视网膜血氧饱和度检测仪在眼部应用的研究进展

视网膜血氧饱和度检查是一种快速、无创的新型视网膜血管成像技术,可测量视网膜主要动脉及静脉的血氧饱和度并进行量化分析,可应用于视网膜动脉阻塞、视网膜静脉阻塞、糖尿病视网膜病变、老年性黄斑变性及青光眼等许多眼科疾病的诊断及随访,可有助于加深疾病的病因及发病机制的理解,并应用于疾病病情的评估及预后分析,是现有影像检查设备的重要补充.     

Dual wavelength retinal vessel oximetry – influence of fundus pigmentation

BackgroundClinical methods examining oxygenation parameters in humans have been used in many different care settings, but concerns have been raised regarding their clinical utility when assessing people with darker skin pigmentation. While saturation values can be crucial in emergency medicine, they are equally valuable in assessing disease mechanisms and monitoring change in disease progression. Retinal pigmentation varies across individuals and hence, can impact on retinal oxygen parameters. The objective of this study was to quantify and eliminate the impact of retinal pigmentation on retinal vessel oxygen saturation parameters measured in the superficial retinal arterioles and venules.Methods105 healthy individuals of varying skin colour, iris colour and heritage were included. Following a full eye exam to exclude any ocular abnormality, all participants underwent intraocular pressure, systemic blood pressure measurements and dilated dual wavelength retinal photography. Rotation matrices were employed to minimise the dependency of retinal pigmentation on arterial and venous oxygen saturation measurements determined in a concentric measurement annulus.ResultsRetinal oxygen saturation in venules showed a linear correlation with retinal pigmentation (y = 0.34 × x + 38.598), whereas arterial saturation followed a polynomial pattern (y = 0.0089 × x² + 0.7499 × x + 85.073). Both arterial and venous saturation values were corrected using local fundus pigmentation. Pre-correction retinal arterial and venous oxygen saturation were 89.0% (±13.1) and 43.7% (±11.5), respectively, and post- correction values were 94.8% (±8.7) for arteries and 56.3% (±7.0) veins.ConclusionsWhen assessing multi-ethnic cohorts, it is important to consider the impact of pigmentation on imaging parameters and to account for it prior to clinical interpretation.Subject terms: Prognostic markers, Prognostic markers     

Optical coherence tomography 3: Automatic delineation of the outer neural retinal boundary and its influence on retinal thickness measurements

PURPOSE: To investigate the automatic delineation of the outer limits of the macular neural retina, by using the optical coherence tomography (OCT)-3 built-in software, and to determine its influence in assessing retinal thickness in the normal macula. METHODS: Retrospective analysis of the OCT3 data at a tertiary-care referral center was performed to study the automatic delineation of the outer neural retina boundary generated by the OCT built-in software. In parallel, a cross-sectional study was designed to compare retinal thickness measurements obtained at specific macular regions of nine normal eyes by the automatic measurement tool with those obtained using a manual-caliper-assisted technique. RESULTS: OCT data from 121 eyes were evaluated. Two parallel, linear highly reflective layers (HRL) were visible at the level of the outer retinal boundary in normal macular regions. Disappearance of the inner and maintenance of the outer HRL was noted in the presence of eye conditions affecting the external retinal layers. The automated software delineation for the outer retinal border was primarily guided by the presence of the inner HRL, whereas the correlation of the OCT findings with the expected clinical and angiographic features on eyes presenting specific macular conditions pointed toward a deeper retinal pigment epithelium-retina interface occurring at the level of the outer HRL. There was a statistically significant difference between the retinal thickness in specific normal macular regions obtained by the automatic measurement tool and the caliper-assisted technique in which the outer retinal border delineation was based on the outer HRL (P = 0.008, Wilcoxon signed rank test). CONCLUSIONS: Incorrect delineation of the outer neural retina boundary is occurring with the automated retinal thickness measurement tool of the OCT3 software. At specific regions of the normal macula, retinal thicknesses were significantly underestimated due to such misalignment.     

Retinal oximetry using intravitreal illumination

PURPOSE: To demonstrate spectroscopic retinal oximetry measurements on arteries and veins in swine using intravitreal illumination. Retinal arterial and venous saturations are measured for a range of inspired O2 levels after pars plana vitrectomy. METHODS: Pars plana vitrectomy and intravitreal manipulations were performed on two female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiberoptic intraocular illuminator inserted into the vitreous. The retinal vessels were illuminated obliquely, minimizing vessel glints. Multispectral images of the retinal vasculature were obtained as the swine's arterial blood oxygen saturation was decreased from 100% to 67% in decrements of approximately 10%. Retinal vessel spectra were used to calculate oxygen saturation in selected arteries and veins. Arterial oxygen saturations were calibrated using blood gas analysis on blood drawn from a Swan-Ganz catheter placed in the femoral artery. RESULTS: Oblique illumination of retinal vessels using an intravitreal fiberoptic illuminator provided a substantial reduction in the central vessel glint usually seen in fundus images, thus simplifying the analysis of spectral data. The vessel shadows were displaced from the vessel image simplifying the light paths in the eye. Using a full spectral analysis simplified by the light path reductions, we calculated retinal vessel saturations. The reduction of glint allowed for increased accuracy in measuring retinal vessel spectral optical density. Abnormally low retinal venous oxygen saturations were observed shortly after pars plana vitrectomy. CONCLUSIONS: Retinal oximetry using intravitreal illumination has been demonstrated. As a research tool, intravitreal illumination addresses several difficulties encountered when performing retinal oximetry with transcorneal illumination.     

