 Diabetic retinopathy is the leading cause of blindness among adults worldwide. One key to managing this condition is predicting which patients are most likely to require treatment. Photographs of the retina can be adopted for this purpose. However, the correlation between structural features of the retina and the probability of receiving intervention for diabetic retinopathy is not always reliable. For example, the ETDRS trial reported that patients with high-risk diabetic retinopathy have only a 16% probability of having severe vision loss in the next five years. This study demonstrates a powerful way for clinicians to better predict which patients may need treatment by using the red eval device. Unlike fundus photography, which assesses structural features, the red eval device measures the function of the retina in two distinct ways. One is through an electroretinogram, or ERG, which measures the functional status of the rods and cones, much like an electrocardiogram, and the other is the pupillary response. The red eval device combines these responses into a single number called the DR score. To understand how well photography and the DR score predicted the need for intervention, alone or in combination, clinicians examined the medical records of 279 patients with varying levels of diabetic retinopathy over three years. For fundus photography, patients were considered at-risk if they showed signs of severe proliferative or non-proliferative diabetic retinopathy, or if they had clinically significant macular edema as seen in fundus imaging. For the red eval device, patients were considered at-risk if they registered a DR score of 23.5 or higher. Findings showed that after two years, 22% of patients needed an intervention when showing signs of proliferative or non-proliferative diabetic retinopathy, while 35% of patients who had a score of 23.5 or higher on the red eval device received an intervention. Thus, the red eval score showed a 60% improvement in assessing the risk of intervention, not only versus those with a lower score, but also versus those who showed signs of diabetic retinopathy using the fundus photography criterion. This higher predictability of the red eval test persisted at three years. In fact, the red eval DR score was found to indicate the highest risk of requiring ocular intervention in this study. Patients scoring 23.5 or higher were 11 times more likely to have a future ocular intervention than patients scoring below 23.5, compared to a 3.5 fold increase using the fundus photograph retinopathy severity criterion. When both the red eval and the fundus criteria were positive, the risk was determinant. In fact, 70% of patients required an intervention within three years when both tests were positive. Conversely, if the photographic results were positive, but the red eval results were negative, the intervention rate was only 18%. But if both tests were negative, the rate was 6%. Overall, the results demonstrate that incorporating ERG and fundus imaging would improve clinicians' ability to predict which patients will likely need an intervention and which will not, well beyond what is currently possible with fundus photography alone. Patients with a high DR score are much more likely to require an intervention, even if photography indicates that they have normal structural features. The red eval test is quick, comfortable for the patient, and easy to perform, providing simple numerical results that can be useful in managing diabetic retinopathy. Alone or in combination with observation of retinal structure, the red eval device will allow you to make better management decisions and improve programs designed to manage visual health in patients with diabetes.