Blind Vision

“You Don’t Look Blind!”

I’ve not yet found a suitable quip to answer this often-received comment. I’m not certain if it is a good thing or a bad thing to appear differently from the way people expect. I’m not entirely sure how a blind person is supposed to look. Ok, I realise there is a largely inappropriate stereotyped image: Perhaps blackout spectacles, tapping a white cane side-to-side, head held at a slightly unusual angle, perhaps even hands held out in front to feel the way around…Actually, that is a rather insulting portrayal to most of us ‘blinkies’. (yes, I do refer to myself as a blinky!). Some aspects may perhaps be applicable to a few individuals, but, as a rule, very few blinkies would wish to be thought of like this.

Blindness / Vision Impairment is a huge spectrum. Arguably, it ranges all the way from a tiny deviation from so-called 20/20 vision (in other words, perhaps a person who might need prescription glasses just to tweak the crispness of their focus), to the other extreme which is total black blindness (absolutely no vision or even light perception). It can be caused by a huge variety of injuries, illnesses, conditions and, in some cases such as mine, by an unknown trigger. The variation in vision also is as wide as the range of people living with it. (I use the term ‘living with’ rather than ‘suffering with or from’ because we don’t all consider ourselves as suffering. We learn to live with our lack of sight).

Vision Impairments can take the form of general blurring, restricted field of vision, blurred or absent central vision, spots and patches of blurring or blindness, distortion, flickering or movement, lighting changes, light sensitivity… and so the list goes on.

The cause of the sightloss may be within the structure of the eye itself, or it could be caused by a brain or optic nerve problem. This could be a direct and isolated issue or it could be connected with, or emanating from, another disease or illness.

For some folk, this may be from birth, for some it may develop gradually as life progresses, for others, it may be the result of a sudden and traumatic accident or illness. For yet others, it could be a late-in-life development (age-related macular degeneration for example, is a widely known cause of progressive sightloss in senior years). The spectrum is about as broad and long as is the range of individuals who fall within it. Every one of us is different. Every one of us has a unique story and experience. Every one of us has our own way of dealing with not seeing so well in a sight-dominated world.

Technically speaking, here in the UK, we have two categories into which we may be placed if our eyesight problem cannot be corrected with standard prescription spectacles. We may be:

1. Vision Impaired (VI) / Partially Sighted, or,
2. Severely Vision Impaired (SVI) / Blind.

There seems to be a regional variation in the exact terminology used – in some areas we are (Severely) Vision Impaired, whilst elsewhere we would be (Severely) Sight Impaired.

Please note though – we are VISION impaired – not VISUALLY impaired! To be visually impaired implies that it is our appearance that is disfunctional rather than our eyesight.

These are legal registration terms that come with a Certificate of Vision Impairment (CVI), which is issued by a Consultant Ophthalmologist. These terms are determined, in essence, by numbers. It is all to do with one’s Field of Vision (FOV) and/or the clarity of the functional ‘window’ within that FOV.

https://www.rnib.org.uk/eye-health/registering-your-sight-loss/criteria-certification

I shall do my best to explain how it works:

Eligibility for a CVI is determined by the results of tests of both Visual Acuity (central vision used to see detail) and Visual Field (the full sphere of vision, or perhaps what some might call – what you see in the corner of the eye whilst looking straight ahead).

• Visual Acuity is measured using a Snellen Chart while wearing any glasses or contact lenses normally needed. Read on for more information.
• Field of Vision is measured by a “visual field test”. This is carried out using a dome-shaped instrument with a chin rest in front. There is a focal point in the back of the dome (usually a dot of red light). As you stare at this focal point, a series of tiny white lights flash briefly, one at a time, in varying degrees of brightness and intensity, around the inside of the dome. Usually there is a button to press every time a light is seen. The instrument records which lights are noted by the button-press and a printed readout is produced at the end.

There are specified results of these two tests that determine eligibility to be registered either VI or SVI.

The Snellen Test

Visual acuity is measured using the Snellen scale. A Snellen test usually consists of rows of letters that decrease in size as you read down the chart. There are pictorial versions for children and those who cannot read.

This means of measuring visual acuity was developed in 1862 by Dutch ophthalmologist Herman Snellen and is now used around the world. There is the traditional imperial measurement version as well as the now, more commonly used in the UK, metric equivalent. The term 20/20 vision refers to the results sitting 20 feet away from the chart and being able to read what is deemed as normal range. In the metric version, this is 6/6 – where you would be sitting 6 meters away. The biggest letter on the first line represents 20/200 or 6/60 vision. If you can read this, but nothing smaller on the chart, then you can see from 20 feet / 6 metres what a person with normal visual acuity can read from 200 feet / 60 metres. Occasionally, this is referred to as a percentage of ‘normal vision’ so, in this case would be 10%.

Reading down each row on the chart corresponds to better visual acuity. The fifth line represents 20/40  or 6/12 vision, which is the minimum required for driving. It is possible, but unusual, to have vision better than 20/20 or 6/6. Less than 1% of the general population have 20/10 or 6/3 vision. However most young, healthy eyes may be able to discern at least some of the letters on the 20/15 or 6/4.5 line.

In other words, a person with 20/10 (6/3) vision has visual acuity twice as good as the average person, while a Snellen score of 20/40 (6/12) represents a visual acuity twice as bad as average. 20/20 or 6/6 will enable comfortable reading of all the print in a newspaper. 20/80 or 6/24 will discern just the headlines, while 20/200 or 6/60 vision means that you can see little more than huge letters on an advertising board just as you bump into it!

Just to add a further head-spinner to this hefty lesson; occasionally the first number in the written scale could be a 3. This is for when the test is carried out in a small room or space where a 6 metre distance from the chart is not possible. In this case, the chart would have to be placed 3 metres away and a result of, for example, 6/60 might be recorded as 3/30.

In summary, whichever set of numbers is used, the larger the second number, the worse the person’s visual acuity is.

Phew! That is the end of part one of the heavy lesson done. Hopefully it makes some sense. If it is still as clear as mud then welcome to my world!! Haha! Seriously though, it takes a bit of doing to ‘get your head around it, but it is quite logical and clever really!

So – back to the subject of registration:

Eligibility for, and level of certification is determined using a combination of both visual acuity and visual field results. Generally, to be certified as Severely Vision Impaired (Blind), one of the following categories, while wearing any needed glasses or contact lenses, has to apply:

• Visual acuity of less than 3/60 with a full visual field.
• Visual acuity between 3/60 and 6/60 with a severe reduction of field of vision, such as tunnel vision.
• Visual acuity of 6/60 or above but with a very reduced field of vision, especially if a lot of sight is missing in the lower part of the field.

To be certified as Vision Impaired (Partially Sighted) one of the following categories must apply in the same way:

• Visual acuity of 3/60 to 6/60 with a full field of vision.
• Visual acuity of up to 6/24 with a moderate reduction of field of vision or with a central part of vision that is cloudy or blurry.
• Visual acuity of 6/18 or even better if a large part of your field of vision, for example a whole half of your vision, is missing or a lot of your peripheral vision is missing.

Sight loss in one eye

Both eyes will normally be tested and if only one eye is affected by sightloss, then the other will generally be likely to compensate. This means that certification is unlikely.

Certification / registration is not compulsory and some people choose not to have it. For many, though, it is helpful, not least because the registration with the Social Services system opens up much easier access to all sorts of help and support.

I hope this goes some way to demystifying the technical details of blindness/sightloss. In the next blog I shall try to explain a little about my experience and how I see the world.