Cornea and Anterior Seg Flashcards
What is the shape of the typical cornea?
(prolate or oblate)
prolate
steeper centrally, gradually flattens as you move to the periphery
How much of the refractive power of the eye comes from the cornea?
~2/3 or 43 D
What are the four geographic zones of the cornea starting centrally?
- Apex: central 4 mm
- Paracentral: cornea starts to flatten
- Peripheral
- Limbal
Where is an oblate cornea steepest?
In the periphery
The keratometer measures the central ____ mm of the cornea
3 mm
in 2 meridians
The Carl Zeiss Humphrey is a reflection/ projection topographer that uses ___________ _________ to measure curvature of the anterior surface
reflection, placido discs
assumes posterior radius of curvature is 82% of anterior
high rate of error
The Oculus Pentacam is a reflection/ projection topographer that uses the S_________ imaging principle.
projection; Scheimpflug
The pentacam creates 3D images of which surface(s) of the cornea?
anterior and posterior
How is topography helpful before cataract surgery?
determine sphere vs toric IOL
Topography is a useful tool in which 3 ocular surface diseases?
scars, pterygium, nodules
What are 4 causes of artifacts in topography?
- ocular surface/ poor tear quality
- lid position
- lashes
- corneal pathology
Regarding the Humphrey Atlas, What is the the spacing of placido disc circles for a steeper curve?
closer spacing
look for sharp/ crisp lines when determining reliability of the image
What are the three data points captured in the axial map for Humphrey Atlas?
- corneal power: power of sphere with same radius of curvature as the cornea at that point; helps with base curve selection; averages the data; more accurate centrally
- eccentricity: degree of asphericity
- Shape factor: measure of asphericity; negative = oblate and positive= prolate
Which map on the Humphrey Atlas measures both power AND curvature?
Tangential
more accurate and sensitive than axial map
What is Q?
shape of the cornea
average: -0.37 (prolate)
