Types of Aberrations Flashcards
How does Marginal Astigmatism effect Visual clarity?
it has the greatest effect on image quality because of an undesired power gain when looking away from the optical center
How does Spherical aberration effect Visual clarity?
a slight blurring of the image when a lens focuses light rays from the periphery sooner than the rays passing through the central portion of the lens. The separate focal points prevent a clear image on the retina.
FYI: generally not a problem in lens manufacturing b/c the small size of the pupil will keep the peripheral rays out.
What is a Coma and how does it effect visual clarity?
a spherical aberration of oblique axis resulting in multiple focal points causing a blurred image rather than a singular sharp image.
Where do Coma’s exist?
to a small degree they exist in all lenses and limits optical clarity when viewing images at a distance or in low light when the pupil is at it’s largest.
What causes visual distortion?
occurs when a patient looks in the periphery of a strong minus causing a barrel effect or a strong plus lens causing a pincushion effect
Astigmatic Error Chart: When looking 30 degrees from the lens OC, how much Cylinder is induced with these 4 spherical lens powers? -4.00, -2.00, +2.00, +4.00
Sph. -4.00 Cyl. +1.34
Sph. -2.00 Cyl. +0.69
Sph. +2.00 Cyl. -1.22
Sph. +4.00 Cyl. -2.75
