lec 4: anatomy and physiology terminology

Question 1

Radius of curvature of the central posterior optical section

in millimeters

Answer 1

Base curve radius (BCR)

Question 2

• 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

Answer 2

back vertex power (BVP)

Question 3

• Dioptric power of the contact lens, usually expressed as

back vertex power

Answer 3

Contact lens power

Question 4

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

Answer 4

edge clearance

Question 5

• Power of the contact lens at the corneal plane

Answer 5

effective power

Question 6

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

Answer 6

Flat-K or (K)

Question 7

what has a longer radius? flatter or steeper

Answer 7

flatter

Question 8

• current generation of rigid GP CL

- consists of fl, si, and methyl methacrylate

Answer 8

fluoro-silicone/acrylate (FSA)

Question 9

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

Answer 9

front vertex power (FVP)

Question 10

• 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= -)

Answer 10

lacrimal lens (LL)

Question 11

• BOZD = Zone in which the BCR is present

* Provides the visual optics for both GP and soft lenses

Answer 11

• Optical zone diameter (OZD, FOZD, BOZD)

Question 12

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

Answer 12

• Overall diameter (OAD, TD)

Question 13

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

Answer 13

• Oxygen permeability (Dk)

Question 14

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

Answer 14

• Oxygen transmissibility (Dk/t)

Question 15

• 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

Answer 15

• Prism (in CL)

Question 16

• Measured from the lens edge perpendicular to an extension

of the BCR

Answer 16

• Radial edge lift

Question 17

Why do we need to stabilize lenses?

Answer 17

cylinder in lens; a prism can help with stabilization

Question 18

• 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

Answer 18

• Relative spectacle magnification (RSM)

Question 19

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

Answer 19

• Residual astigmatism

Question 20

• 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

Answer 20

• Rigid GP contact lenses (GP lenses)

Question 21

• Current generation of soft lens materials incorporating

silicone within the matrix for higher oxygen permeability

Answer 21

silicone-hydrogel (SiHy)

Question 22

• Soft lens designs that correct for refractive astigmatism

Answer 22

soft toric lenses

Question 23

base curve of soft contact lens relation to flat k

Answer 23

no relationship

Question 24

• 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)

Answer 24

soft lenses

Question 25

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

Answer 25

spectacle magnification