Diabetic retinopathy is one of the three leading causes of visual impairment and blindness in developed countries , and is the main reason for blindness in the working age population in Germany and other developed countries . It is the most common microvascular complication of diabetes ; almost all patients with type 1 diabetes and over 60% of patients with type 2 diabetes develop retinopathy. The development can be classified into stages; nonproliferative or background retinopathy is characterized by retinal vascular abnormalities including microaneurysms and intraretinal hemorrhages, which at first do not have much effect on vision. Nonproliferative diabetic retinopathy can be classified as mild, moderate, or severe according to the extent of these abnormalities. If retinopathy advances further, it is classified as proliferative diabetic retinopathy, which is characterized by the growth of new blood vessels on the retina or into the vitreous cavity. These vessels are weak and may bleed, causing a sudden deterioration of vision. At any stage of the condition, macular edema can occur. Macular edema is characterized by a thickening of the retina due to leaky blood vessels, and impairs central vision [4,5]. Currently, the main treatments are laser photocoagulation or vitrectomy with efforts to improve glycemic control and blood pressure control. Treatment reduces the risk of progression of the condition and may increase the chance of a small improvement in visual acuity [3,5]. Newer treatment approaches include intraocular injections to inhibit vascular endothelial growth factors (VEGF) .
Evaluation of new treatments requires not only assessment of their impact on visual function, but also assessment of patients' satisfaction with the treatments and the impact of the condition and its treatment on individuals' quality of life (QoL). Individual QoL is different from health status and visual function. In asking about health rather than the eye condition, scores on health status measures such as the SF-12  will be affected by comorbid conditions, while respondents may not even consider their eye condition to be an aspect of their health. Similarly, visual function measures such as the NEI-VFQ  will be influenced by ocular comorbidities. Health status and visual function measures ask about the impact of health or vision on daily activities. They do not take account of the relevance or importance of these activities to the individual. When researching the impact of eye conditions and treatments on QoL, both the impact of being unable to perform specific tasks and the importance of the tasks to the person need to be considered. Although it is reasonable to assume that some aspects of life are universally relevant to QoL, the weights attached to these have been shown to differ between individuals and within the same person over time following increased severity of the condition or onset of complications [8,9]. Some aspects such as work or family life may only be relevant to some people. Individualized measures of QoL such as the measure of Retinopathy-Dependent QoL (RetDQoL) are designed to measure the impact of a condition on aspects of life relevant to the individual; relevant aspects are weighted by the individual's ratings of the importance of these aspects of life to their QoL.
The objectives of the current analyses were to evaluate the psychometric properties and to determine optimal scoring of the individualized RetDQoL and to explore QoL in diabetic retinopathy.