lec 4: anatomy and physiology

Question 1

3 categories of CL

Answer 1

1. GP
2. Soft lenses
3. hybrid lenses

Question 2

• small (OAD = 9 mm)

- scleral (OAD= 20 mm)

Answer 2

GP lenses

Question 3

flexible

large OAD=14 MM

Answer 3

soft lenses

Question 4

• GP core and soft skirt

- large OAD = 14 MM

Answer 4

hybrid lenses

Question 5

-maintain their own shape unsupported and are made of transparent optical grade plastics

Answer 5

rigid lenses

Question 6

• easily deformable and may require support for proper shape
• soft hydrophilic cl; made of transparent hydrogels with a water content greater than or equal to 10%
• flexible lenses can also be made of non-hydrogel material (ex flexible polysioloxanes)

Answer 6

flexible lenses

Question 7

used as
a cross-linking agent
• Makes the material stiffer, lower in water content, and less
stretchable

Answer 7

Ethylene glycol dimethacrylate (EGDMA)

Question 8

both increase water content
• Extremely hydrophilic, and adds ionic (charged) properties
to a lens material

Answer 8

Methacrylic acid (MAA) and N-vinyl pyrrolidone
(NVP)

Question 9

lowers water content
and increases hardness and strength of a material
• No oxygen permeability (we dont give this lens to pts anymore due to this)

Answer 9

Methyl methacrylate (MMA)

Question 10

increases wettability
and deposit resistance because it creates smaller
pore sizes
• Lowers the water content and contributes to a lower Dk

Answer 10

Glyceryl methacrylate (GMA)

Question 11

increases water content,
resistance to deposits, Dk, hardness and strength • Completely inert and very stable
*GOOD MATERIAL TO HAVE

Answer 11

Polyvinyl alcohol (PVA)

Question 12

In hydrogel lenses, water content and oxygen permeability are _______ related

Answer 12

• H20↑, Dk↑

DIRECT RELATIONSHIP

Question 13

• In SiHy lenses they are usually _______ related

Answer 13

• H20↑, Dk↓

Question 14

Modern gas permeable materials include

Answer 14

include silicone
acrylate (SA) and fluoro-silicone acrylate (FSA)
• Some newer FSA materials incorporate HEMA into the lens in an effort to optimize surface wettability
• Water is attracted to the lens surface, but not absorbed

Question 15

• Older GP materials include

Answer 15

include cellulose acetate butyrate (CAB) and poly-methyl-methacrylate (PMMA)
• PMMA has no oxygen permeability

Question 16

FIRST GP LENS

Answer 16

PMMA

Question 17

0 OXYGEN PERMEABILITY LENS

Answer 17

PMMA

Question 18

WHAT FDA class are regular soft and GP CL?

Answer 18

class II (moderate to high risk)

Question 19

what FDA class are extended wear CL?

Answer 19

class III (high risk)

Question 20

“filcon” describes what type of lens?

Answer 20

hydrogel soft lens

Question 21

grouping for soft lens depends on what?

Answer 21

water content and ionicity

Question 22

what type of lenses are Group 5?

Answer 22

silicone hydrogel lenses

Question 23

“focon” indicates what type of lens?

Answer 23

non-hydrogel lens (hard lens)

Question 24

grouping for hard lens depends on what type of content?

Answer 24

silicone and fluorine content

Question 25

how are GP lenses manufactured?

Answer 25

lathing and molding

Question 26

advantages of lathe cutting of GP lens

Answer 26

``` • Established technology • Almost unlimited surface designs possible • Wide range of parameters • Suits most materials • Relatively economic to start production ```

Question 27

disadvantages of lathe cutting of GP lens

Answer 27

``` • Disadvantages • Labor intensive • High cost per lens • Variable surface finish • Relatively slow • Volume production difficult • Reproducibility with older generation lathes difficult ```

Question 28

A. Liquid monomer added to mold B. Posterior mold added to form a lens; monomer polymerizes C. Molds are removed, lens is finished

Answer 28

• Cast molding of soft lenses

Question 29

A. Liquid monomer added to mold B. Monomer polymerizes in spinning mold C. Edges are polished D. Lens is finished

Answer 29

• Spin casting of soft lenses

Question 30

advantage of molding soft lens

Answer 30

``` • Low cost per lens, one volume production starts • Rapid • Volume production easy • Good surface quality • Good reproducibility ```

Question 31

disadvantages of soft lens

Answer 31

