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Contact lenses year 3 > Keratoconus > Flashcards

Keratoconus Flashcards

1
Q

what is the incidence of keratoconus
where are most keratoconus px’s found
what can their cause be down to

A
  • approx. 1 in 2,000
  • most found in mountain area 1 in 500
  • in closed communities which are remote
  • maybe genetic link
  • maybe due to low pressure in upper mountain area which encourages the eye to bulge out because of IOP
  • but in fact we dont know what its down to
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2
Q

list the 4 facts about keratoconus

A 
- The condition occurs in every
country throughout the world.
Rules out:
1.environment
2. diet
  • Occurs equally in men and
    women
  • Usually begins between the
    ages of 12 and 32
  • Condition of unknown etiology
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3
Q

how many % of people with KC undergo corneal transplant surgery
and what do the other 90% end up needing

A
  • only 10% but these px’s also end up needing optical correction afterwards
  • other 90% only end up needing optical correction
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4
Q

what is the pattern of KC between both eyes

A

it is mostly in one eye more than the other

it is rarely advanced in both eyes

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5
Q

what is the normal D power of the cornea and the radius of curvature
what is the extreme D power of a KC cornea and the radius of curvature

A

Normal:

  • 43.00D
  • 7.85mm

KC cornea:

  • 102.50D
  • 3.30mm
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6
Q

what 3 types of keratoconous are there

A
  • puberty onset
  • late onset
  • Keratoconus Fruste
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7
Q

when does puberty onset begin
how are both eyes affected
what causes the condition to be more severe

A
  • Begins in early adolescence
    approx. age 12 to 16

- Usually bilateral with one eye
affected worse than the other

- The younger the patient, at the time of diagnosis, the more severe the condition

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8
Q

when does late onset puberty onset begin
how are both eyes affected
what causes the incidence of progression to reduce

A
  • Usually begins in late 20’s or early 30’s

- Both eyes can be affected the
same

- The incidence of progression
reduces greatly with the age of
onset
(so doesn’t get as bad as it will for a 12/13 y/o)

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9
Q

what type of KC is keratoconus fruste
when can it occur
what do the slit lamp findings show
what is the cornea like

A
  • A mild non-progressive form KC
  •  Can occur anytime throughout life

- No positive slit lamp findings
associated with KC (but you get a distortion of the cornea)

  •  Normal corneal thickness and does not progress
  • It is just like a pseudo KC
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10
Q

what are the 2 types of KC topography called

A
  • Nipple cone/symmetrical

- Oval cone/asymmetrical

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11
Q

describe what is seen with the nipple cone

A
  • cone is fairly central
  • cone is less than 5mm
  • it is normally circular
  • cone will move down and IN (towards nose)
  • easy to fit CLs on because you still get a regular shape
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12
Q

describe what is seen with a oval cone

A
  • oval in shape
  • cone can grow beyond 5mm
  • cone will move down and OUT (temporally)
  • as the cone moves more into the periphery, it gets difficult to fit
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13
Q

what is the similarity with both cones and what differentiates them

A
  • similarity = as they progress they both tend to move down
    as both move into the periphery, CL fitting gets more difficult
  • Nipple cone - moves down and IN
  • oval cone - moves down and OUT
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14
Q

what are the 5 hallmark signs/symptoms of KC

A
  • Decline in visual acuity
    - Changes in cylindrical power and axis
    - Increased myopia (as cornea starts to pretude)
    - Squeezing of the eyelids, artificially
    creating a pinhole effect
    - Appearance of halos around street lights
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15
Q

what 4 tissue changes occurs in KC and how can it get picked up
and name one other sign that isn’t necessarily picked up by SL

A

picked up by SL

  • Vertical Striae – Vogt’s Striae
  • Fleischer’s Ring
  • Increased Visibility of the Corneal Nerve Fibres
  • Thinning of the Central Cornea
  • Munson’s Sign
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16
Q

what are vogt’s striae

A
  • striations/stress marks in the cornea
  • this gives change in the refractive index
  • is vertical orientation
  • they disappear and change when push thumb on sclera, which alters the shape of the cornea and changing/relieving the stress
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17
Q

what are Fleischer’s Ring

A
  • rust marks around the cornea
  • from iron deposits that settle in the cornea and haven’t been swept away by the lids
  • the iron mark defines the position of the cone
  • it is very uniform and goes around the cone
  • can be offset is cone is offset
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18
Q

what is seen with corneal thinking

A
  • the normal 550nm of cornea can get much thinner over the cone
  • can be judged by optic section of SL and flourescein layer compared to cornea when fitting a scleral lens
  • it can become half its thickness
  • the thinner the cornea = the more pronounced the cone
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19
Q

what is a ddx of Fleischer’s Ring

A

Kaiser Fleischer’s Ring = copper deposits which is linked to wilson’s disease which collects around the limbus

