5.5 My Low Vision Exam Routine


If my patient wants to read fluently, but they have poor VA or symptoms suggestive of serious patchiness of macular fields, I move them straight to a CCTV to check whether fluent reading is a realistic possibility. If the VA is good and the macula doesn’t seem to patchy, I try a magnifier lamp first.

If they only have spot-reading needs, I use a more traditional approach with increasing powers of optical magnifiers (but as often as possible they will be illuminated magnifiers).

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.

If their word-reading accuracy or fluency above threshold is a lot worse than it should be, that’s also a sign that the macular integrity might be worse than I thought from the single-letter VA task, or that ‘something funny’ is going on. I reclassify them into the second group (see below), but I might come back to the reading chart if they do well on the CCTV.

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.

I prescribe a lot of magnifying lamps. We use a very affordable model, and even patients who get other aids usually get a magnifier lamp as well, as it’s a great problem solver for lots of day-to-day tasks. I have one permanently set up right next to the consulting room chair.

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.

When trying magnifiers for spot reading tasks, I draw from the full range of optical and electronic aids. But if I’m looking for a magnifier that is to help with a fluent reading task, I don’t bother showing any magnifier that doesn’t have a high speed limit. This is a big time-saver.

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.

You might remember that this process (starting at high mag, high contrast, optimal illumination and then reducing magnification) is the empirical way of finding the edge of the Optimal Visual Volume (OVV). If one of their goals is fluent reading, this is a critical finding, giving guidance on what sorts of devices might be effective.

After that I’ll keep reducing the magnification to find out how small the text has to become before the patient can’t read it at all, which gives me the edge of the absolute VV.

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.

As we try optical magnifiers, their much-reduced field of view is immediately evident to the patient, which makes it a good time to discuss the ‘porthole principle’ and why they need to hold the magnifier close to the eye.

If the patient does choose an optical magnifier, I find the final magnification chosen is often a bit lower than predicted by the CCTV, as the patient finds their best compromise between the reduced field of view and the magnification.

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?



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