Toolkits

Video Otoscopes - Technology Overview

Video otoscopes have played a useful role in telemedicine programs for many years, with applications in both store-and-forward and live videoconferencing systems. The market has undergone changes in recent years as imaging technologies have become cheaper and various high-resolution devices have been developed. Changes in optics, lighting, sensors, and data transfer have resulted in a diverse group of products with widely varying levels of performance. Understanding how these devices work is an important step in selecting the right otoscope for your telehealth program.

Figures 1 and 2 show two different styles of otoscope. The first image shows a probe-based otoscope, while the second image shows a model that does not have a probe. Additional information is included beneath each image.

Video Otoscope - Lightbox Graphic
Video Otoscope - USB Graphic
Image 1 - Video Otoscope with Lightbox Image 2 - Video Otoscope with USB

Parts:

  1. Specula
  2. Barrel
  3. Probe
  4. Coupler
  5. Focus Ring
  6. Cables
  7. Light Box

Parts:

  1. Specula
  2. Camera Body
  3. Focus Ring
  4. Cables
  5. Battery

 

Note that there are slight variations of these basic components in different manufacturers’ products.  These possible differences will be discussed as each part of the otoscope is examined in more detail.

The specula is typically the only surface of the otoscope that will contact the patient when imaging the ear canal and tympanic membrane.  The exact size and model of specula that an otoscope can accept will vary by manufacturer.  Some devices provide washable speculum, while others accept disposable versions.  A handful of manufacturers support various Welch Allyn speculum, but this is not the case for all devices.  It is advisable to check with each manufacturer to see if your organization’s existing speculum may be used with the video otoscopes.

The probe and barrel are not features shared between all of the otoscopes.  The probe includes an outer fiber optic ring, which provides illumination while imaging.  There is also a central element in the probe that serves as a lens, allowing the imaging area to be captured by an imaging sensor within the camera body.  

The barrel provides some level of protection to exposed probes, as well as a way to mount specula to narrower probes.  Some providers may choose to remove the barrel, resulting in a very narrow device and the inability to use the device with a speculum.  Using the barrel or not can be a matter of personal preference; some clinicians find it easier to hold an otoscope with a barrel, while others prefer to image entirely without a barrel and specula. Clinicians should use extreme caution to protect patient safety when choosing not to use the barrel and/or specula features of a video otoscope.

Some otoscopes forego a barrel and probe assembly, instead incorporating an imaging sensor with a series of surface-mounted LEDs for illumination.  These devices require a specula in order to image the tympanic membrane, but may be used without a specula for intraoral or external imaging. 

The coupler element, present on some otoscopes, is used to attach the barrel and probe assembly to the camera body and imaging sensor.  It is important to consider the alignment of the barrel and probe assembly with the camera assembly; ensure continued proper alignment by securing any locking mechanisms once the initial alignment is verified to be correct.  There may be a marker or icon on the coupler or camera body that indicates which side is “up”.  It may be possible to use barrel and probe assemblies from one manufacturer with the camera body and coupler of another.  Note that this may not be a supported configuration and should be verified on a case-by-case basis should your organization be interested in using existing probes with new video otoscopes.

Camera bodies come in many different shapes and styles.  The bodies contain the imaging sensor.  They also either contain built-in light sources or fiber optic connections that transmit light from external sources.  The majority of devices will have cables coming from the camera body, connecting the otoscope either to a light box, PC, or external video input (such as a videoconferencing codec or capture card).  Additionally, the camera body may contain a focus ring.

The focus ring allows the user to adjust the focal point of the lens, or how far away an object can be while staying clear and sharp.  Some products do not have a focus ring, and instead maintain a fixed focus that is pre-set to allow good imaging of the tympanic membrane.  Some products support a very wide focal range, while others are much more limited.  There are many possible factors in how well a device can be focused.  The subject of focus is an important one with video otoscopes.  

The cables and chords connected to otoscopes vary between manufacturers.  The connections can generally be broken into a handful of categories of transmission, including light, video, data, and power.  Data transmission cables, which are USB cables in the current video otoscope market, can also double as power cables for some video otoscopes.

Cables responsible for the direct transmission of light are fiber optic cables.  These are composed of many long strands of glass that transfer light from a light source in a light box to the probe assembly.  Use caution to prevent damaging these cables, as they are susceptible to internal breakage by crushing or crimping, which reduces the ability of the cable to transmit light. A damaged cable can ultimately result in a poorly-illuminated or grainy image. Only devices that have a separate lightbox, with the illumination source in the box, utilize a fiber optic cable.

Video cables are predominantly s-video or composite cables.  Some manufacturers are beginning to add support for high-definition video signals, which means that connectors for HDMI and DVI may exist.  At this time, the AMD-500 is the only device on the market that offers a high-definition connection, though Sometech has an upcoming product that will also provide high-definition connectivity.  Many otoscopes – with the exception of those that send data over a USB cable – provide this video connection to an external device, such as a videoconferencing system or a video input on a PC. Some otoscopes that utilize a lightbox also have a proprietary video connector from the probe assembly to the lightbox unit, which is then later passed to the video output connector.