20
Q

how is Munson’s sign seen

A

you lift the lid up and get px to look down = can see cone sticking out against the lower lid

is easy to check for suspect cone

21
Q

what can be used to assess the type and amount of KC

how large can an advance cone get and what implications can this have

A
  • topography
  • advance cone is only ~200um
  • but if on optical axis it can cause large vision changes
22
Q

how was a lens for KC historically fitted, name 2 ways

explain the disadvantages that these methods had

A
  • Large Diameter, Flat Lenses
    that align the flat superior cornea:
  • this was by lid attachment = lazy way to fit lenses
  • just used to fit the lens flat and lid used to hold the flat edge and hold the lenses when it moved up and down when blinking
  • worked well with a central cone as the gap between cornea and lens will fill up with tears and correct the vision
  • the problem was the cornea would get pressure from the flat fit on the cone and this would cause corneal scarring and a detriment to vision
  • Small Diameter, Spherical Lenses with small posterior OZ’s, and multiple, flat, secondary and
    peripheral curves:
  • very steep lenses to go over the top of the cone
  • only good if cone was central
  • if off centre, the lens would rock around
  • so was difficult to create lens to fit perfectly over the curve due to lack of technology
23
Q

what is the 5 more recent types of CLs for KC

A
  • Large Diameter, Aspheric Lenses
    apical clearance designs
  • Semi-scleral lenses
  • Piggyback lenses
  • Custom soft lenses
  • Hybrid lenses
24
Q

what is a piggy back lens for KC

A

a soft lens which has a GP lens hooked on top of it

25
Q

which type of cone is easiest to manage

what tends to happen as it develops

A
  • central/symmetrical KC

- tends to move down and nasally as it develops

26
Q

which type of cone is less easier to manage

what tends to happen as it develops

A
  • inferior/asymmetrical KC
  • tends to move more down and temporally
  • it gets more difficult to manage as it gets to the periphery of the cornea
27
Q

what are the 3 fitting goals for KC with spherical lenses

A
  • Peripheral Landing: want 3 and 9 o’clock landing then it doesnt matter if the lens rocks as it can handle the weight
  • 360 degree edge lift
  • Apical Clearance: but not too much central clearance, still want to see pupil through flourescein
28
Q

what 2 machines does not tell you anything about how the lens will fit and therefore what is a better method to assess

A
  • keratometer and topographer

- flourescein is best way to assess

29
Q

which type of lens gives a better transition

A

aspheric lens designs

30
Q 
what type of design is the aspheric lens 
what type of optics does it have 
what is the diameter 
what many options does it have 
how many fitting sets can you get
A
  • Adjustable posterior aspheric designs
  • Compensating anterior aspheric optics
  • Diameter: 8.8 mm-10.4mm
  • Many material options
  • Reasonable 12 to 22 lens diagnostic sets
31
Q

with a piggy back lens, what is the soft lens used for and what is the hard lens used for
what is advantage
what is the disadvantage

A
  • soft lens: +ve lens for dampening down the KC
  • RGP lens: to cancel out the KC
  • adv: comfortabel and good vision
  • disadv: 2 lenses to deal with
32
Q

how does a semi scleral lens work with KC
what size range does it come in
when doesn’t a semi scleral lens work for KC

A
  • it has a fenestration hole
  • all the irregularity is bridged and all the weight is on the limbus and sclera
  • 13.0 to 18.0mm GP Lenses
  • but doesn’t work if the KC cone is on the lower cornea/close o the limbus = need larger lens for pellucid margin
33
Q 
what is pellucid marginal degeneration 
what type of rx is seen 
what does the topography look like 
what gives good va's 
when does it occur 
when can it be more difficult to fit 
what is the only lens that can work
A
  • Thinning of inferior cornea: is not KC
  • Ectasia
  • Irregular Astigmatism
  • Kissing birds topography: where the high spots tend to kiss
  • VA can be quite good with spectacles
  • Occurs later
  • Can be more difficult to fit as ectasia is more peripheral because the lens is then touching the top of the cone
  • Only a large scleral lensman work
34
Q

what different shapes can a cornea become from a corneal graft
what type of rx is seen
which lens is best to fit for this and why

