2021 OCT in Glaucoma (1) : OCT physics

This video explains the difference between the three modalities of OCT : time-domain, Spectrum-domain and Swept source OCT.
A simple explanation of FFT is included

[@maryamsolouti8104]

I saw several videos for OCT and this was the best one that I finally understood the concept vividly. Thank You :)

[@AH-oo1oq]

Very informative, very nice way of explaining. One thing to also note here is that the intensity of the light is also affected by the absorption of the tissue, which means that sometimes the constructive interference does not lead to the maximum amplitude even though the object is focused. In other words, noise can be generated by light traveres different types of tissues with different absorption factors. This effect makes the images sometimes blurry and noisy. Allow me to add something here, Fast-fourier Transformation OCT is only achieved using specialized line-cameras.

[@aatt3209]

One of the very best tutorials out there on OCT (concept + setup), very glad I saw this video, thank you so much!

[@adelabdelshafik]

Welcome. Glad to hear your opinion.

[@melmel1820]

You saved my life and you helped me understand something I couldn't understood a really long time ago

[@135prashant]

You are a genius sir to explain the complicated principle with such patience and ease. I love your presentation

[@adelabdelshafik]

Thanks. Glad to hear your opinion.

[@lachezarkolev3059]

This is some world class explanation. You broke the topic into relevant parts and explained everything so clearly and fluently. Amazing job. Thanks.

[@adelabdelshafik]

Thanks. Glad to hear your opinion.

[@melmel1820]

Thank you very much, you are the best teacher ever on KZbin THE BEST

[@adelabdelshafik]

Glad to hear your opinion

[@PreangkaRoy]

Really, after seeing this lecture, I thought that I have learned more...waiting for the new lecture

[@adelabdelshafik]

Glad to hear your opinion. Thanks.

[@Muhammadusman-zi9uz]

Very good presentation Sir. Easy to understand and nicely explained. Thank you

[@adelabdelshafik]

Glad to hear your opinion.

[@stelthirdeyeproductions5819]

This was just what I was looking for, linking the theory with the practice. Thank you Sir! I wonder what is the reason that the swept single frequency light ray method (narrow-band) can get to and hence measure the deeper layers, when compared to the broad band light source method? Is it a matter of increased light power density assuming distances are kept the same? Looking forward to watch your other two videos. Thank you.

[@marialiseth7633]

incredible explanation! congratulations! thanks for sharing

[@lambda4931]

The beam splitters in you diagrams are facing the wrong way.

[@jovanantic136]

Very Helpful

[@adelabdelshafik]

Thanks

[@convex9345]

Hello Sir, I have a doubt. As you mentioned, in TDOCT the light source is monochromatic, but in the literature, it is mentioned that the light source is broadband with continuous waveform. If we use a monochromatic light source then the interference pattern still observes at the unequal path length difference. Thanks in advance

[@fadyabsy]

تسلم يا بروف شرح اكثر من رائع

[@adelabdelshafik]

thanks

[@Tenjayy]

Perfect

[@abdulrahmanalotaibi1370]

Thank you for a very good explanation!!!!!

[@adelabdelshafik]

Glade to hear your opinion

[@soheilaakbari181]

Thanks,perfect

[@adelabdelshafik]

Welcome

[@majidakhzari5071]

The Source of light in SS and SD is same ? SLD?

[@sachinmdesai]

Thanks sir. Waiting eagerly for more in this series

[@adelabdelshafik]

welcome. I am preparing an new one these says.

[@bspkhaleghi]

Very informative Thanks

[@adelabdelshafik]

Glad to hear your opinion

[@dawnlh]

Thanks for the wonderful tutorial, it's vary helpful! I wander is it convenient for you share the lecture slides or notes, hope to make a note for future reference!

[@adelabdelshafik]

OK. I will work on it. Thanks for your suggestion.

[@danielaperezguerrero2697]

Nice explanation!

[@adelabdelshafik]

Glad to hear your opinion

[@AH-oo1oq]

One thing is left open here, how to map between FFT Domain to the spacial domain.

[@adelabdelshafik]

I did not understand the question. FFT domain OCT is another name for spectral domain OCT.

[@AH-oo1oq]

@@adelabdelshafik For spectal OCT, an inverse FFT is necessary to transform light spectrum (from the line camera) into time/spacial domain relevant to the pachymetry of eye.

[@adelabdelshafik]

@@AH-oo1oq I believe an engineer is needed to discuss such statement, which is beyond my ability as an ophthalmologist. If you find it useful for ophthalmologists following this channel, you may further explain that point.

[@manmathkumardas5856]

very good video sir, learned a lot

[@adelabdelshafik]

Glad to hear you opinion.

[@srisridurga]

Well explained sir.. Thank u so much

[@adelabdelshafik]

Welcome

[@bumkyukim9950]

Both TD and SD(SS) use micro purse light source?

[@adelabdelshafik]

Yes. You are right.

[@user-nx1rg9tn7z]

Hi thanks for the video, some basic ideas are still unclear to me: is the mirror movable in time domain OCT so we do not get destructive interference? How do we know when to move the mirror? Is this a closed loop system where the detector tells the mirror to move back when destructive interference is detected? thanks!

[@adelabdelshafik]

Hi. To start with I am not an engineer, , I guess the mirror is moving all the time for a fixed distance , as rays are reflected from different layers of retina simultaneously the detector will capture subsequent layers with constructive interface, this will result in detecting 5-6 layers of the retina with certain distance in between with no layer detected hence we can get a section in the retina. Finally have a look at this video : kzbin.info/www/bejne/oF7YZHx7nMiHn7M

[@kimbich7235]

Thanks u😊.

[@adelabdelshafik]

Welocme

[@kimbich7235]

​@@adelabdelshafik Hi, sir, Can you talk something more about enhanced depth imaging, and difference between EDI- Cirrus HD OCT 5000 and EDI Heidelberg Spectralis. I don't understand how EDI technique works "Spectral domain can show to a little extend these deep structures when using a technique known as enhanced depth imaging, by pushing the instrument closer to the eye " . Thank you so much.

[@adelabdelshafik]

@@kimbich7235 sorry at present time I do not have much information regarding EDI, may be in the future.