Download Dynamic Accommodation in Reading

Dynamic Accommodation
in Reading
Vision and Computer Displays Conference
June 4-5, 2009
Scott C. Cooper, OD, MEd, FAAO
James Kundart, OD, MEd, FAAO
Hannu R.V. Laukkanen, OD, MEd, FAAO
Introduction
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Describe accommodation and its function and
related visual perception
Explain its role in vision, especially nearpoint
Convey how it interacts with other visual
functions and perceptions
Provide an idea of the impact of poor
accommodation
Outline approaches to improve
accommodation and/or related perception
…in about 5 minutes
Accommodation: A simplified
description

Regulation of Focus
o
Functional goal: clarity of vision for the desired level
of detail
Accommodation: A simplified
description

Regulation of Focus
Accommodation: A simplified
description

Regulation of Focus
Accommodation: A simplified
description

Regulation of Focus
Accommodation: A simplified
description
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Regulation of Focus
DOF
Accommodation: A simplified
description

Regulation of Focus
DOF
Accommodation: A simplified
description

Regulation of Focus
o
o
o
Amplitude
Facility
Accuracy / Stability
• Note “accuracy”
Accommodation: LESS simplified

Dual innervation
o
Parasympathetic
• Increase accommodation
• Reduce pupil size (increase depth of focus)

o
Allows reduced accuracy / effort
Sympathetic
• Decrease accommodation (far viewing)
• Increase pupil size (smaller depth of focus)

Requires better accuracy, control and effort
Accommodation: LESS simplified
Input Variables

Optical
o
o
o
o
Target distanceLenses
Pupil size
Physical or physiological
limitations to clarity
• Cataract
• Poor tear film
• Other ocular defects
Accommodation: LESS simplified
Input Variables

“Non-optical”
Target’s visual features
• Examples: size, contrast, motion, screen or print
quality, other
o Vergence requirement / feedback
o Proprioception
o Proximal awareness
o Other
• Autonomic nervous system
changes…possibly/probably/maybe
o
Accommodation: LESS simplified
Output Variables

Garbage in – out
o
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See Input Variable list
Physical limitation (presbyopia)Predisposition to poor development / control
Practice effect
Vergence control
Many others: fatigue, medications, head
injuries, etc.
Accommodation: An EVEN LESS
simplified description
Synergistically intertwined with vergence (twoeyed control)
 Example: AC/A and CA/C

DOF
Accommodation: An EVEN LESS
LESS simplified description

Bioengineering models of accommodation
and vergence
Accommodative
Adaptation
Blur
“Neuro-optical”
Tonic
Accommodation
Accommodative
Response
Phasic
Accommodation
AC/A
CA/C
Fixation
Disparity
Phasic
Vergence
Vergence
Response
Vergence
Adaptation
Tonic
Vergence
Accommodation: An EVEN LESS
LESS simplified description

150 years of research
 Normal and abnormal variability
 Chromatic aberration as directional cue
 Changes with position of gaze
 Etc.
Accommodative Performance:
A “learned habit”
Result of processing many physical and sensory
cues
 Moderate variability from person to person
 Responses to cue changes are predictable
overall, but may also vary from person to
person
 Over time, accommodative performance can
change or deliberately be modified to some
extent

Accommodative Performance:
Links to other visual functions

Accommodation and vergence interaction
and “skill” varies from person to person
o
o
A complete analysis of accommodation and
vergence shows each individual’s challenge to
clear, single vision without perception of effort or
strain
Vergence performance has the same themes of
individualized visual “habits” that respond to visual
cue changes, and will change over time
Accommodative Performance:
Links to other visual functions

Eye movements in reading:
o
For some, the effort, control and visual perception of
accommodation (and vergence) are key for
support of eye movement accuracy in reading
Accommodative Performance:
Links to other visual functions

