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Geometric dimensioning and tolerancing ( GD&T) is a system for defining and communicating engineering tolerances via a symbolic language on engineering drawings and computer-generated 3D models that describes a physical object's nominal geometry and the permissible variation thereof. GD&T is used to define the nominal (theoretically perfect ...
The prism fusion range ( PFR) or fusional vergence amplitude is a clinical eye test performed by orthoptists, optometrists, and ophthalmologists to assess motor fusion, specifically the extent to which a patient can maintain binocular single vision ( BSV) in the presence of increasing vergence demands. Motor fusion is largely accounted to ...
Level (optical instrument) A level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling. It is used in conjunction with a levelling staff to establish the relative height or levels (the vertical separation) of objects or marks. It is widely used in surveying and construction to ...
Engineering tolerance is the permissible limit or limits of variation in: a physical dimension; a measured value or physical property of a material, manufactured object, system, or service; other measured values (such as temperature, humidity, etc.); in engineering and safety, a physical distance or space (tolerance), as in a truck (lorry ...
Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]
An oblique prism is a prism in which the joining edges and faces are not perpendicular to the base faces. Example: a parallelepiped is an oblique prism whose base is a parallelogram, or equivalently a polyhedron with six parallelogram faces. Right Prism. A right prism is a prism in which the joining edges and faces are perpendicular to the base ...
The prism cover test ( PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
4 dioptre prism, either loose or prism bar; Bright lighting conditions; Method of assessment. As it is an objective test, few instructions are required to be given to the patient. The patient is asked to fixate on a target while the examiner places a 4 prism dioptre base-out prism over the patient's eye, observing the response of the fellow eye.
As a result, the vertical axis is a 2n-fold rotoreflection axis. D nh is the symmetry group for a regular n-sided prism and also for a regular n-sided bipyramid. D nd is the symmetry group for a regular n-sided antiprism, and also for a regular n-sided trapezohedron. D n is the symmetry group of a partially rotated prism.
Conversely, the range of cyclovergence-based cyclofusion can be trained using dove prisms that actively rotate the field of view: "The patient fixates a vertical line target, and the dove prism is rotated in the direction to increase the action of the insufficient muscle while fusion is maintained."