Centration of Hyperopic Corneal Ablations: Corneal Vertex vs. Pupil Center
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This study compared centering hyperopic corneal refractive surgery ablations on the corneal vertex versus the pupil center. The study included 60 eyes divided into groups with small or large angle kappa. All ablations were centered on the corneal vertex. The study found no significant differences in accuracy, safety, or night vision between groups. However, eyes with large angle kappa had significantly worse contrast sensitivity and increased coma and spherical aberration when measured at the pupil center, but not at the corneal vertex. The conclusion was that ablations should be centered on the corneal vertex rather than the pupil center.
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Centration of Hyperopic Corneal Ablations: Corneal Vertex vs. Pupil Center
- 1. Centration of Hyperopic Corneal Ablations: Corneal Vertex vs. Pupil Center Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth 1,2,3,4 1. London Vision Clinic, London, UK 2. St. Thomas’ Hospital - Kings College, London, UK 3. Weill Medical College of Cornell University, New York, USA 4. Center Hospitalier National d’Ophtalmologie, (Pr. Laroche), Paris, France
- 2. Financial Disclosure The author acknowledges a financial interest in Artemis™ VHF digital ultrasound The author is a consultant for Carl Zeiss Meditec AG (Jena, Germany)
- 4. Centration: Visual Axis vs Entrance Pupil Phoroptor Lens No Angle Kappa Phoroptor Manifest Refraction Excimer Laser Ablation Large Angle Kappa Ablation Profile Phoroptor Lens
- 8. Study Design: Outcome Measures IF: PUPIL CENTER = CORRECT TREATMENT Small Angle Kappa Large Angle Kappa Safety Good Worse Accuracy Good Worse Contrast Sensitivity Good Worse Pupil wavefront Good Worse Corneal wavefront Good Good Night vision Good Worse
- 9. Study Design: Outcome Measures IF: CORNEAL VERTEX = CORRECT TREATMENT Small Angle Kappa Large Angle Kappa Safety Good Good Accuracy Good Good Contrast Sensitivity Good Good Pupil wavefront Good Worse Corneal wavefront Good Good Night vision Good Good
- 10. Methods: Matched Groups Pupillary offset Pupillary offset (mm) Within 0.25 mm 0.17 ± 0.05 mm More than 0.55 mm 0.69 ± 0.10 mm Small angle kappa Large angle kappa N (eyes) 30 30 Min hyperopic meridian (D) +3.85 ± 0.98 D (+2.50 to +5.50D) +3.87 ± 0.90 D (+2.50 to +5.50D) BSCVA 93% eyes ≥ 20/20 7% eyes = 20/25 93% eyes ≥ 20/20 7% eyes = 20/25
- 11. Results
- 13. Results: Surgical Outcomes - Accuracy Post-operative spherical equivalent: Small angle kappa : 0.38D ± 0.80D Large angle kappa : 0.48D ± 0.73D No statistically significant difference (p=0.171) Χ 2 contingency table
- 14. Results: Surgical Outcomes - Safety % of eyes No statistically significant difference (p=0.315) Χ 2 contingency table
- 15. Results: Contrast Sensitivity * * * Small angle kappa Large angle kappa Statistically significant (p<0.05) *
- 16. Results: Pupil center wavefront - WASCA * p=0.004 Aberrations reported in OSA nomenclature All values are in microns and for a 6 mm pupil Small angle kappa Large angle kappa Change in coma and spherical aberration (SA) Pre Post Coma 0.18 ± 0.11 0.55 ± 0.29 SA 0.22 ± 0.15 -0.24 ± 0.19 Pre Post Coma 0.25 ± 0.12 0.87 ± 0.33 SA 0.24 ± 0.13 -0.25 ± 0.22
- 17. Results: Corneal vertex wavefront Aberrations reported in OSA nomenclature All values are in microns and for a 6 mm pupil Small angle kappa Large angle kappa Change in coma and spherical aberration (SA) * p>0.05 * p>0.05 Pre Post Coma 0.34 ± 0.17 0.69 ± 0.34 SA 0.26 ± 0.08 -0.13 ± 0.21 Pre Post Coma 0.38 ± 0.19 0.72 ± 0.50 SA 0.20 ± 0.09 -0.19 ± 0.19
- 18. Results: Subjective - Night Vision None Slight Mild Visually Significant Surgical Eyes Visual Effects Simulator (Adam Bogart, Toronto, Canada) No statistically significant difference (p=0.252) – Χ 2 contingency table POST None Slight Mild Visually Significant Severe Small angle kappa 67% n=20 27% n=8 7% n=2 0% n=0 0% n=0 Large angle kappa 70% n=21 23% n=7 0% n=0 7% n=2 0% n=0
- 19. Conclusion
- 20. Conclusion Ablation Corneal Vertex Centration Ablation Pupil Centred Centration
- 21. Centration of Hyperopic Corneal Ablations: Corneal Vertex vs. Pupil Center Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth 1,2,3,4 1. London Vision Clinic, London, UK 2. St. Thomas’ Hospital - Kings College, London, UK 3. Weill Medical College of Cornell University, New York, USA 4. Center Hospitalier National d’Ophtalmologie, (Pr. Laroche), Paris, France Thank You
Editor's Notes
- I have a financial interest in the Artemis technology and I am a consultant for Carl Zeiss Meditec
- One of the big unresolved questions in refractive surgery is where to center ablations How many of you treat on the pupil center? How many treat on the corneal vertex?