Depth Perception
Stereopsis
• Clarity, balanced clarity for each eye, same time
• Vergence control
o Perspective / converging parallel lines
o Texture
o Interposition
o Shadow
o Kinesthetic perception
o Accommodative effort
o
Accommodative Dysfunctions
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Hypo-responsive
Amplitude
o Accuracy
o Facility
o
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Hyper-responsive
o
o
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Accuracy
Residual “tonus” when looking at far
• Distance blur
• Diplopia
Warning: all prevalence studies have bias
o
o
~20 to >30% of prepresbyopic patients
General agreement: more symptoms from
accommodation than vergence dysfunctions
Accommodative Dysfunctions
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Common Symptom Examples
o
o
o
o
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Reduced reading comprehension
“Floating” text
“Eye strain”
Headaches
Impact on productivity:
o
o
o
Incorrect intrepretation of detall
Increased time and effort to correctly resolve and
process detail
Avoidance of tasks due to resulting symptoms
Treatment Approaches
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Treating the dysfunctions
o
o
o
o
General lens prescriptions
Prescriptions to optimize function and minimize
symptoms
Vision training
As possible, address physiological problems that
may degrade clarity and/or accommodative
performance
• Examples: dry eye, cataract
Treatment Approaches
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“Treating” the visual circumstance
o
o
Ergonomic features of the room/workstation
• Viewing distance, position
• Lighting, glare
• Posture
• Many other variables
Visual cues of the task
• Contrast
• Color
• Size
• Etc
Internal Symptoms Due to
Accommodation
and Video Displays
Including a Pilot Study of Live
Accommodative Measurements
Vision and Computer Displays Conference
June 4-5, 2009
Scott C. Cooper, OD, MEd, FAAO
James Kundart, OD, MEd, FAAO
Hannu R.V. Laukkanen, OD, Med, FAAO
Introduction

