7.1.5 Assesses patients with impaired visual function and understands the use of specialist charts for distance and near vision and the effects of lighting, contrast and glare.

Question 1

Assesses Vision & Adapts Routine

Age

Answer 1

• Use an amsler chart
• Use larger steps e.g. 0.50 or 1.00
• Don’t binocular balance! As they have no accommodation. Must be monocular refraction
• Don’t do spherical manipulation! As they have no accommodation
• Duochrome is more sided to the red with small pupils & media opacities
• Retinoscopy might work if obtaining unreliable responses but be careful of lens opacities. May need to change working distance
• Pinhole
• You must check pupils!
• Do not measure NPC unless indicated
• • Astigmatism generally greater in elderly so changes from WTR (horizontal axis) to ATR (vertical axis) due to blepharitis and lid margin changes causing patient to blink more
• Myopic & hyperopic shifts (cataract or macular oedema)

Question 2

Assesses Vision & Adapts Routine

Amblyopia:

Answer 2

• No binocular balancing! Must be monocular refraction
• If binocular amblyopia, then not much difference in routine besides what has already been said
• Might not be able to look at their ear so straight ahead instead
• Shining light from slit lamp into non-amblyopic eye first not good idea as it will blind them then they cannot focus well afterwards

Question 3

Assesses Vision & Adapts Routine

Visually Impaired:

Answer 3

• Large fixation target - for cross cyl, preferably big round target (larger than best corrected acuity)
• Larger steps, from 2D to 4D to 6D to 8D until response & large cross cyl steps
• Spin the cyl & see if patient prefers an axis or use Stenopaic slit - spin slit until axis found. Second axis will be 90 degrees. You can show patient a cyl at either axis & see what is preferred.
• Should only prescribe if actually seeing better i.e. line improvement
• DO NOT attempt +1.00 blur or binocular balance (unless applicable)
• NEVER USE DUOCHROME - only for 6/12 or better patients!
• Use pinhole - checking if reading same line as before rather than looking for improvement

Question 4

“What does the low vision clinic do?” / “I’d like to be able to see better again”

Answer 4

We aim to help people use their remaining vision more effectively and will try to promote their independance as a result. This doesn’t mean we make people “see better” but it does mean we can help with practical problems associated with visual impairment

Question 5

“I just want stronger glasses” - Is there a way of showing why stronger glasses won’t help?

Answer 5

Progressively introduce +4.00 Adds to show how it won’t work.

For example, if patient had Macular degeneration. This is an age-related eye disease that involves damage to the retina and often causes low vision. Since the damage to retina is not related to the shape of the cornea, the length of the eyeball, or the power of the lens, it cannot be corrected with eyeglasses or contact lenses. In certain cases of moderate vision loss, stronger reading glasses may help up to a point, because they have some magnification power.

Question 6

You gave a hand magnifier to a patient who saw N5 in the LV clinic but at home, they complain of seeing nothing. How can you explain this?

Answer 6

Contrast or Lighting not the same as in LV clinic

Using LVA for wrong task

Need further training to use LVA

Vision has fluctated although unlikely!

Question 7

Advantages of Snellen

Answer 7

• Cheap
• Commonly available
• Universally understood
• Portable

Question 8

Disadvantages of Snellen

Answer 8

• Requires literacy
• Requires communication
• Different number of letters per line (think of 6/60 Vs 6/6)
• Different spacing between lines & letters i.e. 6/24 does NOT = 3/12
• Acuity steps are uneven

Question 9

Advantages of LogMAR chart for Low Vision

Answer 9

1. Each line has several letters whereas the snellen has 1 on 6/120 so less choice & potential accuracy
2. Testing at alternative distance is easier & more accurate if needed but must add 0.3 to final result everytime working distance is halved
3. At 6m, can measure lower level of vision than just 6/60 for example

Question 10

How to read off the LogMAR chart?

Answer 10

• What line the patient read to & are there any letters they can read on the next line? (this is the systematic approach to getting the acuity)
• Remember: each letter is 0.02 log units & the score becomes smaller as the patient reads more letters.
• For example, on the chart above, if the patient can read 0.4 & 3 letters on the 0.3 line, what is their logMAR acuity?

Question 11

Snellen to Logmar chart

Answer 11

• 1.00 = 6/60
• 0.90 = 6/48
• 0.80 = 6/36
• 0.70 = 6/30
• 0.60 = 6/24
• 0.50 = 6/18
• 0.40 = 6/15
• 0.30 = 6/12
• 0.20 = 6/9
• 0.10 = 6/7.5
• 0.00 = 6/6

Question 12

What is the main advantage of measuring contrast sensitivity (CS) in low vision patients?