``` • Expensive to start production • Expense limits parameter range • Not all materials suitable • For stock lenses only ```

Question 32

types of GP lenses

Answer 32

1. aspheric lens | 2. multicurve lens

Question 33

The most popular GP lenses in the US

Answer 33

multi curve lens * Typically these lenses have either three (tri-curve) or four (tetra-curve) distinct zones * Within these zones, the radii are spherical

Question 34

which curve has the shortest radius (steepest)?

Answer 34

base curve of CL central zone of our cl which is the steepest, thus mimics the actual cornea

Question 35

In multi-curve GP lenses, where is the steepest radius?

Answer 35

BCR

Question 36

Whats the difference b/w tetracurve and tricurve?

Answer 36

fill out later

Question 37

The OZD of a GP lens is?

Answer 37

OAD minus twice the peripheral curve widths • OZD = 9.00mm – 2 x (0.30mm + 0.30mm) = 7.80mm

Question 38

• The transition between curves (junction) is what?

Answer 38

blended • The blend can be light, medium, or heavy • Its radius is the average of the two curves forming the junction

Question 39

• C.T. is dictated by what?

Answer 39

lens power

Question 40

For powers greater than ±5.00D, this can affect what?

Answer 40

lens positioning

Question 41

• If C.T. too high, as in high plus powers, what can happen?

Answer 41

the lens is too heavy for the lid to support and will drop

Question 42

• In high minus lenses, what can happen?

Answer 42

edge thickness may be too high and the lid will push the lens down

Question 43

• C.T. can range from______ (high minus ultrathin soft lenses) to _____ (high plus soft & GP lenses)

Answer 43

0.035 mm to 0.60 mm

Question 44

The OAD of a regular GP lens is ______ than the cornea

Answer 44

smaller | • Typically between 9.00 and 10.00mm

Question 45

• The OAD change of a multi-curve lens changes its what?

Answer 45

fit • With the same BCR, a larger lens fits tighter, a smaller lens fits looser • A large lens moves less, and therefore may be more comfortable • Constant upper lid attachment • A small lens covers a small corneal surface area • Beneficial for oxygen supply and tear exchange

Question 46

If u change diameter of multi curve gp lens, what do we have to change after?

Answer 46

base curve (radius)

Question 47

THE single most important factor for GP lens comfort

Answer 47

edge design | • Most crucial is the shape if the anterior edge

Question 48

• According to LaHood (1988) most comfortable CL are what?

Answer 48

- Round anterior and round posterior - Round anterior and square posterior • A well rounded, centrally located edge apex is best

Question 49

• Rigid lens comfort is determined by the relationship of what?

Answer 49

lens edge and lid, and not lens edge and cornea

Question 50

Distance from the edge of a CL to the hypothetical circle that would be formed by the continuation of a spherical representation of the BCR

Answer 50

Axial edge lift

Question 51

Relationship between the lens edge and the corneal | surface

Answer 51

Axial edge clearance | • Aka edge standoff or lift-off

Question 52

To reduce the center thickness and to increase the edge | thickness in high plus lenses (>+3.00D)

Answer 52

Minus carrier

Question 53

• To reduce edge thickness of high minus lenses • CN bevel -4.00 to -6.00; lenticular > -6.00 • ***Tapering and rolling the edge inward may also work in high minus lenses (not a true lenticular design)

Answer 53

Plus carrier, or CN bevel

Question 54

what type of lenses are marked with: calibration lines to determine in-vivo lens rotation • Lines can be horizontal, inferior, or both • Multiple lines with an angular separation may be present

Answer 54

soft toric and toric gp lens

Question 55

* A ventilation hole drilled in a large GP lens * Provides additional oxygen to the cornea * May assist the dispersal of air bubbles or dimples * Prevents a large lens from getting stuck on the eye

Answer 55

Fenestrations

Question 56

general fitting rule for soft lenses

Answer 56

BCR=flat K + 1 mm

Question 57

general fitting rule for GP lenses

Answer 57

BCR=flat k