The Power of Lenses

Brenda Heinke Montecalvo, FCOVD, FAAO

Vision‘s purpose is to guide actions, growth,
understanding and the quality of life. The
sensory component of vision is to serve as a
feedback mechanism to evaluate the adequacy to
our actions. Vision problems should be
explained in performance terms.
John Streff, OD, DOS, FCOVD,FAAO
 Objectives
• Understand optics of lenses and prisms
• Be able to evaluate vision using lenses and prism
• Be able to determine a good performance lens
• Be able to perform dynamic retinoscopy
• Use lenses and prisms in vision therapy
• Use occlusion for improving vision
What is your paradigm?
When vision works well it guides and leads,
when it does not it interferes.
John Streff, OD, DOS, FACOVD, FAAO
Prescribing a lens is based on the observer’s
model of vision and his/her understanding
of the visual process.
 Therapeutic Performance Lenses

The therapeutic performance lens’ purpose is to

guide one’s action, growth, understanding and
the quality of life. Arriving at such a prescription
is determined when a visual movement is made
that matches the perceived time of the event.
 Clarifying Vision
• Meaningful vision depends upon what one does to
see. It depends on how one habitually looks and
controls seeing.
• Vision is the ability to learn and understand the
language of light.
• Vision is understanding the communication gained
through seeing.
• Vision is understanding what light tells us.
Seeing is a learned, controlled
action that requires

DOING.

It is an active process.
Examples of Different Responses
• +1.00 Hyperope rejects a +0.50 Rx
• +1.00 Hyperope accepts a +0.50 Rx

• BD prism shifts posture anterior

• BD prism shifts posture posterior

• Base is perceived compressing space

• Base is perceived expanding space
 Preferred Response to Lens
The response can more easily match the
expected response when there is flexibility
and freedom to allow vision to direct
thinking and perception.

When not flexible, the response often is in

the opposite direction indicating much of
the available information is ignored.
 Compensatory or Corrective?
• Compensatory lenses change the response
only when being used.
• Corrective lenses change the response so
the benefit remains after the lenses are
removed.
 Compensatory or Corrective?
• Subjective Refraction
• Binocular Cross Cylinder
• MEM
• Bell Retinoscopy
• Book Retinoscopy
• Yoked Prism and Walk Rail
• Therapeutic Lens
Understanding the Importance of
Visual Motor & Ambient/Focal
 Visual Motor (VM)
Guides
Visual Sensory (VS)

VM:(Movement), Focus, Track, Teaming

VS:Eyesight (20/20) and Sensory Fusion
 Visual Motor
The Visual Motor Model recognizes that
difficulties in processing visual information
can occur at several levels, which may have
no or minimal effect on optics but huge
effects on the visual process.
 Visual Motor / Visual Sensory
• Visual Motor
– Movement
• Extra Ocular Muscles
• Iris
• Ciliary Muscle
– Guides Sensory
– Response searching for the stimulus
– Motor nerves develop before sensory
Constant motion of micro eye movements
and accommodative shifts are critical for
scanning and visual clarification.

