BLOG: Can you use OCT angiography for the cornea?
Has your clinic gotten OCT angiography yet? We got one earlier this year, and we were all pretty excited to use it.
I haven’t had too much experience with it yet because COVID-19 slowed all ocular imaging way down. But I’ve been reading up and listening to lectures on the technology so I can be more familiar with it when the clinic gets rolling again.
In the past, I mostly turned it on when I saw a vascular anomaly in the retina, typically related to macular degeneration or diabetes; but sometimes I used it for other retinal findings that I just thought were strange. Hopefully, I’ll have more to write about with OCTA in the near future, but last week I saw a patient with an unusual keratitis, and it got me thinking about the title question: Would OCTA work for the cornea?
The answer is, yes, people are doing this. I won’t get into which brands provide the technology at this moment — because that can change so quickly — but a paper came out in Cornea (Nanji et al.) just last month that explored anterior segment OCTA, and I’d urge you to read it. A quick search yielded several studies about the topic, and I thought it would be an interesting thought to explore this month.
The first question with new technology is always: Why is this necessary? For corneal OCTA, the finding being measured is neovascularization, and literature focuses on three reasons: better visibility, better depth evaluation and better quantification.
The first one is pretty obvious. If you’re trying to examine a patient with a keratitis, you know they are uncomfortable. They can’t keep their eye open. There’s so much corneal edema that you have a hard time seeing anything when they do manage to open their eye. It’s difficult to shine white light on a clear(ish) tissue and look for abnormalities. A good slit-lamp photo of these patients is invaluable, but if you’ve ever attempted one you know how difficult it can be even on a cooperative patient. Seeing the neovascularization with good delineation and good contrast would be quite valuable.
Second, OCTA has been shown to provide good information on just how deep the corneal neovascularization is. Can you do this yourself by observing it closely? Yes, but sometimes it’s hard. Why is depth important? Because it very much helps guide the differential diagnosis. Conditions like interstitial keratitis have a sine qua non of relatively deep neovascularization in the stroma; whereas conditions like limbal stem cell deficiency and pterygia have superficial neovascularization.
The third justification for corneal OCTA has to do with quantification and follow-up over time. The more accurately the neovascularization is documented, the more accurately we can determine if the treatment is working as the patient returns for follow-up visits. Even a corneal OCTA of average quality would be a vast improvement over my pathetic free-hand drawings of a limbus with some red lines intersecting it.
Software developments can quantify the area (mm2) of the neovascularization at any visit, thereby giving a number we could reference at each patient encounter. And speaking of software tweaks, some clinicians use OCTA to calculate blood vessel density in affected areas, which might help differentiate pingueculum from pterygium and perhaps other vascular surface anomalies.
Quantifiable data like vascular density, depth and area are what would propel corneal OCTA forward. It could be more than just an interesting way to look at blood vessels; it could be a useful tool to help make a diagnosis and help determine if the past treatment is working.
OCTA is still in its infancy right now, but it’s exciting to think where it might be in the not-too-distant future.
References:
Ang M, et al. Ophthalmol. 2015;doi:10.1016/j.ophtha.2015.05.017.
Mannis MJ, Holland EJ. Cornea. 4th ed, 2017.
Nanji A, et al. Cornea. 2020;doi:10.1097/ICO.0000000000002232.
Yan Li, et al. Invest Ophthalmol Vis Sci. 2018;59(9):3333.
Zhao FMM, et al. Cornea. 2020;doi:10.1097/ICO.0000000000002114.
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