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

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-6

-5

-4

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-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"

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Refractive Error = W Curvature

Partial derivatives

YYXY

XYXX

WWWW

CSCCCS

045

450

Sphericalequivalent Cylinder 0º Cylinder 45º

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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

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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

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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?

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Full pupil

(huge amount of coma)

ABERROMETRY: SPHERE

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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