A
  • sunken, tilted, proud, ectatic
  • Irregular astigmatism
  • scleral lenses as it bridges all of the graft
35
Q

what 4 laser surgeries can cause thinner corneas
what type of topography will show in myopic eyes
what CLs will be needed for this
which CLs may not fit well
what type of topography will show in hyperopic eyes

A
  • LASIK/LASEK/PRK/RK
  • MYOPIC - Flat central topography
  • REVERSE GEOMETRY NEEDED
  • SOFT LENSES MAY NOT FIT WELL
  • HYPEROPIC – Steepened central
    topography
36
Q

what condition post laser surgery makes it look like the px has KC

what is the incidence of this

what is the outcome of the eye of this condition

A
  • Post Laser Ectasia – looks like keratoconus
  • Incidence approx 0.5/1000
  • Irregular astigmatism and thinned cornea
37
Q

list 4 features of a CL fit that will show an ideal fit for KC
where is the only place you should look when assessing your fit

A
  • light feather touch at apex of cone, a small amount of apical clearance is ok
  • close to alignment as possible over the cornea
  • edge clearance should be producing a flourescein band of 0.5-0.8mm all around
  • good centration
  • only look at whats happening along the 180 meridian. you want some edge lift as the lens is going to rock
38
Q

what 2 signs is seen in a CL fit that is too flat for KC

what do you need to do to correct this

A
  • excessive bearing, increases the risk of damage
  • increased scarring
  • steepen the BC until the feather light touch is achieved
39
Q

what are the 3 signs if a CL fit has too much central clearance for KC
what do you need to do to correct this

A
  • excessive apical clearance
  • may result in reduced visual acuity
  • reduced edge lift which causes the lens to dig in
  • flatten the BC until theres a very light apical touch
  • when flattening, go one step down for a slight touch and this will cause increased edge lift
40
Q

what is a quadrant specific design lens
what is the advantage to this lens
what condition can this help with

A
  • a different curve in each quadrant
  • so can specify is want to tighten/loosen in a part of the quadrant and the manufacturer will adjust by steps to improve the fitting
  • this allows the edge quadrant to be made flatter or steeper than others
  • help combat edge stand off found in the 270 deg due to inferior steepening i.e. with pellucid marginal degeneration, where bottom edge is pressing
    this mechanism can be used to tighten the bottom edge = to tuck it a bit under the cone
41
Q

what size of scleral lens can be quite comfortable for KC
how can this be easier for practitioners and px to fit/use
what is the fitting technique like
what appearance gives an indication of a good fit

A
  • 15-16mm TD (similar to SCL)
  • the practitioners are familiar with handling a soft lens
  • the px is familiar with putting something that size in their eyes
  • fitting technique: same as for all lenses = start to look at centre and work towards edge
  • good fit: just see pupil through the flourescein
42
Q

how will you assess the corneal clearance on a px with KC
what should be seen
after how long
what does a bigger lens cause

A
  • check central clearance with flourescein and white light at 60deg
  • the clearance should be the same as the lens thickness ~350um underneath the lens
  • after 2-4 hours wear, the lens settles and the clearance should be 180-200um i.e. half the lens thickness
  • so you need 2-4 hours to make an assessment and not done straight away
  • which will reduce from ~350um to ~150um
  • the bigger the lens = the less the lens will sink in as the weight is larger on the sclera
43
Q

when assessing the central clearance, and slight touch is seen, what do you need to do with your fitting

A
  • increase the sag by one step

- one step = 200um

44
Q

when assessing the central clearance and theres too much clearance, what do you need to do with your fitting and what sign shows there is too much clearance

A
  • decrease the sag by one step
    i. e. No 5 to No 8
  • the pupil will no longer be visible under the flourescein when clearance is too much
45
Q

when assessing the edge lift:
how should it look
why is it easy to see with a scleral lens is its too tight
what way should you not assess it

A
  • the edge should be parallel to the sclera
  • with scleral lens if too tight can see no blood in the limbal vessels
  • do not assess the limbal clearance before you have the correct edge/landing zone

Contact lenses year 3 (15 decks)

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