There are also drifts and corrections (side

scans) that are important to consider since
they help awareness of the peripheral.
 Visual Motor / Visual Sensory
• Visual Sensory
– Eyesight
– Acuity
– Optic Nerve
– Sensory fusion
 Visual Motor / Visual Sensory
• Visual Motor versus Visual Sensory
– Hand
– Wall
• With reduced visual motor
• With visual motor
• What gives more information?
• Yoked 20pd BR
• Fixate dot
• Run hand up and
down door frame
• Watch hand as it goes
up and down
• What is the
difference?
Ambient(peripheral) / Focal(central)
• A prescription can improve the ambient /
focal relationship allowing the patient to be
more aware of the ambient visual
processing system.
• A prescription can inhibit the patients
ability to expand and be aware of the
ambient visual processing system.
 Ambient / Focal
• Ambient
– All vision processed as the whole
– Anti-Gravity (Skeffington circle)
– More magno some parvo cells
– Ground, less conscious
– Dominant at birth
• Focal
– Visual information being attended to
– Final stage of Centering
– More parvo some magno cells
– Figure, more conscious
 Gus Forkiotis
• Place heal in front of
toes
• Look at toes
• Bend at waist
• Raise back up
• Increase awareness of
periphery while
looking at toes
• Bend forward at waist
• Raise back up
• Note difference in
balance
 Workshop
• Which is best to gain most information?
• Hand: Still or moving?
• Wall with Yoked Prism: With reduced
visual motor or with more visual motor
• Ambient / Focal: Decreasing or increasing
peripheral awareness
Understanding Lenses
 What do Lenses Really Do?
• Bend light
• Influence or guide patient response
• Transform light
 Considerations in Prescribing
Lenses and prisms are only light transformers. While it is
possible to calculate the light transformation, one cannot
predict an individual’s perceptual responses. The
individual viewing through the lens interprets the
transform within the context of her or his frame world.
When there is a significant limitation of attention, the
perceived response often is the opposite of the
transformation. (Minus looks bigger, base-out looks
bigger, plus looks smaller, etc.)
John Streff, OD, DOS
 Clinical Pearls--General
• Use the smallest amount of power to create the change
desired
– With small lens powers 0.12 sph or 0.25 prism diopter can
cause a large change in visual motor performance.
– Small changes to higher power lens will have little or no
effect.
• Use best optical quality material
• Match pupil distance for visual distance demand
• Use lined bifocal instead of progressive, especially
with prism
 Clinical Pearls--Cylinder
• Lenses as symmetrical as possible (exactly the same if
possible)
– Can lenses or spherical equivalents be the same?
• Cylinder as low as possible
• Axis as close to 180 or 90 as possible
• Axis as symmetrical as possible
• If both lenses cannot be the same, can one meridian be the
same?
• Can one meridian be plano?
 Clinical Pearls--Hyperopia
• Hyperopes who have never worn lenses
– 3.00D hyperope or less:
+0.62 or less
– 4.00D hyperope or greater:
+2.00 sph OR
CL Rx with therapeutic lens over CL
• Hyperopes who already wear high Rx are difficult
to change if they wear their glasses all the time
 Clinical Pearls--Myopia
• 0.75 myope or less:
Low plus with very small BI prism or BU or
BD yoked prism
• Higher myope:
Rx in Contacts (CL) with therapeutic Rx in
eyeglasses worn over CL
• Myopes or Hyperopes unable to use CL:
Use small BI, BD yoked or BU yoked
 Clinical Pearls—Exo or Eso
• Exo posture (exophoria, exotropia):
BI prism or BU yoked prism
• Eso posture (esophoria, esotropia):
BD yoked prism
 Trial Lenses to Have on Hand
• Low plus lenses in frame / holder
+0.12, 0.25, 0.37, 0.50, 0.62, 0.75, 2.00
• Low cylinder in frame / holder
-0.25 x 090, -0.50 x 090
• Curved prisms
– 0.50 OU [BI, BD, BU, BO] in frame / holder
• Rotating prisms
– 1pd, 2pd, 3pd
 Optics:
Characteristics of
Lenses and Prisms
 Traditional Thinking Regarding
Optics of the Eye

“We know that the image formed must be

real, because it is projected onto the retina
(which is like a screen). Any time an image
is projected, it must be real.”
Karen Wu, The Optics
 Optics of the Eye
Convention:
• Light rays drawn from left to right
• Light reflects off of a surface and goes
toward the eye where refraction occurs so
that the image is “projected” onto the retina.
 Traditional Ophthalmic Optics
• Refractive conditions are viewed as a mis-
focusing of the optical system that is the eye
due to problems with any of the optical
parts including the eyeball being too long or
short for the system.
• Light must then be refracted by a corrective
lens in such a way as to move the focal
point back in myopia and forward in
hyperopia.
 Consider Inverting the Optics

What happens to our thinking about the optics if we consider

the person actively looking through the lens?
(Rather than just considering the light coming from the object
through the lens to the eye.)

Look at the ray tracings from the opposite direction!

 Thin Lens Equation

1/di + 1/do = 1/f

di= distance from lens to image

do= distance from lens to object
f = focal distance of lens
 Concave Lens
• Optics: Real Object anywhere in space
always creates a Virtual Image closer
to the lens and smaller. (Small In)
• We can calculate the location of the
virtual image if we know the lens
power and the distance the object is
from the lens.
 Concave Lens
• Perception: Person looks through the lens at
the virtual image and must put it back out in
space to the distance they think the object
actually physically is from them.
This perceptual problem is compounded by
optics in the periphery of the lens.
 Convex Lens (Object between Focal
Distance and Lens)
• Optics: Real Object between the focal
point and the lens creates a Virtual
Image farther away and larger. (Large
Out)
• We can calculate the location of the
virtual image if we know the lens
power and the distance the object is
from the lens.
 Convex Lens (Object between Focal
Distance and Lens)

