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contact lens > SOFT AND HARD CONTACT LENS > Flashcards

SOFT AND HARD CONTACT LENS Flashcards

1
Q

lens types

A
  • Soft Contact Lens (SCLs)
  • Rigid Gas Permeable (RGP)
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2
Q

There are 2 types of CL type in the market today:

A

Hard and Soft.

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3
Q

what is SOFT LENS?

A

● Soft Lenses are flexible.
● Developed by Wichterle and Lim
● Soft Lenses soak up or take in solutions.
● Soft lenses are also called “hydrophilic” or “hydrogel” lenses.

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4
Q

soft lenses are also called?

A

“hydrophilic” or “hydrogel” lenses

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5
Q

these type of lenses are smaller than the cornea.

they Contain little water and are less flexible.

they Provide less comfort than soft, flexible lenses.

A

RGP

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6
Q

RGP VS SOFT in terms of size

A

RGP: HVID -2mm
Soft: +2mm

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7
Q

Advantages of SCL Wear over SPectacles

A

● Greater Convenience
● Freedom from Spectacles
● Enhanced personal appearance.
● Better and more natural vision.

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8
Q

Why wear SCLs?

A

● Freedom from Spectacles
● Enhanced personal appearance.
● Convenient for certain occupations and sport.
● Vision is truer to size.
● Vertex distance eliminated.
● Contact Lenses provide more “natural” vision.

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9
Q

Types of SCLs in terms of refraction

A

● Myopia: spherical CL
● Hyperopia: spherical CL
● Astigmatism: toric CL
● Presbyopia: multifocal CL
● Cosmetic applications: colored CL

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10
Q

Also used to hide corneal scars, coloboma (to avoid glare)

A

Prosthetic opaque with clear pupil

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11
Q

there are PX that has scar at the center of the pupil disabling them to see. Not for Px with leukocoria.

A

Prosthetic opaque CL with black pupil

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12
Q

● Correct for Myopia or Hyperopia
● Same power in every meridian of lens

A

Spherical Soft Contact Lenses

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13
Q

● For mild astigmatism, a spherical lens will be sufficient for correcting vision
● Moderate to High astigmatism needs to be corrected with a toric soft lens.
● A toric soft lens incorporates two major power meridians to correct the astigmatism.

A

Toric Soft Contact Lens

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14
Q

________ has markings that enable you to see dislocations of axis.

A

Toric lenses

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15
Q

● Correct for presbyopia.
● Different lens powers in different portions of the lens for viewing different distances.
● Designs vary.

A

Multifocal Soft Contact Lens

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16
Q

There 2 powers in one CL:

A
  • Internal near design
  • External distance design
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17
Q

It operates on the size of the pupil. When you read, the pupil gets smaller, and it goes to the center near design. When you look at the distance, pupil gets bigger locating at the center distance design. Basically, there are 2 powers in a pupil. The Px will operate with suppression.

The Px will suppress the blur image and will let the clear image to pass through.

Center near design has different power than center distance design.

A

Multifocal Soft Contact Lens

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18
Q

internal design is PL and external design is +1. When the Px reads, as the pupil gets smaller, it will focus on the “Plano” power thus allowing him to read clearly.

A

Multifocal Soft Contact Lens

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19
Q

What is the Ideal Lens Material? (SCLs)

A

● Provides sufficient oxygen to the cornea
● Compatible with the ocular tissue
● Remains clean, wet, and hydrated
● Easy to handle, insert and remove.
● Flexible for comfort
● Ease of fitting

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20
Q

SCL Properties

A

● Minimum level of oxygen transmissibility is needed.
● Termed as Oxygen Permeability or Dk
● The higher the water content, the higher amount of oxygen passes through it.
● Oxygen transmissibility is also influenced by lens thickness.

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21
Q

● Developed for continuous wear.
● Highly oxygen transmissible
● Current generation of silicone polymers can be worn for 30 days of continuous wear.

A

Silicone Hydrogel Contact Lenses

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22
Q

Also called as “breathable” CL

A

Silicone Hydrogel Contact Lenses

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23
Q

Surface Qualities of silicone hydrogel CL

A

● Wettable
● Maintain stable tear film
● Easy to care for and resist spoilage
● Transparent
● Durable
● Machinable: suitable for mass produce

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24
Q

Hydration Qualities of silicone hydrogel CL

A

● Soft lenses attract debris, proteins, lipids, inorganic salts. (Since it is hydrophilic)
● Lens deposits may lead to complications.
● Lenses must be disinfected and replaced regularly.

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25
Q

Handling Qualities of silicone hydrogel

A

● Material needs proper stiffness:
- To hold its shape
- For ease in handling

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26
Q

materials of ideal lens wear

A
  • Lens Replacement
  • Polymer Type
  • Wearing Mode
27
Q

Lens Replacement

A

● Conventional: 30 days
● Frequent or planned replacement: weekly/monthly/every 2 months.
● Disposable: daily/weekly/monthly
● Daily disposable

28
Q

Worn once then discarded.

