend. Van hen is 79% 65 jaar of ouder. Van de ouderen in instellingen is 20% blind (32.000) en 22% slechtziend (34.000). Bij 62% van hen is de visuele beperking te behandelen of was te voorkomen geweest (‘vermijdbaar’). Van de zelfstandig wonende ouderen is 1,2% blind (27.000) en 6,8% slechtziend (154.000). Bij 57% van hen is de aandoening vermijdbaar. Conclusie In 2008 hebben 247.000 ouderen een visuele beperking die bij 143.000 (58%) van hen te behandelen is of te voorkomen was geweest. Screening en behandeling van ouderen in instellingen lijkt aangewezen, evenals voorlichting aan en gerichte screening van zelfstandig wonende ouderen

Effective and Efficient Stand Magnifier Use in Visually Impaired Children

Contains fulltext : 167758.pdf (publisher's version ) (Open Access)PURPOSE: The main objective of this study was to analyze the effectiveness and efficiency of magnifier use in children with visual impairment who did not use a low vision aid earlier, in an ecologically valid goal-directed perceptuomotor task. METHODS: Participants were twenty-nine 4- to 8-year-old children with visual impairment and 47 age-matched children with normal vision. After seeing a first symbol (an Lea Hyvarinen [LH] symbol), children were instructed to (1) move the stand magnifier as quickly as possible toward a small target symbol (another LH symbol that could only be seen by using the magnifier), (2) compare the two symbols, and (3) move the magnifier to one of two response areas to indicate whether the two symbols were identical. Performance was measured in terms of accuracy, response time, identification time, and movement time. Viewing distance, as well as hand and eye dominance while using the magnifier was assessed. RESULTS: There were no significant differences between the two groups in accuracy, reaction time, and movement time. Contrary to the prediction, children with visual impairment required less time to identify small symbols than children with normal vision. Both within-subject and between-subject variability in viewing distance were smaller in the visually impaired group than in the normally sighted group. In the visually impaired group, a larger viewing distance was associated with shorter identification time, which in turn was associated with higher accuracy. In the normally sighted group, a faster movement with the magnifier and a faster identification were associated with increasing age. CONCLUSION: The findings indicate that children with visual impairment can use the stand magnifier adequately and efficiently. The normally sighted children show an age-related development in movement time and identification time and show more variability in viewing distance, which is not found in visually impaired children. Visually impaired children seem to choose a standard but less adaptive strategy in which they primarily used their preferred hand to manipulate the magnifier and their preferred eye to identify the symbol. TRIAL REGISTRATION: Registered at http://www.trialregister.nl; NTR2380.11 p

Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence

The cross section for coherent pair production by linearly polarised photons in the 20-170 GeV energy range was measured for photon aligned incidence on ultra-high quality diamond and germanium crystals. The theoretical description of coherent bremsstrahlung and coherent pair production phenomena is an area of active theoretical debate and development. However, under our experimental conditions, the theory predicted the combined cross section and polarisation experimental observables very well indeed. In macroscopic terms, our experiment measured a birefringence effect in pair production in a crystal. This study of this effect also constituted a measurement of the energy dependent linear polarisation of photons produced by coherent bremsstrahlung in aligned crystals. New technologies for manipulating high energy photon beams can be realised based on an improved understanding of QED phenomena at these energies. In particular, this experiment demonstrates an efficient new polarimetry technique. The pair production measurements were done using two independent methods simultaneously. The more complex method using a magnet spectrometer showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for publicatio

Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons

We present the first experimental results on the use of a thick aligned Si crystal acting as a quarter wave plate to induce a degree of circular polarisation in a high energy linearly polarised photon beam. The linearly polarised photon beam is produced from coherent bremsstrahlung radiation by 178 GeV unpolarised electrons incident on an aligned Si crystal, acting as a radiator. The linear polarisation of the photon beam is characterised by measuring the asymmetry in electron-positron pair production in a Ge crystal, for different crystal orientations. The Ge crystal therefore acts as an analyser. The birefringence phenomenon, which converts the linear polarisation to circular polarisation, is observed by letting the linearly polarised photons beam pass through a thick Si quarter wave plate crystal, and then measuring the asymmetry in electron-positron pair production again for a selection of relative angles between the crystallographic planes of the radiator, analyser and quarter wave plate. The systematics of the difference between the measured asymmetries with and without the quarter wave plate are predicted by theory to reveal an evolution in the Stokes parameters from which the appearance of a circularly polarised component in the photon beam can be demonstrated. The measured magnitude of the circularly polarised component was consistent with the theoretical predictions, and therefore is in indication of the existence of the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for publicatio

Results on the Coherent Interaction of High Energy Electrons and Photons in Oriented Single Crystals

The CERN-NA-59 experiment examined a wide range of electromagnetic processes for multi-GeV electrons and photons interacting with oriented single crystals. The various types of crystals and their orientations were used for producing photon beams and for converting and measuring their polarisation. The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised photon beams. A new crystal polarimetry technique was established for measuring the linear polarisation of the photon beam. The polarimeter is based on the dependence of the Coherent Pair Production (CPP) cross section in oriented single crystals on the direction of the photon polarisation with respect to the crystal plane. Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set of synthetic Diamond crystals were used as analyzers of the linear polarisation. A birefringence phenomenon, the conversion of the linear polarisation of the photon beam into circular polarisation, was observed. This was achieved by letting the linearly polarised photon beam pass through a 10 cm thick Silicon single crystal that acted as a "quarter wave plate" (QWP) as suggested by N. Cabibbo et al.Comment: Presented at International workshop "Relativistic Channeling and Related Coherent Phenomena", Frascati (Rome) 23-26 March 200

Coherent bremsstrahlung, boherent pair production, birefringence and polarimetry in the 20-170 GeV energy range using aligned crystals

The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20-170 GeV. The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences. This is significant as the theoretical description of CB and CPP is an area of active theoretical debate and development. With the theoretical approach used in this paper both the measured cross sections and polarization observables are predicted very well. This indicates a proper understanding of CB and CPP up to energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements. New technologies for high energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment. Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal. Our measurements and our calculations indicate low photon polarizations for the high energy SOS photons.Comment: 23 pages, 27 figures, 2 tables, REVTeX4 two column