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Refractive error sensing in natural multifocal eyes
Rafael Navarro
Universidad de Murcia
Vicente Fernández-Sánchez& Norberto López-Gil
Bifocal eyes? Progressive?
Bifocal designs: Spherical aberration
(aspherical, axicons, etc.)
Coma Combinations of HOA
IntroductionLENTIS Mplus
MPlus +3D
• Koomen et al., 1949; Ivanoff, 1953• Charman & Walsh, 1989• Legras & Bernard, 2011; Legras et al. 2012
Refraction changes across pupil
Human Eyes:
Introduction
(Legras & Bernard, ARVO2011)
Trough focus visual quality(SA4 ± SA6 induced by adaptive optics)
MonofocalBiofocal
Experiment···VSR Metrics
Introduction
y = 0.9279x ‐ 0.1662R² = 0.9366
‐10
‐8
‐6
‐4
‐2
0
2
4
6
‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6
RMS metric versus subjective (clinical) refraction
(López-Gil et al. 2009)
Good overall agreement
But Individual discrepancies
Problem: Individual discrepanciesDiscrepancies > 1 D are frequent; in a few cases > 2.5 D
Explanations?- Wrong aberrometric Metric? But Most metrics give similar results- Bad subjective refraction? But all methods give consistent values- Different conditions? Illumination, pupil, individual neural response,…
Cannot explain large discrepancies
Cue: High discrepancy ↔ High HOA (coma, SA)
Unsatisfactory!
Hypothesis: Bifocal eyes?
WavefrontSubjective
Methods1.- Data: from 178 normal eyes taken from previous study
(López-Gil et al., 2009)
Objective refraction: retinoscopy & autorefractometer (Canon T1000)Subjective refraction: Standard & custom Badal systemAberrometry: (irx3, Imagine Eyes)
2.- Refractive Error Sensing (RES):Refractive error from aberrometry
(Navarro, 2010)
YYXY
XYXX
WWWW
CSCCCS
045
450
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
-2
0
2
4
6
8
-6
-4
-2
0
2
4
Refractive Error = W Curvature
3.- Identify bifocals > 1 D: 8/178
4.- Analysis: Generalized RES for inhomogeneous/irregular pupils
Standard RE sensingin monofocal eyes
Aberrometer
CentroidsSpots
W
W curvature
YYXY
XYXX
WWWW
W"
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
-2
0
2
4
6
8
-6
-4
-2
0
2
4
Refractive Error = W Curvature
Partial derivatives
YYXY
XYXX
WWWW
CSCCCS
045
450
Sphericalequivalent Cylinder 0º Cylinder 45º
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Diopters
Distributions of refractive errorSpherical Equivalent
Monofocal Bifocal
Spatial (pupil)distribution
Probabilitydensity
distribution(histogram)
-1
0
1
2
3
4
Diopters
0 2 4 6 8 10-2 -1 0 1 2 3 4 5 6
3.125 D
0.75 D
Diopters
BimodalUnimodal-0.5 D
Diopters
Multifocals(examples)
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
-5 -4 -3 -2 -1 0 1 2
3 modes
D ≈ 2D
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
-1 0 1 2 3 4 5 6
D ≈ 1.5D
Modes?Bimodal
-12 -11 -10 -9 -8 -7 -6 -5
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
D ≈ 2.75D
Bimodal
Discussion. Part 1
A small but significant number (5%) of eyes show bifocal or even multifocal properties
They show large amounts of HOA: Poor image quality
Highest discrepancies aberrometric/standard refraction
Questions: Strategies of the HVS to improve visual quality?
Role of SCE? neural response?
Generalization of RE Sensing to account for that?
Generalized RE sensing
Irregular pupil shape
Inhomogeneous pupil transmission (SCE, etc.)
Probability(RE) =0 outside real pupil
Effective transmission
-3
-2.5
-2
-1.5
-1
-0.5
0
Analysis of Eye #43Refraction (SE)
Retinoscopy: -0.5D Subjective (Badal): -0.4D
HOA: Coma: 0.125 m Spherical A.: 0.16 m RMS HOA: 0.29 m
= 5.6 mm
Diopters
Parax=-0.4D
Refraction: -0.4 D
RMSw=-1D
-2D ?Stiles-Crawford
effect
Spherical equivalent
-5 -4 -3 -2 -1 0 1 2 3
SE histogram
Analysis of Eye #74
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Spherical equivalentRefraction (SE) Retinoscopy: -8.5D Subjective (Badal): -8.25D
HOA: Coma: 0.56 m Spherical A.: 0.37 m RMS HOA: 0.76 m
= 5.4 mm
-12 -11 -10 -9 -8 -7 -6 -5
Diopters
Parax=-5.25D Refraction
RMSw=-7.6D
Secondarymode refraction
?
Strategies to improve vision?
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
-12 -11 -10 -9 -8 -7 -6 -5
Full pupil
(huge amount of coma)
ABERROMETRY: SPHERE
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
-12 -11 -10 -9 -8 -7 -6 -5
EyelidVignetting
SingleMode !
Refraction
His eyelid blocks the upper part of the pupil
(both eyes)
Summary & Conclusions The eyes studied often show a complex distribution of RE.~5% show bimodal or multimodal histograms with peak distances > 1D (multifocality.) These eyes show large amounts of HOA (poor image quality) and discrepancies between aberrometric and standard refraction.
Generalized RE sensing seems well suited to analyze these cases, including irregular and/or inhomogeneous pupils.
SCE or even eyelid vignetting may help to avoid bifocality & improve image quality.
Future work- Implementation of complete & automatic histogram analysis
- Selection an deep study of potential multifocal eyes.
Thanks for your attention
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