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OD3 (S1&2) > CLM - Keratoconus I - Week 2 > Flashcards

CLM - Keratoconus I - Week 2 Flashcards

1
Q

Describe what keratoconus is.

A

A condition in which the cornea assumes a conical shape as a result of non-inflammatory thinning of the stroma

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2
Q

Is keratoconus inflammatory or non-inflammatory?

A

No

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3
Q

True or false
Keratoconus is the most common corneal ectasia.

A

True

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4
Q

What is the main force behind the distortion of the corneal shape with progressive thinning?

A

IOP

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5
Q

Is keratoconus progressive or acute?

A

Progressive

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6
Q

What kind of astigmatism is generally the result of keratoconus?

A

Irregular astigmatism

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7
Q

Give corneal thicknesses for the following stages of keratoconus:
Normal
Subclinical
Mild
Moderate
Severe

A

Normal - 545um
Subclinical - 500um
Mild - 475um
Moderate - 440um
Severe - 415um

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8
Q

List the three types of keratoconus and ther proportion of cases they form, the area of cornea affected, and the percentage of cornea involved if applicable.

A

Nipple - 45% near the corneal centre or inferior nasal region
Sagging - 50% larger, below the centre or inferior
Globus - 5% involving up to 75% of the cornea

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9
Q

What kind of ametropia and astigmatism (2) may be seen in keratoconic eyes?

A

High myopia and either oblique or against the rule astigmatism

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10
Q

What is a sensitive and reliable test for detecting keratoconus?

A

Retinoscopy - scissors reflex

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11
Q

Can keratoconus be present in a cornea of normal thickness?

A

Yesd

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12
Q

How do corneal nerves appear in a keratoconic eye?

A

Increased visibility

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13
Q

What are Vogts striae and how do they appear?

A

Fine, whitish, usually vertical lines produced by the compression of descemets membrane and deep stroma

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14
Q

What is fleischers ring and which layer of the cornea is it generally? What can be used for increased visibility?

A

Brownish partial or complete iron deposition ring in the deep epithelium at the base of the cone
Increased visibility with blue light

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15
Q

Describe munsons sign.

A

Bulging of the lower lid on the downward gaze caused by the corneal protrusion - advanced cases only

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16
Q

What are acute hydrops and why do they form?

A

Splits in descemets layer, which allows aqueous to enter the stroma with gross epithelial and stromal oedema

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17
Q

What is the incidence of acute hydrops in keratoconus?

A

3%

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18
Q

Is keratoconus significantly uni- or bilateral?

A

Bilateral (5-15% monocular)

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19
Q

Until what age does keratoconus generally progress until?

A

Until the 3rd or 4th decade

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20
Q

Is the cause of keratoconus known?

A

Unknown

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21
Q

Is there a genetic predisposition for keratoconus or is it purely environmental?

A

There is a genetic link

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22
Q

List 7 risk factors for keratoconus. List the main three first.

A

Ocular allergies
Atopy
Eye rubbing
Ethnicity factors
Downs syndrome
Relative of affected individuals
Connective tissue disorders

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23
Q

What three ethnicities are at higher risk of keratoconus?

A

Asian
Maori
Arabian

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24
Q

Give a possible cause of keratoconus.

A

Stromal thinning possibly caused by increased activity of proteinase enzymes and decreased proteinase inhibitors, causing reduced biochemical stability

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25
Q

What is the most common instrument used by optometrists to quantify corneal shape? Can this device be used to measure keratoconus? Is it considered the standard of care?

A

A keratometer, can be used to measure increased corneal curvature, but no longer the standard of care

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26
Q

What can be seen on a keratometer measurement of a keratoconic eye?

A

Irregular or distorted mires

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27
Q

Are keratometers generally able to deal with the range of corneal curvature seen in keratoconus?

A

Corneal curvature of keratoconic eyes may be greater than the range of the leratometer
Supplementary lenses may be required

28
Q

Describe the basics behind how corneal topography does its measurements.

A

A series of illuminated annular rings are projected onto the cornea/tear film
Reflected image is captured by video and analysed, and curvature is reconstructed into a colour-coded display

29
Q

List four advantages of corneal topography.

A

Superior analysis of curneal shape
Computer assisted contact lens designs
Detection of corneal pathology/irregularity
Accurate monitoring of progression of corneal pathology

30
Q

Describe what axial maps in corneal topography are, what is it referenced from and what does it assume of the radius of curvature?

A

It relates to refraction/corneal power
It is referenced from the optical (sagittal) axis
It assumes the centre of the radius of curvature is on the central axis

31
Q

What kind of estimate can an axial map of a cornea provide on corneal shape, and is it able to highlight minor variations in curvature?

A

Provides a good estimate of overall corneal shape
Does not highlight minor variations in curvature

32
Q

Do axial maps of corneal curvature closely mimic keratometry values or are they not comparable?

A

Closely mimicked

33
Q

On an axial map, what does a change in corneal curvature at a selected point correlate with?

A

The change in refractive power, and therefore the change in refraction

34
Q

What does a tangential map display?

A

True curvature

35
Q

What does a tangential map calculate?
Is the radius of curvature dependent on the central axis?

A

Calculates each measured point of data at a 90 degree tangent to its surface
Local radius of curvature is independent of the central axis

36
Q

What is a more accurate representation of the actual corneal curvature, axial or tangential maps?

A

Tangential

37
Q

Can tangential maps show the exact location of any corneal irregularity?

