Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OV2006 contact lenses > Principals of rigid lens fitting || > Flashcards

Principals of rigid lens fitting || Flashcards

1
Q

What does the cornea need?

A

centration and mobility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is mobility important ?

A

to support tear exchange so oxygen can reach the cornea and bacteria and other waste products can be washed away with each blink

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is centration important ?

A
  • to prevent the lens crossing the limbus causing staining and damage to the gimbal area where the limbal stem cells are located.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What do sub optimal length fits do ?

A

affects lens comfort and cause 3 and 9 o’clock corneal staining
-cause corneal warpage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is corneal warpage ?

A

that’s when the corneal shape particularly in the centre becomes completely distorted and the px can not see anymore

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the tear layer do between the contact lens and cornea ?

A

reduces friction between the 2 surfaces and avoids significant mechanical interaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the rigid lens have ?

A

several curvature and the one in the centre is the BOZR- first curve

  • then have c2, c3 , multi-curve etc etc
  • the curvature goes flatter and flatter as you get to the periphery
  • there is also another line- which is an extension of the curvature from the centre (BOZR)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the axial edge lift ?

A

is the distance between the apex/ edge of the lens edge (highest point) and the continuation of the base curve (EXTENSION of the BOZR) , measured parallel to the lens axis- STRAIGHT DOWN

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the axial edge lift (AEL)?

A

is the distance between the apex/ edge of the lens edge (highest point) and the continuation of the base curve (EXTENSION of the BOZR) , measured parallel to the lens axis- STRAIGHT DOWN

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the radial edge lift (REL)?

A

is the distance between the apex of the lens edge and the continuation of the base curve (extension of BOZR), measured along the radius of the base curve.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the edge clearance?

A

measured to the cornea

-much more clinical and axially is the axial distance between the lens edge apex to the peripheral cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the radial edge clearance (REC)?

A

is the radial distance between the apex of the lens edge and the peripheral cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the difference of the edge lift and edge clearance ?

A

Edge lift is measured from lens edge to the continuation of the back optic zone radius
and Edge clearance is measured from lens edge to cornea- which is much more clinical
-the Axial edge lift or clearance will always be more than radial edge lift or clearance
- when the larger the diameter of the C lens, the greater the difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are axial measurements?

A

when we view the lens straight on when its on the eye- easier to describe than radial measurements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the distance measurement in AXIAL edge lift used for (AEL)?

A

by manufacturers when describing the lens design

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the distance in AEC used for ?

A

what we observe when he lens is on the eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why is it not really possible to measure axial edge clearance (AEC) ?

A
  • you can only describe brightness of fluroscene as it tells us how far the edge COMES off from the cornea
  • because the tears have filled that space and fluroscene dye is visualising the tears.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do we describe the edge width ?

A

it is from the width of band that is coming off the cornea- which is what describes the edge of the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the optimum edge width ?

A

80um

0.8mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why can the edge width be different nasally and temporally ?

A

because the cl is not sitting exactly in the middle of the cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What can a steep fit look like ?

A

narrow - edge clearance is very very small

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What must the rigid lens be able to do when blinking?

A

move to enable oxygen exchange

-significant exchange

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the base curve fit of a rigid lens?

A

is fitted to create an alignment fit in at least one meridian
-that then distributes the weight of the lens over a larger area of the cornea and forms tear fluid layer- 10-25 microns between the back surface of the lens and the anterior surface of the cornea.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

When observing the central part of the lens what do you look at ?

A

-pick BOZR(which is related to lens fit) on the flattest
K- should see be aligned or slightly steep- can see central pooling , bit of clearance between lens and cornea because there is fluroscene which means there is tears
-BOZD (related to vision ) should be larger than pupil size under mesopic conditions
-have a mid peripheral touch-should be aligned so there is no space between the lens and the cornea
-peripheral - should have an edge clearance of 1mm or less.
-bottom picture- have a lens that is fitted on flattest K as it is fairly aligned on the horizontal meridian (the darker bit)
-can see a little bit of alignment and touch on the periperhy
-can see a lot of standing off in theoretical meridian- very flat fit and aligned fitting
-the total diameter should 2mm smaller than HVID- EXPECT TO FIND 1MM ON EACH SIDE
- or if 2mm on one side and no space on the other - ti is still correct however the fitting is just not good.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What do you keep for record keeping?- check the slide for the values

A
  1. comfort
    2.coverage - if lens is small then it goes towards - and if it is bigger it goes towards plus- the range is between +2 and -2
  2. centration
    L- whether or not the lens crosses the limbus
    P -crosses pupil run dim light
    C- contained within limbus- lens remain mobile but stays on cornea
  3. Movement - on blink
    - using a +2 to -2 scale - tell you what the approx movemnent - vertical lens movement (looking 1-1.5mm ) if it is more then go towards + and if less goes towards minus.
  4. In primary position-When the lens is centred on the middle of the cornea - we write down the fluroscene pattern in both principal meridians
    0- alignment and towards plus is steep and towards minus is flat
  5. Edge width in the principal meridian
    0 (-1mm band) if its more then it goes towards + and if its less it goes -
26
Q

What is really important in a fluroscene pattern and how do you record ?

