7.1.5 Assesses pxs with impaired visual function & understands use of specialist charts

Question 1

What are the visual requirements for severely sight impaired?

Answer 1

• VA of <3/60 with full VF
• VA 3/60-6/60 and severe reduction in VF (tunnel vision)
• VA 6/60 or above but v reduced VF (especially lower 1/2)

Question 2

What are the visual requirements for sight impaired?

Answer 2

• VA 3/60 - 6/60 with full VF
• VA up to 6/24 with reduction of VF or central cloudy/ blurry vision
• VA of 6/18 or better with significatn reduction in VF (1/2 of VF missing, or loss of peripheral vision)

Question 3

Describe testing distance and near vision in low vision pxs?

Answer 3

Distance Vision:
logMAR:
at 4m, lower logMAR = better VA
5 letters on each line, each letter is 0.02
To grade: value of line +0.02 for every letter missed
If chart broug closer: at 2m add +0.3 to final score, at 1m +0.06, at 50cm +0.09
Near Vision: Bailey-Lovie at 25cm distance, each line is 0.1logMAR, N numbers

Question 4

Describe testing contrast sensitvity in low vision pxs? Pelli Robson

Answer 4

Pelli-Robson: 1m testing distance, 6/18 optotype
- Each triplet is same contrast
- Each letter is worth 0.05 and each triplet is 0.15: <1.0 = visual disability, <1.50 = visual impairement, 2= normal
- Score is recorded by faintest triplet at which at least 2 of letters are correctly identified

Question 5

Describe contrast senesitivity testing in low vision px? MARS

Answer 5

• Handheld near constrast sens test
• Used at 50cm (range from 40-59 acceptable)
• Chart should have good and uniform illumination
• Px should wear near Rx or distance Rx with +2.00 add
• Contrast of each letter decrease by constant factor (0.04 log units)
• End test when px incorrectly reads 2 consecturive letters or reach end of chart
• (log CS value at final correct letter) - (no. of errors prior to final correct letter x 0.04) = log CS
• <0.48 profound loss
• 0.52-1.00 severe loss
• 1.04 -1.48 moderate loss
• 1.56-1.76 normal for >60s
  -1.72-1.92 normal for middle/young adult

Question 6

Describe contrast sensitivity testing in low vision pxs? CSV-1000

Answer 6

• distance is 2.5m
• px has to identify whether stripes are at top or bottom
• mark on form which duo px can see up to
• rows of circles

Question 7

Describe lighting and low vision patients? What can be done to help?

Answer 7

Amount of light entering visual system reduces with ageing
Due to:
* Clouding of ocular media
* Pupillary meiosis
* Changes in rods and RGCs density Proper lighting could result in gaining one or
more lines of VA
To help:
* Increase general lighting (ambient)
* Ensure uniform lighting
* Avoid need for dark/light adaptations
* Task specific lighting:
o Head mounted lights
o LED light strips
o Lights with magnifiers
o Position the light facing the text
* 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.
* Mobility – using a simple pen torch for mobility at night, RP

Question 8

Which conditions require high illumination or low illumination?

Answer 8

High: ARMD, glaucoma, DR, macular holes, retinitis pigmentosa (esp in dark)
Low: albinism, achromatopsia, aniridia, cataracts (central, post subcap), severe ARMD

Question 9

What is dicomfort glare and what can be done?

Answer 9

Discomfort glare
o High intensity of light on retina causing discomfort by bleaching
photoreceptors
o e.g. in patients with Anirida, albinism etc.
o May not effect visual acuity on its own
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

Question 10

What is disability glare and what can be done?

Answer 10

• Disability glare
  o High intensity of light reflecting within the eye ball. e.g. due to
  reflections from corneal/lens opacities
  o Effects visual acuity as glare reduces contrast
  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

Question 11

What are the management options for glare?

Answer 11

• Tints – Reduces overall amount of light
• Photochromatic lenses
• Filters – corning filter
• Caps, visors, side shields etc.
• Typoscopes,
• reverse contrast reading materials

Question 12

Describe ARMD, RP and Albinism and requirements for tints?

Answer 12

Age-Related Macular Degeneration
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
Retinitis pigmentosa
o Photophobia
o disability glare under low illumination conditions e.g. under night
illumination
o Due to defective RPE and reduced rods that makes adaptation to
different lighting levels difficult.
o Torch light / flashlights are useful for mobility in dark
o Yellow filters that absorbs short-wavelength light improves visual
discrimination under low illumination conditions
Albinism
o Very high sensitivity to light, need light reduction even indoors.
o Dark tints