Low Vision Flashcards

Question

What non optical measures can improve lighting glare etc

Answer 1

 Increase lighting o Angle lamp perpendicular to task o Bright wall colours o Clean windows Increase natural daylight * Open curtains * Sit near the natural light but avoid glare and shadows on objects of interest * Pale wall colour - light reflection but not glossy as can create glare * Use dimmer switches for controlling the amount of light in the room * Extra lighting where it could be difficult to move around, such as hallways and stairs * Aim the light directly on the task at hand.  Reduce glare o Window blinds o Lamp shades o Wrap around sunglasses o Typoscopes

Answer 2

reduced by lowering the amount of light hitting the eye. o Neutral density filters useful – absorbs lights of all wavelength o Tints also absorb all wavelengths o Not appropriate for constant use as might require more light indoors

Answer 3

reduce the scattered light in the eye, while leaving unscattered light intact. o Shorter wavelength light scatters more in the eye compared to the longer wavelength light. o Filters to absorb short wavelength light is useful for people with visual impairment. o Reducing disability glare also improves VA

Answer 4

o Loss of contrast sensitivity and glare o AMD px prefer Yellow and Orange filters over Blue, Brown, etc. - Improves as it improves CS and VA

Answer 5

Immediate effects Glare can cause immediate discomfort, such as squinting, tearing, or looking away. It can also cause visual fatigue, which can lead to headaches, burning, or increased light sensitivity blurred/reduced vision

Answer 6

Contrast sensitivity is a very important measure of visual function, especially in situations of low light, fog or glare, when the contrast between objects and their background is often reduced. Driving at night is an example of an activity that, for safety, requires good contrast sensitivity - some jobs require it to be normal can be a symptom of eye conditions like cataract, DM, glaucoma, AMD

Answer 7

Common cause of VI  Children - optic atrophy, cataracts, nystagmus  Early adult life: stargardt’s, AMD, RP  Working years: DR, myopia, corneal dystrophies  Retirement: cataract, AMD  Others: RD, glaucoma, myopic degeneration

Answer 8

Instructions:  Distance Rx worn for longer mag-eye distance (light leaving magnifier is parallel)  Lay magnifier on page & slowly pull-away from page until image clear  To improve FoV; move eye closer  Possibly need near rx if short mag-eye distance being used (for wider field of view)  Should be held parallel to reading material  Move head & magnifier as a unit together  If px says hand magnifier is not strong enough; best option is to tell them to move the lens & object closer to their glasses  Portable & lightweight  No flat surface required  Socially acceptable  Inexpensive  Wide range of mags  Distance rx needed (confusing)  Requires steady hand & fixed WD  Limited FoV

Answer 9

Instructions:  Ensure flat surface  Use tracking strategies – use card to follow a line  Near rx required (light leaving magnifier is divergent – when focal length is less than f1)  Better for poor dexterity px’s (arthritis, parkinsons)  Logical – SVN required  Can be written under if required e.g. crosswords  Wide range of mags available  Require flat surface  Heavy / bulky  Limited FoV  Posture & fatigue problems

Answer 10

 Used for prolonged reading, wide FoV  May be useful for px’s with hand tremors  Reduced reading speed as very close WD  Blurred DV  Not likely to work if >+12.00  Hands free; useful for pronged reading  Worst field of view (shortest eye-mag distance)  Cosmesis  Can incorporate astigmatism  Close WD o Illumination difficult o Fatigue, HAs, dizziness o Binocularity/convergence problems (over +12D)

Answer 11

Galilean telescopes are made up of 2 lenses. The objective lens is a convex (plus) lens (which is held close to the object you are viewing) and the ocular lens is a minus lens and closer to the eye. Advantages § Widens the visual field, great for patients with peripheral vision loss § Lighter, shorter and cheaper Disadvantages § Quality of visual image and detail is sometimes poor

Answer 12

Keplerian Telescopes use two convex (plus) lenses. The objective lens is of a smaller diopter power than the ocular lens. This produces a real image but it is inverted & requires a prism to reverse the image. Advantages § Larger visual field than Galilean § Better optical image quality than Galilean Disadvantages § Longer, heavier & more expensive than Galilean

