This document discusses the evolution of technologies used to evaluate corneal astigmatism and irregularities. It summarizes several technologies including manual keratometry, video keratoscopy, topography, Orbscan, Pentacam, and IOL Master. Newer technologies like Pentacam and IOL Master provide more accurate and repeatable measurements of the cornea and lens compared to older methods. However, manual keratometry remains useful when budget is limited if performed carefully with calibration and multiple readings. Overall accuracy, affordability, and repeatability must be considered when selecting a technology for corneal evaluation.

1. REMOVE THE STIGMA IN
ASTIGMATISM
DR KAUSHIK

2. • Author has no financial interest in any of the
products or companies mentioned in the
following talk

3. ASTIGMATISM

5. IRREGULAR CORNEA

6. EVOLUTION IN CORNEAL
EVALUATION
• MADDOX ROD
• PLACIDO DISC
• MANUAL KERATOMETER
• VIDEO KERATOSCOPY
• TOPOGRAPHY
• ORBSCAN
• PENTACAM
• IOL MASTER

7. MADDOX ROD

8. PLACIDO DISC

9. MANUAL KERATOMETER

10. MANUAL KERATOMETER

11. Auto keratometer
• Super luminescent diode
• Light emitting diode
• Pupil zone 3.3 mm - extendable to 6mm
• Gives average of 3 values per eye

12. Auto K
• Correlate well with subjective refraction.
• MSE and cylindrical power measured slightly
more negative compared to subjective
refraction; however, this was not a clinically
significant difference
• Keratometric axes were slightly less reliable.
• Intersession repeatability was excellent
Clinical Evaluation of the Nidek ARK-530A
Auto Refractor/Keratometer
George A Gibson BSc, MCOptom and Leon N Davies PhD, MCOptom, FAAO

13. TOPOGRAPHY

14. ORBSCAN

16. PENTACAM

17. IOL MASTER

18. • A non-contact optical device that measures
the distance from the corneal vertex to the
retinal pigment epithelium by partial
coherence interferometry, the IOL Master is
consistently accurate to within ±0.02 mm or
better.
• resolution of 0.10 mm to 0.12 mm, axial
length measurements by the IOL Master
represent a fivefold increase in accuracy.

19. Lenstar Haag Streit

20. Lenstar Haag Streit
• (Optical Low-Coherence Reflectometry) for all
its measurements, including ACD and lens
thickness. OLCR is an advanced technology,
similar to Time Domain OCT.
• 16 individual full eye scans and 4 individual
keratometric scans, taken on 2 concentric
rings, along the patient's visual axis.

21. CONCEPTS OF CORNEAL IMAGING
• PLACIDO DISC
• CURVATURE MAPPING
• ELEVATION MAPPING
• REFRACTION MAPPING

22. What to do
• Availability
• Affordability
• Accuracy
• Repeatability

24. Heidelberg
IOL & refractive surgery
research group
www.lasik-hd.de
mirjam.reuland@med.uni-heidelberg.de
Reliability of Posterior Corneal Elevation
Topography for Orbscan II and a Rotating
Scheimpflug Camera
M.S. Reuland, MD
A.J. Reuland, MD
T.M. Rabsilber, MD
I.J. Limberger, MD
G.U. Auffarth, MD Prof.
Deptm. of Ophthalmology The authors have no financial interests
Ruprecht-Karls-University Heidelberg in any of the products mentioned.
Chair: Prof. Dr. med. H.E.Völcker

25. Results
Comparison of shapes. When comparing the overall forms, again, a better
repeatability was found for Pentacam (fig. 8) than for Orbscan (fig. 9). 27% of
Orbscan measurements showed sometimes quite distinct differences in
shape for repeated measurements. In direct comparison of Pentacam with
Orbscan maps (fig. 10), only half the maps showed the same shape for both
devices.
No difference in shape:61/63 (97%)
2 different shapes: 1/63 (2%)
3 different shapes: 1/63 (2%)
Fig. 8: Patient 1 (OS): 3 repeated Pentacam measurements
No difference in shape:45/62 (73%)
2 different shapes: 15/62 (24%)
3 different shapes: 2/62 (3%)
Fig. 9: Patient 2 (OS): 3 repeated Orbscan measurements
No difference in shape:29/62 (47%)
Different shapes: 33/62 (53%)
Fig. 10: Patient 3 (OS): Pentacam (l) vs. Orbscan (r)

26. Practical problems
• Earlier keratometers worked on Purkinje
images – anterior corneal surface
• Newer ones take the posterior surface also
• Posterior surface accounts for 10% refraction

27. Axis
• All machines unreliable
• Only Pentacam and Aberrometer scored well
• Head tilt / face turn / cyclotorsion
• No standardisation
• No landmarks

28. Manual K
• Takes only purkinje images
• Inter observer error
• Only central 3mm
• Frequent calibration

29. Common mistakes
• Inadequate calibration
• Technique
– Unfocused eye piece
– Distorted mires
– Head tilt
• Cornea problems
– Lid/ lash interference
– Dry eye
– Excessive lacrimation
– Eye ointments
– Surface irregularities / scars

30. Manual Keratometer
• Still excellent
• Train your optometrist well
• Repeat yourself if >46 or <42
• ALWAYS do both eyes
• Repeat if >1D difference
• Do before A scan, AT, invasive procedures
• Cross check with ARK

31. Calibration of Keratometer
• Confirm eye piece focus (1D difference)
• Multiple readings from several steel spheres
• Check for normal individual

32. Topo
• Poor repeatability
• No correction for head tilt
• Poor results in dry eyes, surface issues

33. Where the IOL Master scores
• Average of 5 readings taken
• 3 readings difference less than 0.5D
• Diff between 2 eyes of 1D or 0.2mm
• Measures axial length to RPE not ILM
• Dense cataracts - loses

34. If you don’t have money
• Manual K still very good
• Double check with Auto K

35. If you have the money
• Go for IOL Master or Pentacam

36. Above all else
• Pray

37. Thank you