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Block 15 > Basic Contact Lens > Flashcards

Basic Contact Lens Flashcards

1
Q

USANC stands for what?

A

United States adopted names council

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2
Q

What is the purpose for USANC (United States adopted names council)?

A

Selects simple, informative, and unique nonproprietary names for drugs by establishing logical nomenclature classifications based on pharmacological and/or chemical relationships

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3
Q

Implies the contact lens is in harmony with the eye and has little or no adverse effects

A

Biocompatibility

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4
Q

Ease of manufacture includes what? (10 things)

A

Material must be easy to manufacture
Be inert
Be stress-free, dimensionally stable and durable
Material must be optically homogeneous - unless such variation is intentional (ex: Bifocal and DT1)
Material must be biocompatible: no leachable unreacted chemical components
Be easy to polish/retain surface finish
Have predictable hydration characteristics
Exhibit low friction in SItu
Not induce inflammatory or immunological responses
UV absorbers may cause NaFl pattern detail to be less visible

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5
Q

Filter that will enhance the NaFl pattern

A

Written 12 yellow filter

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6
Q

Does having lower water content make the lens more rigid or less rigid? Is this a good or bad thing?

A

More rigid, easier to handle

Advantage

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7
Q

Low water content advantages

A 
Less susceptible to environment influences
More rigid, easier to handle
Higher refractive index = thinner
Any lens care product can be used
Ease of manufacture
Greater reproducibility
More wettable
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8
Q

If a lens has low water content, what care products may be used on it?

A

Any can be used

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9
Q

If a lens has a higher refractive index, is it thicker or thinner, and does it have low or high water content?

A

Thinner

Low water content

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10
Q

Low water content disadvantages

A 
Low Dk (have to be made thinner > oxygen)
Less flexible (comfort concerns?)
Thin lenses are difficult to handle
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11
Q

High water content advantages

A

Higher Dk
More flexible
Faster restoration of shape following deformation

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12
Q

High water content disadvantages

A 
Fragile
More deposit prone - ionic, pore size
More susceptible to the environment
Lower refractive index
Less stable parameters, lower reproducibility
More difficult to manufacture
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13
Q

If a lens has a lower refractive index, does it have a lower or higher water content? Is this a good thing or a bad thing?

A

Higher water content

Disadvantage

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14
Q

Ionic materials have what charge on the surface?

A

Net negative charge on the surface

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15
Q

Non-ionic materials have what charge on the surface?

A

Still have charged sites within polymer…however, the charges are internal to the matrix = no net surface charge

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16
Q

Advantages to having ionic materials

A

More wettable

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17
Q

Disadvantages to having ionic materials

A

Deposit more readily

More susceptible to pH changes

18
Q

Advantages to having non-ionic materials

A

Less deposit prone
Do not bind charged particles
Less susceptible to pH changes

19
Q

Disadvantages to having non-ionic materials

A

Less wettable

20
Q

Material properties (7)

A 
Oxygen permeability
Wettability
Flexibility (SCL’s)
Rigidity (GP’s)
Scratch resistance
Durability (stability, wear and tear)
Deposit resistance
21
Q

ANSI Standard for ophthalmics - contact lenses - standard terminology, tolerances, measurements and physicochemical properties

A

ANSI Z80.20-2016

22
Q

ANSI Z80.20-2016

A

Applies to contact lenses worn over the front surface of the eye in contact with the preocular tear film. The standard covers rigid intracorneal and haptic (scleral) contact lenses, as well as soft paralimbal contact lenses

23
Q

What is the role of oxygen in the cornea, and where does it mainly come from?

A

Oxygen to maintain corneal integrity and mostly from the atmosphere
Some oxygen is derived from the blood supply (peripheral) and aqueous humor (especially for closed-eye)

24
Q

Atmospheric oxygen

A

~21% or 155 mmHg

25
Q

Closed eye oxygen

A

~1/3 or 55 mmHg

26
Q

What increases oxygen demand in the eye?

A

Eye temperature and

Tear pH

27
Q

Percentage of overnight corneal swelling due to closed eye lack of oxygen

A

4%

28
Q

Minimum oxygen goal for contact lens wear

A

Swelling no greater than normal without a CL - Eye open or closed

29
Q

Low Dk/T corneal changes involves low or high oxygen transmissibility

A

Low oxygen transmissibility

30
Q

Low oxygen transmissibility can result in these corneal changes (low Dk/T)

A 
Microcysts
Polymegethism (endothelium)
Corneal pH
Edema (stroma)
Blebs
31
Q

Disorganized cellular growth, necrotic tissue and cellular debris that accumulates btw cells

A

Epithelial microcysts

32
Q

What may microcysts do?

A

Migrate and rupture, causing discomfort and create a portal for infection and/or ulceration

33
Q

With an increased Dk/l, do microcysts increase or decrease?

A

Decrease

34
Q

What do you use to check for polymegethism?

A

Speculation microscopy

35
Q

Polymegethism

A

Decreased pH
Hypoxia
EW is worse
Hydrogel vs SiHy’s or GP’s

36
Q

Is polymegethism reversible?

A

Some people think so, but typically not

37
Q

Presentation of polymegethism on speculation microscopy

A

Larger, fewer cells

Chronic condition in endothelial architecture

38
Q

What is the cornea’s interaction with carbon dioxide?

A

The cornea is highly permeable to carbon dioxide

39
Q

Dk of CO2

A

About 7 times Dk of oxygen

40
Q

Why is it necessary for CO2 Dk to be so much higher than O2 Dk?

A

To resist pH and metabolic changes in the cornea

41
Q

An acidic shift due to CO2 buildup as a consequence of epithelial hypoxia and an increase in lactic acid

A

pH Shift

Block 15 (4 decks)

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