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You’ll sit down and rest your chin on a support attached to the machine. The OCT equipment will scan one eye at a time. You’ll focus your eyes on a green target within the machine. You may see a red line while you’re having the scan. The test will take minutes.

The larger the full well capacity, yet the better the maximum signal-noise ratio. Consumer cameras with pixel sizes of 1.7 μm require only about 1,000 photons for the pixel saturation. In case of digitalisation with 8, 10, or even 12 bits, other noise effects (photon noise, digitalisation noise, dark noise) can already assume significant scales, interfere with the signal and thus influence the image in an extremely negative way.

The sensors used in standard cameras are clearly smaller and range from 4 to 16 mm image diagonal. These sensor sizes, too, are indicated in inches. The 1-inch sensor has a diagonal of 16 mm.

Optical coherence tomography uses a low-powered laser to create pictures of the layers of your retina and optic nerve. The cross-sectional images are three-dimensional and color-coded.

OCTeye test results

Classic machine vision cameras have varyingly large sensors, depending on the camera and resolution used. The majority of cameras with smaller sensors are used with so-called C-mount or possibly CS-mount optics. The C-mount thread has an actual diameter of 1 inch, i.e. 25.4 mm and a thread pitch of 1/32 inch.

There aren’t any risks or side effects associated with optical coherence tomography scans. However, because this type of test relies on light, OCT isn’t effective if you have thick cataracts or heavy bleeding in the back of your eye.

As a consequence of the miniaturisation of sensors, the pixel sizes grow smaller and smaller. Sensors of consumer cameras (8 to 12 megapixels for 200 euros) have pixel sizes of mostly 1.7 μm today, the light-active surface per pixel is therefore only approximately 3 μm2. This results in an extremely strong sensor noise in case of non-optimal lighting conditions. For quality control using cameras, this is absolutely inacceptable.

Another way to think of OCT is that it functions like an ultrasound, except it uses light* – instead of sound waves – to map the shape of the retina and optic nerve. It is safe, non-invasive, and not destructive to tissue. A camera-like device directs waves of light which bounce back and form an accurate 3-D picture of your eye (your retina). As well as the 3D scan, the OCT takes a photograph of the eye in high resolution. This allows us to pinpoint any area of concern to review in-depth.

OCT stands for Optical Coherence Tomography. Simply put, the OCT is another non-invasive tool that “takes pictures of the back of your eye.”

Important: If you have the choice between a larger and a smaller sensor for the same camera version, please take the larger variant if you…

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The inch data of the CCD and CMOS sensors only have a historic explanation: pick-up tubes of TV cameras were used up to the mid-1980s and were long superior to CCD or CMOS sensors which were invented in the late 1960s.

In general there is the trend that the sensors become smaller and smaller on the mass camera market. If a standard VGA sensor had, in some cases, a size of 2/3" in the late 1980s, it is only 1/3" today. The miniaturisation is a consequence of enhanced production processes which allow for smaller light-sensitive surfaces with a (hopefully) similar performance. It enables the manufacturers to produce a larger number of sensors at a lower price from one wafer. A 1/3" sensor, for example, has only approximately 40% of the surface of a 1/2" sensor and is therefore cheaper.

Industrial cameras usually use 1/3" sensors in case of resolutions of 640 x 480 pixels, cameras with 1280 x 1024 pixels mainly 1/2". The quite popular camera resolution of 1600 x 1200 pixels often uses a somewhat larger sensor with 1/1.8" with the same pixel size.

The actual image converter of the tube cameras was located in a glass vacuum tube, and the different pick-up tubes were, among other things, classified according to their outer diameter of the glass bulb. The diagonal of the light-sensitive surface within the tube was of course smaller and represented approximately two thirds of the outer diameter. Equivalent CCD sensors which are supposed to replace the cathode-ray tubes had to cover exactly this surface. A CCD the light-sensitive surface of which corresponds to a 1/2-inch tube was therefore called 1/2-inch sensor, even if this does not correspond to the real CCD sensor size.

In case of high-resolution area scan or line scan cameras, significantly larger sensors with a size of several centimetres are used. The dimensions of these sensors are normally not standardised and result from the resolution and pixel sizes of the sensors. Everything is permitted and only limited by the budget.

