Day 7 (1): Basics of Low Vision Rehabilitation Flashcards
(32 cards)
Visual Disorder vs Impairment vs Disability vs Handicap?
Disorder: the eye condition causing anatomical changes
- may not necessarily lead to impairment
- e.g. AMD, cataract, glaucoma, retinal detachment
Impairment: functional limitation due to the disorder
- e.g. decrease VA, constricted visual field, diplopia, distortion
Disability: changes in skills and abilities due to the impairment
- e.g. inability to read, travel independently
Handicap: psychosocial and economic consequences of disability
- e.g. loss of independence, inability to work
What is Low Vision?
- Impaired visual function
- VA: worse than 20/60 (6/18) but better than or equal to 20/400 (3/60)
- Visual field: < 10 degrees from fixation point
- Even after treatment and/or best refractive correction
- In the better eye
- Still able to use vision for planning and execution of tasks
Ranges of visual impairment
- Distance Vision Impairment
Normal Vision: 20/12 - 20/60
+ Normal: 20/12 - 20/25
+ Near normal: 20/30 - 20/40
+ Mild: 20/50 - 20/60 (ICD: worse than 20/40)
Low Vision: 20/70 - 20/400
+ Moderate: 20/70 - 20/160 (ICD: worse than 20/60)
+ Severe: 20/170 - 20/400 (ICD: worse than 20/200)
Blindness: worse than 20/400
+ Profound: 20/500 - 20/1000
+ Near Total: 20/1250 - 20/2500
+ Total: No light perception
- Near Vision Impairment: worse then M.08 (20/40)
What is Legal Blindness?
- VA: 20/200 or worse
- Visual field: 20 degrees or less from fixation point
- Even after treatment and/or best refractive correction
- In the better eye
Two most common causes of vision impairment
- Uncorrected refractive errors: 2/5
- Cataract: 1/3
- Two most common causes: 75% of cases
- 18% due to unknown causes
- 80% is avoidable
- Because more people live longer
- Majority > 50 years old
- Low to middle income countries:
+ Adult: Cataract
+ Children: Congenital Cataract - High income countries:
+ Adult: ARMD, Diabetic Retinopathy, Glaucoma
+ Children: Retinopathy of Prematurity - Trachoma: most common infectious cause
5 most common causes of vision impairment, low vision and bilateral blindness in the Philippines
- Cataract
- Uncorrected refractive error
- Glaucoma
- Maculopathy
- Retinopathy
What is vision rehabilitation?
- Individualized treatment and educational plan that helps attain:
+ maximum function
+ sense of well-being
+ independence
+ optimal quality of life - Employing the collaboration of different specialties and rehabilitation services
Objectives:
1. Develop independent living skills
2. Regain self-confidence for re-integrating into the community
Target population:
1. Low vision: 20/70 - 20/400
2. Blind: 20/500 - no light perception
Considerations in creating a vision rehabilitation plan
- Analyze the visual elements of a task
- modify the task and the environment to the equipment being used - Observe the visual environment and assess the patient in different environmental conditions
- adjust lighting, contrast and color as needed - Determine which sense is more efficiently used for a task
- may use either visual, auditory, tactile or combination of either
What are the roles of the Ophthalmologist in the rehabilitation of patients with low vision?
- Leads the team of different rehabilitation services and specialties
- Performs thorough evaluation
- Determines appropriate low vision aids
What are the components of a low vision rehabilitation and care?
- Patient Assessment
- general observation
- history taking
- visual function measurement - Low Vision Refraction
- Choosing the appropriate Optical Devices
Characteristics and components of the initial patient assessment.
- Different objectives compared to assessment of normal vision
- Retrieve previous spectacles and visual aids
- Functional approach: only do tests that would substantiate the complaints and enhance findings
- Modified to focus on:
1. Detailed functional history
2. Exhaustive visual function measurement - Fundoscopy, slit-lamp exam and other high-illumination techniques are done only after visual assessment
Parts of the general observation and history taking in patients with low vision.
