Cortical Vision Loss

• damage of one or both occipital lobes of visual cortex

Progressive Visual Impairment

• regular eye care & self-monitoring

• diabetes

• posterior vitreous detachment

• glaucoma

• cataract

OPTICS & LOW VISION DEVICES

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

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

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

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)

Measurement of Lenses

• focal distance- fd

• power is measured in diopters D

Types of Magnification

• Relative distance magnification

• Relative size magnification

• Angular magnification

• Projection magnification

Near Vision Optical Devices

• Microscopes

• Magnifiers handheld magnifiers

bar magnifiers

Near Vision Optical Devices

• Stand magnifiers

• Illuminated magnifers

Distance Vision Optical Devices

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

• Spectacle-mounted telescopes

• full-field telescope systems

• bioptic telescopes

• Contact lens telescopes

• Behind-the-lens telescopes

Non-Optical Systems

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

Electronic Systems

• Common electronic systems

• Closed circuit TVs (CCTVs)

• Computer systems

• Other magnification systems

Field-Expansion Systems

• Bioptics

• Fresnel prisms

CLINICAL LOW VISION

• Purpose of an evaluation

• Referral for an evaluation

Sequence of a Typical Evaluation

• Members of the Low Vision Team

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

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

Electrophysiological

• VER- Visual Evoked Potential (visual pathways)

• ERG- Electroretinogram (cone & rod retinal function)

• EOG- Electrooculogram (measures charge & potentials of eyes)

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

Visual Efficiency Testing

• ISave (APH)

• Program to Improve Visual Efficiency (Barraga)

Near Visual Acuity Testing

• 1. measurement charts

• 2. near-acuity notations

• 3. special considerations

Refraction

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

Color Vision Testing

• Ishihara color plates

• Farnsworth D15

Contrast Sensitivity Testing

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

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••

Eye Report

• Strabismus

•

• Binocularity

•

• Stereopsis

• Is eye condition stable?

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• Zoom Text• Software• CCTV

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

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

Eye Report

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

• circumstances)

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:

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• Can see direction of moving escalators• Can see unoccupied seat in auditorium bus• Adaptation time from indoors to outdoors• from outdoors to indoors

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• Identifies coins by sight or touch• Primary color identification

Report of Clinical Findings

• Other Considerations

• Individuals with multiple disabilities

• Emotional aspects of the evaluation

• Funding issues

Visual Functioning

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