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.