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O&O Skillz > Unit 6: Contact Lenses > Flashcards

Unit 6: Contact Lenses Flashcards

1
Q

Orthokeratology

A

Gas permeable lenses worn while sleeping to reshape the cornea

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2
Q

Hard contact lens materials

A

-PMMA (Polymethylmethacrylate)
-GP (Gas permeable)

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3
Q

Soft contact lens materials

A

-hydrogel
-Silicone hydrogel

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4
Q

Characteristics of PMMA lenses

A

-worn by less than onepercent of contact lens wearers
-Very durable but not oxygen permeable
-Small diameter to allow cornea to breathe

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5
Q

Characteristics of GP lenses

A

-Less than 10% of contact lens wearers
-Vision is better than with soft lenses
-Last longer
-Less comfortable than soft lenses
-Can’t be used for part time where

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6
Q

Characteristics of HEMA lenses

A

-Worn by 90% of contact lens wearers
-Can be worn occasionally
-More comfortable and stable
-Less durable and more expensive
-Vision not as good
-Prone to deposits

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7
Q

Characteristics of silicone hydrogel lenses

A

-All soft contact characteristics
-More expensive
-Easier to handle
-Reduced lens wettability

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8
Q

Advantages of hybrid lenses

A

-Improved comfort over hard lenses
-Lower cost than scleral lenses
-Easier to remove than scleral
-More stable than soft toric lenses

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9
Q

Disadvantages of hybrid lenses

A

-More expensive than soft or hard lenses
-More chair time to fit
-Limited ability to customize
-Insertion is similar to scleral

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10
Q

Contact lens modalities

A

-Single use
-Two week
-Daily or extended wear
-Monthly
-Daily or extended wear
-Quarterly or yearly
-Daily wear only

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11
Q

Types of ballast for toric lenses

A

-prism ballast
-Peri ballast
-Thin zone

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12
Q

What is monovision

A

-Two different lenses, distance power in one by, near power in the other one
-Good for high astigmatism
-Compromises depth perception

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13
Q

What are lenticular lenses

A

-Used for aphakic patients
-Sharply defined transition between carrier and prescription zone

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14
Q

Eight contact lens fitting parameters

A

-Base curve
-Diameter
-Center thickness
-Edge design
-Oxygen transmissibility
-Water content
-Sagittal depth
-Wetting angle

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15
Q

Base curve

A

-Curvature of the posterior surface
-the HIGHER the number, the FLATTER the lens

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16
Q

Average diameter smallest to largest

A

-PMMA (7.5-8.8mm)
-GP (8.0-9.6mm)
-Soft (13.0-15.0mm)
-Hybrid (14.5mm)
-Scleral (15.0-25.0mm)

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17
Q

How far away from the limbus should a soft contact lens be

A

2mm

18
Q

HVID

A

Horizontal visible iris diameter

19
Q

Center thickness

A

-Distance from the front surface of the lens to the back surface
-Hi plus we’ll have a thicker centre

20
Q

Dk

A

The oxygen permeability of the lens
D=The diffusion coefficient for oxygen movement in the material
k=The solubility constant

21
Q

Dk/t

A

The oxygen transmissibility of the lens
t=Centre thickness

22
Q

Three categories of water contacts and their percentages

A

High- 60%
Medium- 40-60%
Low- <40%

23
Q

What happens to lens characteristics as the water content increases

A

-More oxygen
-Lower stiffness
-Higher evaporation, decreasing comfort
-More fragile

24
Q

Sagittal depth

A

The distance from the centre of the lens to surface it’s sitting on

25
Q

Wetting angle

A

-The angle that the edge of a bead of water makes with the surface of the contact lens
-The smaller the angle the better the wettability

26
Q

Difference between cleaning and disinfecting

A

Cleaning removes debris and deposits
Disinfecting kills bacteria and pathogens

27
Q

Four methods of contact lens care systems

A

-Chemical
-Hydrogen peroxide
-Thermal
-Ultraviolet

28
Q

Parameters to determine if a patient is a good contact lens candidate

A

-Motivation
-Occupation
-Lifestyle
-Ocular history
-General health
-Medications
-Age/ maturity

29
Q

Questions to ask a current contact lens wearer

A

-How long have they been wearing CL?
-How long since last CL check?
-How often replace lenses?
-How old is current pair?
-What is typical wear time?
-How often do they sleep with lenses on?
-What solution do they use?

30
Q

Vertex distance

A

The distance of the lands from the surface of the eyeball
-Closer adds minus power
-Further adds plus power
(So CL must have more plus power)

31
Q

Range of average K values

A

38.00D-46.00D
Higher than 48D is suspicious for keratoconus

32
Q

Average corneal diameter

A

11.8mm

33
Q

Average soft contact lens diameter

A

14.5 mm

34
Q

Monovision

A

Two different contact lenses, distance power on dominant eye, near power on non-dominant eye

35
Q

Modified monovision

A

Single vision distance power on dominant eye, multifocal lens on non-dominant eye. 

36
Q

Some CL insertion methods

A

-Directly on cornea
-On sclera then slide onto cornea
-Slide under upper eyelid for a small aperture


37
Q

Some CL removal methods

A

-Pinch off
-J stroke
-Scissors versus blink

38
Q

Possible lens complications

A

-Chipped cracked or torn lens
-Protein deposits
-Scratched GP lens
-Mucus film
-Lens discolouration

39
Q

GPC

A

Giant papillary conjunctivitis

40
Q

CLARE

A

Contact lens acute red eye

41
Q

SPK

A

Superficial punctate keratitis

O&O Skillz (5 decks)

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