S
- second principal meridian
- segment
- segment centre
- segment depth
- segment diameter
- segment extreme point
- segment extreme point height
- segment extreme point position
- segment height
- segment lens
- segment side
- segment width
- semifinished lens blank
- shape factor
- side
- single-vision lens
- single-vision semifinished lens blank
- Slit-lamp microscope
- spatial resolution
- spectacle lens
- spectacle magnifier
- spectacle microscope
- spectacle telescopes
- Spectral radiance L l (l)
- spectral reflectance
- spectral transmittance
- Spectrally-weighted photochemical aphakic source radiance LA
- Spectrally-weighted photochemical phakic source radiance LB
- sphere
- spherical lens
- spherical power
- spherical power lens
- spherical surface
- Spherical test lenses
- spherocylindrical lens
- Spot retinoscope
- stand magnifier
- static perimeter
- stimulus duration
- stimulus luminance, LS
- straight-top bifocal
- straight-top segment
- Streak retinoscope
- supraliminal strategy
- suprathreshold strategy
- surface astigmatic power
- surface power
- Synoptophore
segment extreme point
Intersection point of a line, perpendicular to the horizontal axis of the lens and passing through the segment centre, with that part of the dividing line nearest the horizontal centre line. NOTE: This point is sometimes known as the "segment top" (for segments in the lower portion of the lens) or "segment bottom" (for segments in the upper portions of the lens).