General Observation:
- bothered by bright lights: (+) glare
- frequently falls or stumbles, needs assistance: (+) scotoma
- head tilting/eccentric viewing: (+) scotoma
- (+/-) tremors
History: functional > anatomical concerns
- goals:
1. recognize vision potential and limitations
2. establish current level of functioning
3. determine what patient needs to function
- should be task-related or oriented
- inquire re: everyday activities, tasks, problems and needs
1. Near: reading, medication labels, money
2. Intermediate: eating, computer use, hobbies
3. Distance: driving, sports, movies
- problems and solutions are prioritized according to pt’s needs
What are the components of the visual function assessment?
- Determine the baseline remaining visual function
- Guides efforts to maximize remaining vision
Components:
1. Visual acuity (distance and near)
2. Contrast sensitivity testing
3. Central visual field testing
4. Full-field perimetry
5. Glare testing
6. Color vision
7. Stereovision
Visual acuity testing in patients with low vision
Purposes:
1. Monitoring of treatment effect or disease progression
2. Estimation of power of optical aids needed for reading
3. Verify eligibility for certain tasks
4. Classification as legally blind
Distance VA: Early Treatment of Diabetic Retinopathy Study Chart
- standard for VA measurement in pts with low vision
- uses Sloan optotypes
- equal level of difficulty for each line
- standardized
- letter-by-letter scoring system for correct responses
- testing up to 20/1000 at 1 m testing distance
- start testing at 2 m distance between examiner and pt –> progress closer to 1 m or 0.5 m if pt unable to read the top parts
Why not Snellen chart?
- not standardized thus impossible to accurately evaluate VA data and compare between studies
1. Unequal number of letters per row
2. Irregularly spaced lines in between rows
3. Irregularly spaced letters in a row
4. Types of letters used
Clues to note when testing:
1. Reading speed
2. Accuracy
3. Shielding eyes: glare
4. Large eye movements: poor extra-foveal fixation
5. Head position: eccentric viewing sec. to scotoma
6. One side consistently left out: visual field cuts/scotoma
7. Consistent errors:
- missing R or L side
- Z becomes 7: inferior scotoma
- O becomes C: right scotoma
Near visual acuity testing in patients with low vision
- Importance: tests ability to read
1. Essential skill for basic daily functioning
2. Involves a larger retinal area
3. Helps predict future function
4. Basis for prescription or magnification for corrective lenses
Properties of the correct Near VA chart
- (+) Geometric progression of letter sizes
- (+) Letter size with M unit notation
- Miniature Letter Chart: Lighthouse Chart
- highly accurate; easy to use; portable
- provides less information - Continuous Text Chart: Colenbrander and MNRead Charts
- provides more relevant information because reading is the endpoint
- more difficult to use
Why not Jaeger chart?
1. Size of chart not proportional to letter size
2. Least desirable letter designation
3. Cards are not standardized
What is the MNRead Test Chart?
- Assesses reading performance depending on the print size
- Uses meaningful sentences in proportionally spaced blocks
- Basis for prescribing magnifiers and reading adds
- 3 parameters for assessment:
1. Reading acuity: smallest print that can be read
2. Maximum reading speed: reading speed when performance is not limited by print size
3. Critical Print Size: smallest print that supports the maximum reading speed
Scoring: record reading speed and print size
- slows down at smaller sizes: needs magnification
- slow at all sizes: no benefit to magnification
- paradoxical (slow with large sizes, fast with small): narrow range of optimal magnification
Contrast sensitivity testing in low vision patients.