Answer 12

Can explain functional difficulties in real world even with good VA e.g. difficulty seeing large objects, detecting steps, food on plate. This may also explain poor results with optical aids. The best is to have black on white contrast

Patient with good VA but reduced CS may require more magnification than expected, or more contrast enhancement in home, or illumination

Some patients can have normal visual acuity and reduced CS at low spatial frequencies, e.g. patients with lens opacities, optic neuritis and multiple sclerosis, Parkinson’s disease, papilloedema, POAG, diabetic retinopathy and compressive lesions of the visual pathways. CS can therefore be used to help screen for visual pathway disorders and to explain symptoms of poor vision in a patient with good visual acuity. When used in combination with VA, CS can be used to help explain symptoms of poor or deteriorating vision and help to justify referral of a cataract patient with reasonable VA.

Question 13

ETDRS

Answer 13

It’s essentially the logMAR chart

This is a form of LogMAR chart developed from the “Early Treatment of Diabetic Retinopathy Study”; it is widely accepted as the gold standard Research tool for measuring vision and visual acuity.
* It has five letters per row
* Equal spacing of the rows on a log scale (the rows are separated by 0.1. log unit)
* Equal spacing of the letters on a log scale
* Individual rows balanced for letter difficulty
Different versions of the ETDRS test chart are available. The three standard versions of the ETDRS chart are R, 1 and 2.

Question 14

ETDRS Vs Bailey Lovie Chart

Answer 14

Bailey-Lovie Charts and ETDRS are both LogMAR charts but they are different.

Bailey-Lovie charts are designed to be used at 6, 3 and 1.5 meters and EDTRS at 4, 2 and 1 meters.

ETDRS charts are available printed on a plastic sheet designed to be used in a back illuminated chart, Bailey-Lovie charts are printed on a cardboard sheet and are designed to be front illuminated.

Bailey-Lovie letter sizes are rectangular e.g. for the Bailey-Lovie Chart Design, a 6/6 letter is 4 minutes of arc in height by 5 minutes of arc in width. ETDRS letters are all square, i.e. 5 by 5 minutes of arc.

Question 15

General Lighting

Answer 15

• Too far away for detailed tasks due to inverse square law of light
• Best for at home to locate and get around safely
• Ambient illumination best for recognising faces & other household items
• 3000lux better than 300 lux
• Optimise environment:
  
  • Daylight, Remove net curtains, White paint, Increase watts in bulbs. More lighting near stairs & landings
  • Even illumination best as patients have bad light to dark adaptation

Question 16

Task Lighting

Answer 16

• Always advice to half lamp distance to quadruple the light. Remember inverse square law!
• CFLs typically best for prolonged reading & other prolonged tasks

Question 17

Glare: Types

Answer 17

1. Disability - casts veil over retinal image such as turning lights on in slide show (almost blinding). Doesn’t cause discomfort & patients report it can reduce visual function in the moment & that dull weather is best to stop this glare
2. Discomfort - discomfort but no reduction in visual function. Brightness differences become tiring to deal with
3. Photophobia - discomfort/pain in excess light

Question 18

What factors impact glare?

Answer 18

In general glare is dependent upon several factors: The Luminance and the intensity of the glare source. The angle or glare source relative to the line of sight. The area of the glare source.

• Cataracts can cause both disabling & discomfort glare
• Conditions affecting cornea & lens e.g. keratoconus, cataract, aphakia, & lens subluxation causing patient to experience both disability & discomfort glare

Question 19

How is the Pelli-Robson Chart used?

Answer 19

1m WD with optimal refraction ~ +0.75D added to distance Rx if presbyopic to account for wd

Measure binocularly for low vision

If they get 2/3 correct, then move on to next 3 letters. Px starts from top & goes left to right

A score of 2.0 indicates a normal CS of 100%
1.80 – 2.25 Normal
1.20 – 1.65 Mild loss
0.60 – 1.05 Moderate loss
0.00 – 0.45 Severe loss

Question 20

techniques to Reducing glare:

Answer 20

• Hat with a brim
• Sunglasses - red or yellowy as it reduces blue light because it’s a short wavelength & so it scatters in the eyeball more compared to red light for example. Clip ons are also good
• Too dark a tint compromises patient safety!
• Side shields are worthwhile
• Albinism - no pigment means light scattering inside eyeball all the time so tint needed for FT wear