lec 4: anatomy and physiology terminology Flashcards Preview

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Flashcards in lec 4: anatomy and physiology terminology Deck (25):

Radius of curvature of the central posterior optical section
in millimeters

Base curve radius (BCR)


• Commonly used to express the power of a contact lens • Determined from a fixed position with the concave surface
of the lens against the lensometer lens stop

back vertex power (BVP)


• Dioptric power of the contact lens, usually expressed as
back vertex power

Contact lens power


• Actual distance from lens edge to cornea
• Less than the calculated edge lift due to corneal asphericity
(situation on patients eye!!!!)

edge clearance


• Power of the contact lens at the corneal plane

effective power


• Flatter (longer) of the two principal keratometry readings • GP lenses are generally selected with a BCR slightly steeper
or flatter than Flat-K

Flat-K or (K)


what has a longer radius? flatter or steeper



-current generation of rigid GP CL
-consists of fl, si, and methyl methacrylate

fluoro-silicone/acrylate (FSA)


-power determined from a fixed position with the convex surface of the lens against the lensometer lens stop
-RARELY USED; unless measuring bifocal lens

front vertex power (FVP)


-tear lens b/w GP CL and corneal surface
-plus power if lens exhibits apical clearance (LLP= +)
-minus power if the lens exhibits apical BEARING (LLP= -)

lacrimal lens (LL)


• BOZD = Zone in which the BCR is present
• Provides the visual optics for both GP and soft lenses

• Optical zone diameter (OZD, FOZD, BOZD)


• Linear edge-to-edge measurement of the lens in mm

• Overall diameter (OAD, TD)


• Potential of a contact lens material to transmit oxygen
• Considers both, solubility and diffusion
• Unit = Barrer

• Oxygen permeability (Dk)


• Describes oxygen transmission is a specific contact lens • Calculation: Dk/t

• Oxygen transmissibility (Dk/t)


• Produced by varying the thickness from the superior to the
inferior region of a contact lens while maintaining the same front and back surface curvatures

• Prism (in CL)


• Measured from the lens edge perpendicular to an extension
of the BCR

• Radial edge lift


Why do we need to stabilize lenses?

cylinder in lens; a prism can help with stabilization


• Compares the corrected ametropic retinal image to that of a standard emmetropic schematic eye
• Ametropia can be
• Purely axial (axial elongation of the globe)
• Purely refractive (abnormal refractive components)
• A combination of both factors

• Relative spectacle magnification (RSM)


• Spherical GP CL = refractive cylinder minus corneal cylinder
• Spherical soft CL = refractive cylinder

• Residual astigmatism


• Rigid material; typically methyl methacrylate, silicone, and
fluorine within the polymer matrix
• Relatively small in diameter—smaller than the cornea
• Higher optical quality than soft lenses

• Rigid GP contact lenses (GP lenses)


• Current generation of soft lens materials incorporating
silicone within the matrix for higher oxygen permeability

silicone-hydrogel (SiHy)


• Soft lens designs that correct for refractive astigmatism

soft toric lenses


base curve of soft contact lens relation to flat k

no relationship


-flexible material; hydrogel or silicone-hydrogel
-relatively large in diamter; larger than cornea
-some water content
-BCR and Flat K quite different (BCR is about Flat K +1 mm)

soft lenses


ratio of retinal image size of a corrected ametropic eye to retinal image size of the same eye uncorrected

spectacle magnification