Wide Field Imaging: The Future of Retinal Photography?
I recently had the opportunity for an extended trial use of the Optos 200Tx ultra-widefield high resolution imaging device. As the name implies, the main advantage over "conventional" retinal photography is that the field of view is expanded from 30 degrees or 50 degrees to a 200 degree field of view, which covers approximately 80% of the retina in a single view.
When I first heard of the device, my first thought was that this device would have a very limited application, because most "diagnostically significant" retinal diseases have manifestations in the posterior pole, which is covered in a 30 degree field of view. I had also heard that this device was primarily marketed to optometrists, as an "add on" service for a more "state of the art" eye exam. In other words, for an additional fee, the patient can have an instant examination of the entire retina without the discomfort of an indirect ophthalmoscopic examination. Because of these pre-conceptions, I had thought of this instrument as a gimmick rather than a serious diagnostic device. After using this instrument extensively for several weeks, it has changed my thinking.
Going into our trial period with the instrument, I had three major questions:
1. Does this instrument provide you with information that is not attainable with a conventional fundus camera? If so, how often does this occur?
2. Is the resolution of the posterior pole sufficient for diagnostic purposes? In other words, if you have this instrument, are you also going to need a 30-50 degree fundus camera for the posterior pole?
3. How "operator friendly" is the instrument? In other words, will you need a degree in medical photography in order to obtain good quality images?
For most imaging needs, the instrument is very "operator friendly". The software is intuitive and the basics of patient management/ image capture can be taught/learned in a few minutes time. The patient "peeks" through a hole and the eye fixes on a bright target. The operator aligns the eye by guiding the patent's head. Because the imaging device is a scanning laser ophthalmoscope, no focusing is required, and no exposure adjustments are needed. Some operator skill is required if you desire an image that is not in the central 200 degrees. If you want an image farther out into the periphery, which is possible, then some "unconventional" techniques are required.
Does this instrument provide you with information that is not attainable with a conventional fundus camera? Yes. Border to border images of nevi/tumors in the periphery are attainable with this camera, which are not attainable with a conventional fundus camera. Peripheral diabetic eye disease that is easily missed with a conventional fundus camera (even with a survey), is easily seen with this camera. Name any peripheral eye disease, and what may be impossible to document with a conventional fundus camera now becomes relatively easy to image.
Is the resolution of the posterior pole sufficient for diagnostic purposes? Yes, see images below. Photographs can be captured in two "zoom" modes, 200 degrees and 100 degrees. The 100 degree mode provides a zoomed in view of the posterior pole that includes the Superior and inferior arcades.
Is this the future of retinal photography/fluorescein angiography? Why would you settle for 50 degrees when you can have 200 degrees? Why would you drive a Ford instead of a Ferrari? Yup, it always boils down to the price tag, especially if that Ford is already paid off.
Optos images: Keep in mind that the resolution of these images has been reduced by me in order to fit the article and to keep the download time reasonable. The images on the instrument would easily fill a 32 inch screen and would zoom in to nice detail.
Below is a typical 200 degree color image from the Optos. This is an image of a diabetic retina with laser scars. Notice the eyelashes in the image superiorly and inferiorly. This is typical. Because of the ultra-wide angle, it is difficult to totally eliminate lashes from the image. The lashes can be cropped out to produce an image for presentation.
Below is an image of a horseshoe retinal tear. This was taken on the 200 degree setting, but I have cropped it for presentation.
The image below of a treated malignant melanoma is in the 200 degree mode and it is not cropped. This is not the typical straight ahead view. The patient is looking up and temporally in order to get the entire lesion in view. There are peripheral fixation aids for the patient to fix on, but this technique does require some operator skill.
The 200 degree image below is a fluorescein angiogram of diabetic retinopathy. Again, this is not the typical straight ahead view. The patient is looking temporally in order to get a better view of the far periphery, where diabetic disease is evident that would not typically be documented with a 30 or 50 degree fundus camera. The image has been cropped at the top and bottom of the image. We have found that fluorescein angiography on diabetics with this instrument often reveals pathology that would not otherwise be detected.
The image below is a 100 degree field of view that has been cropped to correspond to roughly the 50 degree angle of view. This is to demonstrate that the detail of the macula is very nice and is comparable to the detail of a 30 or 50 degree fundus camera.
The image below is the full 100 degree view, without any cropping. This is an auto-fluorescence image of optic nerve head drusen.