corneal astigmatism
TRANSCRIPT
REMOVE THE STIGMA IN ASTIGMATISM
DR KAUSHIK
• Author has no financial interest in any of the products or companies mentioned in the following talk
ASTIGMATISM
IRREGULAR CORNEA
EVOLUTION IN CORNEAL EVALUATION
• MADDOX ROD• PLACIDO DISC• MANUAL KERATOMETER• VIDEO KERATOSCOPY• TOPOGRAPHY• ORBSCAN• PENTACAM• IOL MASTER
MADDOX ROD
PLACIDO DISC
MANUAL KERATOMETER
MANUAL KERATOMETER
Auto keratometer
• Super luminescent diode• Light emitting diode• Pupil zone 3.3 mm - extendable to 6mm• Gives average of 3 values per eye
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-530AAuto Refractor/KeratometerGeorge A Gibson BSc, MCOptom and Leon N Davies PhD, MCOptom, FAAO
TOPOGRAPHY
ORBSCAN
PENTACAM
IOL MASTER
• 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.
Lenstar Haag Streit
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.
CONCEPTS OF CORNEAL IMAGING
• PLACIDO DISC• CURVATURE MAPPING• ELEVATION MAPPING• REFRACTION MAPPING
What to do
• Availability • Affordability • Accuracy• Repeatability
Deptm. of OphthalmologyRuprecht-Karls-University Heidelberg
Chair: Prof. Dr. med. H.E.Völcker
Reliability of Posterior Corneal Elevation Topography for Orbscan II and a Rotating
Scheimpflug CameraM.S. Reuland, MD A.J. Reuland, MDT.M. Rabsilber, MDI.J. Limberger, MD
G.U. Auffarth, MD Prof.
HeidelbergIOL & refractive surgery
research group
www.lasik-hd.de [email protected]
The authors have no financial interests in any of the products mentioned.
Results
No difference in shape: 61/63 (97%)
2 different shapes: 1/63 (2%)
3 different shapes: 1/63 (2%)
No difference in shape: 45/62 (73%)
2 different shapes: 15/62 (24%)
3 different shapes: 2/62 (3%)
No difference in shape: 29/62 (47%)
Different shapes: 33/62 (53%)
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.
Fig. 8: Patient 1 (OS): 3 repeated Pentacam measurements
Fig. 9: Patient 2 (OS): 3 repeated Orbscan measurements
Fig. 10: Patient 3 (OS): Pentacam (l) vs. Orbscan (r)
Practical problems
• Earlier keratometers worked on Purkinje images – anterior corneal surface
• Newer ones take the posterior surface also• Posterior surface accounts for 10% refraction
Axis
• All machines unreliable• Only Pentacam and Aberrometer scored well• Head tilt / face turn / cyclotorsion• No standardisation• No landmarks
Manual K
• Takes only purkinje images• Inter observer error• Only central 3mm • Frequent calibration
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
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
Calibration of Keratometer
• Confirm eye piece focus (1D difference)• Multiple readings from several steel spheres• Check for normal individual
Topo
• Poor repeatability• No correction for head tilt• Poor results in dry eyes, surface issues
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
If you don’t have money
• Manual K still very good• Double check with Auto K
If you have the money
• Go for IOL Master or Pentacam
Above all else
• Pray
Thank you