A

Yesd

38
Q

What is the gold standard for the detection of keratoconus?
What does this technique measure?

A

Corneal tomogprahy
Accurately measures the whole anterior and posterior corneal surface

39
Q

What does corneal tomography provide and what does it allow for the monitoring of? What else can it detect (think posterior)?

A

Provides a complete corneal thickness map and the thinnest corneal point
Allows for the monitoring of progression from the thinnest corneal point to the periphery
Can also detect early posterior corneal shape change despite a stable anterior corneal surface

40
Q

Do keratoconics tend to have greater difficulty with night visiond?

A

Yes

41
Q

List four visual symptoms of keratoconus.

A

Distorted vision
Haloes
Ghosting
Flaring of lights

42
Q

What can increase higher order aberrations in keratoconics, and especially which kind?

A

Increasing corneal asymmetry increases higher order aberrations, especially vertical coma

43
Q

Are clinical signs of early keratoconus often visible on slitlamp examination? What is the recommendation (2)?

A

No
Need to measure with topography and pachymetry

44
Q

How is forme fruste keratoconus diagnosed (2)? What is is exactly? How does it affect visiond? What does the eye look like on slitlamp examination?

A

Diagnosis is confirmed by topography or tomography
Is a very slight corneal distortion
Little or no effect on the quality of vision
Slit lamp exam of the cornea is normal

45
Q

How does forme fruste keratoconus tend to progress over the years and how should it be monitored (2)?

A

Minimal or no progression over the years
Monitored by pachmetry and topography

46
Q

Which of the following are common for good myopia correction in forme fruste keratoconus:
Spectacles
Soft contact lenses
RGP lenses

A

Spectacles and soft lenses are successful for correction
No need for RGPs

47
Q

How is early keratoconus diagnosed (2)? Are there any significant symptoms and what is the corneal distortion like? What does the eye look like on slitlamp examination (4)?

A

Diagnosis is confirmed by topography or tomography
No significant symptoms
Minimal corneal distortion
Slitlamp may appear normal
-striae may be visibled
-fleischers ring may be visible
-no scarring or obvious thinning

48
Q

Which of the following are common for good myopia correction in mild keratoconus:
Spectacles
Soft contact lenses
RGP lenses

A

Spectacles give normal or near normal acuity
Soft lenses can be successful
Ocassionally patients may prefer RGPs for better acuity

49
Q

What is vision like with correction for individuals with moderate keratoconus? What does the eye look like on slitlamp examination (3)?

A

Patient is aware of poor quality vision with spectacles or soft lenses
Striae may be more obvious
Fleischers ring may be visible
Sutble stromal scarring may be visible

50
Q

What four visual disturbances are patients with moderate keratoconus increasingly aware of?

A

Ghosting
Doubling of edges
Flaring - especially at night
Increasing difference of quality of vision between the eyes

51
Q

How well do RGPs work for reducing distortion and correcting visiond for those with moderate keratoconus? Can normal or near normal vision be achieved? Do they reduce higher order aberrations?

A

Substantially reduced distortion and better acuity with RGPs
They can restore vision to normal or near normal
RGP lenses reduced higher order aberrations by up to 90%

52
Q

If using RGPs for a case of moderate keratoconus, when can residual distortion be expected and what is it dependent on?

A

At night, is dependent on pupil size

53
Q

What is vision like for an individual with severe keratoconus corrected with RGPs?

A

May have slight to moderately reduced VA

54
Q

What does an RGP designed for severe keratoconus need and why?

A

Very steep curvatures to clear the cone

55
Q

With severe keratoconus, if corrected with RGPs, what may eventually be developed? What may be needed in such cases?

A

Reduced tolerance to the RGP with reduced wearing time, even with a good fit
May need special soft carrier lenses underneath the RGP

56
Q

Consider severe keratoconus. Once VA with lenses on drops below 6/12 or 6/18, what generally happens next (2)?

A

Patient is then referred for a corneal transplant or corneal graft

57
Q

What percentage of patients with keratoconus need to have a corneal transplant?

A

10-15%

58
Q

List three treatment options for keratoconus.

A

Strongly advise patients against eye rubbing
Treat underlying ocular allergies if applicable with dual action mast cell stabilisers and antihistamines
Progressive keratoconus can be treated with corneal crosslinking

59
Q

What magnitude of progression is generally an indication for corneal crosslinking and what percentage effectivity does it have in stopping progressive corneal steepening?

A

> 1.00D in 12 months
90% effective in stoppung corneal steepening

60
Q

List the 8 contact lens options for keratoconus.

A

Soft lenses
RGPs
Intralimbal
Corneoscleral
SiHy carrier lenses underneath RGPs
Hybrid (RGP centre - soft skirt)
Minisclerals
Sclerals

61
Q

What impacts the type of contact lens chosen for a keratonic patient from history (4)?

A

Work environment
Allergies
Dry eye
Sport

62
Q

What impacts the type of contact lens chosen for a keratonic patient from slit lamp examination (4)?

A

Corneal abnormalities
Corneal scarring
Corneal staining
Tear film quality
Upper palpebral conjunctiva (papillae)

63
Q

What is the standard contact lens option for forme fruste keratoconus?

A

If spectacle VA is good, soft lenses

64
Q

What is the standard contact lens option for moderate and severe keratoconus?

A

If soft lenses do not give good VA, then RGPs may be requried

65
Q

What can happen with too little fluorescein when assessing an RGP fit?

A

It can appear steeper than it really is

OD3 (S1&2) (114 decks)

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