• Perception: Again, the person looks

through the lens at the virtual image.
• Don’t forget optics in the periphery of the
lens. (Periphery = anywhere in lens not at
the optical center.)
• We need to consider projection and
perception to understand where in space
the person perceives the object to be.
 Convex Lens (Object between Focal
Distance and Lens)
• Low power plus lenses are important to think about
in this category.
• With low plus lenses, most near objects will fall
closer to the lens than the focal distance, so a virtual
image farther away in space and larger is created by
the optics of the lens. (Remember, we are looking
through the lens.)
• This is an important reason that low power plus
lenses are so useful.
 Convex Lens (Object Beyond Focal
Distance of Lens)
• Optics: Real Object beyond the focal distance of the
lens creates a Real Image on the opposite side of the
lens.
• In this case the calculated location in space of the real
image ends up in the person’s eye/head or often quite
a distance behind the person. Of course, now the
optics of the eye would also have an effect on the
final calculated distance of the image.
• Perception: The person looking through this lens has
some interesting perceptual transformations to make!
Web Sites with Interactive Lens
Models
These are fun to play with if you like optics and
maybe can help you with understanding
optics if you don’t:
• http://www.geocities.com/capecanaveral/hall/
6645/Lens/lens_e.html
• www.shermanlab.com/science/physics/optics
/ThinLens.php
 Optical Characteristics of Lenses
and Prisms
See handout for comprehensive list of optical
characteristics of different types of lenses and prisms.
• These are the optical transformations of the lens and
can be determined mathematically.
• Be careful in prescribing as the individual’s
perceptual response may be quite different (often
opposite.)
– The individual viewing through the lens interprets the
transformation within the context of her or his frame world.
 Thin lens vs. Thick lens optics
• All of ray tracings so far have been “thin
lens” optics.
• Ophthalmic lenses are more complicated.
• “Power” of the lens away from the optical
center (OC) is not the same as at the OC.
• Prism effects must also be considered.
Optics
• Image displacement
1 prism diopter =
1 cm at 1 meter

• Three dimensional
perceptual effects
– Predictable based on
optics
– See next slide
Prism Image Formation
 Optics: 3D Spatial Perception
(Slant!)
• Prisms not only change the direction of light:
– They rotate spatial aspects of the visual field
• Base: Expands space
— as if things moved farther away
• Apex: Constricts space
— as if things moved closer
– We cannot fully understand the optics of prisms if we limit
our concept of changes to a flat plane.
– Prisms produce a gradient of simultaneous magnification
and minification.
 Prism Distortions
“The ophthalmic optics of prisms is characterized by having a
non-uniform deviation of light rays.” Ron Jones, OD, PhD

• Asymmetric magnification
• Curvature of lines perpendicular to base-apex
• Rotation of lines parallel to base-apex
• Overall magnification

Base-curve dependent!
 Spatial Distortions of Prisms
1. Asymmetric magnification

Effect is equivalent to an induced slant

Only apparent with an extended surface.
R. Jones, OD, PhD
 Prisms cause:
• Shift – the main optical effect of prisms
• Slant – extended surfaces may appear
rotated.
• Curvature – extended surfaces may
appear curved

R. Jones, OD, PhD

 Effects of a Prism
Shift and Slant

Where would you have to be looking without prism

to have this slant?
R. Jones, OD, PhD
 Curvature with Prisms
Curvature of lines perpendicular to base-apex.
R Jones, OD, PhD

L R R L
image

convex concave

object Base-in Base-out

 Effects of Prisms

1. Yoked prisms (left, right, up, down).

• Cause shift and slant
2. Opposing base prisms (BO, BI)
• Cause distortions of space, distance, size
Important Visual Spatial Perception
Concepts
• SOLI vs. SILO
– Small Out Large In (SOLI)
• Real objects moving in real space
• Objects appear larger when they are closer and smaller when they are
farther away.
– Small In Large Out (SILO)
• Perceived movement of the target.
• Target should appear smaller and closer with Base Out prism or
minus, larger and farther for Base In prism or plus
• Form Constancy
• Figure-Ground
 Monocular Cues to Depth
• Overlay
• Light and Shadow
• Relative Height
• Linear Perspective
• Familiar Size (Form Constancy)
• Texture Gradient, Aerial Perspective
• Motion Parallax
 Misjudged Distance
• If you over estimate distance of an object
separation between objects will be expanded.