A

Daily Disposable:

29
Q

Replaced > 1 week to 1 month

A

Disposable

30
Q

Replaced > 1 month to 6 months

A

Frequent or Planned Replacement

31
Q

Replaced > 6 monthly

A

Conventional

32
Q

The 1st one to invent disposable CL:

A

Johnson & Johnson.

33
Q

Polymer Type: Low Water Content Lenses

A

● HEMA
● 38% water content
● “Original” soft lens material
● Excellent durability
● More limited oxygen transmissibility

34
Q

Polymer Type: Medium and High Water Content Lenses

A

● Medium Water Content: Ratio between plastic and fluid is balanced (50-50)
● High Water Content: Unique advantages/disadvantages, less common.

35
Q

Disadvantage of polymer type cl

A

with high water content, the water stays on the eyes. Ex. Cl has 60% water. If placed on the eyes, and you’re exposed on a windy place or enclosed place, the CL maintains the 60% water. If the Cl dries, the Cl gets water on the tear film causing the tear film to dry.

36
Q

Lens wear during waking hours you remove when you sleep.

A

Daily Wear

37
Q

Lenses worn continuously for 24hrs to 30 days.

A

Extended Wear

38
Q

why Not all lens type or people are suitable for extended wear?

A

If the person has dry eyes, he is not suitable for extended wear.

39
Q

why is extended wear with hydrogels is largely avoided?

A

The more you sleep with Cl, the dirtier it gets. All dirt can be absorbed by the CL.

40
Q

extended wear cl

A

● Weekly or 2 weekly mid water disposable lenes have been prescribed for extended wear to meet wearer demand.
● Flexible water schedules have also been prescribed.

41
Q

this material cl is the best. It supplies sufficient oxygen.

A

Silicone hydrogel lens

42
Q

WEAR MODE BASICALLY IS?

A

● Patient’s refractive error determine lens type.
● Lenses prescribed according to recommended replacement period.
● Lenses prescribed for daily wear or extended wear.

43
Q

● Weekly or 2 weekly mid water disposable lenes have been prescribed for extended wear to meet wearer demand.
● Flexible water schedules have also been prescribed.

A

EXTENDED WEAR

44
Q

● Open back mould, spun in centrifuge.
● Moulde defines the front surface.
● Back surface defined by speed, tension, and gravity.

A

Spin Casting Technique

45
Q

Like Gelatin: in hot stage, it is liquid. When you put it in the mould, it would be solid.

A

Spin Casting Technique

46
Q

● A dry button (like a button in the uniform) of lens material is used
● This is lathed or cut to specification
● There is great precision in lathing lens surface.
● Surface polishing not usually required.

A

Lathing Techniques

47
Q

During this technique, the button is still hard. If the button already in its correct shape, it would be submerged in a solution to become a soft lens.

A

Lathing Techniques

48
Q

● Lenses may be dry or wet moulded
● Economical method of manufacture
● High volume possible with good reproducibility.

A

Moulding Technique

49
Q

Easy to mass produce.
There is also combination Technique: Lathing and Moulding combined or Spin casting and Lathing combined using a button.
Whichever technique you would use, the best one is the one that could mass produce.

A

Moulding Technique

50
Q

SCL MANUFACTURING TECHNIQUES

A

Spin Casting Technique
Lathing Techniques
Moulding Technique

51
Q

BEST SCL MANUFACTURING TECHNIQUE

A

MOULDING TECHNIQUE

52
Q

WHY US BACK CURVE IMPORTANT?

A

Back curve is important: it comes contact with the cornea. Called the “Base Curve” means the curvature at the back.

53
Q

Corneal Astigmatism FORMULA

A

Formula: F= (n-1)/r

F= corneal power in Diopter
n= index of refraction (of Kera) – 1.3375 unless otherwise is stated
r= radius of curvature (K rdg)

54
Q

F=

A

corneal power in Diopter

55
Q

n=

A

index of refraction (of Kera)

56
Q

r=

A

radius of curvature (K rdg)

57
Q

Diopters or the power of the eye:

A
  • The higher the number, the steeper the cornea
  • The lower the number, the flatter the cornea.
58
Q

radius of curvature:

A
  • The higher the number, the flatter it is.
  • The lower the number, the steeper it is.
59
Q

Internal Astigmatism FORMULA

A

Formula: IA= SA – CA

SA= spectacle astigmatism
Astigmatism of the Px
CA= corneal astigmatism

60
Q

SA=

A

spectacle astigmatism
Astigmatism of the Px

61
Q

CA=

A

corneal astigmatism

62
Q

CA=

A

corneal astigmatism

63
Q

Internal Astigmatism is also equivalent to_____. Astigmatism not on the cornea but on the lens. RGP CL is only used.

A

residual astigmatism

64
Q

WHAT IF CA AND SA ARE NOT OF THE SAME AXES?

A

If CA and SA are not of the same axes, you should match the direction of the axes.

To do that:
Change the sign of the cyl and move the axis 90 degrees away.
(Pick any cyl) Reverse and Rotate

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