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Pictures Worth A Thousand Words

By Dr. A. Paul Chous

If you asked a group of eye doctors, “What is the single most significant advancement in the diagnosis and treatment of retinal disease in the last 50 years?” odds are the majority of them would say ‘fluorescein angiography’ (pronounced ‘floor-eh-seen angie-ah-graffy,’ or ‘FA’ for short), a test with which many of us with diabetes are familiar.

FA involves injecting a fluorescent dye into a vein of the hand or arm, waiting about ten seconds for that dye to travel through the circulatory system into the retina at the back, inside surface of the eye, and then photographing the blood vessels within and below the retina with a specialized filter that ‘excites’ the dye (makes it glow). This technique allows eye specialists to visualize retinal circulation, identify areas where the dye does not flow (indicating poor circulation) or leaks (corresponding to damaged or abnormal blood vessels), as happens in diabetic retinopathy, and monitor the effectiveness of various treatments (see figures below).

                  
      Normal FA                                   Abnormal FA showing
                                                         absence of dye

                      
                       Abnormal FA showing
                       dye leakage due to diabetes

Because a series of precisely timed photographs are taken during the procedure, FA is very helpful in allowing eye doctors to track dynamically the flow of blood through the back of the eye, and because many retinal diseases have very characteristic patterns of blood flow and leakage, FA often makes or confirms the clinical diagnosis, particularly in cases where that diagnosis is uncertain.

In addition to FA, two other imaging technologies have also helped revolutionize the detection, diagnosis and management of retinal diseases, including several eye diseases that disproportionately affect patients with diabetes: digital retinal imaging (DRI) and optical coherence tomography (OCT). DRI utilizes medical quality digital optical sensors, akin to those used in commercially available digital cameras, in tandem with other optical components to instantaneously image the retina. Images can subsequently be manipulated (magnified, filtered, viewed in 3-D, montaged) to meticulously study areas of interest, assess change over time and the effectiveness of treatment. Although DRI does not reveal details that cannot be appreciated by traditional, diligent examination techniques, it allows the examiner to study those details without subjecting patients to bright examination lights for long periods of time. This said, it is interesting to note that one study found that a single black and white digital retinal image was more accurate at detecting the earliest stages of diabetic retinopathy than examination by ophthalmologists.

                      
        Normal Retina                                    Diabetic Retinopathy

OCT is another non-invasive imaging technology that uses a scanning infrared light to create two and three-dimensional optical cross-sections of the retina, yielding an ‘optical biopsy’ that gives examiners a detailed view of retinal anatomy and allowing for definitive diagnosis of some retinal disease that could not be made otherwise (see images below). With a spatial resolution of as low as 6 microns (6/1000 of a millimeter or two ten-thousandths of an inch), OCT can reliably and consistently detect miniscule changes in retinal thickness as happens, for example, when patients develop diabetic macular edema. Though expensive, experts predict that this technology will become routinely available for early diagnosis, differential diagnosis, and more sensitive monitoring of a variety of ocular abnormalities, including glaucoma, retinal and anterior eye diseases. Within a few years, even better resolution will be possible, and OCT systems will likely be integrated with FA and DRI in one convenient package.


                     
                        OCT image of a normal retina
                        showing various anatomic layers


                    
                      OCT image of diabetic macular edema
               (DME) showing thickening and dis-ruption of retinal layers

For more information on diabetic eye disease, consult Dr. Chous’ book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.

Read more about Dr. Chous here.

Visit Dr. Chous' website here.