• If you under estimate distance of an object

separation between objects will be foreshortened.
 Spectacle Correction Prismatic
Effect

Minus lenses:
– directions are less than actual.
Plus lenses:
– directions are greater than actual.
 Wearing Plus Spectacles
The prismatic effects of plus lenses require the eye
to rotate more than the normal amount.
R Jones, OD, PhD
True location
False location

 Wearing Minus Spectacles
The prismatic effects of minus lenses require the eye
to rotate less than the normal amount.
R Jones, OD, PhD
False location

True location

 Adaptation to Spectacle Prismatic Effects

 Myope moves eyes less than

No lens
an emmetrope. Perceived
Direction
 Perceived direction in Myopia

myopia is less than actual.

 To adapt, myope needs to Actual Direction
recalibrate eye movement
information

R. Jones, OD, PhD

 Remember Lenses ONLY
Transform Light
The optometrist benefits by observing the patient’s
response to the lens probes, not by anticipating
what they think the lens is supposed to do.

This aids the optometrist in assessing two patients

with assumed similar visual systems who respond
differently to the same lens.
 Evaluation of …
• Reach - Grasp - Manipulate - Release using
dynamic near point retinoscopy
 Reach-Grasp-Manipulate
• Reach
– When beginning to look
• Grasp
– When vision connects
• Manipulate
– Exploration of what is being looked at
• Release
– Let go
 Observing
Reach-Grasp-Manipulate-Release
while performing
Dynamic Near Point Retinoscopy
Dynamic Near Point Retinoscopy
• Done at near
• Visual attention and retinoscope at the same
distance (no working distance lens)
• Originated by Cross to find near Rx
– Yielded too much plus
– “lag” developed to account for difference
• No need for working distance calculations
• No cycloplegics
• No neutralization of a reflex
Dynamic Near Point Retinoscopy
• Book
• Stress Point
• Bell

Prefer Book because also watching visual sequencing

MEM is more repeatable inter- and intra-examiner because it

is a “neutralizing” type of retinoscopy. It is not dynamic.
 Book Retinoscopy
• Appropriate reading material at Harmon
distance
• Observe how probe lenses change reflex
• Observe changes in brightness, color,
stability over time
• Takes cognitive level into account
• Allows one to see changes over time
• Lots of information can be seen in the reflex
 Dynamic Book Retinoscopy
• Spot retinoscope versus streak retinoscope
• Reading Cards/Near Target
– Gray Oral set up for Book Retinoscopy
Richard Apell, OD
15 Thelbridge Street
Madison, CT 06443-3412
• Lenses
• HARMON DISTANCE (Don’t be too far away)
 Book Retinoscopy Target

Use target appropriate for patient.

 Important Considerations
• Attend to change!!
• Our training was to recognize motion and cylinder and to
ignore other reflex properties.
• In optometry school we were judged on how the
retinoscopy matched the subjective.
• We have been trained to ignore the most important
information.
• It is going to take time and practice! Be patient.
• OPEN YOUR EYES, LOOK AND SEE!
Dynamic Near Point Retinoscopy
CHANGE WHAT YOU ARE LOOKING FOR:
THINK DISTRIBUTION AND BRIGHTNESS
VARIABILITIES AND CHANGES

