4.2.1 Advises on the use of and dispenses simple low vision aids including simple hand and stand magnifiers, typoscopes and handheld telescopes. Flashcards
Difficulties with simple scenario for reading - suggests appropriate power of aid but not correct spectacles. Confused about acuity reserve, watch the College webinar on 28th and then I will ask more questions (35 cards)
Reading example questions
- Can you read the post for example? Does anybody help you? What do you do when this nobody to help you?
- What other kinds of tasks do you do that require you to read?
- Do you use a lamp when reading? Get them to describe how they use it i.e., angle and position it and what benefits there are to task lighting.
- Do you use any magnifiers? If they mention a magnifier, ask them what they use it for.
- Is there anything you are struggling to see, even with the magnifier?
Cooking example questions
- For example: has your wife always done it? Does patient want help with cooking, vision wise?
- Are you okay seeing the dials?
- What do you do when there is nobody to help you?
- Getting things out of ovens
- Pouring hot liquids?
- Can put cup in sink, liquid indicator which makes noise when too high
- Any burns or scolds? (note abscense)
- If bad VA in one eye and good in other, bad depth perception
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What patients benefit from low vision aids?
- Patients with low vision! Such as severe dry AMD
- Where cataract removal not possible or they don’t want it
- Patients wanting to have more comfortable reading
- E.g. stand magnifier for prolonged reading or writing
- Wanting to improve reading speed
- Spot/survival tasks like shopping e.g. with a hand magnifier
Figuring out Magnification
- Maximum Vs Nominal Magnification
- Estimate near VA from current vision —> e.g. 6/60 means divide the denominator by 3 to get N20 with a +4.00 ADD. In reality, this is not always the case & is normally worse than this!!
- How much magnification? Try increasing reading add and consider WD i.e. 4.00D is 25cm, 8.00D is 12.5cm, 12.00D is 8.33cm, 16.00D is 6.25cm. Shows why stronger spex don’t always help!
- Optimise the lighting & tell px to bring close to their nose then further away to get into focus. Be encouraging but know when to stop!!
- Calculate —> What the px can see/What the px wants to see —> QUICK METHOD
- It’s all an estimate!
You should know what happens when magnification increases, what happens to FOV & WD
WD = 1/F
Assessment of Visual Function
- Good communication is essential.
- Remember that low vision patients have reduced vision so the way
in which you approach vision tests is likely to be different than how
you may approach the same tests for patients with good vision. - Do not say “What is the smallest line you can see?”.
- First establish if they can see the chart and then work down the
chart starting from the top. - We do not want to make the patient upset or more anxious about
their level of vision.
Measuring logMAR Visual Acuity
- Each letter has a value of 0.02 log units.
- Each line contains 5 letters → each line is worth 0.1
log units. - For each letter read incorrectly add 0.02 to the
score for that line. - If the Px cannot read the top line, move chart closer
by half the distance. Add 0.30 to the logMAR score
to account for this. - Always record logMAR values to 2 decimal places.
Near Visual Acuities before magnifiers
o We need to be set up appropriately to measure near visual
acuities.
o Instruct our patient to wear her reading spectacles.
o Ensure you have a tape measure to measure the working
distance.
o Ensure that there is sufficient lighting directed onto the page,
e.g. use an angle poised lamp.
Contrast Sensitivity affect on visual acuity
- Conditions including cataract,
glaucoma and diabetic retinopathy can
cause reduced contrast sensitivity. - Most visual tasks in daily life are not
high contrast. - Patients are likely to struggle with their
vision if they have poor contrast
sensitivity even if their visual acuity is
good. - Poor contrast sensitivity can increase
risk of falls e.g. patients may struggle
to see edges of curbs or steps.
Patients with reduced contrast sensitivity
can be advised about:
* Task lighting, e.g. angle poised lamp
* Contrasting coloured kitchen equipment
and utensils, e.g. use different coloured
chopping boards for different coloured
foods.
* Writing in bold black pen.
* Contrast enhancement settings on
smartphones and computers.
Pelli-Robson Contrast Sensitivity
- For use at 1m (often wall
mounted). - Chart should have good and
uniform illumination. - The patient should wear their
distance correction with an
add of +0.75D if presbyopic to
account for the 1 metre
distance. - The letter sequences are
organized into groups of three
(triplets) with two triplets per
line. - All letters have the same
contrast within each triplet. - The contrast decreases from
one triplet to the next.
he score is recorded by the
faintest triplet at which at least
2 of the letters are correctly
identified. - The log contrast sensitivity
value is given by the number on
the scoring pad.
Mars Contrast Sensitivity
- Handheld near contrast sensitivity test.
- Designed to be used at 50cm (range from 40-59cm is
acceptable). - Chart should have good and uniform illumination.
- Patient should wear their appropriate near correction,
or their distance correction with an add of +2.00D. - The contrast of each letter
decreases by a constant factor
(0.04 log units). - End the test when the patient
incorrectly reads 2 consecutive
letters or they reach the end of the
chart. - Use the score sheet to record the
patient’s responses and calculate
your score.
