R
- Radiance L
- reading cap
- reading portion
- reduce-aperture trial case lens
- reduced aperture trial frame
- reduced-aperture lens
- Reference distance
- reference IOP
- Reference plane
- reference seeing distance (RSD)
- reference wavelength
- refracting angle
- refracting edge
- refractive index
- Refractor head
- relative distance magnification
- relative visual attenuation coefficient
- resolution
- resolving power of the fundus camera
- retinal hazard limit
- Retinoscope
- reverse polarity system
- round segment
reference seeing distance (RSD)
Agreed distance of 250 mm between the object side (first) nodal point of the eye and the object observed. The reference seeing distance is used, above all, as a reference parameter for calculating the magnification of optical instruments used for near vis.