- If a patient has no angle kappa and we’re refracting them in the phoroptor, then the visual axis and entrance pupil are both aligned with the phoropter lens. But, if there is an angle kappa, we do not then move the lens away from the corneal vetex to align the lens we are refracting with the entrance pupil, the eye presents it’s vertex to the world, not it’s entrance pupil. So, it’s baffling that most companies are still telling surgeons to centre their treatments on the entrance pupil – which creates a new vertex for the cornea, rather than maintaining the one that God provided! So, ablations need to be centred on the corneal vertex which best approximates the visual axis thank-you Milind.
- The purpose of this study was to prove that ablations should be centred on the corneal vertex and not the entrance pupil center
- The ideal study design would be to prospectively randomize pupil or vertex centration on a large number of eyes with a large angle kappa, and observe whether pupil or vertex centered eyes did better. The problem with this is that by definition, depending on the answer, a number of eyes would suffer from poor outcomes due to decentration.
- Therefore, we designed our study as a proof by contradiction In proof by contradiction, you start with an assumption, then if the result turns out to be different to the expected result, the initial assumption must be wrong The assumption to be tested was therefore that: Ablations should be centred on the pupil center In my practice, with all eyes receiving corneal vertex ablations, we’d expect patients with a large angle kappa to do worse, as these eyes according to the assumption, should have been treated on the entrance pupil center.
- The outcome measures were to look at safety, accuracy, contrast sensitivity, ocular wavefront – which is measured from the center of the pupil, vertex centered corneal wavefront, and subjective night vision through a night vision simulator program. If ablations should be centred on the pupil center, the outcomes should be worse for the large angle kappa group – except for the corneal vertex wavefront as the aberrations measured would be aligned with the vertex centered ablation
- If ablations should be centred on the corneal vertex, there should be equally good outcomes for both groups – the only exception would be for the pupil centered wavefront – where we would expect the large angle kappa eyes to have increased coma as they would have been ablated “off-center”
- The two groups were constructed from a consecutive series of hyperopic LASIK cases. For group 1, the small angle kappa group, the pupil offset was within 1/4-mm of the pupil center, while for group 2, the pupil offset had to be greater than 0.55-mm. Thirty eyes with a minimum of +2.5 D of hyperopia were recruited for each group, ensuring that they were matched for minimum hyperopic meridian and BSCVA (with all eyes being at least 20/25). The cylinder was restricted to a maximum of +2.00 D and the age was restricted up to 60.
- Results
- First, we measured the centration of the ablation on topography to confirm that the ablation was well centred on the corneal vertex in both groups We found a mean decentration of less than 0.1-mm in each group, and there was no difference in centration between groups.
- There was no difference in accuracy between the two groups
- There was no difference in safety between the two groups
- There was no difference in contrast sensitivity between the two groups
- According to pupil centred wavefront measurements, there was no difference in the change in spherical aberration, but there was statistically significantly more induced coma in the large angle kappa group
- Vertex centered corneal wavefront showed no difference between groups in the change of either spherical aberration or coma
- There was no difference in subjective night vision disturbances between the two groups
- There was no difference between groups for any of the outcome measures other than the pupil wavefront The results were NOT worse in the large angle kappa group, which contradicts the initial assumption that ablations should be centered on the entrance pupil
- Therefore, this study suggests that ablations should be centred on the corneal vertex and not on the entrance pupil center
- Thank you.