Diabetes PRP and OCT

Diabetic retinopathy (DR) refers to changes in the blood vessels of the retina associated with long-term diabetes mellitus. These changes can be found in patients both with Type I and II diabetes. DR is a leading cause of blindness in the United States. It is categorized as either non-proliferative (NPDR) or proliferative (PDR). In the PDR progress, the lack of oxygen in the retina causes fragile, new blood vessels to grow along the retina and in the clear, gel-like vitreous humour. Without timely treatment, the new vessels can bleed, cloud vision, and destroy the retina. So, the PDR is classified as either the existence of retinal neovascularization or vitreous or pre-retinal hemorrhage. PDR is typically treated with a laser, known as panretinal photocoagulation (PRP), which will create 1,600-2,000 burns in the retina to reduce the retinal oxygen demand, and then reduce the possibility of ischemia, or with an injection of an anti-vascular endothelial growth factor (anti-VEGF) drug into the vitreous, which always needs multiple injections. In cases of severe bleeding, a vitrectomy may be performed under local anesthesia. However, an eye patch and medicated eye drops are always needed after the operation to protect against infection and the outcomes are not always as good as expected.

PDR is currently diagnosed by a comprehensive eye exam including a visual acuity test, ophthalmoscopy or fundus photography, fluorescein angiography (FA) and optical coherence tomography (OCT). If the PDR is thought to require treatment, the subsequent assessment of disease severity and treatment planning utilizes FA. FA requires the injection of sodium fluorescein into the systemic circulation. However, 1 in 3 people have adverse reactions to sodium fluorescein, which can include nausea, vomiting, hives, and acute hypotension. Severe reactions such as anaphylaxis and related anaphylactoid reactions, causing cardiac arrest and sudden death due to anaphylactic shock, have also been reported. Finally, because the risks of sodium fluorescein to a developing fetus are unknown, its use in pregnant women is contraindicated. Replacing FA with a less invasive and better tolerated method would reduce the risk in the patient population. One option is OCT angiography.

Optical coherence tomography is an imaging technology that can perform non-contact cross-sectional imaging of tissue structure in real time. It has a number of features that make it attractive as a diagnostic imaging modality: 1) It has micron-level resolution, which is not possible with any other non-contact technique; 2) No potentially allergenic dyes or contrast agents are required; 3) OCT images are generated in electronic form, which facilitates the use of digital image processing techniques to extract quantitative parameters regarding the imaged tissue anatomy. For these reasons, structural OCT is already routinely used to assess the early stage of DR (NPDR) by imaging the areas of macular edema and response to treatment. Novel functional OCT including Doppler OCT and OCT angiography may allow an assessment of retinal blood flow and alleviate the need for the more invasive FA test. Thus, if the diagnostic data provided by functional OCT are at least equivalent or superior to those achieved by FA, patients and healthcare providers could realize a substantial benefit in utilizing this technology in the management of PDR and the evaluation of PRP.

Therefore, we propose a pilot study to evaluate the feasibility of Doppler OCT to measure total retinal blood flow to assess global retinal ischemia after PRP treatment and OCT angiography of the retina to assess proliferative changes in the management of PDR subjects in comparison to standard FA. Functional OCT data (Doppler OCT and OCT angiography) are acquired using the Swept Source-OCT (SS-OCT) with a depth resolution of 5 microns and an ultrafast scan rate of 100 kHz which allows us to obtain detailed 3D OCT images. OCT angiography performs noninvasive microcirculation measurement and visualization which are not options on commercially available OCT systems. Though not FDA-approved, the SS-OCT prototype satisfies the American national standards for laser safety (ANSI) safety requirement. The power level is low enough to be classified as a non-significant risk device.