Functionality of night vision spectacles for night blind people

Night blindness Night blindness is a functional impairment due to a lack of light sensitivity of the retina and can be congenital or caused by a degenerative process. Most subjects suffering from the degenerative type experience the loss of night vision earlier than loss of visual acuity or visual field. Night blindness and daily life Being not or slightly visually impaired in day light conditions, a night-blind subject perceives the outdoor environment after sunset as almost completely dark, even under standard street lighting conditions. This seriously hampers orientation and secure mobility. The disability to travel independently and safely after sunset severely limit the opportunities to participate in normal life. For outdoor use a luminance-enhancing device seems to be useful and to offer the opportunity to perceive enough details to travel independently. In earlier days this concept has been proposed, but the devices (either handheld or mounted in a helmet) were rather bulky and did not satisfy the daily needs of the night-blind people (Berson et al. 1973ab) Night vision device Recently a European consortium developed a compact night vision system, called NiViS2. The size of NiViS2 is comparable to ski goggles, combined with a separate control box (600 gram, including accu-pack). The image of the integrated video camera is viewed as a bright image on the built-in binocular monitor system displays. A built-in infrared light source can illuminate dark environments. Two studies on this device are published (Rohrschneider et al, 2000; Friedburg et al, 1999). Aim and key objectives of the test The aim of this research project is to assess the benefit of the use of a night vision device in orientation and mobility by night-blind people in everyday life. Our key objectives are to get answers on the following questions: 1. is a night vision device adequately helpful to cover a route in the evening outside the direct and familiar environment (town centre, residential area).2. do night-blind people feel themselves more independent and safe by the use of the night vision device.3. do subjects benefit from the use of a night vision device in the long-term. Approach We will start with tests of orientation and mobility of night-blind participants in dim lit laboratory conditions and in real outdoor environments, without and with the use of NiViS2. Additionally during the consecutive four weeks the subjects practice the application of NiViS2 and receive weekly mobility instruction and support of a professional mobility trainer. During that period the subjects will register the use of NiViS2 in their own environment. At the end the orientation and mobility tests will be repeated. Subjects who perform better by the use of NiViS2 and are willing to use it in everyday life will get it permanently. After one year (related to the expected low need of use in summer) the subjects will be interviewed about the use of NiViS2, especially in the new winter season. Innovative elements This study differs from former 'night-vision spectacles' studies as it delivers extended instructions of use and it evaluates the effect of prolonged use.Former studies assessed the influence of the spectacles on vision in the laboratory and the subjective visual impression without and with night vision spectacles while walking along an urban route. However no data on mobility performance on the outdoor routes are provided, except "Von den 37 Patienten, bei denen Erprobung im Freien durchgeführt wurde, konnten sich 21 gut mit dem Nachtsichtgerät orientieren, weiter 7 Patienten konnten sich einigermaßen orientieren.". Finally the participants in that study were asked whether they would accept night-vision spectacles as a mobility aid.We expect that initial enthusiasm about the device or embarrassment to walk around with the device prevent a reliable judgement of the value of the device in everyday life. Our study with a four-week and twelve-month evaluation will present data about the long term use and benefit of the night-vision spectacles.This project will show the strong and weak aspects of the device during the tests and in long-term everyday use. This is important information to be used to improve the design of future developments of night-vision spectacles. For the time being the results of the experiments will indicate the value of night vision spectacles for people's participation; not just a short impression, but at the long run. If the device proves to have a positive influence on participation it's worth to be prescribed by the rehabilitation institute and reimbursed (for instance by a health insurance) from that time on. To differentiate between the effect of prolonged use and the additional instruction as we provide in this study, a control group should be included. This implicates that the number of first and final test sessions has to be doubled. Our design without control group implicates already that the post-doc will perform tests on participants 4 times a week during the whole winter season. Inclusion of a control group would imply the need for more test capacity. However the size of the research team prevents the use of this design. Therefore we prefer to test primarily the potential usefulness of the nigh-sight spectacles; the need for training can be tested later on in new and more extensive study.