In the past, our lab has studied mostly external
symptom factors, such as:
o
o
o
Squint
Dry eye
Blink rate
Yet, the internal symptom factors, like blur,
have remained largely unstudied
 Internal symptoms are at least in part due to
accommodation (focusing) of the eye
 This was the first experiment designed to study
real-time accommodation while reading
continuous text
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Why Live Accommodative
Research is Needed
Previously, there were no published studies of
dynamic accommodation, such as during the
reading task
 While established methods (such as dynamic
retinoscopy) have been used to sample
accommodation, continuous methods were
not available
 It would be highly useful for both the
researcher and clinician to have a means to
measure accommodation continuously during
reading
 Over a dozen studies have been done with
the WAM series of autorefractors to date
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The Pacific Pilot Study
http://www.aitindustries.com/pages/products/ecp/ophthalmic/wam5500_binocular_autorefractor.html
Purpose of Our Pilot Study
Note that NONE of previous studies
investigated accommodation during text
reading -- why?
 This was thought to be impossible to do
accurately, because of off-axis effects
 To determine the feasibility of collecting
accurate, continuous accommodative data
during reading
 Questions we hope to answer:
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o
o
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How wide a window can we use?
How many readings/second?
How accurate is each reading (in diopters)?
Subjects
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Nine subjects (5 female, 4 male) were asked
to complete three conditions while
accommodation is measured:
Gaze at eccentric targets every 5 minutes from +15º
to -15º targets
o At +7.5º, 0º, and -7.5º from primary gaze, and
o Subjects read from an electronically presented
text
o
Apparatus
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Two computers were used; one collected
data from the WAM-5500 via a serial cable
o
This computer was enabled with data collection
software WCS-1
The second computer was used as a testing
stimulus with a 12-pt Tahoma font
 Additionally, a Pocket PC device (HP iPAQ)
was used as a stimulus
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o
The iPAQ screen measures 5.5 cm square
The 4.75 m (>0.25D)
Accommodative Target
Targets are 2.5 degrees apart
Typical Window Size
for Desktop Display
Note the small vertical dimension
Participants
View from
behind the
autorefractor
The Handheld Display Setup
Typical Window Size
for Handheld Display
Raw and Smoothed
Autorefractor Data
2
1.5
1
0
0
1
-0.5
-1
186 371
556 741 926 1111 1296 1481 1666 1851 2036 2221 2406 2591 2776
Accommodative measures (Diopter)
0.5
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
Time
Note that all the autorefractor thinks it’s measuring is
refractive error (negative = myopia)
Viewing distance (cm)
The Accommodative Response
vs. Demand
50
Upper bound of 84% confidence interval
Mean accommodative measure
Lower bound of 84% confidence interval
40
33
25
-3.5
-3
-2.5
-2
-1.5
-1
Accommodative measure (Diopter)
-0.5
0
Accommodative Lag and
Working Distance
84% Confidence Interval of the M ean
Central
40
Left
Right
Central
33
Left
Right
Central
Left
25
Viewing Distance (cm) x Gaze Position
50
Right
Right
Central
Left
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
Av erage Accommodative Me asure (Diopte r)
Left and Right Gaze were each
7.5 degrees off primary gaze
Distance is Significant, Gaze
Position is Not
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A two-way repeated ANOVA was used to analyze the
effects of the viewing distance and gaze position on
accommodative measure
The results show significant main effect of viewing
distance (F(3, 24)=174.288, p<0.0001) but no significant
effect from gaze position (F(1.105, 8.838)= 1.067,
p=0.367) and interaction (F(1.702, 1.157)=0.569,
p=0.552)
This finding indicates that the derived
accommodative measures were responsive to the
change of viewing distance and were consistent with
the testing range
Conclusions
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The Grand Seiko WAM-5500 open field
autorefractor can accurately measure the
accommodative response under certain
parameters:
Within 3-4 text lines of central gaze vertically
o Within ± 15 degrees of central gaze horizontally, if
accommodative responses are > 1 D apart, as on
the desktop display
o Within ± 5 degrees of central gaze horizontally if
accommodative responses are ≤ 1 D apart, as on a
handheld display
o
What have we learned about the
visual response with visually
comfortable and uncomfortable
subjects recently?
In recent studies, we learned how
to measure dynamic
accommodative response and
pupil size when subjects were
engaged in the actual reading
process
Unexpected pupil results
asthenopic vs. non-asthenopic
Counterintuitive
pupil response
differences to (+)
lens
Equally surprising
pupil response
differences to baseout prism
Unexpected accom results
asthenopic vs. non-asthenopic
Unexpected accom
differences to (+) lenses
Unexpected accom
differences to (-) lenses
What next should be investigated?
o What
about vergence?
o Accommodation,
vergence, and pupil
responses are all linked via the near
triad
o Simultaneously
monitoring all 3 legs of
the near triad will likely further advance
understanding of the near response
o Having
3 aggregate measures could
conceivably better predict comfort,
asthenopia, and visual efficiency
Our vergence measure tools
EyeLink II
•Fast: 500 Hz sampling
•Precise: 0.5º accuracy
0.01º RMS resolution
•Straightforward setup,
calibration, validation
•Would need to dismantle
in order to work with
Grand Seiko
Our vergence measure tools
Visagraph III
•Not as quick: 60 Hz sampling
•Not as precise: >0.5º accuracy
•Straightforward setup, calibration
•May be possible to get Visagraph
and Grand Seiko results
simultaneously
What is visual response in artificial 3D environment
and why are some people asthenopic?
Acknowledgements
This research was funded by
The ClearType and
Advanced Reading Technologies Group
of Microsoft Corporation
References
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Benzoni Jaclyn, Rosenfield Mark , Collier Juanita, McHugh
Kimberley, Portello Joan. Does The Dynamic Cross Cylinder
Test Measure The Accommodative Response Accurately?
AAO Denver, 2006.
Berntsen David A, Mutti Donald O, Zadnik Karla. Validation
Of Aberrometry-based Relative Peripheral Refraction
Measurements. AAO Denver, 2006.
Bozic James M, McDaniel John, Mutti Donald O, Bullimore
Mark A. Measuring The Accommodative Convergence To
Accommodation (AC/A) Ratio With The Grand Seiko WR5100K. AAO Philadelphia, 2001.
Coffey Bradley, Kosir Kristen, Plavin Joanna. Effects Of
Laptop Computer Gaming On Refractive Condition And
Visual Acuity. AAO Tampa, 2004.
References
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Collier Juanita, Rosenfield Mark. Accommodation And
Convergence During Sustained Computer Work. AAO
Denver, 2006.
Huffman Sara J, Mutti Donald O, Zadnik Karla. The
Repeatability Of Autorefractors. AAO Philadelphia, 2001.
Win-Hall Dorothy M, Ostrin Lisa, Kasthurirangan Sanjeev,
Glasser Adrian. Open-field Autorefractor Measurements Of
Accommodation In Human Subjects. AAO Tampa, 2004.
Win-Hall Dorothy, Cole Jason, Glasser Adrian. Comparison
Of Objective And Subjective Measures Of Accommodation
In Standard Pseudophakic Subjects. AAO Denver, 2006.