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Stage 1 Visit 3 > 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

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

1
Q

What patients benefit from low vision aids?

A
  • 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
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2
Q

Figuring out Magnification

A
  • 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!
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3
Q

Calculation for Working distance

A

WD = 1/F

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4
Q

Spectacle LVA:

A
  • MAGNIFICATION: Up to X4 (generally X3 is maximum for most people)
  • FIELD OF VIEW: Spectacles Up to X4 (generally X3 is maximum for most people) Close eye-to-magnifier distance allowing max FOV
  • WORKING DISTANCE: Depends on level of mag. If X1 mag then 25cm etc. * Hands free (sewing)
  • ADVANTAGES: * Good FOV
  • Binoc viewing
  • Cosmesis
  • Cyl incorporation
  • DISADVANTAGES: * Short WD * Need more illumination
  • Convergence probs (1 BI per 1D above +4.00D needed if binoc)
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5
Q

Hand Magnifier

A
  • MAGNIFICATION: Hand Magnifier Up to 12.5. Normally X3 to X7
  • FIELD OF VIEW: Small FOV
  • WORKING DISTANCE: Short
  • ADVANTAGES: * Can be illuminated
  • Widely available
  • Wide range of power
  • Socially acceptable
  • Easy to use
  • Inexpensive
  • Portable (spot tasks)
  • Robust even if dropped on floor
  • DISADVANTAGES: * Good dexterity!
  • If held closer to reading than focal point then less mag but greater FOV
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6
Q

Stand magnifier

A
  • MAGNIFICATION: Stand Magnifier Up to 22. Normally X3 to X7
  • FIELD OF VIEW: Small FOV
  • WORKING DISTANCE: VERY short
  • ADVANTAGES: * Can be illuminated
  • Fixed WD; accurate (hand tremors)
  • Wide range of power
  • Binoc viewing for lower powers
  • DISADVANTAGES: * Short WD = reduced illumination
  • Usually need reading Rx
  • Bulky/heavier
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7
Q

Handheld telescope

A
  • MAGNIFICATION: Handheld Telescope X4 to X12 normally
  • FIELD OF VIEW: Keplerian higher FOV than Gallilean. Less FOV than magnifier!
  • WORKING DISTANCE: Held to eye
  • ADVANTAGES: * For distance
  • Good at adjusting magnification & hence WD
  • DISADVANTAGES: * Can’t walk with them from distortion of space & movement perception
  • Manual skill, dexterity & practice espec if object moving
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8
Q

CCTV:

A
  • MAGNIFICATION: CCTV Up to 70X mag, TV reader up to 24X
  • FIELD OF VIEW: Good FOV due to screen use
  • WORKING DISTANCE: As you want it
  • ADVANTAGES: * High mag
  • Better FOV depending on mag
  • Binocular
  • Longer WD
  • Cosmesis
  • DISADVANTAGES: Bulky
  • Difficult to use
  • Expensive
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9
Q
A
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10
Q

Depth of focus

A

how much a retinal image can be moved out of focus before the patient notices i.e. in this case, how much a magnifier can move from its WD/positioning before the patient notices distortion. Obviously, a high powered magnifier such as x7 will have less depth of focus for patient, so more movement will make things worse for the patient! This is why stand magnifiers are so useful!

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11
Q

Hand magnifier

A

When using a reading addition (e.g., reading glasses or patient accommodation), consider the optics involved.
The magnifier’s focal point is where light converges; the object should be placed at this point.
Placing the object too close to the magnifier positions it in front of the focal point, causing divergent rays and a blurry image.
To correct this, use the reading addition or accommodation to convert divergent rays into convergent (or parallel) rays.
Teach patients to hold the magnifier with the object at its focal point for optimal clarity.

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12
Q

Stand magnifier

A
  • Stand magnifiers are positioned with the magnifier-to-object distance shorter than the anterior focal length to reduce chromatic aberration.
  • This setup results in divergent rays, requiring a reading addition or accommodation to make them convergent.
  • The fixed distance of stand magnifiers varies by model, necessitating adjustments to the reading addition.
  • The need to vary the reading addition for different magnifiers can be frustrating.
  • This means you need to trial multiple stand magnifiers with the current reading addition to get it just right
  • Lower powered stand magnifiers produce more divergent rays generally so reading addition is definitiely needed (or adequate accommodation). Those >28D (X7) generally have the focal point lined up with the object & so no reading addition needed.
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13
Q

Typoscopes

A
  • Many people with low vision experience “visual crowding”, when trying to read everyday information or study a document. This happens when there is too much information crammed into a small area, making it difficult to concentrate on the section you want. White paper, especially when it is glossy may reflect light in such a way that it can also create a lot of glare.
  • A typoscope (reading guide) can help with this problem. It is a rectangular piece of black matt plastic card with a viewing slot cut out, which can be placed over the text you want to read. This allows greater concentration on the text, and cuts out the reflections from the white background.
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14
Q

How to use? Typoscope

A
  • The typoscope, with its slot at the top, should be placed over the first few lines of the text to be read.
    Read the text that appears in the typoscope viewing slot and move the typoscope down to continue reading the text.
  • When patient reaches lower half of the page, they can turn the typoscope 180 degrees to make it easier to use for this section. It depends on the design of the typoscope. It may look like the one in the image below
  • For best results, use a typoscope together with a good light illuminating the page.
    Avoid lights that shine directly into your eyes. A typoscope can also be used in conjunction with a magnifier, clipboard, or other low vision aids.
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15
Q

