Low Vision News

For low vision specialists and those who consult them

Monthly Archives: September 2009

Aesthetics of low vision aids

As a low vision clinician, one of the most dispiriting experiences is demonstrating that a telescope or other low vision aid can enable a task to be performed, only to hear “yes, but I don’t think I’d use it” (or worse, laughter when you show someone a device and explain it may be useful).

It is particularly difficult when children accept a device but their parents are reluctant to let the child use it. In some cases this is because they think that it will lead to their child being bullied; in others because they think their child will become dependent on it; and sometimes because it will change other peoples’ perception of their child.

There are obviously many reasons which underlie this response, such as the psychological reactions to sight loss (accepting that extra help beyond ‘nornal’ glasses is required is a huge, almost life-changing adjustment), but I think some responsibility must lie with device manufacturers.

Electronic devices are great in this regard: systems like the SenseView and compact+ look more like PDAs or video game players than assistive devices. This will only improve as technology advances: at envision Bob Massof showed images of the earliest LVES head mounted electronic magnifier and it’s ten times the size of today’s best devices.

Whilst optical devices must by their nature be fairly big and bulky, that doesn’t mean they can’t look cool as well. I would welcome an illuminated stand magnifier that didn’t look like a child’s torch, or an increase in the number of pleasingly designed telescopes like the Eschenbach microlux. I hope that device manufacturers think more about this.

There won’t be any updates to lowvisionnews for the next ten days or so, but I will be back with some more scientific posts then…

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Conference review: Envision 2009

I have just returned from the Envision Conference in San Antonio, Texas, and I was very impressed by it.

The conference is relatively small – about 400 delegates – and attracts a range of optometrists, occupational therapists, low vision rehab professionals and researchers. I wasn’t surprised that the standard of clinical education was high, but I must admit that I hadn’t expected the research sessions to be as strong as they were.

Many of the big names in low vision research were presenting- Eli Peli, Bob Massof, George Timberlake, Greg Goodrich, Olga Overbury et al, as were several of the people I respect from ‘my’ generation of researchers such as Shirin Hassan and Walter Wittich. I also particularly enjoyed Duane Geruschat’s presentation on street crossing, Bob Massof’s review of electronic low vision aids, and Joan Stelmack’s update on the LOVIT trial.

The size of the meeting made it very sociable as well, and I had some great Mexican food down on the riverfront.

I was not able to attend the whole conference this year and missed several talks I would have liked to attend. However, I’ll definitely go back to envision again, and will recommend it to my colleagues too.

Back to basics: What is low vision?

I went for dinner with some non-optometrist, non-medical friends at the weekend and I realised that whilst within the community we use the phrase “low vision” very widely, it isn’t a term which is particularly well understood by the wider population. There also isn’t a unified definition of low vision: if I use the phrase “low vision” it may be interpreted differently by an ophthalmologist, a rehab worker and someone with (for example) retinitis pigmentosa.

There are many definitions of low vision, but lets start with the one by the World Health Organisation (WHO). They define someone with low vision in a fairly wordy, legalese way:
“a person with low vision is one who has impairment of visual functioning even after treatment and/or standard refractive correction;
* and has a visual acuity of less than 6/18 to light perception, or a visual field less than 10 degrees from the point of fixation,
* but who uses, or is potentially able to use, vision for the planning and/or execution of a task for which vision is essential”

In simpler language, this is saying that someone with low vision has poor vision, even with the best specs or contacts, but has enough vision to perform certain visual tasks.

There is a visual acuity criterion – to be defined as having low vision, the best visual acuity with the optimal glasses or contact lenses must be worse than 6/18 (20/60, 0.50logMAR). This is about half way down a conventional sight chart and slightly poorer than the driving standard in most countries. I wonder what people with visual acuity of 20/50 think of this, who may not be able to receive a driving licence because of their visual acuity but are not classified as having low vision?

There is also a visual field criterion which relates to how far you can see around the central point of your vision without moving your eyes. The WHO low vision definition is again fairly strict, especially when you consider a normal visual field extends around 170ยบ horizontally.

There is an increasing awareness that visual acuity and visual field are not the only determinants of how well you see – the WHO definition has no mention of contrast sensitivity (how well you can see faint objects) and no mention of vision in different lighting conditions (people with some retinal diseases have very poor vision at night but relatively good sight in bright conditions).

My biggest concern with the WHO defintion is that it makes no mention of function. If your visual acuity and visual field fall outside the levels prescribed by the WHO but your greatest passion is sewing, or reading old manuscripts, or fly fishing, and you can’t see to perform these tasks, shouldn’t you be defined as having low vision, and be entitled to a low vision assessment to prescribe magnifiers for this task? Conversely, if your vision is poor enough to meet the WHO definition but you are able to perform every activity you want to without any difficulty is it appropriate to be labelled as having a visual problem?

I think a better definition of low vision is the one advocated by Dr Gordon Legge in Minnesota: “The inability to read regular newsprint with optimal refractive correction”. This is better in that it includes a functional statement, but may exclude people who have good reading acuity but are unable to perform other tasks using vision – such as to safely cross a street or to watch television.

A consensus paper by Morimoto Noriko in Japan suggests this definition, which I quite like even if it does sound slightly strong in translation:
“visual function or vision that interferes with growth and development of children or interferes with any individual’s activities of daily living and functioning in society”. They deliberately do not exclude people with no sight at all from their analysis, who many of us would feel have no vision rather than low vision.

A final question is whether “low vision” is an inappropriate term. We wouldn’t talk about someone with “low intelligence” or “low hearing” – do people take offense from being told they have “low vision”? I am glad we have moved away from using “visually disabled” (or worse, “subnormal vision”) – but should a new phrase be used? Some organisations refer to VIPs (visually impaired persons) – maybe our low vision clinics should be called VIP centres?!

I would be really interested to hear readers’ thoughts on this – should the WHO definition be changed? Should I rename lowvisionnews? Am I inappropriately confusing low vision and visual impairment? The comments section is open…

Journal Article: Functional Tests for Low Vision

I have just read a good paper by Dougherty and colleagues in the August issue of Optometry and Vision Science discussing the development of some new functional tests for low vision research.

A key question of low vision rehabilitation is “how useful is intervention x, y or z?”. This is surprisingly difficult to answer, even when x is as simple as prescribing magnification.

Historically, we answered this question by looking at easy to measure clinical tests, such as visual acuity, contrast sensitivity, reading speed or glare sensitivity. More recently, questionnaires have been used to determine the impact of rehabilitation on vision-related quality of life, using instruments such as the Visual Function Questionnaire (VFQ) or Massof Activity Inventory.

Dougherty and colleagues have used a third approach: to develop some real world tasks, which can be performed under controlled conditions, to measure visual function. These are:
*Reading rate at set print sizes
*Finding a number in a telephone directory
*Identifying prescription medication from a medicine bottle
*Reading utility bills
*Finding cooking time on a food packet
*Sorting coins to total a specified amount
*Identifying a playing card
* Recognising facial expression

To investigate the use of these tasks as a research outcome, the authors investigated the effect of a single low vision appointment on these variables. They found measurable changes on many of the tests, with the biggest improvements in reading medicine bottle labels and cooking instructions.

Using functional tests to measure visual performance is not new, but the development of a standardised battery of visual function tests is an excellent development. It would be extremely beneficial for the field if these tests were adopted by other research groups so that outcomes can be compared between different rehabilitation approaches, in different clinical settings, in different countries.