• Color and color change

• Brightness and relative brightness
• Central/peripheral light distribution and change
• Small fluctuations in reflex and reflex areas
 Clinical Pearls
• With motion:
– The individual is projecting relatively closer than the
physical distance.
• As projects closer, reflex farther to keep contact=increase in
with motion
• Against motion:
– The individual is projecting relative distance than
physical distance.
• As projects far AS IF closer=increase in against motion
 Trial Lenses to Have on Hand
• Low plus lenses in frame / holder
+0.12, 0.25, 0.37, 0.50, 0.62, 0.75, 2.00
• Low cylinder in frame / holder
-0.25 x 090, -0.50 x 090
• Curved prisms
– 0.50 OU [BI, BD, BU, BO] in frame / holder
• Rotating prisms
– 1pd, 2pd, 3pd
 Important Considerations
• Just observe – don’t over-analyze
• Observe
– Color, brightness, motion
– Central and peripheral light distribution
– Changes over time / stability of reflex
Dynamic Near Point Retinoscopy
• HARMON’S DISTANCE!!!
• Look for Best Reflex with Best Lens
• Near Point Target:Reading Card
 Take Home Message
• Be sure you understand how dynamic
retinoscopy is set up
• Just Look
• Be aware of any change
 Workshop
• Hold retinoscope still
• Keep both eyes open
• Keep retinoscope @ plane of target
• Stay close
• Working distance is the patient’s reading distance
• Have 2 people evaluate same person and compare
observations
• Observe a variety of individuals in your group
How to Determine the Therapeutic
Performance Prescription
 Theories / Models of
Prescribing
• Refraction
– History
– BVA
– Full Compensation of RE
• AC/A Ratio
• Graphical Analysis
• Von Graffe
 Theories / Models of
Prescribing
• OEP 21 Point Analysis
• Developmental
• Performance
• Behavioral
• Functional
 G.N. Getman
• The Basic Sequence of Development
G. N. Getman believed that development of
learning followed a specific sequence in the
pre-school years.
 Elliot Forrest
• Elliot A. Forrest's research on functional
astigmatism revealed the crucial
importance of the relationship between
eye movements and head movements
when scanning horizontally as opposed to
scanning vertically.
 D.B. Harmon
• In 1958, Harmon (the scientist who gave his
name to the standard reading distance, i.e.,
elbow to middle finger knuckle) noticed
postural patterns in subjects with
different eye disorders.
 Ann Sutton Nichols
• Ann Sutton Nichols, in her studies,
remarked the presence of different styles of
vision in myopes and hyperopes according
to a specific plane of vision.
 Arnold Gesell
Growth is a process of organization. It is a unitary and an
integrative process; if it were not unitary, the organism
would lack wholeness; if it were not integrative, the
organism would lack individuality ... This principle
(motor priority) is so fundamental that virtually all
behavior ontogenetically has a motor origin and
aspect. Vision, for example, has a motor as well as
sensory basis; likewise, speech, mental imagery, and
conceptual thought. Even emotions trace to motor
attitudes and tensions."
 Robert Kraskin
Kraskin found that lenses could change the
location in space where the patient made the
shift from fight to flight. Extremely low
powered plus lenses over the patients’
habitual shifted the stress point towards to
patient, increased the volume of space
within which the patient could remain in
fight.
 Keith Holland
Behavioural Optometry is about exploring the relationship
between the neurobiological and mechanical processes of
seeing and the functional requirements of living and surviving
in a dynamic environment - in other words about vision. Vision
is the dominant component of all human behaviour, it is in part
innate - we can all see at birth, but it is also learned. From the
infant’s first explorations of the world about them, right
through life, we are learning to see - enhancing our visual
processes.
 Jiang & Morse (1999)
“ Near work causes changes in the
oculomotor characteristics of susceptible
individuals which begin even before the
development of refractive error. This series
of changes in oculomotor function
apparently results in optical defocus, which
has the potential to induce ocular
compensatory changes resulting in
myopia.”
 Ciuffreda (1999)
Confirms the differing responses to near work seen, with one
group showing rapid recovery from close work, and no apparent
long term changes. A second group showed a near point stress
response with rapid recovery after cessation of the task, whilst a
third group showed a very long recovery time after removal of the
near task. This same paper also advocates the use of plus lenses
as a means of breaking the cycle of stress, and reports on
positive long term responses to this approach.
 Studies
• Pirman and Lamb (1982) & Caden (1984) have both
shown improved performance on pattern copying tasks
with the use of lenses prescribed on the basis of
accommodative lag determination.
• Pierce and Greenspan have often been quoted in support of
low plus, but they show a clear and unequivocal link
between the application of low powers of lenses and
improvements in visual performance.
 Applications for Lenses
• Therapeutic
• Performance
• Developmental
• Comfort
• Functional
• Behavioral
 Possible Goals for a Prescription
• Influence visual thinking
• Influence visual motor to guide visual sensory
• Influence symmetrical posture
• Guide projection to equal perception
• Improve visual grasp, release and manipulation
• Speech and language
• Efficient visual processing
• Increase reading speed
Possible Goals for a Prescription
• Gain awareness
• Improve comprehension
• Improve insight
• Improve understanding of the world
• Disrupt warped visual system
• Guide visual development
• Balance visual system at near
 Possible Goals for a Prescription
• Make performance easier
• Sustain performance
• Increase ease and comfort
• Allow more efficient productive performance
• Heighten discernment over a larger viewing field
• Change behavior
• Improve function
Specific Optometric Lens Applications

