LENSAS / Technical reading
Optical knowledge
Concepts, examples and references for optical dispensing. Explore 12 topics and three educational calculations.
Pupillary distance: which measurements should you record?
Binocular PD is the distance between the pupils. Monocular PD records each eye relative to the nasal reference used during measurement.
Read explanation →Optical centration: from measurement to fitting
Centration positions lens references relative to the eyes and adjusted frame, following the lens design and manufacturer instructions.
Read explanation →How to calculate horizontal decentration
For a symmetric frame model, geometric centre distance is A + bridge. Nasal decentration per eye is (A + bridge) / 2 minus monocular PD.
Read explanation →Frame geometry: A, B and bridge
In the boxing system, A is the horizontal width and B the vertical height of the box enclosing the lens shape. The bridge separates the two eyewire boxes.
Read explanation →Refractive index: why prescription power alone is not enough
Index describes an optical property of a material. Choosing a lens also requires considering the frame, design, fitting and wearer priorities.
Read explanation →Lens materials: compare more than index
A useful comparison considers the complete product: material, design, treatments and use conditions, as well as refractive index.
Read explanation →Lens thickness: inputs needed for an estimate
An estimate depends on prescription, material, shape and fitting. Refractive index alone does not determine final thickness.
Read explanation →Vertex distance: record the wearing position
Back vertex distance is the separation between the back surface of the lens and the front of the cornea.
Read explanation →Pantoscopic tilt: measurement and convention
Pantoscopic tilt describes the vertical tilt of the frame front in its wearing position, relative to the instrument or procedure reference.
Read explanation →Transposition: another notation for the same prescription
Transposition adds cylinder to sphere, reverses the cylinder sign and rotates the axis by 90°, preserving the optical equivalence of the representation.
Read explanation →Prentice’s rule: approximate prism magnitude
Approximate prism magnitude is the absolute meridional power multiplied by displacement in centimetres: |F × c|.
Read explanation →Remote edging: what must travel with a shape
A remote workflow must preserve shape, scale, orientation and side identification, and agree on verification with the laboratory performing the mounting.
Read explanation →Explore LensAs tools
Public knowledge to verify concepts. A complete platform to continue the dispensing workflow.
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