Embed Size (px)
Citation preview
Solve Your Patient’s Visual Acuity Complaints by Prescribing NeuroVision Technology
Peter Shaw-McMinn, ODAssistant Professor
Southern California College of Optometry
One of the advantages of our profession is we have the opportunity to improve the quality of
our patient’s life on a daily basis.
We have the opportunity to improve the quality of life of:
• Patients• Staff• Ourselves• Our professions• The Eyecare Industry• Society
Today’s ObjectivesToday’s Objectives
You will be able to:• Explain what limits visual acuity • Describe the brain processes that
allow us to see clearly• Understand how the NeuroVision
technology works• Recognize how the NeuroVision
program can benefit patients
What Determines Our Visual Acuity?
Retinal image + Neural Processing
Visual system
Cells in the retina
Neuronal morphology• Dendrites: shaft, spines,
specialized synaptic structures
• Extensions of cell body, with same membrane & organelles
• Shape and number characteristic of each type of neuron; shape determines number of synaptic sites, physiological properties
Light hits photoreceptor
The initial step in the translation of light information from a spot of light into an electric signal propagating to the visual cortex takes place in the photoreceptors in a process known as transduction. This consists of the cis-trans isomerization of the carotenoid chromophore, which leads to a transient change in the membrane potential of the cell. The result consists of a graded response, seen as a hyperpolarization of the photoreceptor, and an electrotonic current linking the outer and inner segments. A photoreceptor is capable of transducing the energy of a single photon (about 4×10-12erg) into a pulsed reduction of axial current of about 1 pA lasting about 1 s with an energy equivalent of 2×10-7erg (Levick and Dvorak, 1986). Thus, a photoreceptor serves as a photomultiplier with an energy gain of some 105 times.
Chemical reaction releases glutamate
How we see - at the Retinal LevelPhotoreceptors use a biochemical process to convert light in
electrical signals that are transmitted via bipolar cells to ganglion cells. The axons of the ganglion cells form the optic nerve that connects the retina with visual centers of the brain. This vertical signal transduction is mediated by the excitatory neurotransmitter glutamate, and is modulated laterally by horizontal and amacrine cells that use the inhibitory neurotransmitters γ-aminobutyric acid (GABA) and glycine. This horizontal inhibition causes a negative feed-back for the vertical excitatory signal pathway. This feed-back increases the signal to noise ratio of the light signal, regulates the light sensitivity of the retina (adaptation), causes selectivity in ganglion cell responses for the orientation of objects and the direction of their movements, and is important for the generation of receptive fields.
Receptive fieldHartline introduced the concept of 'receptive field' to
describe the spatial properties of retinal ganglion cells. He used 'spot mapping' to define such fields. Cells were found to respond to relatively dim spots when the stimulus was positioned in the 'center' of the receptive field but brighter stimuli were required as the spots were moved away from this region. Hartline concluded that ganglion cell receptive fields were fixed in space and immobile, typically did not extend beyond 1 mm in diameter, and were graded in sensitivity over this region. Receptive fields were much larger than expected of individual photoreceptors, suggesting signal processing and integration through retinal circuitry.
Receptive Fields and Contrast Sensitivity
• The characteristic 'spatial tuning' of ganglion cell receptive fields is reflected in peaked contrast sensitivity functions
• This tuning reflects in part the variable dendritic span in ganglion cells.
• Dendritic span is one of the factors allowing ganglion cells to collect visual signals over a broad reach of visual space.
• But dendritic field span in itself does not provide for a decline in sensitivity as stimulus sizes become large. Surrounds are required.
• Contrast sensitivity is one measure of size selectivity in ganglion cells.
• Another measure is 'hyperacuity'. This is the ability to detect movements within the ganglion cell receptive field. Examples are:
Lateral Geniculate Body
LGN has six layers of cells
1 .3 million neurons same as number of ganglion cells
• The mangocellular layers process visual information concerned with low spatial frequencies, high temporal frequencies, low contrast and luminance. (Peripheral retina)
• The parvocellular layers process visual information concerned with high spatial frequencies, low temporal frequencies, high contrast and color. (Central retina)
Sharpest vision at fovea
The specialized cone pathways of the central fovea of human and monkey retinas are designed to have the least convergence and the greatest resolution capabilities of the visual system. This is accomplished by making the connections as "private" as possible and narrowing them to a one to one relationship in the so-called midget pathways.
The midget pathways consist of midget bipolar cells and midget ganglion cells, the latter of which project to individual parvocellular layer cells of the lateral geniculate nucleus in the brain. Because of the need for the high acuity midget pathways also to be organized into ON- and OFF-center channels like the diffuse cone pathways for maximization of contrast, it means that every cone of the fovea will have dual midget pathways. The two midget bipolars will be an ON-center type and an OFF-center type and will connect with ON-center and OFF-center midget ganglion cells respectively. This improves contrast sensitivity for high spatial frequencies.
