Hyperspectral Computed Tomographic Imaging Spectroscopy of Vascular Oxygen Gradients in the Rabbit Retina In Vivo

Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10–15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology

Diabetic retinopathy: current and future methods for early screening from a retinal hemodynamic and geometric approach

Diabetic retinopathy (DR) is a major disease and is the number one cause of blindness in the UK. In England alone, 4200 new cases appear every year and 1280 lead to blindness. DR is a result of diabetes mellitus, which affects the retina of the eye and specifically the vessel structure. Elevated levels of glucose cause a malfunction in the cell structure, which affects the vessel wall and, in severe conditions, leads to their breakage. Much research has been carried out on detecting the different stages of DR but not enough versatile research has been carried out on the detection of early DR before the appearance of any lesions. In this review, the authors approach the topic from the functional side of the human eye and how hemodynamic factors that are impaired by diabetes affect the vascular structur

Reversal of blood flow in experimental branch retinal vein occlusion

To demonstrate that the obstructed vascular lumen of the experimentally induced branch retinal vein occlusion (BRVO) induces retrograde blood flow, resulting in flow from the occluded vein to the feeder arterioles. Photocoagulation was used to create occlusion of the branch retinal vein in a monkey model (n = 2; 1 cynomolgus, 1 rhesus). Twenty-four hours following photocoagulation, the eyes were examined for evidence of vascular occlusive disease. Vascular occlusion was proven by fluorescent vesicle angiography with scanning laser ophthalmoscopy; these results were recorded to SVHS videotape. The images were then serially analyzed frame by frame to track individual microsphere movement. The authors observed retrograde flow proximal to the point of vessel obstruction and extending backward into the arterial system. This demonstrates the existence of retrograde flow in an experimental model of BRVO and might explain vascular complications seen in this disease process

Ocular vascular thrombosis following tin ethyl etiopurpurin (SnET2) photodynamic therapy: time dependencies

To evaluate the optimal time from the end of photosensitizer injection to the commencement of light application for creating characteristic fundus lesions and the time to vascular occlusion following photodynamic therapy (PDT) with tin ethyl etiopurpurin (SnET2). Following intravenous injection of SnET2 0.5 mg/kg or lipid emulsion alone, the fundus of rabbits was irradiated at different times (5 to 240 minutes) after photosensitizer injection using 664 +/- 7-nm laser light with an irradiance of 354 mW/cm2 and fluence of 20 J/cm2. Ophthalmoscopy and fluorescein angiography were performed 1 day after SnET2 PDT. In separate groups of rabbits, treated areas of the fundus were imaged within 30 minutes following PDT using fluorescein vesicle and microsphere angiography with scanning laser ophthalmoscopy to document time of vascular occlusion. All animals were killed 1 day following treatment and eyes were examined by histopathology. Areas of hypofluorescence (indicating vascular occlusion) were seen when activating laser light was applied 5 to 20 minutes after SnET2 injection. Retinal vessels remained perfused in all cases. The time to vascular occlusion was 70 to 120 and 40 to 90 minutes in nonpigmented and pigmented rabbits, respectively. No safety issues were seen. PDT with SnET2 was effective in occluding the choriocapillaris. Activating light needs to be applied within a specific time frame after photosensitizer injection to achieve vascular occlusion