OCTin Cardiology

Optical coherence tomography

OCT is a great tool in diagnosing different eye diseases like: glaucoma, macular degeneration, diabetic retinopathy, retina tears, retinal detachments, central serous retinopathy, retinal/macular cysts, macular hole, macular pucker, and macular edema. In some cases OCT can help your eye care practitioner diagnose eye disease early, which allows for more effective treatment. Because the OCT images provide such a detailed view of your retina, they can detect even the smallest indications of eye disease. In addition to early disease diagnosis, OCT can also help with monitoring the progression of eye disease, diagnosing eye disease in children, which can other be difficult, and diagnosing other diseases like hypertension, multiple sclerosis, and other vascular diseases,

The advancing technological development of CCD and CMOS sensors allows for the production of finer and finer semiconductor structures. As a general trend, sensor and pixel sizes shrink in order to cut more and more sensors out of one wafer. This is possible because the sensitivity of the pixels increasingly enhances, too, as much as the noise performance of the electronics is being optimised.

These cameras typically use Nikon bayonet (F-mount) or M42 to M72 as lens connections. Only then high-resolution sensors with large pixels can be used in order to build line scan cameras with up to 12k pixels or area scan cameras with up to 28 million pixels.

A larger sensor with larger pixels is in almost every case the technically better choice, however, the price is always higher.

This specification describes how many electrons a pixel element can hold before it is completely saturated. A pixel of 5.5 μm structure size can accumulate approximately 20,000 electrons, a 7.4 μm pixel 40,000 electrons.

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OCTeye test price

A line scan camera with 2048 pixels with 10 μm pixel sizes has a line length of 10.48 mm, in case of 14 μm pixel size the sensor is already 28.6 mm long. From 20 mm sensor diagonal on, the C-mount lens connection can no longer be used.

Your eye care practitioner will likely recommend an OCT exam if you have an increased risk of eye disease. You may have an increased risk of eye disease if you are over the age of 50 or have: a personal history of certain eye conditions, a family history of eye disease, diabetes, hypertension, other vascular health conditions, and/or if you are taking high risk medications. Even if you don’t have a high risk of eye disease, OCT exams are still a great way to help protect your eye health. By having OCT exams regularly, it creates a baseline that your optometrist can reference. Using this baseline, your optometrist can detect the smallest changes to your eyes over time. Reno Family Eye Care performs a one time screening OCT scan on all new or existing patients presenting for their comprehensive exam at the age 40 or older at no cost. If necessary, further OCT scans can be performed, and the interval at which scans are performed are determined by your eye care practitioner.

Machine vision cameras (C-mount) with resolutions from VGA to 2 megapixels normally have pixels of 4.6 to 6.5 μm with a 10 - 15 times larger light-active surfaces and thus clearly better signal results. If you need images as noise-free as possible and precise measuring results, look for preferably large sensor pixels, even if these cameras are more expensive!

OCTinterpretation PDF

The larger the full well capacity, yet the better the maximum signal-noise ratio. Consumer cameras with pixel sizes of 1.7 μm require only about 1,000 photons for the pixel saturation. In case of digitalisation with 8, 10, or even 12 bits, other noise effects (photon noise, digitalisation noise, dark noise) can already assume significant scales, interfere with the signal and thus influence the image in an extremely negative way.

As technical limits are reached in this respect, too, it is worthwhile to compare cameras with different sensor and pixel sizes with the same resolution, especially if…

Pixels with an edge length of 14 or 10 μm are preferentially used in line scan cameras. Due to the high line frequency of 18 Hz, for instance, the maximum exposure time is 1000/18000 = 55 μs for one captured image line. The light-active surface of the pixel can never be large enough in this case.

Your healthcare provider will evaluate the images from the optical coherence tomography test and go over them with you. They may need time to compare older scans to the newest ones. You should have the results quickly.

Reno Family Eye Care performs a one time screening OCT scan on all new or existing patients presenting for their comprehensive exam at the age 40 and older at no cost. Further OCT scans are then used to monitor medical conditions like glaucoma, macular degeneration, diabetic retinopathy if warranted.