Striate Cortex
Striate Cortex has 6 layers• 1.3 million ganglion and LGN cells diverge to 260 million
neurons in the visual cortex• Layers 5 and 6 project back to the LGN• Layer 4 goes on to higher cortical layers• Cells are arranged retinotopically as in the LGN, so cells
located next to one another in the cortex process information from areas of the visual field located next to one another.
• More cortical cells are devoted to processing macular information than peripheral information. 50% of the striate cortex is devoted to processing information from the central 10 degrees of visual field. Borish.
Visual Cortical Cells
• In 1959 Hubel and Wiesal discovered that cortical cells responded to certain orientation of bar targets. All cells within a column through the 6 cortical layers have roughly the same orientation preference.
Receptive fields in V1 of visual cortex
Recall that the receptive fields of both ganglion cells and LGN neurons were center-surround, and that they responded optimally to points of light. Neurons in the cortex, however, respond very poorly to points of light. The optimal stimulus for most cortical neurons turns out to be a bar of light, in a very specific orientation. How did this come about?
How we see
Light strikes our retinal photoreceptors which converts chemicals into energy releasing electrical stimulation to the bipolar cells with lateral interactions modulated by the horizontal cells which releases energy to ganglion cells whose lateral interactions are modulated by amacrine cells. The 1.3 million ganglion cells compose the optic nerve which goes to the lateral geniculate nucleus and organized into 6 layers where lateral interactions occur between on/off midget cells. From there 1.3 million cells terminate in the striate cortex where lateral interactions occur in 260 million cells which further process the image allowing us to see.
What happens when something goes wrong with this?
AMBLYOPIA
Amblyopia
• In amblyopia radiographic visual evoked response studies show that cells in the LGN and visual cortex are smaller and have fewer connections.
• Electrophysiologically, Amblyopic cells have decreased CSF with higher spatial frequencies.
• Temporal timing functions are also reduced, meaning they can detect slower moving targets versus faster moving targets.
Amblyopia
• Biochemically, autoradiographic analysis of enzymes used in transporting information show less energy production so there is less activity among neural connections. Less lateral interactions.
How does Patching work?
• Patching results in increased cell size and more connections by making pathway function more efficiently improving the response.
• It is important that the amblyopic eye looks at targets which stress the eye at the limit of it’s ability.
How does loss of the good eye affect the amblyopic eye?
When good eye is lost, connections which were turned off by interactions with good eye are now allowed to turn on. The inhibiting connections from the good eye are gone, unmasking the good connections already present. The more connections, the better the acuity.
So, who is amblyopic?• Could a 20/20 eye be amblyopic?• During our developmental years, the visual
pathway efficiency depends upon a sharp image on the retina. No sharp image, less cell interactions and decreased v.a.
• How many of us have sharp images on our retina during our formative years?
Refractive error and age
Lack of sharp image on retina
• Most kids are hyperopic, going into and out of focus.• Many have uncorrected astigmatism. At age 4 2/3
have astigmatism. Borish• Many have higher order aberrations. (20% of blur in
average person.)
Only a few of us have our visual pathways developed for maximal v.a. (Think Ted Williams)
What if we could improve the visual pathway efficiency in the adult?
What if we could increase the cell size and number of connections throughout the visual pathway in adults?
Scientific Basic Principles
Enhance neuronal Lateral Interactions Neuronal Plasticity Perceptual Learning
Neuronal Network of Lateral Interactions
Target excites cortical cells
Area of lateral excitation provided by interaction of similar orientations
Area of lateral inhibition (orientation of little relevance)
The Visual Cortex
Cortical cells (neurons) are highly specialized and optimized image analyzers
They respond only to a limited range of parameters (filters) of the visual image
The Visual Cortex (cont)
Individual neurons respond to
• Precise location• Specific orientation• Specific spatial
frequency
Adapted from:Hubel & Wiesel (1959). Receptive fields of single neurons in the cat’s striate cortex. J Physiol (Lond) 148:574-591
The Visual Cortex (cont) To characterize an image, visual processing involves
the cooperative activity of many neurons, these neuronal interactions are contributing both excitation and inhibition.
