4.2 The OVV in AMD (in theory)

 

TLDR
People with vision impairment have a smaller OVV than people with normal vision.

In the previous page I introduced the Optimal Visual Volume (OVV) for a person with normal vision. Let’s consider now, how would this apply for a person with impaired vision?

Applying Standard Reserves to Alice’s VV

In theory, the same reserves would apply. That is, we could step in from the patients VV by a standard level of reserve all around, which would directly map out their OVV. Here’s how that would look for Alice, our archetypal patient with mild-to-moderate AMD:

Alice’s theoretical OVV.

Again the normal VV is show in magenta as a comparison. It’s easy to see that Alice’s OVV is getting quite small. Now let’s compare Alice’s OVV with the normal VV:

Alice’s OVV compared to the normal OVV.

Notice how Alice’s OVV doesn’t encompass the range of most common print sizes, even at optimal levels. In practical terms, it means that Alice might still be able to read most things, but not comfortably.

Discussion
This is what we see so often. Patients who are avid readers that get AMD tend to report problems with their reading comfort and stamina before just about anything else. They might describe it as eye strain or watering eyes, but it’s all about the lack of reserve.

Applying Standard Reserves to Bob’s VV

Let’s do the same for Bob, our archetypal patient with more advanced AMD:

Bob’s VV and OVV.

The thing to take note of here is that Bob’s OVV is almost gone. For Bob to read with fluency and comfort, he’s going to need very high contrast print that is also very large, which is quite a practical challenge.

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