|The compact Optovue iVue offers the same scanning speed and resolution as a larger OCT.|
|The Eidon True Color Confocal Scanner
provides 60Â° field in a single exposure.
|Image of non proliferative diabetic
retinopathy from the Spectralis OCT from
|Topcon’s TRC-50DX Mydriatic retinal camera, and the TRC-NW8F Plus non-myd/mydriatric camera both use Spaide autofluorescence filters.|
Retinal cameras, wide angle viewing, and OCTs help with the detection, diagnosis, and disease management of the leading cause of blindness in people with diabetes.
In the U.S., diabetes has been characterized as prevalent in epidemic proportions. Data from the Centers for Disease Control and Prevention estimate that 37% of U.S. adults have prediabetes and that the prevalence of total diagnosed and undiagnosed diabetes in the U.S. will rise from roughly 10% in 2010 to between 20% and 33% by 2050. These startling statistics point to the growing trend that will likely parallel the penetration of diabetic retinopathy seen by optometrists.
STEREOSCOPIC FUNDUS PHOTOGRAPHY
The landmark study defining the presence and severity of diabetic retinopathy is the Early Treatment Diabetic Retinopathy Study (ETDRS). It set the standard for fundus evaluation using stereoscopic examination of the posterior pole, and more specifically, the diagnosis of macular edema. Sight preservation and improvement are now possible with early identification.
Stereoscopic fundus photography images have been shown to be sufficient for screening for diabetic macular edema. With additional interpretation under red-free light, diagnostic capability is further improved. One example of this technology is the Canon CR-2 AF retinal camera. Photographic documentation for grading diabetic retinopathy now allows not only high resolution but image manipulation using various software applications.
Diabetic macular edema assessment can be complemented by new technologies. These include optical coherence tomography (OCT), fundus autofluorescence (FAF) and widefield imaging.
OPTICAL COHERENCE TOMOGRAPHY
OCT is especially helpful in diagnosing diabetic macular edema and to monitor treatment progress. The resolution of current spectral, or Fourier domain OCT instruments, approaches 3 microns. This capability enables detection of subtle retinal thickening or early accumulation of fluid. In fact, central macular thickening of an average of only 10% (25 microns) has been shown to have excellent sensitivity and specificity for identification.
OCT instruments, such as the Cirrus HD-OCT from Carl Zeiss Meditec, Inc., iVue from Optovue, and the Spectralis OCT from Heidelberg Engineering, are key for decision-making in care and are firmly placed for the detection of diabetic macular edema. Imaging can be accomplished in less than two seconds per eye, and a number of data sets can be collected. These include high-resolution as well as volumetric information. In addition, topographic representation of retinal layers allows quantitation of retinal thickening that can then be monitored for progression or response to treatment. Select manufacturers also offer angiography capabilities.
FAF is an emerging technology with application to both early age-related macular changes and diabetic retinopathy/macular edema. FAF is performed using a confocal scanning laser ophthalmoscope. Lipofuscin deposition occurs from digestion of photoreceptor outer segments. Early in the process these departures from normal are difficult to impossible to observe with standard fundus evaluation. Lipofuscin is the main compound that causes RPE fluorescence that can be imaged with the technology. FAF imaging is obtained with instruments similar to a fundus camera with specialized exciter and barrier filters and accessory software.
Areas of macular edema may exhibit either hyper- or hypo-autofluorescence. In cases of macular edema, the hyper areas are thought to be due to dispersion of normally arranged macular pigment by the accumulation of intraretinal fluid. The degree of change in autofluorescence has been correlated with severity of edema. Therefore FAF is poised to complement standard clinical examination and perhaps show early macular edema amenable to treatment for vision preservation. There are very good fundus autofluoresence cameras available from multiple instrument manufacturers including: Visucam 500 from Carl Zeiss Meditec, Inc. Canon CR-2 Plus AF, Topcon TRC-50DX mydriatic camera with optional Spaide FAF Filters and the Topcon TRC-NW8F Plus combo non-myd/mydriatic camera VX-20 with optional Spaide FAF filters.
One of the derivative outcomes of the ETDRS was the establishment of standard 7-field film photography documentation of the posterior pole. What utility does ultra-widefield imaging have? Does capturing a panoramic view of fundus obtained in a single imaging snapshot give equivalent information for analysis of diabetic retinopathy and allow grading of severity? Comparison studies demonstrated slightly greater level of diabetic retinopathy lesions in the peripheral retina not identified by the standard posterior pole photographs.
For those already using ultra-widefield imaging technology, this represents a valuable addition to current regimens of stereoscopic observation with precorneal lenses and by BIO and stereoscopic fundus photography. Take, for example, the new Daytona ultra-widefield imager from Optos. This instrument is significantly smaller than previous widefield imagers. With this technology, image manipulation allows segmentation of retinal layers as well as the potential for FAF imaging. What’s more, the Daytona, along with the California (also from Optos and shown on the cover), provides more than 80% or 200Â° of the retina in a single capture.
Also of note: The Eidon True Color Confocal Scanner from CenterVue. The scanner provides true color retinal images, with widefield capability in a confocal non-mydriatic scanning instrument.
From our earliest monocular ophthalmoscopic views of diabetic retinopathy to contemporary OCT and laser scanning imaging of the retina, evaluation and characterization of diabetic retinopathy, and more significantly, diabetic macular edema, have come a long way. The future is bright for identifying early and subtle retinal changes that can signal progression of diabetic retinopathy.
Leo Semes OD, FAAO, is a Professor of Optometry at the University of Alabama School of Optometry in Birmingham, AL.
WHERE TO FIND IT:
800.970.7227 | usa.canon.com/eye-care
Carl Zeiss Meditec, Inc.
800.342.9821 | meditec.zeiss.com/usa
408.988.8404 | centervue.com
Heidelberg Engineering, Inc.
800.931.2230 | heidelbergengineering.com
866.OPTOMAP | optos.com
866.344.8948 | optovue.com
Topcon Medical Systems, Inc.
800.223.1130 | topconmedical.com