CLM - Keratoconus I - Week 2 Flashcards
Describe what keratoconus is.
A condition in which the cornea assumes a conical shape as a result of non-inflammatory thinning of the stroma
Is keratoconus inflammatory or non-inflammatory?
No
True or false
Keratoconus is the most common corneal ectasia.
True
What is the main force behind the distortion of the corneal shape with progressive thinning?
IOP
Is keratoconus progressive or acute?
Progressive
What kind of astigmatism is generally the result of keratoconus?
Irregular astigmatism
Give corneal thicknesses for the following stages of keratoconus: Normal Subclinical Mild Moderate Severe
Normal - 545um Subclinical - 500um Mild - 475um Moderate - 440um Severe - 415um
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
What kind of ametropia and astigmatism (2) may be seen in keratoconic eyes?
High myopia and either oblique or against the rule astigmatism
What is a sensitive and reliable test for detecting keratoconus?
Retinoscopy - scissors reflex
Can keratoconus be present in a cornea of normal thickness?
Yesd
How do corneal nerves appear in a keratoconic eye?
Increased visibility
What are Vogts striae and how do they appear?
Fine, whitish, usually vertical lines produced by the compression of descemets membrane and deep stroma
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
Describe munsons sign.
Bulging of the lower lid on the downward gaze caused by the corneal protrusion - advanced cases only
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
What is the incidence of acute hydrops in keratoconus?
3%
Is keratoconus significantly uni- or bilateral?
Bilateral (5-15% monocular)
Until what age does keratoconus generally progress until?
Until the 3rd or 4th decade
Is the cause of keratoconus known?
Unknown
Is there a genetic predisposition for keratoconus or is it purely environmental?
There is a genetic link
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
What three ethnicities are at higher risk of keratoconus?
Asian
Maori
Arabian
Give a possible cause of keratoconus.
Stromal thinning possibly caused by increased activity of proteinase enzymes and decreased proteinase inhibitors, causing reduced biochemical stability
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
