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Medical Forum / General / Vision / November 2005Optical Coherence Tomography question
Hi, When a doctor uses OCT. Does the machine "default" to scan the entire 360 degree retinal surface of the eye from the peripheral or edge to the center or macula. Or does he has to input regions to scan such as macula or even optic disc or selected retinal locations?? Kyle He/she (or his tech) scans a particular area. Usually the optic disc (to measure cupping or the retina nerve fiber layer) or the macula. Depends on what he/she is looking for. > Hi, > [quoted text clipped - 5 lines] > > Kyle > He/she (or his tech) scans a particular area. Usually the optic disc (to > measure cupping or the retina nerve fiber layer) or the macula. Depends on > what he/she is looking for. I see. In the case of cupping, isn't it that one can measure the cup-to-disc ratio by noting how big is the optic disk and the cupping. So what do you mean measuring cupping in particular? Is there any chance (even 0.01%) or no matter how tiny as it may seem that the laser can damage the rods and cones. Also it is possible to scan the entire retinal surface from the macula to optic disk to peripheral portions in one sitting. How long would this take? Tnx. Kyle > > Hi, > > [quoted text clipped - 5 lines] > > > > Kyle >> He/she (or his tech) scans a particular area. Usually the optic disc (to >> measure cupping or the retina nerve fiber layer) or the macula. Depends [quoted text clipped - 4 lines] > the cup-to-disc ratio by noting how big is the optic disk and > the cupping. So what do you mean measuring cupping in particular? The doctor does measure by estimating the ratio, but using the OCT actually gives a 3 D image with 6 different views. With the OCT you can actually see the cupping from the back of the eye (optic nerve) towards the retina. The retina nerve fiber layer scans around the optic disc and measures the thickness of the nerve layers to check for thinning. > Is there any chance (even 0.01%) or no matter how tiny as it may seem > that the laser can damage the rods and cones. I haven't read up that much on risks, but I believe it is more like ultrasound. I will check the manual and get back to you. > Also it is possible to scan the entire retinal surface from the > macula to optic disk to peripheral portions in one sitting. How > long would this take? We have only scanned the optic disk and macula. This can be done in one setting. It is a very quick procedure (less than 5 minutes per eye), unless the patient has trouble with fixation. The periphery isn't scanned, at least not as far as I know (but I'll look into it too). > Tnx. > [quoted text clipped - 9 lines] >> > >> > Kyle > I haven't read up that much on risks, but I believe it is more like > ultrasound. I will check the manual and get back to you. The OCT is not an ultrasonic device, but utilizes a beam of light in the 700-800 nm range. While I have not had it performed on me, I have observed that patients have not displayed any signs of discomfort. The peak senstivity of the rods is in the 500-600 nm region. DrG There must > >> He/she (or his tech) scans a particular area. Usually the optic disc (to > >> measure cupping or the retina nerve fiber layer) or the macula. Depends [quoted text clipped - 10 lines] > retina nerve fiber layer scans around the optic disc and measures the > thickness of the nerve layers to check for thinning. > > Is there any chance (even 0.01%) or no matter how tiny as it may seem > > that the laser can damage the rods and cones. [quoted text clipped - 10 lines] > the patient has trouble with fixation. The periphery isn't scanned, at > least not as far as I know (but I'll look into it too). My doctor said OCT measured 16 different sectors of the retinal nerve fiber layer. Is that what you mean by different views? My HRT's have measured cup to disk ratio but I didn't know OCT would do this. All my doctor mentioned was thickness of the nerve fiber layer in each sector, but presumably that's all he was looking for. When my husband had OCT it was to examine subretinal fluid. -Gudrun > There must > [quoted text clipped - 41 lines] > it was to examine subretinal fluid. > -Gudrun The retinal nerve fiber layer and the macula scans both scan 6 different angles. It is not the same as the sectors your doctor refers to. (Maybe sectors are layers of the retina??) By scanning in different angles we can then choose to scan just one particular angle at a higher resolution to get a better view of something, like subretinal fluid. The optic nerve scan makes one 360 degree scan around the nerve. > >> He/she (or his tech) scans a particular area. Usually the optic disc (to > >> measure cupping or the retina nerve fiber layer) or the macula. Depends [quoted text clipped - 10 lines] > retina nerve fiber layer scans around the optic disc and measures the > thickness of the nerve layers to check for thinning. Is it possible to have thin retina nerve layer yet the nerve fiber going to the optic disk is normal?? For example. A person has an average cup to ratio of 0.3. Is it possible the nerve layer beneath the retina is thin yet the nerve fiber going into the optic disk is normal? kyle > > Is there any chance (even 0.01%) or no matter how tiny as it may seem > > that the laser can damage the rods and cones. [quoted text clipped - 24 lines] > >> > > >> > Kyle Kyle: Your question about risks, the manual was pretty vague, I read a portion of it today (meant to bring it home, but forgot it), but to summarize you would have to scan the exact same portion of the retina for a long period every day to cause any risk. No percentages were given. The OCT is not ultrasound, it is like ultrasound in that it measures the light reflections, whereas the ultrasound measures sound reflections. It is only used for the portions previously discussed (not the periphery). I don't know if there are any "off label" uses. When we measure the RNFL (retina nerve fiber layer) it measures 360 degrees around the optic nerve. We are usually checking for thinning of the RNFL caused by glaucoma. We also do the ON (optic nerve) scan to check the cupping at that time. I'm not sure what you're asking in your last posted question regarding a thin retina nerve fiber layer with a normal nerve fiber going into the optic disk. That would be a question for your doctor to answer. If you or a family member has a question about test results - the best thing to do is ask. We have patients who even bring a list of questions in with them so they don't forget to ask them all. It's your right to be informed. If indicated we scan the macula. Usually done in patients who have macular degeneration, macular edema, macular hole, macular pucker, premacular fibrosis, the list goes on. It is very sensitive and can detect early holes, fluid (edema), holes, etc.. >> >> He/she (or his tech) scans a particular area. Usually the optic disc >> >> (to [quoted text clipped - 55 lines] >> >> > >> >> > Kyle . If you or a family member has a question about test results - the > best thing to do is ask. We have patients who even bring a list of > questions in with them so they don't forget to ask them all. It's your > right to be informed. Just wondering... how is that right defined? Sometimes it's very difficult to even buttonhole the doc. Don W.. Maybe I should have said "your right and your responsibility to stay informed about your health." Doctors do have a huge demand on their time, but for the most part if you ask questions they answer them. Some patients want the information in the simplest terms possible, others want more complex. Either way, it's hard for the doctor to read the patient's level of understanding in a short time while being pushed for time and making a diagnosis (and sometimes determining a treatment plan). So slow things down and ask questions. It's your time. When he walks in the room and the door closes behind him, he's on your time. I hate to say this, but if your doctor isn't willing or able to take time to explain things to you or answer your questions, maybe you need a different provider. The doctor I work for is guilty of running behind schedule (who isn't), but for the most part, by the time he's done with the patients they don't mind, they feel they were treated right and not rushed through just because he was behind. >. If you or a family member has a question about test results - the >> best thing to do is ask. We have patients who even bring a list of [quoted text clipped - 5 lines] > > Don W.. |
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