A
  • when the lens is centred on the cornea
  • push lens to centre of cornea
  • record fluroscen intensity on +2 to -2 scale in both principal meridans
    • is very steep and - is very flat
      2. lens movement on blink - using +2 to -2 scale- measure first - so that VLM (vertical lens movement) in mm.
  • can measure this with height of the calibrated slit lamp beam
27
Q

What does coverage represent ?

A

the total diameter - too large or small ro correct

  • has to be approx 1mm distance between the distance and edge lens on each side
  • correct (-1, 0, +1)
28
Q

How is edge width measured ?

A
  • again can use the the beam width of the slit lamp to measure
  • aim for about 1mm in both principal meridian
29
Q

What is the comfort record ?

A

0 means no comfort 10 perfect

30
Q

Example of using rigid corneal lens fit scheme to describe a comfortable RGL 20 mins after application

A

RE
Comfort 9/10 after 20min adaptation
-corneal Coverage -1: 1.5mm smaller than HVID
-Centration C: not crossing limbus or
expose pupil
- Movement +1: between 1.6-2.0mm between
blinks
- Horizontal : fit +1 (slightly steep) edge 0 about
1mm
V: fit -2 (flat fit) edge +1 about 1.5mm

31
Q

What is HVID

A

Horizontal visible iris diameter

32
Q

What happens when you asses rigid corneal lens fitting ? pg 11

A
  • want to first look at it with white light
  • positions of the eyelid and contact lens both need to be viewed
  • measure the eyelids as a preliminary matter- draw the superior eyelid and inferior eyelid in relation to the cornea - shown as a dotted circle
  • can see superior eyelid goes bait over the cornea
  • the inferior eyelid goes right on the limbus or above or below
  • sit opposite the px at same height and let them look into your eyes - allows to explain the behaviour of the rgp lens when on eyE
  • then you want to have a look with white light at the position of the rigid lens when the px looks straight ahead- habitual position- lens may have dropped or may sit high- which is fine
  • just record where the lens fits
  • on the record card you will se a cross which represents the cornea - centre of the cross is the centre of the cornea
  • important to observer the Cl stay within the limbus when the px is looking to the right and left (horizontal versions)
33
Q

What else do we look at with the white light ? pg 11

A
  • the movement after blink
  • the amount of movement indicates whether or not that lens may be aligned too flat or too steep
  • this is an indication when the lens has really well adapted to the eye
  • but depends as there can be a lot of tearing which can cause the CL to swim over the cornea- whether or not the lens is steep or flat
  • observe what the lens does In between blink- gravity pulls the lens down- put the slit beam of a certain height where the lens sits at the stop, then watch the lens drops because of gravity and can see where it ends and can measure the distance that the lens has moved
  • use a calibrated slit lamp beam to calculate how much the bottom party of the lens moves from tis most superior position to inferior position before the px blinks again
  • can do the measurement a few times
34
Q

What to do if lens does not move down- in the movement after blink measurements ?

A
  • there is a possibility that can happen so
  • so we assume there is a vertical lens movement
  • sometimes that lens curves - and the movement should be smooth and unobstructed in a vertical plane - indicates near alignment and lens fitting if between 1-1.5mm.
35
Q

When does lens movement occur ?

A
  • occurs as a response to the eyelid force or by the upper lid attachment
  • whenever px blinks- the superior eyelid will come down- as the px open eye again the superior eyelid will drag that lens up and In between the blinks the lens will drop due to gravity
36
Q

What does an immobile lens cause ?

A

causes tears to. stagnate between its surface leading to corneal staining and distortion

37
Q

What does a lens with excessive movemement cause ?

A
  • px discomfort
  • inconsisntent vision
  • may b associated with conjuctival staining
38
Q

What happens when a movement is very curved ?

A

indicates it is a flat fit

  • as the lens prefers to stay on the periphery of the cornea - it doesnt like to go over the apex of the cornea
  • that normally indicates the area in the centre is too steep for the lens
  • the lens prefers to move all the way down by moving over the peripheral area of the cornea -as the peripheral area of the cornea is flat - it indicates the that the lens is a little too flat aswell .
39
Q

What else do you look at the lens with apart from white light ?

A
  • blue light and fluroscene
  • make sure inserting flurosccein inferinorly (when px is looking down ) - to prevent excessive lacrimation , looking up with rigid lens in eye is uncomfortable , especially in new px
  • then asses whether fluroscein pattern in primary age is
    1. Alignment
    2. Steep 3. Flat 4. Toric
40
Q

When observing the fluroscein pattern what do you make sure ?