Gabor Patch
“Gabor Patches” 1 are widely used in the field of visual neuroscience. Having been shown to efficiently describe the shape of receptive fields of neurons in the primary visual cortex they thus represent the most effective stimulation.2
1. Gabor (1946), Theory of Communication. Journal of the Institute of Electrical Engineers, London, 93, 429-457).
2. Daugman. Two-dimensional spectral analysis of cortical receptive field profiles. Vision Res 1980; 20:847-56.
Precise Control of Variables
Spatial Frequency
Local Orientation
Contrast
Target-Flankers Separation
Target Displacement
Global Orientation
Excitation from outside the CRF
Adapted from:Polat U., Mizobe, K., Kasamatsu, T., Norcia A.M. (1998). Collinear stimuli regulate visual responses depending on Cell's contrast threshold. Nature, 391, 580-584
Contrast response of a single neuron can be modulated by activity of neighboring neurons (single-unit recordings in cats and monkeys1)
1. Chen, Kasamatsu, Polat, & Norcia, 2001; Kapadia, Ito, Gilbert, & Westheimer, 1995; Levitt & Lund, 1997;Mizobe, Polat, Pettet, & Kasamatsu, 2001; Polat, Mizobe, Pettet, Kasamatsu, & Norcia, 1998; Sillito, Grieve, Jones, Cudeiro, & Davis, 1995
Neural Plasticity
Neural plasticity - relates to the ability of the nervous system to adapt to changed conditions, in acquiring new skills. The new required skills are retained for years
Evidence for Neural plasticity - Visual acuity improvement in adults with amblyopia has been reported after prolonged patching1 or when the better eye’s vision has been lost2 or degraded, by age related macular degeneration3, cataract4 or trauma5
1. Birnbaum MH, Koslowe K, Sanet R. (1977)2. Vereecken EP, Brabant P. (1984)3. El Mallah MK, Chakravarthy U, Hart PM. (2000) 4. Wilson ME. (1992)5. Rabin J. (1984)
Perceptual Learning & Neural Plasticity
The phenomenon - Perception can be modified by experience. Visual performance improves with practice
The technique - Repetitive performance of controlled and specific visual tasks
Perceptual learning has been evidenced in a variety of visual tasks and was found to persist for years without further practice1
Clinical observations2 and experimental evidence3 indicate the presence of residual neural plasticity well after the critical period.
1. Gilbert, 1998; Sagi & Tanne, 1994).2. Moseley, Fielder (2001) 3. Polat, Sagi(1994); Levi, Polat (1996); Levi, Polat, Hu (1997)
Lateral Masking – NVC Fundamental Technique
This stimulation-control technique is called “Lateral Masking”, where collinearly-oriented flanking gabors are displayed in addition to the target gabor image, in a specific controlled manner
Neuro scientists demonstrated that the contrast sensitivity function of adult subjects can be increased significantly through precise control of stimulus parameters
Summary
• Image quality depends both on the sharpness of the image on the retinal and the processing in the visual part in the brain (visual cortex)
• The visual system in the brain has mechanisms for further ‘enhancing’ the visual processing (lateral interactions)
• Amblyopia treatments enhance the under-developed neural processing to better process the clear image coming from the retina
• Few of us have maximally developed visual pathways.
What are the NeuroVision Treatments?
• The patient is examined and best prescription is determined.
• Baseline data is gathered on uncorrected v.a.s and best corrected v.a.s
• Baseline data on Contrast Sensitivity Function is obtained with uncorrected v.a.s and best corrected v.a.s
• Baseline data is entered into the NeuroVision system over the internet for the patient. This allows NeuroVision to determine at what level to begin the treatments.
FACT CSF chart and ETDRS Acuity chart
Treatment sessions
• The patient is seated at a computer 5 feet away.
• Each session lasts 25 to 30 minutes and is composed of 10 – 12 sections.
• During each session only one orientation of target is shown.
Treatment session
• The patient is asked to make a forced choice between flashes of targets.– Which one had the target (limits on spatial
frequency threshold)– Which target was brighter (contrast differential)– Which one was aligned higher or lower (vernier
acuity)
Treatment Targets
Spatial Frequency
Local Orientation
Contrast
Target-Flankers Separation
Target Displacement
Global Orientation
Treatment sessions
• 1 treatment a day• 2 to 7 treatments per week.• 15 treatments give 85% of the gain• 20 to 30 treatments total
• Controlled home/clinic environment• Sessions of 25-30 minutes each• 20 to 30 Sessions (depending on the patient) • Once a day or as few as two sessions per week
Patient Management
Treatment end – When patient’s vision does not further improve
Treatment Set-UpBaseline Test by optometrist
Computerized analysis of neural inefficiencies
Administration
Progress
Interim tests by technician
• Results automatically sent to Data Center • Individualized sessions adjust to progress
Customization
Each session directly treats neural inefficiencies
Treatment
Results of Clinicals in US
• Amblyopia• Low myopia• Presbyopia
Visual Acuity Improvement in FDA Amblyopia Study – 2000
-0.1
0.1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.0
LogMar
6/36
6/30
6/24
6/18
6/15
6/12
6/9
6/4.5
6/7.5
6/6
Snellen Equiv
Individual VA Improvement – 44 Patients Completed
Stability of VA Improvement in FDA Amblyopia Study - 2000
Amblyopia FDA Study - Aniso & MyopesCompared to the Group
Treatment Treatment 3 Months 6 Months 9 Months 12 Months
Vis
ual A
cuit
y
20/16
20/20
20/25
20/32
20/40
20/50
20/63The Entire GroupAniso & Myopes
Start End
(normal)
6/18
6/15
6/12
6/9
6/4.5
6/7.5
6/6
Contrast Sensitivity Improvement in FDA Amblyopia Study - 2000
Before treatment
At end of treatment
12 months post treatment
Binocular Functions (Worth-4dot) in FDA Amblyopia Study - 2000
0
5
10
15
20
0 1 2 3 4
No.
