Optical Characteristics of Ophthalmic Lenses

Optic Axis

Line connecting the centers of curvature of two lens surfaces

Lens Poles

Points on the front and back surface of a lens which intersect the optic axis

Also called vertices

Image formation for a sph lens

Parallel rays of light from a distance object form a point image at the secondary focal point

Any other distance behind the lens that is not the secondary focal point will be a blur circle

Size of blur circle is dependent on…

• Distance from secondary focal point

• Size of lens aperture

Where should glasses put their image?

At the patients retina → Conjugate with the retina (eye’s secondary focal point)

Circle of Least Confusion

Dioptric midpoint between line foci

Location is determined by SE

Interval of Stern

Space between 2 line foci

Spherical Equivalent

Puts COLC on the retina providing the best image possible for cyl pts

Which meridian are we most concerned with when determining edge thickness?

Meridian with the longest distance from OC to edge

Power induced by spherical lens tilt

Causes incident light to enter obliquely

Change in spherical power and induces cyl

Pantoscopic tilt

Tilt is vertical

Toward or away from cheeks

Axis in new Rx will be along 180

Faceform/Wrap

Tilt is horizontal

Toward or away from temples

Axis in new Rx will be along 90