CLM - Keratoconus I - Week 2 Flashcards by B H

Describe what keratoconus is.

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

How well did you know this?

Not at all

Perfectly

Is keratoconus inflammatory or non-inflammatory?

How well did you know this?

Not at all

Perfectly

True or false
Keratoconus is the most common corneal ectasia.

True

How well did you know this?

Not at all

Perfectly

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

IOP

How well did you know this?

Not at all

Perfectly

Is keratoconus progressive or acute?

Progressive

How well did you know this?

Not at all

Perfectly

What kind of astigmatism is generally the result of keratoconus?

Irregular astigmatism

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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.

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

How well did you know this?

Not at all

Perfectly

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

High myopia and either oblique or against the rule astigmatism

How well did you know this?

Not at all

Perfectly

What is a sensitive and reliable test for detecting keratoconus?

Retinoscopy - scissors reflex

How well did you know this?

Not at all

Perfectly

Can keratoconus be present in a cornea of normal thickness?

Yesd

How well did you know this?

Not at all

Perfectly

How do corneal nerves appear in a keratoconic eye?

Increased visibility

How well did you know this?

Not at all

Perfectly

What are Vogts striae and how do they appear?

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

Describe munsons sign.

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

How well did you know this?

Not at all

Perfectly

What are acute hydrops and why do they form?

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

How well did you know this?

Not at all

Perfectly

What is the incidence of acute hydrops in keratoconus?

How well did you know this?

Not at all

Perfectly

Is keratoconus significantly uni- or bilateral?

Bilateral (5-15% monocular)

How well did you know this?

Not at all

Perfectly

Until what age does keratoconus generally progress until?

Until the 3rd or 4th decade

How well did you know this?

Not at all

Perfectly

Is the cause of keratoconus known?

Unknown

How well did you know this?

Not at all

Perfectly

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

There is a genetic link

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

What three ethnicities are at higher risk of keratoconus?

Asian
Maori
Arabian

How well did you know this?

Not at all

Perfectly

Give a possible cause of keratoconus.

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

How well did you know this?

Not at all

Perfectly

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

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

Irregular or distorted mires

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

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

Describe the basics behind how corneal topography does its measurements.

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

List four advantages of corneal topography.

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

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

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

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?

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

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

Closely mimicked

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

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

What does a tangential map display?

True curvature

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

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

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

Tangential

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

Yesd

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

Corneal tomogprahy Accurately measures the whole anterior and posterior corneal surface

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

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

Do keratoconics tend to have greater difficulty with night visiond?

Yes

List four visual symptoms of keratoconus.

Distorted vision Haloes Ghosting Flaring of lights

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

Increasing corneal asymmetry increases higher order aberrations, especially vertical coma

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

No Need to measure with topography and pachymetry

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?

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

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

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

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

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

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)?

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

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

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

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

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

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

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

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?

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%

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

At night, is dependent on pupil size

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

May have slight to moderately reduced VA

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

Very steep curvatures to clear the cone

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

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

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

Patient is then referred for a corneal transplant or corneal graft

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

10-15%

List three treatment options for keratoconus.

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

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

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

List the 8 contact lens options for keratoconus.

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

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

Work environment Allergies Dry eye Sport

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

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

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

If spectacle VA is good, soft lenses

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

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

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

It can appear steeper than it really is