• Doug Cook

A 21st Century Retinal Camera

This is a review of the Nidek AFC-230 retinal camera. I had been waiting for years for a company to develop a retinal camera design that would be future-proof. I think Nidek has done it.

The trend for so many opthalmic instruments over the past 20 years was to build an all encompassing product that produces clean sleek lines that project state of the art in it’s outward appearance. This required compromises as the imaging technology would quickly lag behind soon after a purchase when the megapixel count or more important the imager sensitivity improved as they quickly do in regular commercial photography equipment. The result is a sleek looking 2.5 megapixel (or insert your outdated feature here) imaging box that quickly becomes obsolescent.


Nideks AFC 230 & Dell Vostro sits an ARK-530A Autorefkeratometer


Nidek designed their retinal camera right. They adopted a strategy of utilizing the best of prosumer grade photography imaging capture devices. In this case, the Canon 5D mark II – a 21 megapixel camera body that became a darling for photographers and videographers alike. Nidek then did what I think they are best – designing a “lens” or more appropriate an “imaging system” For retinal cameras this is where the precise engineering should be focused. They adapted autotracking systems originally developed for refractive surgical lasers and autorefractors and applied them to their alignment system to keep the camera in alignment. Inside sophisticated optics work to keep the focus in sharp check and provide the user with a standard monochrome image for alignment.

Real World Use

After 70 days I would describe the learning curve as fast especially if you ever used a slide based fundus camera. Cameras got dumbed down in the 1990’s as digital imaging came into the scene. The settings for this camera are set by knobs and dials on the unit – you touch nothing on the camera body itself. A laminated cheat sheet supplied guides the user for the modes less often used. Nidek supplied an LED lite to illuminate the adjustment knobs down below – a well thought out addition. Practical peripheral use limits seems to reach the equator for most patients. I have on a few occasions gone further. Peripheral imaging requires the use of the supplied fixation stalk which is an adjustable cable stalk with an LED fixation light to get those extreme views.

One necessary engineering requirement in this design involves exterior cabling. In order to create a future upgradable product using the body of a prosumer SLR, cabling is needed to attach to the SLR, the supplied/attached adjustable video display and to the computer. This for me is much preferred compared to a one piece but obsolete white elephant after 10 years of use.

The model of notebook supplied was a Dell Vostro 1015 with Windows 7 Professional installed.  It’s not a powerhouse but it does what it is supposed to do efficiently and serves as the server to the practice for the images captured.  I easily integrated this computer into my daily backup routine for onsite and offsite backups.

A hot pixel was observed on all images since the day of first use.   It was a Canon problem – hot or dead pixels can occur with image sensors so a quick swap was the remedy covered under the warranty.

Imaging and Electronic Medical Records

Digital photography can integrate most likely with your current practice management software. It’s likely however you will have to pay an annual fee for this feature. This is a planned annuity that is a scheme of the practice management software folks who set up the hostage fees for every little nook and cranny their software should have supplied in the first place.. Nidek does have a very workable substitute that’s included free with their cameras. It’s called NAVIS-Lite. You will have to dedicate a PC to use with your retinal camera and Nidek offers a Dell Vostro along with their units. It’s sufficient to capture and store your images and act as a server to the rest of the practice for displaying or working with the images. I bought a laptop bracket to connect with our machine to get it secured from falling and raised to a users level for data entry. Because it does not link with your PM software, you will have to enter a chart number, patient first and last name and birthdate and gender. The later two entries are optional and configured via it’s setup software. After done, you will want to close the record so you can access images from other locations – just like many other database systems. Wireless networking works just fine with minimal lags (1 to 3 seconds) observed maybe 5 to 10 % of the time. This is most likely would be a wireless interference issue of your network more than a Nidek problem. Cabled ethernet would give flawless instantaneous responses all the time.

