Dear reader: This page is part of a series of articles written for vision professionals. If that’s not you, it might not make much sense. If you’d like to learn all about eyes, vision impairment and what you can do about it, I strongly recommend you start by reading the article series I wrote for everyone, which starts here (click).
This site is in the process of being updated, with extra content designed for the layperson as well as vision professionals. I’m afraid the formatting of existing pages has been affected — sorry about that. It’s still readable, but hopefully it will all be fixed up soon, better than before.
Ocular pathology tends to cause impairment of low contrast vision before it affects high contrast or VA.
As I mentioned earlier, high-contrast VA is often one of the last things to be affected by most common eye pathologies, but low-contrast vision is one of the first (especially true of macular degeneration).
Here’s an example of someone with normal vision compared with a curve that’s fairly typical for someone with early AMD:
Notably, the high-contrast VA isn’t much affected (that’s the point where the curve intersects the bottom of the chart). In many people with even quite advanced AMD, the VA is hardly affected at all, but they are still experiencing very severe functional loss (more on that later).
That’s a pretty common presentation, for patients you might see in your general optometry practice, who might not even realise they have low vision yet (they tend to know that something’s not right, but they often haven’t quite twigged that it’s not simply ‘just getting older’).
CSF is very individual
What about other types of low vision conditions? And how similar are people with the same condition?
Here, I think of Tolstoy:
“Happy families are all alike; every unhappy family is unhappy in its own way.”
Leo Tolstoy: Anna Karenina (1877)
I recently came across an amazing article in Investigative Ophthalmology & Vision Science. In it, there is this page, which illustrates the point beautifully:
Different patients show different deviations from the normal. But it’s not random — we can see patterns and groupings, typical presentations in the same way that we see typical patterns of field loss in glaucoma, etc. More on that later.