Mars Contrast Sensitivity Scoring
- On the score sheet mark an X on each letter that is read
incorrectly. - The log contrast sensitivity (log CS) score is given by the log
contrast sensitivity value at the final correct letter before two
incorrectly identified letters, minus a scoring correction.
Example:
* Score for final correct letter before ending test: 1.32
* Number of errors before ending test: 3
* Scoring correction: number of errors multiplied by 0.04: 3 x 0.04 = 0.12
* Final score: score for final correct letter MINUS scoring correction
1.32 – 0.12 = 1.20
Hand Magnifiers adv vs disadv
Advantages:
* Portable.
* Can be lightweight and discrete.
* Does not require a flat surface to
be used, e.g. can use to read tins.
* Socially acceptable and often
already familiar to patients.
* Internal illumination is possible.
* Available in a wide range of
magnification.
Disadvantages:
* Requires a steady hand and the
ability to maintain a fixed
working distance.
* Should be used with distance
spectacles – this can be
confusing for the patient
because the magnifier is used
for near tasks.
* Limited field of view – can be
improved by reducing eye to
magnifier distance.
Spectacles and magnifiers?…
Distance spectacles are required to be used with a hand magnifier because the light leaving the magnifier is parallel
Stand Magnifiers adv vs disadv
Advantages:
* Better for patients with tremor or poor
dexterity because it rests flat on the page.
* Should be used with near spectacles – patients easily accept this because they are used to wearing their near spectacles for near tasks.
* It is possible to write under lower powered stand magnifiers.
* Internal illumination is possible.
* Available in a wide range of magnification.
Disadvantages:
* Can be more heavy and bulky.
* Requires a flat surface for easy use – often recommend a reading stand to be used with the magnifier.
* Limited field of view.
Spectacles and stand magnifiers
Near spectacles are required to be used with a stand magnifier because the light leaving the magnifier is divergent.
Bright Field Magnifiers
Advantages:
* Easy to use.
* Very socially acceptable.
* Light gathering.
Disadvantages:
* Can only provide very low
magnification (~2x).
* Needs to be used on a flat surface.
Calculating Magnification
Predicted magnification =
What they can see/ What they want to see
Example: A patient can read N12.
Their task requires them to read N6.
Predicted magnification =N12/ N6 = 2x
- Remember to take into account acuity reserve.
- Acuity reserve – the ratio of the size of letters to be read to
the smallest letters the patient can see.
Type of task Acuity reserve
Fluent reading, e.g. Reading a book At least 2:1
Spot reading, e.g. Reading a food label 1:1
Example: A patient wants to read a large print book that is size N16.
This is a fluent reading task so we need to allow 2:1 acuity reserve –
aim for the patient to read print size N8 with the magnifier.
Formulae to calculate power of magnifier in dioptres from magnification:
Magnification = Power Dioptres/4
Power Dioptres = Magnification x 4
Telescope labelling
- Telescopes are always labelled with 2 numbers in the format:
Magnification x Objective lens diameter (mm) - A larger objective lens diameter should offer a wider field of view.
- Some telescopes have a third marking which
represents the field of view. This may be written in degrees or as a linear field of view visible at a specific distance.
Certification & Registration
- Certification
Completion of CVI form by a Consultant
Ophthalmologist to certify the Px as SI/SSI. - Registration
Local social services will contact the patient after receiving the CVI to ask if they want to be included on its register of people who are SI/SSI.I.
SI is described as:
- Visual acuity of 3/60 (1.30logMAR) to 6/60 (1.00 logMAR) with a full
field of vision. - Visual acuity of up to 6/24 (0.60 logMAR) with a moderate reduction of
field of vision or with a central part of vision that is cloudy or blurry. - Visual acuity of 6/18 (0.50 logMAR) or even better if a large part of
your field of vision, for example a whole half of your vision, is missing
or a lot of your peripheral vision is missing.
SSI is described as:
- Visual acuity of less than 3/60 (1.30 logMAR) with a full visual field.
- Visual acuity between 3/60 (1.30 logMAR) and 6/60 (1.00 logMAR)
with a severe reduction of field of vision, such as tunnel vision. - Visual acuity of 6/60 (1.00 logMAR) or above but with a very reduced
field of vision, especially if a lot of sight is missing in the lower part of
the field.
Low Vision Leaflet (LVL)
- A High Street Optometrist can give a LVL to anyone with a sight impairment who would benefit from advice and support from social services.
- A LVL contains contact details for sources of information, advice and help.
- It has a tear-off form with questions for the patient to answer about their home situation, difficulties and additional disabilities and then send to their local social services to ask for an assessment.
Mobility support
- Sensory services from local councils can offer a mobility assessment and subsequent training to give a person with sight loss the skills and confidence to go out independently.
This may include:
* Working out the safest routes to travel to specific locations
* Tips about the safest places to cross roads
* Cane training
