Corneal Topography 3A

Who measured the local slope of the cornea in one meridian?

Von Helmholtz

Who designed the first Keratometer?

Javal and Shiotz

Who invented the Keratoscope in 1880?

Antonio Placido

Who modified the technique to Photokeratoscopy?

Allvar Gullstrand

**Allowed for measuring radius of curvature

Who introduced “curved bowl placido disks” in 1950?

Wesley-Jessen Company

What happened with the topography in 1980s?

Projected images are digitized

Allowed for computer analysis of images

What changed in 1990s for Topography?

Automated systems

Martin Gersten- corneal modeling system

What is corneal TOMography?

Projection technology with scanning slit

Creates cross-sectional images of the anterior segment

What are the 3 primary types of measuring corneal curvature?

Keratometry

Reflection based topography

Projection topography

What are the characteristics of Keratometry?

Reflection of two images

Measures the curvature of the 2 principal meridians (flattest and steepest)

ONLY MEASURES central 3 mm

Measures flexure when done over hard CL

How does manual Keratometry work?

Doubling prisms (horizontal and vertical)

Measures horizontal and vertical meridians

Mires reflected off cornea, used to align to find radius of curvature

What are the characteristics of Auto Keratometer?

Reflected image

Uses computer algorithm to measure curvature

Repeatable

Less SUBJECTIVE than manual

Practitioner can evaluate mire quality

What are the characteristics of Reflection based topography?

Placido disc topography

Measures ONLY anterior surface of the eye

Reflected off of TEAR film

Tear stability important and centration

Flat device— Larger working distance

Curved/cone pattern— shorter working distance, more accurate, less distorted peripheral cornea

What are characteristics of Projection Topography? (Tomography)

Scanning slit illumination

Scheimpflug imaging

Cross-sectional images

True elevation and data acquisition

ANTERIOR and POSTERIOR cornea

Epithelial thickness and full corneal thickness

Examples: Orbscan, Pentacam, Galilei

What are the characteristics of Projection Topography? (Profilometry)

Projects series of lines across entire corneal surface

Elevation data of entire ocular surface: Cornea, sclera, conjunctiva

Important in scleral contact lens design

No significant corneal details

What do cooler colors display on a topographer?

Flatter cornea

What do warmer colors display on a topographer?

Steeper cornea

What do SIM-K’s show?

Corneal thickness

Average of 42.00-45.00 D

What else does a topography display show?

Pupil zone/diameter

Irregularity indices

Corneal diameter

Grid/degree measurements

What is RELATIVE scale on a topographer?

Curves available on that cornea

SPECIFIC to the cornea you are looking at

More DETAIL

Difficult to make comparisons

What is ABSOLUTE scale on a topographer?

Representation of ALL AVAILABLE corneal curves

Colors are distributed over that range

LESS DETAIL specific to this cornea

Potentially better for contact lens practice.