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contact lens > lec 4: anatomy and physiology > Flashcards

lec 4: anatomy and physiology Flashcards

1
Q

3 categories of CL

A
  1. GP
  2. Soft lenses
  3. hybrid lenses
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2
Q
  • small (OAD = 9 mm)

- scleral (OAD= 20 mm)

A

GP lenses

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3
Q

flexible

large OAD=14 MM

A

soft lenses

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4
Q
  • GP core and soft skirt

- large OAD = 14 MM

A

hybrid lenses

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5
Q

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

A

rigid lenses

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6
Q
  • 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)
A

flexible lenses

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7
Q

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

A

Ethylene glycol dimethacrylate (EGDMA)

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8
Q

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

A 
Methacrylic acid (MAA) and N-vinyl pyrrolidone
(NVP)
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9
Q

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)

A

Methyl methacrylate (MMA)

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10
Q

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

A

Glyceryl methacrylate (GMA)

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11
Q

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

A

Polyvinyl alcohol (PVA)

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12
Q

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

A

• H20↑, Dk↑

DIRECT RELATIONSHIP

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13
Q

• In SiHy lenses they are usually _______ related

A

• H20↑, Dk↓

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14
Q

Modern gas permeable materials include

A

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

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15
Q

• Older GP materials include

A

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

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16
Q

FIRST GP LENS

A

PMMA

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17
Q

0 OXYGEN PERMEABILITY LENS

A

PMMA

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18
Q

WHAT FDA class are regular soft and GP CL?

A

class II (moderate to high risk)

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19
Q

what FDA class are extended wear CL?

A

class III (high risk)

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20
Q

“filcon” describes what type of lens?

A

hydrogel soft lens

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21
Q

grouping for soft lens depends on what?

A

water content and ionicity

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22
Q

what type of lenses are Group 5?

A

silicone hydrogel lenses

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23
Q

“focon” indicates what type of lens?

A

non-hydrogel lens (hard lens)

24
Q

grouping for hard lens depends on what type of content?

A

silicone and fluorine content

25
Q

how are GP lenses manufactured?

A

lathing and molding

26
Q

advantages of lathe cutting of GP lens

A 
• Established technology 
• Almost unlimited surface
designs possible
• Wide range of parameters 
• Suits most materials 
• Relatively economic to start production
27
Q

disadvantages of lathe cutting of GP lens

A 
• Disadvantages
• Labor intensive
• High cost per lens
• Variable surface finish 
• Relatively slow
• Volume production difficult 
• Reproducibility with older
generation lathes difficult
28
Q

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

A

• Cast molding of soft lenses

29
Q

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

A

• Spin casting of soft lenses

30
Q

advantage of molding soft lens

A 
• Low cost per lens, one
volume production starts 
• Rapid
• Volume production easy 
• Good surface quality 
• Good reproducibility
31
Q

disadvantages of soft lens

A 
• Expensive to start
production
• Expense limits parameter
range
• Not all materials suitable 
• For stock lenses only
32
Q

types of GP lenses

A
  1. aspheric lens

2. multicurve lens

33
Q

The most popular GP lenses in the US

A

multi curve lens

  • Typically these lenses have either three (tri-curve) or four (tetra-curve) distinct zones
  • Within these zones, the radii are spherical
34
Q

which curve has the shortest radius (steepest)?

A

base curve of CL

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

35
Q

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

A

BCR

36
Q

Whats the difference b/w tetracurve and tricurve?

A

fill out later

37
Q

The OZD of a GP lens is?

A

OAD minus twice the peripheral curve widths

• OZD = 9.00mm – 2 x (0.30mm + 0.30mm) = 7.80mm

38
Q

• The transition between curves (junction) is what?

A

blended

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

39
Q

• C.T. is dictated by what?

A

lens power

40
Q

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

A

lens positioning

41
Q

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

A

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

42
Q

• In high minus lenses, what can happen?

A

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

43
Q

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

A

0.035 mm to 0.60 mm

44
Q

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

A

smaller

• Typically between 9.00 and 10.00mm

45
Q

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

A

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

46
Q

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

A

base curve (radius)

47
Q

THE single most important factor for GP lens comfort

A

edge design

• Most crucial is the shape if the anterior edge

48
Q

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

A
  • Round anterior and round posterior
  • Round anterior and square posterior

• A well rounded, centrally located edge apex is best

49
Q

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

A

lens edge and lid, and not lens edge and cornea

50
Q

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

A

Axial edge lift

51
Q

Relationship between the lens edge and the corneal

surface

A

Axial edge clearance

• Aka edge standoff or lift-off

52
Q

To reduce the center thickness and to increase the edge

thickness in high plus lenses (>+3.00D)

A

Minus carrier

53
Q

• 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)

A

Plus carrier, or CN bevel

54
Q

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

A

soft toric and toric gp lens

55
Q
  • 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
A

Fenestrations

56
Q

general fitting rule for soft lenses

A

BCR=flat K + 1 mm

57
Q

general fitting rule for GP lenses

A

BCR=flat k

contact lens (4 decks)

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