Low Vision News

For low vision specialists and those who consult them

Monthly Archives: November 2009

Peripheral prisms for hemianopia

Nearly 1% of people over 50 years of age have visual field problems following a stroke or brain injury. The classic pattern of this visual field loss is to lose half of the visual field from each eye, which is known as homonymous (meaning the same side) hemianopia (meaning a loss of half of the visual field). The effect of this is to not be able to see anything to the left or right side of the central point of the vision. As you can imagine this has a significant impact on reading, navigating, and walking in crowded environments.

One strategy to overcome this is to make more eye movements into the blind side of the vision – for example, if the right side of the visual field is missing, the person makes repeated head and eye movements to their right in order to move the region of good vision to the right hand side. However this is a difficult strategy to learn. An obvious alternative approach is to use prism lenses to move the image of objects which fall on the non-seeing side into the healthy part of the visual field. A problem with this is that they create central double vision – which can be more disabling than having missing visual field.

For the past 10 years or so, Dr Eli Peli from Harvard Medical School has been using an alternative approach – a peripheral prism system which is fitted on the top and bottom of a spectacle lens, leaving the central region clear. The idea of this system is that things which fall into the top or bottom of the nonseeing visual field are moved into the seeing region, alerting the person to make a head or eye movement to examine what is there.

A report on this system appeared in Archives of Ophthalmology last year, reporting that 74% of people who were fitted with the prisms still used them six weeks after they were dispensed, and that about half of the people who were fitted with the prisms still used them one year later. People with hemianopia report these glasses as being particularly useful for avoiding obstacles at home, in shops and shopping centres, and when walking in unfamiliar environments.

More information on this system can be found at www.hemianopia.org.

It is good news that peripheral prism spectacles seem to be useful for walking and navigation for a reasonable proportion of people with hemianopia. Unfortunately they are less useful for reading and computer work, which in my experience is a very frequent complaint of people with this type of visual field loss. However given that 1% of the older population has heminaopia, and that the population are ageing, I would not be surprised if adaptive devices to help reading with visual field loss are developed in the future.


Aaopt review 2/2: Nyctalopia

As I mentioned in my previous post, one of the highlights of the low vision programme at the American Academy of Optometry meeting last week was a special evening session on Nyctalopia.

The first speaker was Dr John Musick who spoke entertainingly on the identification and management of people with night vision problems.

He emphasised the difficulty of identifying poor night vision as people often assume everyone can’t see in the dark. He suggested asking ‘have you ever seen the stars?’ as a screening question. He also stressed the need for referral to an ophthalmologist who specialises in hereditary retinal disease rather than a general ophthalmologist given the rare nature of some of these conditions. He mentioned the importance of referral to orientation and mobility experts, and to ensure that people had a ‘caring community’ for support: be it family, friends or colleagues. He touched briefly on the need for occupational counselling, given the typical age of presentation of people with nyctalopia (age 10-20).

Next, Dr Roanne Flom gave an excellent overview of low vision rehabilitation for people with poor night vision. This ranged from the importance of arranging a workplace evaluation (she cited warehouses in particular as being dim environments to work in); to ensuring good task lighting (she demonstrated various head mounted led systems which can be used when walking). She also discussed the use of dark adaptometry, glare testing and night vision camcorders in people with nyctalopia. My favourite clinical pearl from this talk was ‘you can spot people with poor night vision as they come in with a torch and dark glasses, as the range of optimal illumination is so critical.

The final speaker was Dr Byron Lam from Bascom Palmer in Miami. He gave an overview of gene therapy, stem cell therapy, retinal implantation and dietary supplements in retinal disease. His talk was good, but not as impressive as Alan Bird’s award lecture on similar topics at this year’s ARVO. A salient point made by Dr Lam was the importance of counselling people appropriately before they enter a clinical trial, as that could well be their only chance of entering a study: participation in a previous treatment trial is often an exclusion criterion for entering future clinical trials.

In all, it was an excellent and interesting symposium on a frequently ignored topic.

Aaopt review 1/2: Overview

I am just back from the American Academy of Optometry meeting in Orlando, Florida. There was a full low vision programme and I thought I would share some of the highlights here.