Answer 13

F/4 = Magnification Power of the lens (F: Dioptres) e.g. 10/4 = 2.5x – a 10 dioptre lens has a magnification power of 2.5x 1/F = Focal Length of a lens (m) (F: Dioptres) e.g. 1/10 = 0.1 m – a 10 dioptre lens has a focal length of 10cm (the object has to be held 10cm away from the lens to be perfectly in focus) Current ‘N’ reading ability/Desired ‘N’ reading ability = magnification needed to achieve this e.g. Patient currently reads N10 with reading rx, but wants to read N5: 10/5 = 2 Therefore we need to supply the patient with a 2x magnifier to achieve this

Answer 14

Acuity Reserve is calculated at 2:1 for the patient to achieve fluent reading. Example: A patient currently sees N24. They would like to read N12 fluently. On the basis of a 2:1 acuity reserve, this means the patient must be able to spot read N6. (N12/2 = N6) Therefore, you must tailor the ‘current reading ability’ magnification equation listed just above to N24/N6 = 4 (rather than N24/N12 as this will not allow for fluent reading) Therefore the patient will need a 4x magnifier to fluently read N12, and spot read N6.

Answer 15

ADV  Bright – light gathering  Useful for px’s with hand tremor  Clear image across entire lens (aberrations have minimal effect)  Combo of bar & spec mounted magnifier can increase mag while maintain long viewing distance  Normal reading posture possible DIS  Large lenses – heavy  Mag typically low  Reading material must be on flat/firm surface

Answer 16

for distance magnification o Wear SVD o Add rx to eyepiece o Or alter telescope length (myope = shorten, hyperope = lengthen) ADV  Can be for DV or NV & either monoc or binoc  Increased WD  Variable focus  Can be spec mounted & hands free DIS  Expensive  Poor cosmesis  Heavy training required  Magnification of body movement  Poor field of view, approx 7 degrees (Field of view is optimised by patching size of exit pupil to px’s pupil (or ensure exit pupil is > px’s pupil) )

Answer 17

 Decreased FoV  Decreased WD  Increased illumination needed

Answer 18

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

Answer 19

o Matt black card with a window cut out the width of a line o Useful if RHS of vision has been lost due to stroke – eye is scanning into nothing so typoscope is used as a guide o Field loss of LHS is not as bad but person may find it hard to find the beginning of the next line

Answer 20

o E.g. 8 x 24 o The number before the x is the magnification e.g. 8x mag o The number after the x represents the diameter of the objective lens in mm e.g. 24mm o Dividing the objective diameter by the mag gives us the exit pupil diameter e.g. 24/8 = 3mm o This gives an indication of how bright an image will be seen px the px, as light leaving the system is determined by the exit pupil  Ideally want the exit pupil to match the px’s pupil, but having the exit pupil > px’s pupil allows for some misalignment, but some loss of field o Some telescopes offer a third marking e.g. 7, representing the field of view

Answer 21

o Symbol cane  Lightweight, folding can  Indicates that the user is visually impaired o White walking stick  As symbol cane but also aids support o Long cane  Most common type of cane  Swung in front of the px in an arc, at the end of travel it touches the ground before swinging the opposite way o Guide cane  Shorter and stronger than the long cane  Back up for those with residual vision o Available from social services, but can be bought from various charities o If a white cane has red stripes, this indicates that the px also has impaired hearing

Answer 22

- Aberration free - Max mag up to 70x higher (limit of 30x is common) - Zoom controls allow variable magnification -Foreground/background colour options, windowing etc - Contract, luminance, enhancing - Contrast reversal (50% of VIP prefer white on black) - Binocular viewing - Normal viewing distance/posture - Variable camera-to-task and eye-to-screen distances - Reading duration > optics LVA - May be more psychologically acceptable than optical aids - Cost: expensive to buy and service/repair - Size depending on type/model - Image quality – depends on screen - Depth of field is limited by the focal length of the camera and can cause problems with thick books (use glass sheet to flatten out)

Answer 23

EVES form a direct cable link between the camera imaging system and monitor viewing system. Whereas plus lens magnifiers are made up of simple plus lenses and can be in the form of hand, spec-mounted, stand or flat field magnifiers. Eves are not available on the NHS, whereas plus lenses magnifiers are, but people tend to buy privately.

Answer 24

* Stand mounted * Still one of the most commonly used designs * Each component fixed and mounted vertically “in-line” * Working space fixed or limited * For distance need second camera to be added * Reading material needs to be flat – depth of focus

Answer 25

* Advantages o Good of physical handicap o Good for extensive VF defects, SES * Disadvantages o Expensive, bulky, servicing and repair o Practice required o Control positions

Answer 26

- hand held/ portable - head mounted - DV and NV mag, high cost - spec, hands free, widest FoV, binocular