Cortical Vision Loss

1
Cortical Vision Loss

• damage of one or both occipital lobes of visual
  cortex

2
Progressive Visual Impairment

• regular eye care self-monitoring
• diabetes
• posterior vitreous detachment
• glaucoma
• cataract

3
OPTICS LOW VISION DEVICES
4
Basic Optics

• The Composition of Light
• The Measurement of Light
• Refraction- the bending of visible light rays
• index of refraction- speed of light passing
  through various media
• Refraction the ocular system

5
The Optics of Lenses

• Structure of a lens
• Snell's law- the line that will travel upon
  exiting glass
• focal point or image point- where light rays
  come together converge on a point

6
Types of lenses

• spherical lenses
• convex or plus lenses bulge outward
• planoconvex- bulges on one side
• chromatic aberration- light disperses as are
  colors in a prism
• biconcave- bulges inward on both planes
• planoconcave- bulges inward on one side
• cylindrical lenses
• plano lenses- lens cut flat on both sides
• combination of lenses
• prism lenses- moves light rays into functional
  field

7
Lenses for Refractive Errors

• Myopia (nearsightedness) biconcave (minus)
• Hyperopia (farsighted) biconvex (plus)
• Astigmatism (irregular cornea) cylindrical
  axis (location on cornea)
• Strabismus prisms (base in or out)

8
Measurement of Lenses

• focal distance- fd
• power is measured in diopters D

9
Types of Magnification

• Relative distance magnification
• Relative size magnification
• Angular magnification
• Projection magnification

10
Near Vision Optical Devices

• Microscopes
• Magnifiers
• handheld magnifiers
• bar magnifiers

11
Near Vision Optical Devices

• Stand magnifiers
• Illuminated magnifers

12
Distance Vision Optical Devices

• Telescopes
• Hand-held monocular telescopes
• Clip-on monocular telescopes

13

• Spectacle-mounted telescopes
• full-field telescope systems
• bioptic telescopes
• Contact lens telescopes
• Behind-the-lens telescopes

14
Non-Optical Systems

• Illumination
• 1. types of light
• 2. position of light
• 3. adaptation of light to dark
• 4. glare
• Illumination control
• Nonoptical magnification

15
Electronic Systems

• Common electronic systems
• Closed circuit TVs (CCTVs)
• Computer systems
• Other magnification systems

16
Field-Expansion Systems

• Bioptics
• Fresnel prisms

17
CLINICAL LOW VISION

• Purpose of an evaluation
• Referral for an evaluation

18
Sequence of a Typical Evaluation

• Members of the Low Vision Team

19
Sequence of a Typical Evaluation

• Case history
• Preliminary observation
• Distance visual acuity testing
• measurement charts
• fixation refers to the ability of the individual
  to hold his attention to the object being viewed
• distance acuity notations
• assessment of young children
• i. observation
• ii. tests of visual functions
• special considerations

20
Functional Vision Testing

• Behavioral
• OKN (optokinetic nystagmus) - cortical
• PLT (preferential looking test)- Teller acuity
• Chromatic Luminance- contrast sensitivity
• Tracking a toy or light- see textbook for sizes
  and distances

21
Electrophysiological

• VER- Visual Evoked Potential (visual pathways)
• ERG- Electroretinogram (cone rod retinal
  function)
• EOG- Electrooculogram (measures charge
  potentials of eyes)

22
Subjective

• Acuity
• LEA Charts
• Snellen
• Tumbling E
• CSF- Contrast Sensitivity Function
• Flicker Fusion- macular function
• Color- Ishihara
• Visual Fields
• Confrontation
• Ganzfeld globe

23
Visual Efficiency Testing

• ISave (APH)
• Program to Improve Visual Efficiency (Barraga)

24
Near Visual Acuity Testing

• 1. measurement charts
• 2. near-acuity notations
• 3. special considerations

25
Refraction

• determination of refraction
• retinoscopy- streak of light reflex
• instruments for refraction
• trial frame lens set

