LOW VISIONNNN INTRODUCTION

Low vision can be defined as any chronic visual condition, not correctable by glasses, contact lenses or medical intervention, that impairs everyday function. It's in between normal and blindness. Blindness should be defined as lack of any useful pattern vision. What the low vision assessment ultimately does is help the patient make the best use of the vision they have left so that they can continue a 'normal' life and maintain independence.

So functional blindness is the absence of form vision which in results in an inability to read/write/manoeuvre/orientate/recognise objects. The layman thinks it's 'no perception of light' but no. NO!

There are standards for blindness and visual impairment that

• allow us to evaluate the patient's elegibility for benefits/welfare rights.
• to get a measure of what the health and social services are required in the region
• for epidemiological studies

The WHO definitions are

• 0 - normal - 6/6-6/18
• 1 - low vision -> visual impairment <6/18-6/60
• 2 - low vision -> severe visual impairment 6/60-3/60
• 3 - blind - <3/60-1/60>
• 4 - blind - <1/60-pol>
• 5 - blind - NPL

The UK definitions (as of National Assistance Act 1948)

Severely sight impaired (blind)

1. Below 3/60 - you would certify most people who have VA below that. If a patient has 1/18 without considerable restriction of visual field then don't certify. It's better to test vision at one metre as 1/18 is slightly better than 3/60.
2. 3/60 but below 6/60 - certifty if fov is v constricted, don't certify if they've had a vf defect for a long time and isn't v contracted. EG Congenital nystagmus, albinism, myopia
3. 6/60 or above - certify if vf v contracted esp in lower part of field. Don't certify if homonymous/bitemp hemianopia with central VA of 6/18

Sight impaired (partially sighted)

• 3/60-6/60 with full field
• Up to 6/24 Snellen w/moderate contraction of field, opacities in media or aphakia
• 6/18 or even better if there's a gross vfd eg hemianopia or marked contraction like in RP.

These definitions don't count for near VA, mobility, adaptation to visual impairment, mental state, differentiation between central/peripheral field loss

Final bunch of definitions

1. Functionally blind - can't see to read or write even with LVAs and can't move in unfamiliar surrounding w/out cane, dog, sighted guide
2. Functionally sighted - visually impaired but can read or identify stuff with LVA and can move in unfamiliar surroundings without dog/cane/sighted guide
3. Functionally sighted w/aided mobility - can read etc but not move w/out dog/cane/guide. Example of this is someone with RP
4. Functionally sighted w/out sighted literacy - can move in unf surroundings but can't see to read even with LVAs. Example of this is someone with ARMD