This document discusses corneal topography, which is the examination and mapping of the shape and curvature of the cornea. It describes different techniques for measuring corneal topography including keratometry, photokeratoscopy, and videokeratography. It outlines the major regions of the cornea and indices used to characterize topography maps. Examples of topography patterns are shown for normal, astigmatic, and diseased corneas. Clinical applications of topography including refractive surgery planning and evaluation, contact lens fitting, and diagnosing corneal conditions are also summarized.
2. Study of shape 0f corneal surface.
Configuration or description of surface.
Aspheric – elliptical shape.
Eccentricity: 0.41 – o.58 ( Aver:0.47 )
3. 1. Central Region/Corneal
Cap/Apical Zone/Optic Cap
3-4 mm
2. Paracentral / Mid
Peripheral Region
4-8mm from cornea.
3. Peripheral Region
8-11mm
Regions
16. Small degrees of abnormalities of corneal shape are
not easily identifiable.
Not used in corneas with epithelial defects and
stromal ulcers .
Clinically significant amounts of corneal
cylinder (up to 3.00 D) may not be diagnosed.
Subtle irregularities cannot be detected.
17. Measurement is restricted to a small central
corneal area (3-3.5mm) in keratometry.
Videokeratoscopes evaluate several thousands of
points from nearly the entire corneal surface.
They measure the entire corneal contour.
18. LSU Corneal Topographic System
(LSUCTS)
PAR CTS
Topographic Modelling
System (TMS)
19. Corneal Lens Analysis
System (CLAS)II Unit
Computerized Corneal
Topographic EH-270
The EyeSys 2000 Corneal
Analysis System
ORBSCAN
PENTACAM
20.
21.
22. Process of building a topographic map of cornea
from keratoscopic data .
Capture video images of the keratoscope rings.
Measure angular size of points on the rings.
Reconstruct the corneal surface point by point.
Assign dioptric or other descriptors for each surface.
Present surface descriptors in a color topographic map.
23. Numerical power plots
Simulated keratometry
view
Photokeratoscopic view
Surface Elevation Maps
Color Coded Maps
27. Simulated keratometry (Sim K )
Surface Regularity Index (SRI)
Surface Asymmetric Index (SAI)
Irregular astigmatic index (IAI )
Differential sector index(DSI)
Opposite sector index(OSI)
Centre/surround index (CSI )
Analyzed area (AA)
28. - Measure differences in corneal power & compares
asymmetry.
-Provides the power and location of the steepest and
flattest meridians
- Equivalent to Conventional Keratometry Reading.
29. Surface Regularity Index (SRI)
-Local fluctuation in central corneal power
-Local surface irregularities
Surface Asymmetric Index (SAI)
-Measures differences in corneal power between
corresponding points at each ring & compares symmetry.
- Used to monitor changes caused by contact Lens
warpage or keratoplasty.
38. Small, near central ectasia,
less than 5.0 mm in cord
diameter
May manifest as moderate to
high with-the-rule corneal
astigmatism
39.
40. In advanced keratoconus.
Corneal apex is displaced
well below the midline
resulting in varying
degrees of inferior mid-
peripheral steepening.
Kissing pigeon pattern
41.
42. Hallmarked by a
thinning of the inferior
peripheral cornea.
The corneal thinning
begins approximately
1.0 to 2.0 mm above the
inferior limbus.
43. High against the rule
astigmatism.
Inferior mid-peripheral
steepening at 4 & 8
o’clock position.
Kissing pigeon pattern
(diagnostic of PMD)
45. Depends upon
◦ Location
◦ Severity(extent & depth)
◦ Type of trauma
Flattening along the meridian
of laceration & steepening
along 90* away.
46. Photorefractive Surgery
Preoperative screening
Surgical planning
Assessment of surgical outcomes
Detection & management of complications
Refinement & development of surgical outcome
Expected shape of cornea after refractive surgery
47. Evaluation Of intraocular Surgery
Cataract
Penetrating keratoplasty
Radial Keratotomy
Epikeratophakia
49. Determination Of
◦ Refraction esp. for poor quality retinoscopic reflex.
◦ Curvature of cornea
◦ Amount and direction of corneal astigmatism
◦ Quality of corneal refracting surface
◦ Stability of corneal refracting surface.
50. In cases of trauma
Progressive Myopia
Aphakia or high ametropia
To calculate the power of Intraocular Lens
51. Contact lens fitting
Choice of trial lens.
Verification of contact lens parameters
Monitoring corneal shape
Orthokeratology
52. Borish’s Clinical Refraction
Benjamin Franklin
Principle and practice of refractive surgery
Elander Robin
Corneal surgery, 3rd
edition
Fredrich Brightbill
Refractive Eye Surgery ,2nd
Edition
Leo D. Bores
Optics - Refraction & Contact Lens
AAO-3
IACLE Contact lens module 1 & 9
Primary care optometry
Theodore & Grosvenor