Irregular Cornea Fitting (M2) Flashcards
What are the possible causes of irregular astigmatism?
- keratoconus
- Pellucids marginal degeneration
- post penetrating keratoplasty
- post refractive surgery
- corneal/ocular trauma
What are the signs of keratoconus?
- irregular astigmatism
- Fleischer’s ring
- stromal thinning and scarring
- corneal steepening on topography
- Vogt’s striae
- Munson sign
- Charleaux sign
What is it called when iron deposits surround the base of a cone in keratoconus?
Fleischer’s ring
What are the stress lines that run parallel with the axis of the cone in the posterior stroma in keratoconus that disappear with gentle pressure?
Vogt’s striae
What is the sign of keratoconus in which there is a V shaped lower lid conformation in downgaze?
Munson sign
What is the sign of keratoconus where there is an oil droplet appearance with retroillumination?
Charleaux sign
What is the keratoconus complication in which breaks in Descemet’s membrane cause aqueous to come into the stroma that eventually results in scarring?
hydrops
What are the treatments for hydrops?
- topical antibiotics
- cycloplegics
- hypertonic solution
- nonsteroidal topical med
- steroid topical med
- bandage CL
Are steeper corneas in keratoconic patients fit flatter or steeper than flatter corneas?
flatter relative to flatter corneas
What lenses are generally used to maximize the vision in irregular cornea patients?
gas permeable with rigid material
What are the issues with wearing soft lenses for the correction of an irregular cornea?
- due to steepness of cornea, soft edge may result in fluting
- lens rotation and stability may not be consistent
What needs to be done for specialty soft CLs for irregular cornea patients to wear them?
increase center thickness
What is an example of a specialty soft keratoconus lens?
Kerasoft IC
What are different about the CLEK lens set lenses?
- steep BC
- small optic zone
- large peripheral widths
As a GP lens gets steeper, does the lens become more plus or minus? 1. The lacrimal lens? 2
- more minus
2. more plus
What are the parameters that are able to be changed in proprietary KCN lens designs? 1. What are some examples of these types of lenses? 2
- BC, OAD, power, PC’s
2. Rose K, CentraCone, Maguire, Dyna Z cone
When are hybrid lenses good to use for irregular corneas?
intolerant to GPs but need GP optics
What is a GP lens on top of a soft lens called?
piggyback
What is the preferred type of soft lens to use while piggy backing?
prefer high Dk SiHy material with low modulus and plus lens can help center
What should be done once the soft lens is fitted for piggybacking?
keratometry over soft CL to determine GP BC
What type of fluorescein should be used to evaluate the GP fit during piggybacking?
high molecular weight fluorescein
What are good conditions to use intralimbal GP lenses with large diameters?
- Pellucids MD
2. post PK
Will a GP lens rest and attempt to center on the flattest or steepest part of the cornea?
steepest
What are the possible desired fluorescein patterns for irregular cornea GP fitting (where is the weight of each lens?)?
- apical bearing (weight of lens on corneal apex)
- apical clearance (weight of lens on mid peripheral cornea)
- three point touch on steepest part and mid peripheral cornea (weight throughout cornea)
Why do KCN GP lenses often have small optic zones and overall diameters?
large OZ diam with steep BC creates large sag depth which causes poor alignment of flatter areas of regular mid peripheral cornea
What are the changes in peripheral curve radius that is clinically significant? 1. PC width? 2
- at least 1.0mm
2. at least 0.2mm
What type of lens is able to create different PC throughout the lens?
ROSE K Asymmetric Corneal Technology
Does corneal topography measure the elevation or curvature of the cornea?
curvature
What is the equation to convert the radius of curvature into diopter power?
radius (mm) = 337.5/(diopter power)
What is the corneal topography map that is the curvature relative to the optical axis? 1. Where on the cornea is this limited? 2
- axial maps or sagittal maps
2. peripheral cornea
What is the corneal topography map that is the curvature measured via tangent to the normal and is the shape at a certain point? 1. What is this especially good for? 2
- tangential map or instantaneous map
2. peripheral corna and identifying pathology
What is the corneal topography map that is the refractive power of the cornea? 1. What is this especially good for? 2
- refractive power map
2. pre and post refractive surgery
What is the corneal topography map that is the difference in height from a reference sphere from reference point?
elevation map
At what amount of gap between lens and cornea do bubbles form?
over 90 microns
If there is inferior edge lift off for a Rose K lens, what should be done?
ACT to steepen PC in inferior
