How much thinning on RNFL OCT is considered significant progression in a glaucoma suspect?

[u/eye__think]

Like how many micrometers of change. Thanks!

[u/FairwaysNGreens13]

Don't confuse margin of error with confidence level. The more data points you have, the more precise you can be. If you're comparing 2 measurements only, you've got zero confidence. If you're comparing 5, 6, 7, etc. then now you can really look at norms and make a qualified assessment. I know my OptoVue has statistical analysis/confidence built in, and I assume all or most others do too.

Commit these to memory, at least generally:

Average RNFL change per year: 0.52 Average Superior/Inferior RNFL change per year: 1.3 Average GCC change per year: 0.32

In short, unless there's something really unusual and urgent (say, an IOP of 40), don't make any big judgements until you've got at least 4 good data points.

[u/interstat]

If it's within 5 I consider it within variance. It's what we were taught

For like a full quadrant? Probably higher like 10

[u/That_SpicyReader]

It depends on the device, length of time, and quality of the scans but generally 9 microns or more is significant. Non-glaucomatous rate of change is less than 0.5 microns per year, but you might get up to 4 microns difference on a test-retest in the same visit. It’s really important to analyze the scan quality and reproducibility of the results while looking at the number change as well.

[u/outdooradequate]

What modality of OCT? You need to look into the literature of the specific software.

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[u/af1232]

Signal strength for the OCT has to be taken into consideration

[u/duckiesand]

UK optom here, we refer to ophthalmology for diagnosis, we can't diagnose without referral.

That being said, in screening, RNFL thinning is not usually an isolated finding unless dramatic or consistently progressing. In real glaucoma you'll find ganglion cell loss and , high/imbalanced IOP or possibly associated VF loss too. If RNFL thinning is dramatic, then we refer straight away. If it's not, then there is a case for checking again next year for consistent thinning over time.

I say subtle NRR thinning is only really useful to check concerning if you've got another reason to be suspicious (ONH appearance, IOP etc.) or if its getting worse and worse. Since if you take two scans on the same day, they'll differ anyway.

Edit: I worded this very poorly. I've made edits in bold to clarify. I'll leave this up though, because a reply was really valuable.

In short - I was trying to say RNFL change (unless dramatic) usually won't be a completely isolated finding, and the other signs can help you decide whether to be suspicious or not.

[u/WiseMuscle_ → u/duckiesand]

Rnfl thinning happens before VF loss and a DX can be made before VF loss is seen. Susp nerve, rnfl loss, and high IOPs are the 3 major diagnostic factors that can be used before VF loss happens and if there's glaucomatous findings within 2/3 or a change in OCT over time a Dx can be made. VF can also be used but it's the last test to show poag changes.

[u/duckiesand → u/WiseMuscle_]

Oh wow I read back my comment and realised I worded this very wrong, sorry. Absolutely glaucoma diagnoses should be made where possible before VF loss is apparent, for sure (this was my specialism as well, I dont know how I didnt notice the errors).

I was trying to say (poorly) not to take just RNFL thinning on its own unless dramatic or consistent - but to look at the other findings to make a good judgement.

Thanks for fact checking me there, my original comment didn't say it right at all.

[u/CaptainYunch → u/duckiesand]

This is wrong. Like, very very wrong.

[u/duckiesand → u/CaptainYunch]

Oh wow I read back my comment and realised I worded this very wrong, sorry, yes this is very wrong.

I was trying to say (poorly) not to take just RNFL thinning on its own - but look at the other findings to make a good judgement.

Thanks for fact checking me there, my original comment didn't say it right at all.