26
Color Vision Testing

• Ishihara color plates
• Farnsworth D15

27
Contrast Sensitivity Testing
28
Interpretation of the Eye Report

• CUMULATIVE RECORD OF VISUAL FUNCTIONING
• Name Sex DOB
• Parent/Guardian
• Address
• Home Telephone Work Telephone
• Schools attended Location Dates
• __________________________________________________
  ____
• Visual Information
• Eye condition
• Ophthalmologic findings
• Eye Surgery
• Eye Medications

29
Eye Report

• Visual Acuity OD OS OU OD OS OU
• (without correction) (with correction)
• Distance vision
• Near vision
• OD OS
• Visual fields
• (tested w/with correction)
• (reported central peripheral
• w/blind spot)
• Color vision
• Sphere Cylinder Axis
• Refractive error
• OD
• bifocal
• OS
• Bifocal

30
Eye Report

• Strabismus
• Binocularity
• Stereopsis
• Is eye condition stable?

31
Eye Report

• Visual Aids
• Glasses prescribed Date
• To be worn when?
• To be worn where?
• Low Vision Aids prescribed
• Classroom aids
• Print point size
• Lighting
• Reading aids (lamps, stands, globes)
• Magnification devices
• Telescopic devices
• Visors
• Shields
• Tables
• Pencils, Pens, Markers
• Paper
• Electronic Aids
• Computer glare filter

32
Eye Report

• I. Conditions for Optimal Visual Functioning
• A. Prefers to control natural light by
• Wearing tinted glasses
• Adjusting window shades
• Wearing visors
• Seeking existing shade areas
• Creating shade areas
• Moving to source of light
• Turning to source of light
• Turning from source of light

33
Eye Report

• B. Prefers to control artificial light by
• Direction of source (specify)
• Degree of intensity (specify)
• Prefers combined diffused and directed
  light Prefers incandescent light
• Prefers fluorescent light
• Prefers halogen light
• Prefers a glare-free work surface (specify)
• Prefers absorbent work surface
• Prefers limited work surface

34
Eye Report

• C. Improves own visual functioning by (specify
  optical aids
• circumstances)

35
Eye Report

• D. Audiovisual viewing
• Prefers print point
• Prefers black white (specify distance)
• Prefers color (specify distance)
• Type of illumination
• Dimly illuminated screen
• Prefers high or low contrast (specify)
• Prefers viewing distance of reading materials
• Prefers viewing distance from computer
• The following audiovisual materil cannot be seen
  from the student's desk

36
Eye Report

• Visual Functioning Under Optimal Conditions
• A. Outdoors
• Can easily adapt to sudden changes in
  illumination
• Can visual identify an individual (specify
  distance)
• Can distinguish between lawn sidewalk
• Can distinguish lines on pavement such as for
  crosswalks safety zones
• Can visually avoid stationary obstructions before
  physical contact
• Can detect variations of walking levels
• steps curbs ramps
• Can detect ball in air (specify size)
• Can recognize features of a persons objects
  (specify distance)
• Can usually see traffic lights at night
• Can usually see traffic lights during the day
• Can use visual landmarks to establish line of
  direction
• Can select own visual landmarks
• While walking
• From a moving vehicle
• Can see if a curb is absent low lying has rounded
  corners
• Can see house numbers from street or sidewalk

37
Eye Report

• . Indoors
• Can locate source of natural light
• Can locate source of artificial light
• Reaches for objects within arm's length without
  search
• Moves toward objects over 5 feet away
• Can see hands on wall clock
• Can differentiate between small large hands
  on clock
• Can identify without touch eating utensils placed
  at random on desk or table
• Can imitate pose or gesture of teacher at
  _____distance
• Uses APH graph paper 4" 1" 1/8"
• Uses APH lines paper with pencil marker pen
• Uses APH outline maps
• Reads chalkboard at ____ distance
• Reads dry-erase at ___ distance
• Can use pictures in large-type books
• color
• black white
• Specify smallest print size
• Can read numerals on paper money

38
Report of Clinical Findings

• Other Considerations
• Individuals with multiple disabilities
• Emotional aspects of the evaluation
• Funding issues

39
Visual Functioning

• Visual Ability Finding Implications
• Visual acuity
• Visual fields
• Contrast sensitivity
• Light sensitivity
• Color vision
• Oculomotor control
• accomodation