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Contact Lens year 1 > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

Radius of curvature

A

Shorter radius - steeper curve
Longer radius - flatter curve

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2
Q

What is radius of curvature measure in?

A

mm

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3
Q

What does radius curvature convert too

A

Dioptric power

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4
Q

What does curvature determine ?

A

Corneal power

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5
Q

Conversion formula

A

P = ( n-1) / r
P- curvature power in diopters
N- 1.3375 (index of refraction for eye) never changes
R- radius of curvature in meters

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6
Q

Converting from mm to m what do u do

A

Divide by 1000

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7
Q

Corneal power

A

Average corneal power value - 43.50D
Steeper cornea- higher value
Flatter cornea- lower value

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8
Q

Keratomer
Measure ?

A

Measure- corneal curvature
Central 3 mm
- curvature of the two principal meridians (k readings) (horizontal and verticals)

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9
Q

Keratometer
Purpose?

A

-amount and type of asitgamistm
-Determine the initial contact lens to be place on the eye
-intraolcular lens implant section
-indicate a compromised cornea
-diagnose keratwconus
-asses tear layer / quality

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10
Q

Theory of keratometer

A

Cornea acts as a convex mirror
Reflection of an object (mires) a known size at a known distance is viewed using a short focus telescope
The corneal power that results from given radius

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11
Q

With the rule

A

Horizontal is the flatter meridian (less curved)

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12
Q

Against the rule

A

Vertical is the flatter meridian

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13
Q

If the minus signs don’t align vertically what does that mean?

A

Irregular astigmatism

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14
Q

Is minus signs horizontal or vertical?

A

Vertical power

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15
Q

Plus signs are ?

A

Horizontal power

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16
Q

Distorted mires are associated to what

A

Poor tear quality
Irregular asstigmatism

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17
Q

What is corneal topography

A

-Describes the shape of the corneal surface in all meridians
-Uses series of concentric targets (a placido disc)
-Allows both central and peripheral curvature to be determined
-Can detect gross irregularities in the corneal surface and very high astigmatism
The map displays the power distribution using colour coded displays

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18
Q

Normal corneas are represented by what colour

A

Greens and yellows

19
Q

Topography
Flatter areas

A

Blues or cool colours

20
Q

Topography
Steep areas

A

Reds or hot colours

21
Q

Purpose of corneal topography

A

Screen for corneal changes (ectasia)
Monitor corneal ectasia
Fitting contact lens

22
Q

Types of topographers

A

Placido disc
Slit scanning & scheimpflug technology

23
Q

Types of maps

A

Axial
Tangential
Elevation
Corneal thickness

24
Q

Axial map

A

Corneal power
Good overview

25
Q

Tengential map

A

Power and curvature at individual points
Most accurate

26
Q

Elevation

A

Placedo disc - calculate elevation
Scheimflug- actual elevation measure

27
Q

Corneal thickness (pachymetery)

A

Scheimflug and scanning slit primarily

28
Q

Elevation knob

A

Raise or lower the instrument until a bright ring refelection is centered in the cornea

29
Q

Focusing knob

A

Clear the circular images

30
Q

How to move the cross to the center of circle

A

Move the instrument or elevation knob

31
Q

Contact Lens Equipment

A
  • Keratometry
    ◦ Automated
    ◦ Manual
  • Slit Lamp
  • Corneal Topography
  • Dry Eye Assessment
    ◦ Tear Break Up Time (TBUT)
    ◦ Schirmer’s test
32
Q

Manual Keratometry Process

A
  • Handout: Procedure for Obtaining Keratometry Readings (Brightspace)
    1. Calibrate instrument
    2. Patient preparation
    ◦ Disinfect chin and head rest
    ◦ Occlude left eye
    ◦ Align reflected mires on patient’s cornea
  • Look into instrument
  • Plus sign in lower right circle
  • Focus mires
    Adjust horizontal power until plus sign tips are near each other
  • Rotate telescope until tips of plus signs align
    ◦ Determine the principal meridians
  • Superimpose plus signs
    ◦ Horizontal power
  • Superimpose minus signs
    ◦ Vertical power
33
Q

Manual Keratometry Documentation

A
  • Record the power and axis for the horizontal meridian
  • Record the power and axis for the vertical meridian
    ◦ You may see the readings recorded with only one axis identified since the other is assumed to be 90 degrees away.
    ◦ There is a smaller chance of error when both axes are recorded.
  • Record whether the mires are clear and regular (MCAR), D0
  • Distorted mires are often associated with poor tear quality or irregular astigmatism
34
Q

Manual Keratometry Documentation ex

A

43.50 @ 175 / 45.00 @ 085 D0
* Amount of astigmatism = 1.50 D

35
Q

Slit-Lamp Biomicroscopy

A
  • Plays an essential role in the preliminary assessment and follow-up care of contact lens wearers
  • May also be used to assess:
    ◦ Posterior eye health
    Vitreous, lens, retina
    ◦ Anterior chamber angle
    ◦ Intraocular pressure
36
Q

Slit-Lamp Biomicroscopy
* Consists of:

A

◦ An illumination system (the slit lamp)
◦ Viewing system (the biomicroscope)
Joystick
◦ Focusing
◦ Lateral movements
* Height control

37
Q

Illumination System

A
  • Brightness is controlled by a rheostat or multiposition switch
    ◦ Can be adjusted to obtain balance between patient comfort and optimal visibility
  • Filters can be incorporated to enhance the visibility of certain conditions
    ◦ Green filter (neovascularization)
    ◦ Neutral-density filter
    ◦ Polarizing filter
    ◦ Diffusing filter
    ◦ Cobalt blue filter*
    ◦ Wratten (yellow) filter
38
Q

Microscope

A
  • Provides a clear image of the eye
  • Sufficient magnification to view all structures of interest
    ◦ Up to 40x should be possible
39
Q

Slit-Lamp Biomicroscopy

A
  • Six areas of the anterior eye should be assessed in the preliminary examination ◦ Fig. 37.2 (Contact Lens Practice)
  • A normal technique is to use a variety of illumination methods – and cobalt blue light for fluorescein staining
40
Q

Recording Slit Lamp Findings

A
  • Lids = clear, uneven lid margin
  • Lashes = clear, Gr 1+ blepharitis
  • Conjunctiva = clear, Gr 1+ GPC, Gr 2+ injection
  • Cornea = clear, no staining, negative SPK, Grade 2+ SPK inferior
  • Angles = Gr 4+ open, narrow angles
  • Iris = flat and even, flat round pigment 1 mm at 6 o’clock
  • A/C = negative for cells or flare; Gr 3+ flare
  • Lens = Gr 1+ NS, clear, Gr 2+ brunescence
41
Q

Asses lipid layer

A
  • There are six clinical techniques:
    Symptoms/history Dry-eye survey
    Slit-lamp
    Tear meniscus height Tear stability tests
     Tear Break Up Time (TBUT) Ocular staining
    Fluorescein or lissamine green Lid surface assessment
    Blink rate
    Tear secretion/quantity
    Schirmer, Phenol red thread
42
Q

Schirmer test

A

◦ Test 1 – basal and reflex (no anesthetic)
◦ Test 2 – basal (with anesthetic)

43
Q

Slit Lamp Direct Illuminations

A

◦ Parallelepiped
◦ Optic section
◦ Specular reflection
◦ Conical
◦ Retroillumination (Retro)
* Indirect Illumination ◦ Retro
◦ Sclerotic scatter

Contact Lens year 1 (9 decks)

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