Wavelengths of light questions

Tue, 10 Nov 2020 23:20:23 GMT

Hello fellow imagers,

I am in the process of shopping for new imaging systems for my practice. I am reviewing all equipment as well as the nm wavelengths in all equipment and I find I have questions the sales reps cannot answer.

If I may start with what I know-

Blue reflectance light utilizing Heidleberg=488nm, vs 435-500nm other equipment

This wavelength shows the internal limiting membrane and RNFL- superficial layers well as the wavelength is shorter and shows the retinal surface.

Green reflectance light utilizing Heidelberg=518nm vs 500-585 nm vs other equipment

This wavelength is a bit longer so it shows the inner retina and retinal vessels.

Red reflective light utilizing Heidleberg=815 nm vs 565-640nm other imaging devices

This layer shows the RPE and BR.

My question for imagers is-

How does FAF work?

How does a short wave length of light that normally shows the inner retinal layers show lipofuscin and melanin reactions since these processes occur in the basement membrane? How does a short wavelength show the basement membrane or RPE? I would think the wavelength would need to be longer.

Any advice would be most appreciated.

Thank you so much!

Julia

Tue, 10 Nov 2020 23:27:30 GMT

Julia,

The Spectralis uses the same wavelength of light for FAF that it uses for FFA. There are fluorophores in the retina (lipofuscin for one) that fluoresce when hit with this wavelength of light. You will not be using reflectance mode to see these structures as you will still need the barrier filter in place to block out all light except the light created by the excited fluorophores. It's all about what is excited by the "Blue Peak" light. I hope this helps.

Wed, 11 Nov 2020 14:09:52 GMT

As I understand it, FAF also can show the fluorescence of hollenhorst plaques, which BR may be an early indicator in some cases, but doesn't always show in FAF, usually because it isn't fully blocking the arterial flow. Also, ONH Drusen show very well, but I've found usually have a different focal distance due to the shallow DOF inherent in cSLO systems, as well as in microscopes in general (low power or high power).

So while the RPE shows fluorescence in lipofuscin very well in the FAF ranges, the utility of the wavelength itself goes beyond the range of the RPE.

I find myself going back to Tim Bennetts description of it here:

https://www.opsweb.org/page/Autofluorescence