[Superior-canal dehiscence syndrome]. / Het 'superior-canal dehiscence'-syndroom.

Superior-canal dehiscence syndrome (SCDS) was first described in 1998; it manifests as symptoms of dizziness and oscillopsia when a sound or pressure stimulus is given to the ear concerned. SCDS is caused by dehiscence ofpetrosal bone overlying the superior, vertical semicircular canal, creating a 'third mobile window' to the labyrinth, in addition to the oval and round windows. Characteristic for this syndrome are eye movements with a vertical-torsion direction, evoked by sound stimuli, or pressure changes via the external ear canal and the Valsalva manoeuvre. The anomaly of the bony structure is visible on a CT scan. With its specific symptoms and characteristics, SCDS is an abnormality of the vestibular system that is relatively easy to diagnose. The syndrome may be treated with conservative or surgical means.

Angular and linear vestibulo-ocular responses in humans.

A new technique is introduced to measure linear and angular vestibulo-ocular responses in three dimensions. Using a three-dimensional motion platform, human subjects underwent whole-body rotations and translations. Eye movements were measured with an infrared video recording device and/or with scleral search coils. Subjects were tested with sinusoidal stimulation and impulses under light and dark conditions. The results show that for sinusoidal stimulation, torsion compensatory eye movements (roll stimulation) have a low gain compared to horizontal (yaw) and vertical (pitch) compensatory eye movements. With impulses, we reliably assessed gain and delay for rotations in yaw, pitch, and roll. Under this stimulus condition the gain for roll (torsion eye movements) was also low compared to yaw and pitch (horizontal and vertical eye movements). For translations, the gain of eye-movement responses varied between 0.7 and 1 in the light. In the dark, responses were lower and more variable.

The building materials decree: an example of a Dutch regulation based on the potential impact of materials on the environment.

Some 20 years ago Dutch society became very aware of the problem of the increasing production of waste materials and of the need to find solutions. Technical solutions had to be developed and introduced into society. Due to the discovery of many soil pollution problems and other environmental calamities, people asked for clear criteria on which proper and safe solutions could be based. Therefore a large number of environmental aspects had to be taken into account in the developing field of environmental policy. The Dutch building materials decree is one of the steps on the road towards a sustainable society. The decree is based on the soil protection act and the surface water protection act. The decree gives quality criteria for the application and re-use of stony materials and earth used as building materials. No difference is made between primary materials, secondary materials and waste materials. The decree is applicable in case these materials are used in constructions where they are in contact with rain, surface water and ground water (e.g. in embankments, road building, outside walls of buildings, foundations and roofs). For implementation of the decree in the construction industry it was necessary to develop standards, methods for testing and certification schemes. In order to guarantee independent testing and judgement, laboratories had to meet quality standards put forward in an accreditation scheme. Although this legislation does not cover all environmental aspects, it has proved to be an important element in judging the environmental quality of construction materials in a direct or indirect way, and a contribution to the management of waste materials. The question of clear and fair criteria was easily put forward. Answering this question, however, turned out to be a complex task in which a great number of aspects had to be considered and a great many tools had to be developed, checked and thoroughly discussed. In some cases practical choices had to be made in order to prevent an unclear situation continuing too long. After an introduction period of three years, the decree came into full operation on 1 July 1999.