A

the rigid lens is in the centre of the cornea

-if it sits bit below- you need to put finger on lower eyelids and push the lens more towards the centre

41
Q

What do you hope to see when observing the fluroscein pattern alighment ? pg14 example image

A
  • centrally very slight clearance - little bit of space between cl and cornea- means tiny bit of pooling- very difficult to see so would call it near alignment lens
  • in the mid periphery - alignment or slight touch -
  • edge width is acceptable - 1mm or slightly less
42
Q

What do you hope to see when observing the fluroscein pattern in a steep lens ? pg 15 example image

A
  • lot more pooling and distance centrally
    -lots of fluroscein centrally- lots more tears visible n between cl and cornea- hence lot more pooling
    -mid periphery is definitely - touch- no space at all- between cornea and contact lens
    edge width is acceptable or too thin
43
Q

What do you hope to see when observing the fluroscein pattern in a steep fit lens? pg 16 example image

A
  • have touch in the centre- central flat- barely any fluroscein
  • mid periphery clearance - pooling
  • edge width too much
44
Q

What are the 2 more fluroscein patterns

A
  • toric fluroscein patterns-
    -similar to each other
    -90 degrees change
  • could be WTR or ATR
    -IF the vertical cornea is steeper than the horizontal- will get therefore 2 fluroscein patterns in different directions
    -
45
Q

What do you observe in a horizontal WTR toric fluroscein pattern ? pg 17

A
  • centrally aligned
  • mid periphery is touch- as there is a darker appearance on both sides
  • edge with acceptable - ever so slight thin
46
Q

What do you observe in a vertical WTR toric fluroscein pattern ? pg 17

A
  • central flat- because cornea is steeper in vertical meridian therefore lens is flatter in vertical- touch
  • can see mid periphery clearance- pooling
  • edge width too much
47
Q

What do you observe in a horiziontal ATR toric fluroscein pattern ? pg 17

A
  • central- flat
  • lot more space in mid periphery - clearance - i.e pooling
  • edge width too much
48
Q

What do you observe in a vertical ATR toric fluroscein pattern ? pg 17

A

-CENTRAL aligned or very slight clearance
-Mid periphery aligned (i.e. slight
touch)
-Edge width acceptable

49
Q

What are the 5 choices for rgp lens? pg 18 images

A
  • aligned
  • steep- means a lot of pooling in the centre and thin edge
  • flat- touch in the centre- lots of clearance in periphery and thick edge
  • WTR toric
  • ATR toric
50
Q

Why can fluroscein pattern be different in the same px of the same lens ?

A
  • if the cl is not in the centre of the cornea
  • can look like something it isn’t so very important to make sure the contact lens is sitting in the centre of the cornea
51
Q

What can happen if you push the lens down or up ?

A

may cause an influx of fluroscein down at the bottom or top due to pushing eyeball too hard

52
Q

What must the fluroscein pattern be ?

A

must be symmetrical

  • in a spherical cornea ( with no astigmatism or very low )- you have a perfectly symmetrical cornea
  • in a astigmatic cornea - you can see a little bit of difference between the top and the bottom depending where the principal meridians are- therefore expect top vs bottom in WTR or temporal vs nasal in ATR astigmatism to be symmetrical
53
Q

What happens if you do not see a symmetrical fluroscein pattern ?

A

lens is not in Centre of cornea

-px may have scarring or keratoconus

54
Q

What do fluroscein patterns look like when too flat ? pg 19

A

too flat lenses like to sit in the periphery of the cornea

-

55
Q

What do fluroscein patterns look like when too steep ? pg 20

A

intensity of fluroscein in the middle gets more - cant see the pupil anymore - edge dark

  • area of pooling becomes smaller
  • the mid periphery touch area becomes bigger and the edge clearance becomes really thin
56
Q

What are the 3 parameters of the CL when looking at it ?

A
  • back optic zone radius
  • total diameter - if you change total diameter you need to change the BOZR to neutralise the change that it caused in fluroscein pattern
  • BVP - back vertex power - power of CL
57
Q

What happens when you are fitting an aligned fluroscene pattern ?

A
  • the tears that sit behind the CL. between Cl and cornea have not got any power- 0D
  • whatever you need in the ocular Rx is what you can prescribe - YOUR BVP - works well
58
Q

What happens when you are fitting a steep fluroscene pattern ?

A
  • cause a positive tear film between the lens and the cornea- if that happens because there is a lot more pooling in the centre which has the convex lens - can see that when you draw- it is a positive lens -so would expect the BVP to be adjusted to neutralist this
  • when you fit a steep cl - you will expect to find more negative in BVP- px will ask for more minus lenses you found more pooling in the centre of the fluroscein pattern
59
Q

What happens when you are fitting a flat fluroscene pattern ?

A

will cause a negative tear film lens- will find more +- the px is overminused so you will find more + in BVP

60
Q

What do you need to do if you are not happy with the steep fluroscein pattern and want to change it to aligned?

A

if you change the BOZR to create a more aligned FP, you need
to change the BVP of lens aswell
-every 0.1mm change in BOZR = BVP 0.5D change
-Or smallest change in BOZR (0.05mm) = smallest change in power
(0.25DS)

61
Q 
Example
Spectacle Rx: -3.00/-0.25 x 90
K readings: 8.10 along 180 x 7.90 along 90 CL trial (BOZR/TD BVP): 8.00/9.50 -3.00 Movement -1, PFP +1
Over refraction: -0.50DS 6/5
CL BVP: -3.50
A

????????

Central pooling causes -ve over refraction to compensate for positive tear film
- BOZR 0.1mm change = BVP 0.50D change

OV2006 contact lenses (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions