An inverted Galilean telescope with an attached camera: that is the simplest way to describe a retinal camera. But today’s retinal cameras are in reality much more than that.
They are automated, high-powered screening and documentation devices. As such, they are exactly the type of machine eyecare practitioners need to boost the quality of care they provide to patients over their lifetimes. Clear, detailed digital images provide a snapshot of the health of the back of the eye. Besides helping to diagnose disease, retinal photographs, over time, become documents to track changes in the eye and monitor progression of diseases as each image provides a solid reference point for future comparisons. Before retinal cameras, this documentation was not available. And before cameras went digital, documentation was there, but it was a tricky, inefficient business: traditional film was costly and capturing a good photograph was time-consuming.
Today, the high-resolution digital cameras in modern machines capture photographs of the back of the eye instantly and relatively easily. The results can be seen immediately and software helps analyze the results. When seen by a trained eye, the images can help catch diseases in their early stages. And in medical environments, the diagnosis of disease and guidelines for treatment are enhanced when retinal imagery is combined with fluorescein angiography.
While fluorescein angiography, usually found on a mydriatic retinal camera, is very useful, it isn’t needed by most eyecare professionals. For most, a non-mydriatic retinal cameras is the tool of choice. Even the latest generation of “entry-level” machines are “very important” tools, says Dr. Ben Szirth, director of the Applied Vision Research Laboratory at New Jersey Medical School and an ophthalmic consultant to Canon. Estimates suggest more than 80 percent of optometrists in Canada have a retinal camera in their practice. That’s impressive, considering how recently it was that the tool of choice for seeing the retina was either an ophthalmoscope or slit lamp. Digital retinal cameras with a 45-degree field of view provide a wider field of view than a traditional direct ophthalmoscope.
Camera vs. ophthalmoscope
The power and efficacy of retinal cameras has been well examined. In 1990s, when retinal cameras were not ubiquitous, several studies declared that non-mydriatic retinal cameras were the preferred tool for screening for major eye diseases. A study of different methods for community-based screening for sight-threatening diabetic eye disease, published in the British Journal of Medicine in 1995, made just such a conclusion. “Even in the hands of an experienced ophthalmologist, direct ophthalmoscopy is limited by weaknesses inherent to the instrument,” the authors wrote.
And in 1998, a study in the Hong Kong Medical Journal concluded, “The sensitivity of detecting diabetic retinopathy by retinal photography was higher than that of direct ophthalmoscopy (64 percent versus 41 percent, respectively). Of five patients who had serious retinopathy, retinal photography failed to detect the disease in two; direct ophthalmoscopy failed to detect the disease in all five patients.” Today, in the UK, a system of digital imaging and electronic documentation has become the cornerstone of the National Health Service’s screening program for diabetic retinopathy.
RGB colour separation of images also makes digital retinal cameras effective at catching other diseases. A photograph of the retina that is separated into red, green and blue layers can then be analyzed by layer for specific diseases: red can be analyzed for age-related macular degeneration, green for diabetic retinopathy and blue for glaucoma. This arms doctors with good information, says Dr. Szirth, and gives them greater confidence as to whether to follow-up with the patient later, keep and treat, or refer to a specialist.
The power of instant images and modern software not only allows doctors to zoom in on pathology but also show patients exactly what’s going on inside their eyes. Patients then can better understand and accept the problems that need to be addressed. This helps build trust between patient and doctor.
From retinal cameras to OCT
Dr. Kerry Salsberg is part of a large, multi-doctor practice in Toronto. His practice is chock-a-block with digital imaging machines, including a retinal camera. And while he believes in the value of all the machines, he thinks the future lies in newer, more powerful technology. In fact, he’s a big fan of optical coherence tomography (OCT). OCT is adjunct technology to photography as it can provide a wide field of view up to 12mm and an impressive cross-section of the eye. “You can visually see what is going on in the deeper layers. It can even show metabolic function,” he says. “This technology takes digital imaging to the next level.”
This is why manufacturers are combining technologies. The 3D OCT-2000 system by Topcon was the first “spectral domain OCT system to incorporate a high resolution fundus camera,” allowing eyecare practitioners to view fundus images along with 3D representations of the retina.
Because OCT allows doctors to measure the thickness of each layer of the retina and get a good look at the optic nerve head, it helps in early detection, and in monitoring the progression, of several conditions that affect these areas of the eye, such as age-related macular degeneration, diabetic retinopathy, macular holes, cystoid macular edema and optic nerve damage. Not long ago, post-mortem histology was the only reliable method to investigate changes in the macula.
But for many optometrists, this technology may not make sense in their practice. Currently, OCT is outside the scope of OHIP coverage, making patient fees the only way to recoup the high cost (approximately $70,000 for Topcon’s OCT-2000). Many doctors price OCT fees around $90-100 per image. Not low by any standard. Al Brooks from Topcon, however, says he already sees OCT becoming more popular, and potential changes to legislation could make it more affordable. “The quality of the images is phenomenal,” he says. “OCT will definitely boost the standard of care.” But until OCT gains traction with optometrists, advances with retinal cameras can also provide improved standard of care. Beyond “entry-level” systems, retinal cameras are coming loaded with enhanced features.
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Advanced features on new cameras
One of these is the Nidek AFC-230. It is the only fundus camera with 3D AutoTracker. Combined with its auto-focus and auto-fire features, the 3D auto tracker makes taking good pictures of the peripheral regions of the retina simpler. “It is not about how simply you can take pictures, but how easy it is to take difficult pictures,” says Wayne Stobie of Innova Medical Ophthalmics. With Nidek’s auto-tracking feature, centering to the eye is simple and stereo pictures are automatic. Stereoscopic retinal photography involves capturing two photographs from slightly different viewpoints that can be viewed together. With automatic stereo, it ensures accurate and consistent lateral movements of the camera that can be reproduced again in the future exactly as before. This is extremely important when screening for glaucoma and looking for cupping of the optic nerve, says Stobie, as the distance between the two photographs can affect the depth seen by.
Hybrid digital cameras, such as Canon’s CX-1, that function in both mydriatic and non-mydriatic modes are putting even more power in the hands of doctors. While the advanced CX-1, at almost $48,995, is much more expensive than Canon’s CR-2 retinal camera (considered a basic clinical instrument costing just under $19,000), it also is much more versatile. One of the major features the CX-1 offers is fundus autofluorescence, or FAF. Topcon and Zeiss also have cameras with this advanced feature. Autofluorescence can record the presence of lipofuscin. Checking for and monitoring autofluorescent lipofuscin is important for AMD detection and management. Also, FAF has applications in nutrition for better ocular health.
Dr. Szirth says that FAF has moved onto the radars of optometrists across the country. They want to learn more about it, he says, as studies confirm the value of wide-field FAF imaging in the evaluation of AMD.
Choosing a digital retinal camera can be difficult (see “Retinal Camera Buyer's Checklist"). Feature by feature, most of the newest standard retinal cameras are roughly the same. For example, most offer colour fundus photography, small pupil imaging, RGB colour separation analysis and zoom. But the quality of imaging usually is a function of more than just a camera’s CMOS sensor. The Nidek AFC-230 system uses a Canon 5D Mark II as its attached camera. It has an amazing 21 megapixels. But getting a good image of the retina relies on more than mega megapixels. Optics are key, says Stobie. The efficiency of an optical system will depend on its lens and its requirement for light, he says. An efficient system will require less flash to achieve a clear picture (thus the less flash reaching and irritating the patient), and this increased efficiency is represented by optimized image clarity.
Technology that pays for itself
Even young doctors starting new practices can recover the cost of the investment fairly quickly. A five-year lease for a retinal camera, demanding about $500 per month would require an optometrist to generate $25 per day for 20 days each month from photography fees. Many offices charge more than that. Dr. Kerry Salsberg in North York says that his office charges about $35–50 for images taken from his Canon fundus camera. But he also stresses with his patients that “ophthalmology provides an alternative where imaging may be covered.” Most patients, however, are willing to pay for instant results instead of requesting a referral and waiting. With most optometrists in Canada using retinal cameras, new graduates are likely to view the machines as standard of care and thus, critical components in their practices. •
Click here to learn more about digital retinal cameras and teleophthalmology