The low vision section of the Academy sponsored a special nighttime symposium, from 8-10PM. This was, appropriately enough, on Nyctalopia (difficulty seeing in the dark) and I will review this session in full in another post.

Other highlights of the low vision sessions were two presentations by Eli Peli (on implantable miniature telescopes for macular disease, and a workshop on fitting his peripheral prisms for hemianopia), George and Stanley Woo’s double act on the basics of low vision, and a well attended scientific paper session on the Friday morning (featuring Walter Wittich, Lei Liu and others).

Mike May (an “inspirational speaker” who lost his sight at age three and regained some vision in his 40s) gave a very amusing lunchtime plenary talk followed by Ione Fine, who performed psychophysical measures of Mike’s visual function after his treatment. I have heard both of these speakers before but it was good to hear them again.

One of the clinical sessions I particularly enjoyed was an excellent overview of psychiatric conditions in optometric practice, which again discussed the importance of screening for depression in people seeking low vision care. This was presented by Dr Schwartz from SUNY in New York.

I am not sure it’s worth me going to Envision and the American Academy in the same year as there is quite a large overlap between the two: and I have to say I preferred Envision this year. I disliked the conference facilities in Orlando, especially the hugely overpriced parking at the conference centre. It also annoyed me that although the organisers encouraged people to use twitter from the conference, there was no free wireless in the conference rooms.

A further report on the conference will follow…

Looking forward to AAOpt09…

Next week I’ll be at the American Academy of Optometry’s annual meeting in Orlando. (I hate the fact that people always think going to conferences in Florida must be an excuse for a vacation when Florida would be amongst my last choices for a holiday destination).

There is a full low vision programme through the conference – indeed on Wednesday I think I’ll be in the meeting from 7AM (for an Eschenbach breakfast meeting) until 10PM (after the night time special symposium on nyctalopia).

I’m particularly looking forward to the nyctalopia symposium by Drs Musick, Flom and Lam. Nyctalopia is night blindness – which is experienced by people with retinitis pigmentosa, congenital stationary night blindness and other, rarer, conditions. It’s an infuriating problem for the clinician as there are few practical solutions — some people advocate using IR night vision systems, but my understanding is that they are not completely helpful as users are still largely dark adapted even when using these.

I’m also looking forward to hearing about Eli Peli’s latest work with peripheral prisms for hemianopia, William Park’s presentation on contact lenses in vision rehabilitation, and on catching up with colleagues from around the world.

Full reports will follow here — and I’ll be twittering from there as well.

Telescope training: is there evidence?

At the moment there is lots of interest in implanted miniature telescopes for people with low vision (where the lens inside the eye is surgically replaced with a magnifying telescope). I will discuss these in another post, but this topic started me thinking about conventional, hand-held monocular telescopes, and the relative benefits of these.

In particular, I am interested in the role of training people to use these telescopes. There are three key things telescopes can be used for: spotting (“what is the name on this street sign?”); tracking (“what is the number on this moving bus?”); and scanning (“I know there is a sign somewhere near here, where is it?”).

Most people can probably manage to spot something with a telescope with practice and no training, as long as the principles of telescopes are explained to them (eg. you need to adjust the length of the tube to focus it; you need to make sure you’re standing still when you’re using it; you need to hold it as close to your eye as you can). However, more complex tasks such as tracking and scanning are difficult to perform without some guided practice or training.

In the UK, some local charities for the visually impaired perform this training, but there are still plenty of people who do not receive training and who just “pick up their telescope” and go home and use it. In the USA telescope training is commonly performed by rehabilitation workers, but there are still people with telescopes who have not received training.

Unless my quick literature search didn’t find it, it doesn’t seem that there has been a systematic study on telescope training to answer some key questions such as:
– what can people with low vision do with a telescope without training?
– how much training is needed to be able to perform certain tasks with a monocular telescope?
– how much better is performance with a telescope once training has been performed?

Once we have answers to questions like these, we can make a much stronger case to funding agencies that device training should be made available to more people. This would also make a nice project for someone looking to do a Masters or PhD in vision rehabilitation too.