Lecture 4 - anatomy and physiology of a CL Flashcards Preview

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1

what is the base curve radius (BCR)?

radius of curvature of the central posterior optical section in mm

2

what is the back vertex power (BVP)?

used to express power of CL -Determined from a fixed position with the concave surface of the lens against the lensometer lens stop

3

what is the contact lens power?

dioptric power of CL - usually expressed as back vertex power

4

what is edge clearance?

actual distance from lens edge to cornea (not inherent property of lens) - less than calculated edge lift due to corneal asphericity

5

what is effective power?

power of CL at the corneal plane

6

what is the Flat-K?

flatter (longer) of the 2 principal meridians (GP lenses are generally selected with BCR slightly steeper or flatter than Flat-K)

7

what is fluoro-silicone/acrylate (FSA)?

used in modern GP CL - consists of fluorine, silicone and methyl methacrylate

8

what is front vertex power (FVP)?

power determined from fixed position with convex surface against lens stop

9

what is the lacrimal lens (LL)?

tear lens between GP and corneal surface

10

what is the optical zone diameter (OZD, FOZD, BOZD)?

provides the visual optics for both GP and soft lenses

11

what is the overall diameter (OAD, TD)?

linear edge-to-edge measurement of the lens in mm

12

what is oxygen permeability (Dk)?

potential of a CL material to transmit oxygen, considers both solubility and diffusion (unit = barrer)

13

what is oxygen transmissibility (Dk/t)?

describes oxygen transmission for a specific CL

14

what is prism (in CL)?

produced by varying thickness from superior to inferior region of CL while maintaining the same front and back surface curvatures (used for cylinder lenses to center themselves)

15

what is radial edge lift?

measured from the lends edge perpendicular to an extension of the BCR (inherent property)

16

what is relative spectacle magnification (RSM)?

compares corrected ametropic retinal image to a standard emmetropic eye

17

what is residual astigmatism?

spherical GP = refractive cylinder - corneal cylinder
spherical soft = refractive cylinder

18

what is a rigid GP CL?

has rigid material (methyl methacrylate, silicone, fluorine), small in diameter (smaller than cornea) and higher optical quality than soft lenses

19

what is a silicone hydrogel (SiHy) lens?

current generation of soft lenses - uses silicone in matrix for higher oxygen permeability

20

what is a soft toric lens?

designed for refractive astigmatism - conforms to cornea (must be stabilized)

21

what is a soft CL?

flexible (hydrogel or SiHy material), large in diameter (larger than cornea) and some water content

22

what is spectacle magnification?

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

23

what is the OAD for a GP lens? soft lens?

GP OAD = 9mm - 10mm
soft OAD = 14mm

24

what is the Bennett scale for Dk values?

low = 25-50
high = 51-99
hyper = equal to or more than 100

25

how is water content and oxygen related in hydrogel lenses? what about in SiHy lenses?

hydrogel = directly related (higher water = higher Dk)
SiHy = inversely related

26

what is the HEMA material used in?

soft lenses - only used with other materials to increase water content

27

what is EGDMA used in?

soft lenses - makes material stiffer/less stretchable

28

what are NVP and MAA used in?

soft lenses - both increase water content

29

what is MMA used in?

soft lenses - lowers water content and increases hardness/strength

30

what is GMA used in?

soft lenses - increases wetability and deposit resistance (smaller pore sizes)