OCT are presented, as well as a discussion of the application of OCT to clinical management of diabetic retinopathy. Finally, additional diagnostic modalities of potential benefit in evaluating DR are presented, including the retinal thickness analyzer (RTA) and scanning laser ophthalmoscopy (SLO). The detection of retinal abnormalities in diabetic patients is vital for preventing the associated complications and subsequent loss of vision. FA and OCT provide information essential to the optimal treatment and management of diabetic retinopathy.

Key Words: Diabetic retinopathy; macular edema, fluorescein angiography; optical coherence tomography; retinal thickness analyzer; scanning laser ophthalmoscopy.

INTRODUCTION

The majority of significant visual loss in patients with diabetic retinopathy (DR) is associated with three conditions: macular edema, macular ischemia, and retinal or optic disc neovascularization. These complications of DR have been diagnosed with funduscopic examination and fluorescein angiography (FA) for over four decades. In recent years, innovative new technologies have been developed to detect DR earlier and more accurately, particularly diabetic macular edema.

Diabetic macular edema is the most common cause of visual loss in diabetic patients, affecting up to one quarter of these patients (1–4). Retinal thickening results from fluid leakage due to breakdown of the blood–retina barrier (5). The gold standard treatment of diabetic macular edema consists of focal laser photocoagulation, which reduces moderate visual loss by 50% (2). However, visual loss persists in a significant proportion of patients after laser treatment as irreversible damage to the retina has occurred. New medical therapies are currently being studied that prevent or reduce the progression of diabetic macular edema. These treatments have necessitated earlier and more quantitative detection of retinal thickening.

Clinically significant macular edema (CSME), as defined in the Early Treatment Diabetic Retinopathy Study (ETDRS), is a clinical diagnosis made at the slit lamp with stereoscopic biomicroscopy (2). Although it is convenient and readily available, this technique is subjective and insensitive to small changes in retinal thickness, making early detection and follow-up for subtle changes after therapy difficult (6, 7). Furthermore, slit lamp biomicroscopy does not quantify the severity or extent of foveal thickening, the retinal layers involved, or allow the physician to visualize ischemia. Similarly, stereo fundus photography is limited by the amount of stereopsis and by the threshold for thickening adopted by individual observers (8, 9). Although stereo fundus photography has been used to follow for changes after treatment, its current use in clinical trials is greatly diminished.

Fluorescein angiography has been used for over 40 years in the evaluation of chorioretinal diseases. It is a dynamic modality that enables the ophthalmologist to assess both the anatomy and function of the retinal and choroidal vasculature. However, FA does not provide ultrastructural anatomic detail, and does not allow quantification of retinal thickness. Due to these limitations, several novel imaging techniques have been developed. The most sensitive, reproducible, and widely used modality has been optical coherence tomography (OCT).