Markup and Analysis Features

The biggest value I find here is the ability to create delineation circles around the edge of the disc and cup. This offers accuracy of a cup/disc ratio down to the .01 decimal point. So an objectively doctor assessed C/D of 4 may end up as a 4.21 with NAVIS-Lite. Time will tell if this offers improved long term sensitivity for detecting cupping changes but my hunch is that it will. Text and drawing features seem rudimentary and go unused in our office.

Stereo Optic Nerve Head Imaging

I first began taking stereo images in the early 1990’s thanks to my video slit lamp and a 60 D lens. You translate the joystick left and right to get the parallax you need to construct an image. Nidek makes it easy with a stereo mode on their camera. You move the fixation target with a woggle type of input device that can move the flashing greed dot LED in any direction. After each capture you can proceed or retake until you have the two necessary views for a stereo image. From there, you can use NAVIS-Lite to autocrop the images to build a convenient stereo image. Nidek supplies a stereoscope to view the image on your PC. For printouts one can try free fusion technique (see my post on Free Fusion of Stereo Optic Nerve Head Images)


Stereo Optic Nerve Head image created by NAVIS-Lite. Click to view larger image. Read my other post linked in the article to learn how to free fuse stereo images


Panorama Retinal Images

Composition is easy with NAVIS-Lite. You should acquire images which sufficient overlap so you can self guide the images one atop the other using retinal landmarks such as vascular bifurcations as reference points. The software then constructs a composite result of your collected images. NAVIS-Lite makes easy work of this. I’ve used panorama stitching software by itself and as plugins in Photoshop and NAVIS Lite seems the most adept at layering and merging the combined images. I was able to get a superimage of about 186 megapixels on a volunteer that agreed to sit as a subject while I collected about 12 snapshots covering most of her retina.


This two image panorama was as easy as stereo photography using the free NAVIS-Lite database and editing software that comes with the camera.


Tricks and Tips

  1. This camera has an undocumented anterior segment mode that works better than the published method of capturing external images.  I’ll detail this function in a future post.

  2. Capturing images can occur with pupils 3.8 mm or smaller,  diffraction and glare become more obvious.  One may have to increase the illumination from a 9 to a 10.  If cataracts are present, the glare becomes excessive – go ahead and dilate anyway.

  3. Buy a notebook desk attachment bracket to elevate your computer so you can type and access the PC from a standing position.

  4. The fixation target projects to the left of center for the right eye and right of center for the left eye.  In low vision cases, wave your hand to the left or right of the display screen to emphasize where the fixation target should be or to align the eye if the patient can not see the target.

  5. NAVIS-Lite displays the whole patient database by default upon bootup.  Once you have more than a dozen patients saved, finding the most recent pics takes more time.  It will streamline your routine significantly if you just display a list today’s patients by default.  From the top menu bar click on Setup > Patient List top tab > click on Tree View and enable the Today checkbox and click OK.  This may be the most important timesaving tip I can offer for current users.

Field of View Inside the Eye – a less technical illustration


Image Resolution

is so keen that the display surpasses what I can get through a direct ophthalmoscope, 60 to 90 D lenses on a slit lamp, or binocular indirect ophthalmoscopy.  While the standard of care involves directly viewing the fundus and I still do, I am seeing more of the posterior pole now better than ever.

Viewfinder Interface

You don’t use the SLR’s optical viewfinder.  Instead, Nidek’s hardware supplies an infrared based image on your screen after you have lined up the Purkinje image reflected from the cornea.  The display has an adjustable view angle and shows good detail and information for image capture.


Summary

For retinal cameras, we are completely happy with the 230.  Sharing images on the computer in each exam room helps with patient education while projecting a 21st century professional image. Nonmydriatic performance is excellent.  While task delegation may not be as simple as 1990’s click and shoot machines it is real close by one or two days of extra staff practice.  Nidek has enabled the user to control more functions with real knobs and dials instead of menu selections – akin to mydriatic cameras used for angiography.

Image resolution is outstanding – far better than slit lamp based funduscopic lenses. It promises to enhance the quality we strive to deliver for eye care.

#Nidek #Retina #RetinalCamera

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