• Strabismus
• Amblyopia
• Anisometropia
• Vertical Deviations
• Asymmetrical Cylinder
• Centering Shift
• Myopia Control
• Hyperopia
• Visual Field Disorders
• Vision Therapy
 Handouts
• Characteristics of Lenses
• Guides for Prescribing Cylinder (Streff)
• Guidelines for Prescribing Therapeutic
Performance Lenses and Prisms
(Montecalvo)
 Prescription Considerations
• Characteristics of lenses and prisms
– Small amounts of plus
– Small amounts of prism
• Lens materials & coatings
• Color of lens
• Occlusion type
• Pupil Distance related to working distance
 Trial Lenses
• Low plus lenses in frame
– 0.12, 0.25, 0.37, 0.50, 0.62, 2.00
• Low cylinder
– -0.25x090, -0.50x090
• Curved prisms
– 0.25, 0.50 (BI, BD, BU, BO) in frame/holder
• Rotating prisms
– 1pd, 2pd, 3pd
Lenses and Prisms
 What lens should I try?
• Goal/reason for prescribing
• Characteristics of lenses and prisms
• Prescribing guides (Streff & Montecalvo)
• There may be more than one lens that works
• Think smaller first, then increase power if
needed
 Performance Testing Helps
Determine Best Prescription

The opportunity to trial the prescription

determined from the data collected
during the analytical and near
retinoscopy and observe how the lenses
impact performance.
Tests to Determine Best Prescription

• Visual Motor Performance Tests

– Dynamic Retinoscopy
– Streff Ball and Cap
– NPC
– Pursuits
– Reading
 Streff Ball and Cap
• Patient fixates ball (Wolff Wand)
• Holds cap at waist level in preferred hand
• Put cap on ball quickly
• Do not look back and forth between cap and
ball
 Streff Ball and Cap Test
• Equipment needed
– Wand gold or silver
• Some people use a pen or other object
– Cap
• Highlighter cap
• Eye drop bottle cap
• Finger
 Performance Testing
• Observe changes in:
– Visual Motor abilities
– Reading
– Walking
– Paper and pencil tasks
– VO Star
 Performance Testing
• Reading
– Fluency
– Speed
– Accuracy
– Working distance

• Clinical Pearl – make up different lenses in a

variety of low plus powers in adult and child
frames
Reading Cards
• Grey Oral - Dr. Apell
• Lighthouse Card
 Performance Testing
• Visual Motor: Look for change
– Saccades
– Pursuits
– Convergence
• “pseudo-convergence insufficiency”
 Performance Testing
• Paper and Pencil Tasks
– Accuracy
– Posture
– Pressure on paper
– Handwriting (Wold test)
– Spacing
 Performance Testing
• Walking
– Balance
– Stride length
– Speed
– Ability to handle steps
• Watch head and exit
sign.
• See gait
• Note head, shoulder
and hip position
• Observe
• See position to walls
• Apply yoked prism
• Observe change
Bi-Nasal Occlusion
 Bi-Nasal Occlusion:
Not Just For Esotropia
Bi-Nasal Occluders
Uses for Bi-Nasal Occluders
• Convergence Insufficiency
• Reduce Asthenopia
• Eso or Exo Posture
• Disequilibrium
• Centering Shift
Uses for Bi-Nasal Occluders
• Accommodative Problems
• Improve Orientation
• Spatial Organization Problems
• Amblyopia
Uses for Bi-Nasal Occlusion
– Diplopia
– Vertigo
– Headache
– Photophobia
 Bi-Nasal Occlusion
• Appears to change how one
judges center.
• Give minimum amount
needed to regain accurate
centering
• Streff Wedge measurements
can be used by optician to
place bi-nasal on lenses
• Helps with orientation
• Improves ability to reduced
veering to one side.
 Understanding The Process
• Phylogentic Development
• Less Spatial Information
• Temporal Retina
– More reactive
• Uncrossed Fibers
Quic k Tim e™ and a H . 263 dec om pres s or are needed t o s ee t his pic t ure.

