There is no question that one of the landmark studies in all of ophthalmology was the Diabetic Retinopathy Study (DRS), which clearly demonstrated the usefulness of laser treatment in avoiding blindness back in the 1970s.2 (Both the DRS and the ETDRS produced a host of papers; the cited reference is an example.)
As part of this study, proliferative diabetic retinopathy was classified into low-risk and high-risk disease. (Nowadays "low-risk" PDR is called PDR without high-risk characteristics—see Table 1.) Determining whether a patient has high-risk PDR involves adding up various factors to assign the level of disease. For instance, high-risk vessels at the disc had to be at least one-quarter to one-third disc area (Figure 8 is the standard example chosen for this), and NVE was considered to be significant if it was greater than one-half disc area. Table 2 (on the next page) shows a good summary of how all the different factors were added up to assign the overall risk. For those of us not employed as biostatisticians, however, each one of the following is an admittedly less elegant but simpler approximation for how to call high-risk PDR:
1: Any NVD that you can easily see is high-risk PDR.
2: Pre-retinal or vitreous blood in the eye with new vessels anywhere is high-risk PDR. 'Nuff said.
Table 2 / Definition of High Risk PDR
High-risk PDR was defined as any one of following:
• mild neovascularization of the disc (NVD) with vitreous hemorrhage
• moderate to severe NVD with or without vitreous hemorrhage (> or = Standard 10A, showing 1/4 to 1/3 disc area of NVD)
• moderate (1/2 disc area) neovascularization elsewhere (NVE) with vitreous hemorrhage
High-risk PDR was also defined by any combination of three of the four retinopathy risk factors:
• presence of vitreous or preretinal hemorrhage
• presence of new vessels
• location of new vessels on or near the optic disc
• moderate to severe extent of new vessels
(American Academy of Ophthalmology, Basic and Clinical Science Course, Section 12, Retina and Vitreous 2007-2008 page 109.)
Once you decide a patient has high-risk PDR, you are obligated to treat with panretinal photocoagulation. The reason is that patients tend to do rather horribly on their own once they have reached high-risk disease. In the DRS, treatment cut the risk of severe vision loss by about 50% over the course of the study—and that was at a time when diabetics were not as well controlled medically, and the treatment was often hammered in all at once (and was therefore more likely to decrease the vision). It is likely that these days we obtain even better results with staged treatment and more emphasis on better medical care. Figure 12 is the classic graph of the overall results.
Figure 12. Cumulative rates of severe visual loss for the DRS (the protocol was changed in 1976 to allow more treatment of high-risk eyes). This graph, and the heroic work behind its discovery, is truly awesome (in the traditional, non-surfer sense of the word). (The Diabetic Retinopathy Study Research Group, DRS report no. 8, Ophthalmology 1981; 88: 583-600, Copyright Elsevier 1981.)
But deciding to treat definite high-risk proliferative disease is the easy part. The hard part is deciding about treatment in situations that are less black and white...
Although the DRS clearly demonstrated the need for treatment in patients with high-risk disease, no one was sure how aggressive to be in patients with less than high-risk disease. One aspect of the ETDRS looked at this and found a trend suggesting a beneficial treatment effect if patients were given PRPs at any level of nonproliferative diabetic retinopathy (NPDR).3 However, the treatment benefits were very small with earlier levels of NPDR. For instance, there was only a dinky subset of patients with mild or moderate NPDR who seemed to benefit from early treatment. Because PRP has definite risks (which will be discussed at length in the upcoming chapters), it is felt that observation is best for these patients.
When the retinopathy progresses to severe NPDR or PDR without high-risk characteristics, it turns out that the treatment benefit was more pronounced — but still fairly small. As a result, the same conservative approach generally applies: Given the hassle and risk of treatment and relatively small benefit, these patients, especially Type 1 diabetics, may be better off with careful observation rather than laser. There are, however, other factors that may make you decide to treat such patients. Here are some:
1. Severe progressive disease in the fellow eye. Diabetic eyes tend to head down the same path, and the first eye will let you know what the second eye may decide to do.
2. The patient's ability to follow up. This may be a very important factor in developing countries, where logistics and economics may prevent careful sequential evaluations, and where early treatment may give a patient much better odds of remaining a functioning member of society.
3. Poor control and/or lots of medical problems may warrant earlier intervention, since these patients may go downhill faster and/or may miss appointments.
4. A patient who needs to be on Coumadin may need earlier treatment, given the risk of more pronounced bleeding if more advanced prolifera-tive disease is allowed to develop.
5. A very important factor is the rate of change of the patient's disease. A patient who has good control and has smoldered along with mild to moderate NPDR can easily be monitored if they slowly begin to develop severe NPDR or low-risk PDR. On the other hand, a patient who is rapidly going through these stages is at much greater risk for rapid progression to high-risk disease, and should have earlier treatment. (Incidentally, the ability to understand terms like "the rate of change" justifies those calculus classes you took years ago. They were worth it.)
When to Do
6. The type of diabetes also plays a role. A later analysis of the data suggested that patients with Type 2 diabetes, or patients older than 40 years old (which is usually the same thing), are more likely to benefit from scatter photocoagulation when they have severe NPDR or early PDR without high-risk characteristics. This did not seem to be true for patients with Type 1 diabetes who had the same degree of retinopathy. It is not clear why this is the case; perhaps older patients are more likely to get a vitreous hemorrhage once they get neo because their vitreous is more jiggly. Whatever the reason, this does data support consideration of earlier treatment in older patients.4
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Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...