That’s it, you’ve completed the theoretical work. Well done! But, you might be thinking, that’s a hell of a lot of work to do to assess a patient.
Far from it, quite the reverse. The point of having a solid theoretical framework is that it saves time. I don’t actually plot out a Visual Volume and Optimal Visual Volume for my patients. But from their history and their initial findings I get a pretty good idea of what sort of VV they’ve got, and that gives me a pretty good idea which visual aids might help them achieve their goals. More importantly, it also tells me which visual aids definitely won’t help, and which goals might be unrealistic.
I’m fairly flexible with my clinical routine (I think you have to be, with low vision). But here’s a rough outline of how things usually go:
History: Without a doubt this is the most important part of low vision. I mean, it’s important to any sort of optometry, but in low vision it’s absolutely central. A key question is whether fluent reading is important to them, or if they only have spot-reading needs. Once I’ve got a good idea of what their eye condition is, what the patient is like and what they are hoping to achieve, we’re already mostly there.
Measure VA (and get an impression of macular field integrity): As noted before, I use a LogMAR chart with 5 letters on every line. This gives me a good idea of their VA (of course) but also the integrity of their macular fields. Checking face acuity helps too.
At this point, I’m thinking of patients who want to achieve fluent reading as being in one of two groups.
- The first group is those whose VA seemed reasonable, about 6/30 (20/100) or better, and their fluency higher up wasn’t terrible. For them, I’ll assess their vision further with a near chart.
- The second group is those who have a poor VA, or a better VA but with poor fluency even much higher up on the chart. That means they have probably have foveal loss and/or considerable para-foveal macular field loss, so the near chart work is probably irrelevant — for them, I assess their vision further using the CCTV.
First Group: Reasonable VA, Reasonable Fluency Above Threshold: Near Chart and Illumination
Near Acuity (High & Low Contrast): I’ll get them to read the Colenbrander reading chart on high and then low contrast. Many do really well with the high contrast, then crash & burn with the low contrast. This is a great time for a discussion about visual quality as opposed to visual acuity, and about safety and falls as well. I’m also listening out for how fluently they read on high contrast lines that are above final threshold, to get insight into how effective low-level magnification will be.
Task Lighting Effect on Mid-Contrast: If they did well with the high contrast reading, I give them the Births column from the local newspaper. (I use the newspaper because it’s difficult — if they can manage the newspaper, they can manage most other documents too). They often struggle, and we discuss how the newspaper print is not as bad as the very pale print on the Colenbrander chart, but it’s not as good as the ‘beautiful black and white print’ either — it’s somewhere in between. Then I add in a task light, a reading lamp brought to within about 25cm (10″) of the page. The improvement is often marked, especially those who have a big loss of low contrast vision.
Luminance and Low Magnification: The lamp I use as a task lamp is actually a floor-mounted magnifier lamp, initially just positioned above the page so it’s just acting as a lamp. But once they’ve seen the improvement with the extra illumination, I change the position of the head so they are looking at the newspaper through the magnifier window. The effect at this point, with both illumination and magnification (and with still a pretty wide field of view too) is frequently a big smile, as the combination of those two vectors is particularly effective at pushing the text well into most VVs. To confirm, I leave the magnifier lamp in position but switch off the lamp — almost all patients report that the magnification alone is not nearly as comfortable.
At this point, I’ve got information about their VA, their level of low contrast loss, their response to extra illumination, and a reasonable idea of their macular field integrity. Those, along with the history, are enough for me to make a pretty good judgement as to what sort of VV they have, and with that knowledge I can move on to demonstrating a small number of other aids (mostly one or another type of illuminated magnifier or electronic LVC) which I can be pretty sure will be helpful and effective for them.
Second Group: Poor VA, or Poor Fluency Above Threshold: Start With Big, Bold & Bright
So far, so good. But what about those who got a poor VA, or whose fluency (single-letter or word) implied significant loss of macular fields? For these patients, I feel it’s not an efficient use of time to go through reading charts and low contrast measurement — I already know they’ll do poorly with both. Instead, I start them at the other end of the scale, with the best-case-scenario.
I sit them in front of the CCTV, put in my newspaper Births column, set it on the colour setting and on the lowest magnification, and then steadily magnify it up to almost maximum.
If we find out that they can’t read even on the so-enormous-it’s-not-even-practical-anymore magnification, then there’s not a lot of point spending time working through any of the other visual magnifiers (electronic or optical). That’s always sad, but because we’ve found out early, we have a good amount of time remaining to demonstrate text-to-speech options, and discuss other appropriate supports (help in the home, audio books, etc). Much better use of the time.
But those who can read the very large print get immediate reinforcement that they still have some ability to read, which can be a huge morale-booster to those that have been in despair. It puts them in a good frame of mind to start exploring options.
The patient also gets an immediate lesson in the tension between magnification and field of view, as the words fill the screen. They often laugh at how few words they can see on maximum magnification. (I might refer them back to this, as we work through other magnifiers later). Assuming they do find it easy to read the words on maximum magnification, I then get them to turn the magnification down slowly, until they are find the reading becoming a bit difficult, and then turn it back up again until it is comfortable.
Then I switch the display to enhanced contrast, and compare enhanced, enhanced-reversed and standard contrast. They will almost always prefer one of the enhanced contrast settings, which makes it a good time to have a little chat with the patient about contrast vision impairment. And then we reassess the minimum magnification at which they find reading comfortable, to see if they do a bit better now that they have enhanced contrast. Once they’re happy with it, I get them to read a Births notice, to confirm their fluency and accuracy, increasing the magnification a little if they stumble, until I’m sure they really are reading comfortably.
That process on the CCTV gives me an empirically-valid starting magnification for trying out other LVAs (optical and electronic) that I know will be in the right ballpark in terms of magnification, both for spot reading and for fluent reading.
Allow Time for Discussion
For a lot of patients, there is no perfect answer, so it’s a matter of coming up with the best compromise, which means a lot of discussion of pros and cons. Can they settle for slow-fluent reading? Might they consider a magnifier for the newspaper, but talking books for novels? Could they afford a CCTV, or apply for funding support? Could they have their favourite reading chair moved to a better-lit part of the house? Might a family member be willing to loan them an iPad to try? Could they read the newspaper with high magnification on the website rather than the buy a magnifier for the print edition?