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 mirjam.reuland@med.uni-heidelberg.de

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