A SNAP - SHOT OF
Non-Mydriatic Fundus Cameras
Look for these features when considering purchasing one of these devices.
JEROME SHERMAN, O.D., F.A.A.O., New York, SANJEEV NATH, M.D., New York & MONICA ASWANI, BIRMINGHAM, ALA.
Every O.D. should consider using a non-mydriatic fundus camera for at least three reasons:
1. You can easily utilize the technology as an addition to the typical patient examination. With all the new non-mydriatic cameras, technicians can learn to quickly obtain highquality images with minimal training.
2. You can obtain “baseline” data on all patients by taking annual pictures — greatly aiding in follow-up care — whether you’re determining a new condition or monitoring a pre-existing one.
3. You can photo-document virtually every retinal, choroidal, and optic nerve head disorder, including the most common ones, such as glaucoma, agerelated macular degeneration (AMD) and diabetic retinopathy. Here are the features of the non-mydriatic fundus cameras that we find most noteworthy:
Useful features of many of the available cameras
• Different frequency lasers. Some cameras employ different frequency lasers, capable of gathering information from multiple layers of the fundus.
for example, in one system, the green laser (532nm) captures information from the neurosensory retina to the retinal pigment epithelium (RPE) whereas the red laser (633nm) scans from that point to deep within the choroid.
You can always obtain both green and red separation views, which are immediately available (in addition to the composite view). For this reason, you can detect subtle findings in the retina (in front of the retinal pigment epithelium [RPE] and visible with the green separation view) as well as the choroid (behind the RPE and visible with the red separation view) and make a differential diagnoses. For example, you can visualize subtle retinal hemorrhages with the high magnification green (most often not the red) separation view, whereas you can visualize a choroidal abnormality, such as a nevus or inflammation, with the red (but usually not the green) separation view.
• 3-D images, 45° and 30° field angles. These features are quite useful when examining patients whose pathology requires in-depth study. The 3-D images are especially helpful for assessing optic disc depression and elevation. Similarly, evaluation of the macula with 3-D images allows you to appreciate subtle macula thickening, as well as loss of tissue in conditions such as lamellar holes.
• Integration of multiple images. A device that creates seamless montages produced by integration of multiple central and peripheral photos (see figure 1) is useful because a single image limited to 30° or 40° cannot capture some disorders.
• Fixation mode. A camera with a fixation mode positions internal targets freely or in a programmed sequence to produce the “big picture.” This enables us to rapidly assemble montages, without creating gaps in the composite image.
• Small pupil-size image capture. A device that captures digital images of the eye through the smallest pupil size (in between 2.0- to 4.0mm) allows you to take fundus photos in the prescreening phase of an examination, prior to determining whether to dilate a patient. Of course, this is extremely helpful in patients with narrow angles whom you judge unsafe to dilate and on those patients you see multiple times for which a dilated exam is not feasible during every visit.
• Automated stereo examinations. This feature, present on some of the fundus cameras, is very useful when evaluating retinal and choroidal diseases that affect the area within the arcades and out to 120° because you can appreciate subtle zones of elevation and depression. Those systems using liquid crystal glasses yield images with high resolution of the posterior pole and remarkable stereopsis.
Improving image quality
To further improve image quality regardless of the nonmydriatic fundus camera you choose, have the patient sit in a dark room for a minute or two to allow his pupils to dilate a bit. Dilation isn’t required on the majority of patients; however, patients who have very small pupils or media opacities are the exception since these conditions obstruct the view of the fundus. Another tip: Meticulously clean the fundus camera’s lens as instructed by the manufacturer. Artifacts often result with a dirty lens (see figure 2).
Fundus photography is a dual-edged sword. In most situations, it is very helpful to document the absence of pathology when none is present. If a pathology is present, it is essential that you identify it.
If another clinician has a photo from a previous exam that illustrates some pathology that you did not diagnose, this can provide damaging evidence in a medical-legal situation. Fortunately, this is very rare and does not outweigh the benefits of obtaining digital fundus images.
Many eye-care practitioners view the non-mydriatic fundus camera as the perfect compromise of cost, image quality and convenience. It provides digital images that add diagnostic and documentation value to your practice. It also offers immediate feedback, allowing you and the patient to make informed decisions about eye care and general health care.
For example, the diabetic who is shown a magnified image of multiple, vivid red hemorrhages and white exudates may become more compliant with diet, exercise, good nutrition and prescribed medications.
Dr. Sherman is a professor at SUNY College of Optometry. He’s also a founding member of the International Foundation for Optic Nerve Disease and the Optometric Retinal Society. E-mail him at email@example.com Dr. Nath is the surgeon/director of the Eye Institute and Laser Center at three NY locations. E-mail him at drnath@ worldeyecare.com Ms. Aswani is a Vision Science Ph.D. candidate at the University of Alabama at Birmingham. E-mail her at firstname.lastname@example.org.
Canon USA, Inc.
Carl Zeiss Meditec
Clarity Medical Systems, Inc.
Escalon Digital Solutions
TopCon America Corp.
Visual Pathways, Inc.
Optometric Management, Issue: May 2007