Handheld telescopes differences

A
  • Angular magnification —> Separation of 2 lenses meaning refraction of incident light from object refracts in a way that increases angle on the retina, causing apparent increase in object size
  • Differences between Gallilean & Keplarien
    • Gallilean is lighter, cosmetically better, shorter (smaller tube length as -ve eyepiece being used)
    • Lower FOV due to exit pupil being in the telescope but exit pupil outside for keplerien
    • Cheaper for Gallilean?
    • Image upright but poorer quality & lower magnification with Gallilean
  • What is the exit pupil & the markings on a telescope
    • Exit pupil is the image of the objective lens formed by the eyepiece
  • Instructions on use of telescope e.g. how to focus it
  • Advantages & disadvantages
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16
Q

Understands acuity reserve + contrast reserve, linking it with magnification

A
  • For spot reading, not required
  • For prolonged tasks, very much needed to make reading more comfortable
  • Acuity reserve of 2-3 is best. E.g. px has 2X mag for spot reading. 2x3 = 6X which would make reading much better for longer reading & is why stand magnifiers have higher mag than hand mags
  • Fluent reading - contrast reserve 10X their contrast threshold i.e. very bold like black felt tip pen on white paper
  • Spot reading - 3x their contrast threshold
  • REMEMBER - IF TEXT IS SMALL AND LOW CONTRAST, THEN VERY DIFFICULT FOR PX!
  • 31% contrast against background is lowest CS permitting spot reading. 3x this is 93%. Cannot do fluent reading very comfortably unless magnification altered.
  • 7.8% contrast against background is lowest CS permitting sustained reading. 10X this is 78%
    • IN PRACTICE, HELPS TO EXPLAIN WHY LVA NOT AS USEFUL AS ONE MIGHT THINK!
17
Q

Giving correct advice

Hand magnifier

A
  • Should be wearing distance Rx
  • Should be parallel to the object being viewed
  • Must hold at its focal length i.e. bring the magnifier against the page then move it outwards until it comes into focus. This is the focal length. For example, using f = 1/d, a 20 dioptre (5x) magnifier will focus at 5cm
    • Must hold at proper eye to magnifier distance. Does this distance change field of view? Yes, moving this distance closer enables larger field of view.
      • Once focal length found, can move magnifier & print away at the same time whilst keeping their distance, to maximise the working distance
      • Encourage bringing the magnifier to eye distance as close as the patient can get it to improve field of view. If patient does not like this, may need to consider higher mag
      • This all takes time getting used to!
  • Use illumination feature. This extra lighting can mean less magnification needed/more comfortable reading. LED is better than incandescent
18
Q

Giving correct advice

Stand Magnifier:

A
  • Wearing reading Rx
  • Put onto page with lens at top
  • Look through its centre
  • Move the magnifier across the page as you read, or hold your head and the magnifier still, and move the print you are reading.
  • Use illuminated!
  • A clipboard might be useful if sitting in a chair to keep the writing flat
19
Q

Giivng correct advice

Handheld telescope:

A
  • E.g. monocular. Choose which eye to use. Generally distance Rx or no Rx used so really depends on how px copes.
  • Use 2 hands to start with. With confidence, one hand can be used in the future. Hold the front end of the telescope where the groove is with 2 fingers & hold the start of the telescope with other hand.
  • Place fleshy part of index finger against eyebrow then put telescope against eye so it stays steady
  • Adjust groove of telescope to adjust the focus on object. You can keep the focus here so you don’t have to keep adjusting the next time you want to use the telescope
  • Stand still & look at target you want to view beforehand, then use the telescope to track it.
  • Practice on an object across the room & move on to going outside & locating traffic lights etc. Can note a bus number on an incoming bus. Difficult to track moving object so best to focus on lamp or other object ahead of the oncoming bus then move from that location to the bus as it comes forward so that you only have to adjust focus a little.
20
Q

Basic advice on lighting, contrast etc

A
  • WAYS TO MAKE THINGS BOLDERBlack on white e.g. black pen on white paperWhite painted edges of stairsPaint door frames & edges around lightsDark table cloth, coloured drinking glasses, pale crockeryColoured chopboards
  • WAYS TO MAKE THINGS BRIGHTERAngle poise lamp. Half the distance from the reading!Position light right to avoid glareCFL bulbs are best
  • WAYS TO MAKE THINGS BIGGERRelative size magnification - Make the object bigger itself. Easy to do on an iPad for example or TV readers (increased retinal image size)Relative distance magnification - Get closer to object (increased retinal image size)Transverse magnification - use a magnifierAngular magnification - use a telescope
21
Q

Sight substitution

A
  • Postural —> Clipboard (reading less flimsy with magnifier), Reading stands (prevents you from stooping over), Double clamp (convert hand into stand magnifier)
  • Audio —> RNIB has thousands of titles, Audiobooks, Mobile text to speech & vice versa, Voice recorder (for making notes), Talking newspapers & magazines on RNIB subscription, Talking labels - RNIB pen friend (message recorded & sticker placed onto object. Pen pressed onto sticker to play message)
  • Others —> Bumpons e.g. on remote control, Plate surrounds (easier to get food onto plate), Pill dispensers (for medication intake), Liquid level indicator
  • Mobility —> Guide dogs (tough, expensive), Sticks & canes (symbol cane to alert others you are visually impaired, long cane to swing right & left infront of you)
  • Reading —> Braile, Moon. Should be available at library
22
Q

Daily Living Aids

A

 Liquid level indicators
 Talking microwaves / kettles
 Talking watches
 Large no. telephones
 Coloured stickers / buttons

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