- measures how well the eyes can distinguish between fine light increments compared to dark
- poor contrast: leads to difficulties in ADL
- important for elderly who are more prone to falls
- options:
- Pelli-Robson Chart
- uses black letters which gradually fade to gray then to white
- determines the lightest contrast that can be distinguished by pt
- if (+) significant deficit, may:
+ provide better lighting
+ enhance contrast
+ magnify - Sine Wave Gratings
- more sensitive
Color Vision testing in low vision patients
- diagnostic value
- to better advise pts in coping with activities requiring color discrimination
- 3 kinds of color blindness:
- Proton/Red Color Blindness
- cannot see RED
- involves L cone: LONG wavelengths - Deuteron/Green Color Blindness
- cannot see GREEN
- involves M cone: MEDIUM wavelengths - Triton/Blue-Yellow Color Blindness
- cannot see BLUE
- involves S cone: SHORT wavelengths
Options:
- Ishihara Test
- most well-known
- tests RED and GREEN blindness - Farnsworth Dichotomous Test
- arrangement test
- cannot differentiate between RED, GREEN or BLUE blindness - Cambridge Test
- screening test
What are the four different plate designs used in Ishihara Test?
Notes:
Plates 1 - 21
- screening red-green defects
Plates 22 - 26
- differentiate protans (red) and deutans (green)
Plates 27 - 38
- for use with illiterates
Interpretation
Normal: 0 - 4 errors
Deficient: greater than or equal to 8 errors
Designs:
1. Demonstation Plate
- seen correctly by ALL patients
- identifies malingering patients
- plate 1
- Transformation Plates
- color blind people will see a DIFFERENT sign than people with good color vision
- plates 2 - 9, 34 - 37 - Vanishing Plates
- seen only if with GOOD color vision
- plates 10 - 17, 30 - 33 - Hidden Digit Plates
- seen only if with color BLINDNESS
- plates 18 - 21, 28 - 29 - Diagnostic Plates
- differentiate between red- & green-blindness
- plates 22 - 27
Visual Field testing in low vision patients
- Measures scope of vision (central and peripheral) of each eye
- Maps the visual fields to detect scotomas and areas of dim vision
- Subjective: requires cooperative patients who can understand instructions
Applications:
1. Detect and quantify scotomas: size, location, density
2. Screening test for glaucoma, retinitis pigmentosa, neurologic diseases
3. Documentation of legal blindness: visual field of 20 degrees or less from the fixation point
4. Requirement for driving
5. Rehabilitation planning
6. Monitoring of disease progression
Tools:
1. Perimetry (Humphrey, Goldman): tests up to central 30 degrees
2. Amsler’s Grid: portable; tests central 20 degrees
3. Confrontation Test: tests peripheral vision
4. Bjerrum’s Screen
5. Perception of Light/Projection of Rays (PLPR)
Common visual field complaints
- Running into objects
- Frequent tripping and falling
- Startled by objects or people that suddenly appear
- Difficulty detecting objects and movement
- Loss of reading trail
Associated visual field defects in ophthalmologic diseases
- Glaucoma: paracentral, arcuate, nasal steps
- Age-Related Macular Degeneration: central or paracentral with normal periphery
- Retinitis Pigmentosa: donut-shaped (starts mid-periphery then extends inward and outward)
- Diabetic Retinopathy: multiple sites
- Retinal Detachment: site of detachment
- Retinopathy of Prematurity: site of neovascularization
- Macular Hole: dense central
- Optic Atrophy: central
- Cataract: generalized depression
- Multiple Sclerosis: altitudinal
- Posterior Staphyloma: central ring, hemianopia, quadrantanopia
What is low vision refraction?
- Done to determine refractive error and amount of correction needed
- Begin with an approximately correct refraction based on:
1. Previous prescription/spectacles/optical aids
2. Retinoscopy
3. Keratometry result
Modifications to Subjective/Manifest Refraction:
- use steps of +/- 2.00 D
- use +/- 1.00 D cyl to optimize clarity of circular letters
- use Stenopeic slit to optimize axis
- compensate for reduced testing distance
- do cover test
What are the common low vision optical devices used in low vision rehabilitation?
- each device with certain advantages and disadvantages
- single device will NOT meet the needs of all tasks
- selection criteria:
1. Specific task requirements
2. Working environment
3. Cost - options:
1. High-Plus Spectacles
2. Hand-Held Magnifiers
3. Stand Magnifiers
4. Telescopes
5. Video Magnifiers
6. Portable Video Magnifiers
7. Wearable Aids
