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.

1. Raman Prasad Sah
Optometrist
B.P. Koirala Lions Centre for Ophthalmic
Studies
Institute of Medicine, Kathmandu, Nepal

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

4. Keratometer (Ophthalmometer )
Keratoscope :
• Placido disc
• Photokeratoscopy
• Video Keratoscopy (Computer assisted
topographic analysis.)

7.  Examination of curvature of anterior surface of
cornea
Nidek keratoscope Kera corneoscope

9. Principle
Use of the first Purkinje
image.
 Consists of equally
spaced alternating black
& white lines.

10.  A luminous object
(target of rings) is
placed in front of
patient’s cornea.
 Image size produced
in the corneal
reflection is measured

11.  Circular Rings -Spherical cornea
 Oval Rings –Regular astigmatism .
 WTR astigmatism
 ATR astigmatism
With long vertical axis –
Against the Rule Astigmatism.

14.  Irregular astigmatism
 Corneal anomaly–
irregular cornea
distorted cornea
scar
 Keratoconus

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

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

24.  1 .Color coding
 2. Scale
 3. Quantitative indices

25. Cool colors (black, blue, azure)
Flatter surfaces
Warm colors (orange, red, white)
Steeper surfaces
Normal (green, yellow)
Normal surfaces

26. Range: 28.o0 D to 65.00 D
Interval : 1.5 D

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.

31. Round: 22.6%

36. Bow- tie patterns indicate astigmatism

38. Small, near central ectasia,
less than 5.0 mm in cord
diameter
May manifest as moderate to
high with-the-rule corneal
astigmatism

40. In advanced keratoconus.
Corneal apex is displaced
well below the midline
resulting in varying
degrees of inferior mid-
peripheral steepening.
Kissing pigeon pattern

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)

44.  Typical with-the-rule
astigmatism is induced.
 Bow-tie pattern oriented
vertically.

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

48. Diagnosis of Corneal degenerations &
dystrophies.
Keratoconus
Keratoglobus
Pellucid Marginal Degeneration
Terrien’s Marginal degenerations

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