• Eliminates near
– Physiological diplopia
 Tools To Use
• Streff Wedge
• Wand/Marker Cap
• Reading Card
• Spot Retinoscope
Streff Wedge
 Demonstration
• Disruptive Blurred Double Lenses
– 30pd BO with +6.00 not a test or training
technique just demo to better understand
process
• Apply Streff Wedge
• Notice Change
 Demonstrating Streff Wedge
• NPC
• Donders
• Center Shift Test
• Dynamic Retinoscopy Quic k Tim e™ and a H . 263 dec om pres s or are needed t o s ee t his pic t ure.
 Bi-Nasal Application
• Nail Polish
• 1 mm Nasal to Limbus
• 7-8 degree angle
• Back surface of lenses
 Applying Bi-Nasal Occluders
• Tape over area not
applying occlusion to
• Place tape on inside
lens
 Applying Bi-Nasal Occluders
• Poor quality nail
polish
• Brush on inside lens
Removing Bi-Nasal Occluders
• Scotch tape
• Solvent for poly
• Solvent for non-poly
• Trivex OK
 Bi-Nasal cay be Applied to a
Variety of Cases
• HH: Headache
• BH: Photophobia
• SS: Convergence Insufficiency
• JJ: Suppression
• AS: Hemianopsia with Midline Shift
• VG: IV CN Palsy
• ED: Constant Diplopia
 Workshop
• Bi-nasal occlusion
• Compare visual motor performance tests
Vision Therapy
 Yoked Prism and Walk Rail
• Materials: 12pd rotating curved prism Rx,
Walk Rail
 Yoked Prism and Walk Rail
• Step 1: With the prisms placed Base up the patient
looks down to get on the walk rail then shift the
focus to a distance target beyond the end of the
walk rail.
• Step 2: The patient walks along the rail until the
end then looks down to step off. Repeat 3 times.
• Step 3: Change prisms to base down and repeat.
• Step 4: Change prisms to Base Up and repeat.
• Step 5: Change prisms to Base Down and repeat.
 Yoked Prism and Walk Rail
• What to ask:
– What do you notice? What does it feel like?
– How far are the walls from you?
• What to watch for:
– Balance.
– Recognize the curve of rail.
– Notice change in shift, size.
– Is breath held?
– Hard to relax.
– Postural rotations, head, upper torso, hips.
 Pursuits and Double Prisms
• Materials: 5pd rotating curved prism Rx,
Walk Rail, Fixation wands (one shiny gold
and one silver ball)

• RE: 5pd BU LE: 5pd BD

• RE: 5pd BD LE: 5pd BU
 Pursuits and Double Prisms
• Have patient sit or lie down with doubling prism glasses on.
• Hold the wand in primary gaze about 16 inches from the
patient.
• Ask the patient to fixate the wand. Have patient explain what
they see. Encourage peripheral awareness.
• Ask the patient to try to line the targets above each other.
• Move the wand in all 9 directions of gaze and closer and
further out. Ultimately the patient should try to keep the
targets in alignment while they are moved.
 Pursuits and Double Prisms
• Ask patient which one is real.
• Have patient touch the wand and ask which
one he or she can feel.
• The goal is to understand that both wands
viewed are real and not real and to be able
to feel both at the same time while touching
the wand that is seen as double.
 Pursuits and Double Prisms
• What to ask:
– What do you notice?
– What does it feel like?
– Probing questions can be included: Are they the same?
How are they different? How are they positioned to
each other?
• What to watch for:
– How they orient the position of the 2 wands to each
other.
– Can they change how the targets are seen?
– Holds breath.
– Cannot relax.
– Posture rotations, head, upper torso, hips.
 Saccades and Double Prism
Materials: 5pd rotating curved prism Rx,
Walk Rail, Fixation wands (one shiny gold
and one silver ball)

• RE: 5pd BU LE: 5pd BD

• RE: 5pd BD LE: 5pd BU
 Saccades and Double Prism
Have patient sit or lie down with double prism
glasses on.
Ask the patient to fixate one of the wands
while it is held in primary gaze.
Have patient explain what they see.
Ask the patient to try to line the targets above
each other.
Ask patient to shift fixation to the other wand
held in on of the 9 secondary positions.
 Saccades and Double Prism
• While patient fixates the second wand the
therapist moves the other wand (the one the
patient is not fixating on) to another
position.
• The patient is then asked to shift fixation to
the wand just moved.
• The therapist calls out “gold” or “silver to
direct the patient to shift fixation.
• Each time the patient performs a saccade
the other wand is moved.
 Saccades and Double Prism
What to ask:
• What do you notice?
• What does it feel like?
• Probing questions might include:Are they the same? How
are they different? How are they positioned to each other?
What to watch for:
• How they orient the position of the 2 wands to each other.
• Can they change how the targets are seen?
• Holds breath.
• Can not relax.
• Posture rotations, head, upper torso, hips.
 Double Prism and Sticks
Materials:5pd rotating curved prism set, 2
Dowel sticks about 3 feet long

