Children's Vision: Causes of Visual Impairments, Assessment and Learning Environments
Presented on 24 November 2009
Assessment of Children's Vision
Teacher of Visual Impairment Inverclyde
Why do teachers of the visually impaired need to assess vision?
- Clinically done by ophthalmologists, optometrists and orthoptists
- TVIs are looking for different information -
The purpose of all assessment should be to obtain information which can be used to plan services and develop appropriate activities. For example, these may relate to the curriculum and may also refer to the need for training in effective use of residual vision.
(Vision for the future; a framework for minimum standards in visual impairment education RNIB, 1995)
Differences between clinical and functional vision assessment?
- Functional assessment looks at HOW the student uses vision in real-life situation.
- Functional assessment includes:
pertinent info obtained from clinical reports, parents, pupil, class teacher(s)
observations by TVI, plus orientation and mobility specialist (if appropriate).
Notes: At home, in school, testing in non-clinical conditions as this is what real life is like. Clinical assessments look at thresholds and parameters of visual function, more quantitative, functional more qualitative
While an optometric or ophthalmological exam in and eye doctor's office can yield vital information about the student's eye condition, the results may not be readily transferable to another setting.
Unless care is taken to observe the student's visual
performance in real-life environments where lighting and contrast cannot
always be controlled, a true picture of a student's functional
vision cannot be obtained.
(Anthony, 2000, p32)
Taking a History
- Why is this important?
- Helps to build a profile of each individual child.
- Can provide info relating to preferred learning style.
- What to consider:
- If pupil now blind, did he/she previously have vision?
- Look for changes between recent and older reports (has visual functioning increased or decreased?).
- Is eye condition stable or degenerative?
- Is VI secondary or other conditions?
- Congenital or acute (accident or illness?)
Notes: In transitions may also seek input from educational psychologist for social and emotional component
- Functional vision is most often assessed through observation
rather than formal testing
(Goodman and Wittenstein, 2003)
- May take place in the home. Especially helpful if:
parents have concerns about daily living skills;
shows families you have real concern for needs of individual child;
allows opportunities for discussion with parents which can provide invaluable information.
- Mostly done in school and involves consultation with class teacher
Notes: because TVI only there part time and may miss something, best to timetable yourself for whole of half day observation if possible
What to look for
- Child's daily routine:
Does s/he have support assistant? If yes, what type of support is offered? How well is it received?
- Number of students in class
- Pupil's regular seating position
Notes: Obvious - DOB, stage, other agencies involved
Next step - Choosing Tests
Cambridge Crowding Cards
Near Visual Acuity
- Results are recorded as a fraction.
- Numerator equates to the distance (in metres) at which the test chart was presented, usually 6m.
- Denominator identifies the position on the chart of the smallest line read by the subject.
- 'Normal' visual acuity usually considered to be the ability to recognise an optotype when it subtends 5 minutes of arc, that is, 6/6 on Snellen chart.
(As with all tests, remember to record whether or not glasses worn during
Notes: Can record parts of a line, eg; 6/12+2. Also record any particular behaviours, eg; AHP
Scoring log MAR
- LogMAR scale converts geometric sequence of a traditional chart to a linear scale.
- Each line represents a change of 0.1 log units
- Each letter has a score value of 0.02 log units; 5 letters per line
- Scores closer to 0 = better VA, closer to 1 = poorer VA
- Minimum Angle of Resolution for a 6/6 letter is 1 second of arc.
-the logarithm of the MAR for a 6/6 size letter is 0
Other useful tests
- BUST: for children with additional difficulties
- Colour vision tests: Ishihara; Color Vision Test Plates for Infants (Handaya); City University Colour Vision Test
- Contrast sensitivity: Hiding Heidi
- Convergence: check for difficulties with prolonged spells of reading or close work
- Stereopsis: Lang, Frisby
Advantages of logMAR vs Snellen
- Equal number of letter per line
- Regular spacing between lines and letters
- Uniform progression in letter size
- Final score based precisely on total of all letters read
- Finer grading scale allows greater accuracy and improved test/retest reliability
- Examples of continuous text in variety of print styles, sizes and layouts – pupils can state preferences;
- TVI can observe working distance
- Selection of toys, threading beads, books (print and tactile)
- Coloured cloths for changing surfaces, texture of background, patterns/different colour for assessing figure/ground
Recording and reporting
May find it helpful to have proforma prepared in advance
What to include in a functional vision report (from Goodman and Wittenstein, 2003):
- Pupils preferred print size and working distance
- Contrast sensitivity
- Colour vision
- Estimated field loss
- Light sensitivity
- Tracking ability
- Use of low vision aids
Notes: Proformas help keep you on track if child is anxious or you're using unfamiliar equipment.
Additional information (from history and observation)
- Writing skills: clarity, size of print, speed, ability to read own work
- Use of vision in variety of situations e.g. indoors/outdoors, different times of the day, different weather conditions
- Reaction to changes in lighting e.g. moving between classrooms, moving from indoors to outdoors
- Use of vision compared to use of other senses when exploring objects, pictures or places
- Figure/ground discrimination
- Fluctuation in vision, causes?
- Usefulness of LVAs, CCTV, software or other equipment
- Posture – is pupil comfortably seated? Any abnormal head posture?
- Most beneficial learning media:print, braille, auditory or combination.
Goodman, SA and Wittenstein, SH (2003) Collaborative Assessment, Working with Students who are Blind of Visually Impaired including those with Additional Difficulties. AFB Press, New York
Rowe, F (2004) Clinical Orthoptics. Blackwell Publishing Ltd
Vision for the Future: a framework for minimum standards in visual impairment education (1995) The Scottish National Steering Committee for the Provision of Educational Standards for Children and Young People with Visual Impairment, RNIB