Topography (Walker - Test 3) Flashcards
Why is corneal topography important?
Allows us to describe and understand what retinal image we are getting. Gives us numbers, elevation, to a more precise number, and assess ocular/corneal shape. **Keratoconus is most common irregular cornea you will see
Classic reasons to use a corneal topographer?
Dz evaluation and monitoring: curvature changes, edema & CL eval: irregular corneas and ortho-k monitoring
Advanced reasons to use a corneal topographer?
Tear film eval, eval of candidacy of refractive surgery, and custom CL fitting (empirical GP lens design)
Tomography vs Topography?
Tomography is both surfaces and topography is anterior surface. Tomography: allows a 3-D section of the cornea to be presented
Topography: helpful in study of the shape of the corneal surface, or corneal curvature
Types of Corneal Topography:
Placido Disk, Scheimpflug Imaging, Scanning Slit
Placido Disk (i.e. Medmont) **following questions are on this
Concentric annular light source onto the corneal surface, reflected light is captured
What type of light projects from the conical instrument?
Red or Infrared
Medmont E300
Small cone; small red concentric circle of red lights, and used for topography data (more precise than large cone)
Oculus Keratopgraph
Large Cone; less sensitive; reflection based system - measure things on tear films and tear film assessment & topography on anterior surface
Placido Disk: Mires
Concentric white circles = mires = reflection on the surface of cornea
Blurrier mires mean?
Evident of a poor tear film
What would keratoconus look like with a placido disk?
Not symmetric and ovalish shape instead of circular shape
On a topographer, what color is indicative of steep?
Hotter color = steeper + more elevated; Red is steepest
On a topographer, what does a blue color indicate?
Cooler color (blue is lowest) = flatter + less elevated/or more depressed
Scheimpflug Imaging (i.e. Pentacam) (Not under Placido Disk)
Off-axis light captures precise measurements of the anterior and posterior surfaces of the cornea
Why is Oculus Pentacam significantly more $?
Allows for posterior measurements
What type of anterior and posterior data does Scheimpflug give?
Optic scan cross section at multiple angles; can see scars, areas of thinning, if pt had keratoconus, etc…
Scanning Slit (i.e. Orbscan)
Slit beams rapidly scan projected light and a camera to capture the reflected beams to create a map of the anterior and posterior corneal surface; Scheimpflug and Placido disk technology
Analyzing a Corneal topography image
Refer to noteservice for images
What do black dots mean in a corneal topography image?
Not reliable data in a particular area. Could be due to eyelashes covering
Axial vs Tangential Corneal Topography?
Axial: Broader average of the curvature. Things are more averaged. Good for basic CL fitting
Tangential: Point by point analysis. Good for molding/finetuning/refractive sx