Data connections, at this time, are limited to USB connectors.  These connections will transmit either live video signals or captured images, and may also communicate with any proprietary software to trigger still image or video capture within the application.  USB connections are also capable of transmitting power to the device.  Some otoscopes are capable of being powered completely through this connection, while others may require additional batteries or alternative power sources and connections.

Power transmission to otoscopes with light boxes is typically done with an IEC-type connector (a common coupler standard).  Devices with light boxes will also need to transfer power to the probe assembly and imaging sensor, which is typically run through a cable into the back of the probe.

Common Video Otoscope Problems and Concepts

Video otoscopes are prone to several problems that can make capturing quality images challenging.  Issues around light control, focusing, and distortion are fairly common, as are overall problems with image quality.  The root causes of these problems are varied.  In some instances, algorithms and embedded controls are responsible for the problems (and correction of them), while others are caused by the hardware itself.

Blooming

The problem of blooming results from the inability of the imaging sensor to compensate for brightly-illuminated regions of a subject, with highly-reflective surfaces being especially prone to causing blooming in an image.  This “over saturation” is visible in the image as a white highlight, and the blooming extends beyond the single point of highlight, often “bleeding out” or “blowing out” details in the image.

Otoscopes implement gain control to mitigate this problem, though they use different techniques and terminology for this function.  Some devices will automatically adjust the gain, while others require manual adjustments. Otoscopes also often allow for the light intensity to be changed, which can also assist in reducing blooming.  Testing revealed that each device has a slight learning curve in order to capture the best image, with a balance between light intensity and gain settings.

Focusing

Being able to properly focus an otoscope is one of the most critical elements in capturing a good image.  Unfortunately, this process is not always easily done with all otoscopes.  Some issues related to depth of field can make focusing challenging.  Depth of field relates to how much “depth” in an image remains in focus.  In some products, the depth of field extends for over a centimeter, while others have only a millimeter or two.  These shorter depths-of-field can be problematic, as it means that miniscule movements of the probe will move the subject out of the area of focus and result in a blurry image.

The physical act of focusing becomes much more important as the depth of field decreases.  A balance needs to be struck with the focus ring, weighing between being easily changed while imaging and being capable of holding focus once set.  

Some devices also suffer from an issue that is loosely related to focusing.  On products with surface-mounted LEDs located on the same plane as the lens, focusing on near surfaces can bring a vignette or halo or light around the edge of the image.

Field-of-View

When imaging a tympanic membrane, a typical clinician will want to be able to capture the entire surface of the TM in a single image.  Some otoscopes have a narrow field of view, which makes this impossible.  The field of view refers to how much of a subject is visible from the lens, often discussed in terms of degrees.  Devices with a narrow field of view will only be able to see a portion of the tympanic membrane, which requires either multiple still images or a moving live video feed to show the complete surface.

Devices with a very wide field of view are prone to barrel distortion.  This distortion can make an image appear to “bulge” out towards the viewer, and may add apparent depth to in image that isn’t actually there.  Extreme cases of this can make an image appear to be spherical.

Image Quality – Color and Detail

Accurate, life-like colors are an important element of the image quality equation.  “White balancing,” or establishing what true white is in an image, is the term often used to describe the process of setting an otoscope to capture true-color images.  Otoscope manufacturers typically take one of two approaches to white balancing, with some automatically, dynamically setting the white balance through algorithms in the device, and others requiring a manual step at each use.

The accuracy of automatic white balancing varies fairly widely across manufacturers.  Some devices will drastically change the white balance with minor movements of the probe, resulting in noticeable variations in color between very similar images.

Manual white balancing typically requires that the user direct the probe at a white sheet of paper while pressing a button.  The otoscope will then take a reading of the incoming image and adjust the interpretation of the color to set a new white balance.  This can be problematic in some rare instances on some otoscopes if capturing images from varying ranges, as the quality and color of the light may change as distance increases from a couple of centimeters to several inches.

Issues in color can also arise with contrast, brightness and darkness, saturation, and hue.  The causes for these problems vary, but are often tied to how the image is processed by the internal components of the otoscope.  Additionally, individual computer monitors can display colors differently, rendering even the most color-accurate device less useful.  Note that it is possible to properly calibrate a computer monitor, and this process is highly recommended when performing both testing and clinical diagnosis.

Image detail can be impacted by several factors, including the resolution of the imaging sensor, the quality of the lighting, the sensitivity of the imaging sensor to light, and the reaction of some lenses to the humid environments of the ear, nose, and throat. Under-illuminated images often appear grainy.  It is important to ensure that the otoscope’s light source is set at the correct level when imaging.  Some otoscopes combat the “clouding” issue of imaging in a humid environment by providing support for insufflation bulbs that allow air to be directed to the tip of the probe.

Back to Top