• Right Eye: 5pd BU Left Eye: 5pd BD

• Right Eye: 5pd BD Left Eye: 5pd BU
 Double Prism and Sticks
• Procedure: Place the prism glasses on the
patient with RE: 5pd BU LE: 5pd BD
 Double Prism and Sticks
• Have patient hold a dowel stick in each hand
with the pointer finger pointing toward the end
of the stick.
• Rest hands with sticks at side. Bring them up to
a point patient is fixating at the same time and
have the tips of the double sticks touch.
• Repeat 5 times. Look in all 9 directions of gaze.
• Repeat with RE: 5pd BD LE: 5pd BU
 Double Prism and Sticks
• What to ask:
– What do you notice?
– What does it feel like?
– Probing questions might include:How can you look differently to help
them touch?
• What to watch for:
– How patient orients the position of the 2 sticks to each other. Note all axis,
X,Y and Z.
– Can patient changes how the targets are seen so they touch with ease?
– Holds breath.
– Can not relax.
– Posture rotations, head, upper torso, hips.
 Double Prism and Rings
Materials:5pd rotating curved prism set, 2
1 set of rings with 2 pegs

• Right Eye: 5pd BU Left Eye: 5pd BD

• Right Eye: 5pd BD Left Eye: 5pd BU
 Double Prism and Rings
• Procedure: Place the prism glasses on the
patient with RE: 5pd BU LE: 5pd BD
 Double Prism and Rings
• Have patient hold a dowel stick in each hand
with the pointer finger pointing toward the end
of the stick.
• Rest hands with sticks at side. Bring sticks up to
grasp one ring on the peg and transfer it to the
other ring.
• Repeat with all rings.
• Repeat with RE: 5pd BD LE: 5pd BU
 Double Prism and Rings
• What to ask:
– What do you notice?
– What does it feel like?
– Probing questions might include:How can you look differently to help
them touch?
• What to watch for:
– Can patient changes how the targets are seen so they touch with ease?
– Holds breath.
– Can not relax.
– Posture rotations, head, upper torso, hips.
 Window Rock

Materials: +2.00 Rx, loose lenses –4.00, -6.00, -8.00,

Near point Snellen acuity card, Distance large sign with
varied letter sizes
 Window Rock

• +2.00 glasses for viewing distance

• Look out beyond 6M
• Be aware of what you see
• Shift to near looking through -2.00
• Attempt to read near VA chart
• Once no progression shift to distance
• Do not try to make it clear, just describe
and see what you can see
 Window Rock
• Patient stands in front of near acuity card set at about 20 inches
while wearing the +2.00 lenses.
• The patient reads the acuity chart beginning at the big E.
• As soon as patient reads the smallest letters possible, fixation is
shifted to distance while the –4.00 lenses are placed in front of the
+2.00 lenses.
• The patient reads as much of the distance sign as possible.
• Repeat looking near and far reading as much information as
possible. Increase the minus used as each is achieved.
 Window Rock
• What to ask:
– What do you notice as you change focus?
– Can you change the focus response?
– What does it feel like?
• What to watch for:
– Trying too hard.
– Not looking soft.
– Holds breath.
– Cannot relax.
– Posture rotations, head, upper torso, hips.
Clinical Pearl to Treat Amblyopia

Montecalvo Barely Blur Technique

 Determining Barely Blur
Occlusion for Amblyopia
• Subjective Refraction in Phoroptor
• Double Full Line of Best Visual Acuity (BVA) of
Amblyopic Eye (AE)
• Patient must see 2 lines
• Blur Non-Amblyopic Eye (NAE) to one line
worse than AE
 Determining Barely Blur
Occlusion for Amblyopia
• Do a Forced Choice on AE
• Present one VA line better and determine if
AE can read smaller letters
• Re-blur NAE to one line worse than newly
determined BVA of AE
• Present a double single letter
• Try to reduce letter size until no longer
visible by AE
 Determining Barely Blur
Occlusion for Amblyopia
• Always keep the NAE barely blurred to one
line worse than BVA of AE
• Fit patient with 3 CL if BVA of AE is 20/50
or worse (2-daily use 1-blur of AE for 2
hrs./day)
• Use only 2 CL if BVA of AE is 20/40 or
better
 Assessing Barely Blur
• Check every 3 days at first
• NAE will build plus
• Change Barely Blur as needed
• Move from 2 hours/day to full time once
BVA is better than 20/40
 Activities During Barely Blur
• Pennies in Bank
• Balloon Toss
• Ball Catch
• Gross Motor / Eye Activities
 Notes for Barely Blur
• Keep posture straight
• Breathing
• Turn head to encourage viewing through
AE if cannot see double
• When CL are not possible use 2 pair of
glasses
 Other Prescribing Opportunities
for Treating Amblyopia

• Monocular Bifocal
• Micro prism