of
pat
ien
ts (
N=
41)
Before – average 1.43 +0.26 (SE) After – average 2.68 +0.24 (SE)
suppression diplopia rivalry faint fusion
fusion
NeuroVision On Going Trial
Dan Durrie, MD
Peter Shaw McMinn, OD
15 15 Presbyopia Treatment Group
15 15 Low Myopia Treatment Group
7 8 Presbyopia Control Group
8 7 Low Myopia Control Group
45 45 Total Number of Subjects
Low Myopia and Presbyopia
NeuroVision On Going TrialInterim Results (As per October 1, 2007)
US Trials(Updated on Oct 1, 2007)
International Data
Presbyopia Improvement in
Unaided Near VA 2.2 Lines
(22 Patients)
2.0 Lines
Low MyopiaImprovement in Unaided Distance VA
2.2 Lines(15 Patients)
2.6 Lines
ControlsImprovement in Unaided Distance VA
0.4 Lines(10 Patients)
NeuroVision On Going TrialInterim Results (As per October 1, 2007)
Presbyopia
Spatial FrequencySpatial Frequency
UCVA=20/28
UCVA=20/54
UCVA=20/30
Spatial FrequencySpatial Frequency
UCVA=20/36
UCVA=20/60
Low Myopia
Spatial FrequencySpatial Frequency
UCVA=20/25
UCVA=20/44
Spatial FrequencySpatial Frequency
UCVA=20/30
UCVA=20/52
Clinical
Visual Acuity Improvement
Contrast SensitivityImprovement
Retention of Improvement 1 Year PostTreatment
Main Functional Outcome
Myopia Up to -1.50D
2.7 Lines ETDRS (Distance)
Above 100% in All Frequencies
90% of the Improvement
Decrease Dependency on Spectacles
Presbyopia Up to +1.5D
2.0 Lines ETDRS(Near)
Average Of 100% in All Frequencies
No Data Available Yet
Delay The Need of Reading Glasses
Post Refractive Surgery
2.3 Lines ETDRS(Distance)
Above 100% in All Frequencies
No Data Available Yet
Increased Quality of Functional Vision
Amblyopia 2.5 Lines ETDRS(Distance)
Above 100% in All Frequencies
90% of the Improvement
Increased Quality of Vision, Improved Binocularity
Implications for our patients
– Amblyopes– Low myopes, hyperopes, astigmats– Early presbyopes– Pathology patients– Post LASIK – Learning disabilities– Individuals who require or desire excellent visual
acuity
Product Line
Existing Presbyopia (Up to Add +1.5D) Low Myopia (Up to -1.5DS + -0.75DC) Pediatric Myopia Post Refractive Surgery Adult Amblyopia (“Lazy Eye”)
Future Super Vision—Sports Vision, Military, etc. IOL Enhancement Contact Lens Enhancement Early AMD Enhancement
attractive for all eye care market segments
Optometry
New Non-surgical Vision Improvement Treatment No Medical Degree Required to be Administered— An Optometric Alternative to LASIK
Specs & Contact Lenses Do Not Always Provide Sharp Vision
Presbyopia Treatment - Premium Revenue Generator People Do Not Invest Much in Reading Glasses
Low Myopia Treatment will Generate Additional New Business
attractive for all eye care market segments (cont’d.)
Optometry (cont)
Can be Performed in Practice or at Home
Home Option Minimizes Management Overhead
Minimal “Chair Time” – Optometrist Needed Only for Baseline Examination. Other Examinations by Technician
For more information:
www.neuro-vision.com
Solve Your Patient’s Acuity Problems by Prescribing NeuroVision Technology!
Thank You for Attending the class!
Peter Shaw-McMinn, [email protected]
Contrast Sensitivity
Contrast sensitivity is a measure of the limit of visibility for low contrast patterns -- how faded or washed out can images be before they become indistinguishable from a uniform field? (Think of driving in a fog). It is a function of the size (coarse/fineness) of image features, or the spatial frequency.