Hemoglobin oxygen saturation (So2) in the human ocular fundus measured by reflectance oximetry: preliminary data in retinal veins

BACKGROUND: Development of a reflectance oximeter to measure non-invasively the changes in oxygen saturation (SO 2 ) in the vessels of the human eye fundus, with the goal of obtaining a better understanding of the retinal circulation in health and disease. MATERIAL AND METHODS: For retinal oximetry, an instrument must image the retina at multiple wavelengths (lambda) and measure the apparent optical density (OD lambda ) of retinal vessels. The new IRO oximeter acquires two-dimensional images of the retina at four different wavelengths simultaneously. The hemoglobin oxygen saturation is calculated using the spectral images at 569 nm (not sensitive to the oxygenation status of hemoglobin) and at 600 nm (sensitive to the oxygenation status). RESULTS: To test the method, two subjects were asked to breathe first room air and then pure oxygen. During hyperoxia (100 % O 2 breathing), the apparent optical density ratio (OD 600 /OD 569 ) decreases significantly, and consequently, the SO 2 in the veins increases. CONCLUSIONS: The optical density ratio method could be used for relative oxygen saturation measurements, for example, for determining the variation of the SO 2 under various physiological conditions, before and after an intervention or for monitoring retinal diseases such as diabetic retinopathy.     

Retinal oximetry in primary open-angle glaucoma

PURPOSE. To determine whether retinal vessel oxygen saturation is affected in primary open-angle glaucoma (POAG) patients. METHODS. Retinal oxygen saturation in patients with POAG was measured in retinal vessels with a spectrophotometric retinal oximeter in darkness, and visual fields were obtained. Oxygen tension (Po(2)) was calculated from oxygen saturation values. Statistical analysis was performed using Pearson's correlation and Student's t-test. RESULTS. Mean oxygen saturation in venules was higher in persons with poor visual fields (68% ± 4%, mean ± SD) than in those with good visual fields (62% ± 3%; P = 0.0018). The mean arteriovenous difference in oxygen saturation was lower in persons with poor visual fields (30% ± 4%, n = 9) than in those with good visual fields (37% ± 4%; P = 0.0003; n = 12). No correlation was found between saturation in retinal arterioles and visual field mean defect (n = 31; r = -0.16; P = 0.38). Oxygen saturation in retinal venules correlated positively with worsening visual field mean defect (r = 0.43; P = 0.015). Arteriovenous difference in oxygen saturation decreased significantly as the visual field mean defect worsened (r = -0.55; P = 0.0013). Mean Po(2) in venules was 38 ± 3 mm Hg. It was significantly higher in persons with poor visual field fields (40 ± 3 mm Hg) than in those with good visual fields (36 ± 2 mm Hg; P = 0.0016). CONCLUSIONS. Deeper glaucomatous visual field defects are associated with increased oxygen saturation in venules and decreased arteriovenous difference in retinal oxygen saturation. The data suggest that oxygen metabolism is affected in the glaucomatous retina, possibly related to tissue atrophy.     

Qualitative fundus oximetry in the albino rabbit's eye

The principle of fundus oximetry, as used by Broadfoot, Gloster and Greaves (1961), has been modified and elaborated, using two monochromatic light bundles, one with minimal, the other with maximal difference in the extinction coefficient for Hb and HbO₂, a high chopping frequency, fibre optics and a Lovac contact lens. Anaesthetized albino rabbits were used with the light entering the dilated pupil. The returning light can be divided into a non-variable part, originating from various planes of transition, and a part that behaves as if passed through a blood film of twice the vascular laye thickness. Using differential recording—the difference made zero at the beginning of the experiment—a higher sensitivity of the system may be employed than in the case of direct recording of the intensity of the returning light. Changes in oxygenation gave reproducible qualitative measurements of the oxygen saturation of the blood in the vascular layer.     

Ultrawide-angle retinal imaging and retinal detachment

PURPOSE: To illustrate the utility of ultrawide-angle fundus imaging in documenting the clinical course of a retinal detachment. DESIGN: Observational case report. METHOD: A 20-year-old man with high myopia and a blind fellow eye noted symptoms of retinal detachment and was imaged with an ultrawide-angle fundus imaging device (Optos P200). Imaging was performed after scleral buckling and before and after additional vitreoretinal surgery. RESULTS: Ultrawide-angle images were useful in delineating the extent of retinal detachment even in the presence of intraocular gas. CONCLUSION: The ability to rapidly image the ocular fundus well anterior to the equator facilitates clinical management and may prove particularly useful in electronic record keeping.     

Avulsed retinal veins without retinal breaks

A localized segment of a retinal vein can be avulsed or torn from the retina by vitreous traction without a concurrent retinal break or tear. Eight eyes in eight patients (five women and three men, 20 to 69 years old) with avulsed retinal veins without retinal breaks showed a wide range of underlying retinal abnormalities, including background diabetic retinopathy, pars planitis, and involutional proliferative retinopathies. Such avulsed retinal veins often cause recurrent vitreous hemorrhage. Despite vitreous hemorrhages in six of the eight eyes, the visual prognoses were excellent in all eyes. An avulsed retinal vein must be considered in the differential diagnosis of those patients with proliferative retinopathies who have vitreous hemorrhage.     

Rhegmatogenous retinal detachment with retinal telangiectasia

A 34-year-old man with unilateral retinal telangiectasia developed a bullous retinal detachment. A horseshoe retinal tear was found at 12 o'clock. The detachment resolved with placement of an encircling scleral buckle. The prompt and permanent resolution of subretinal fluid supported our belief that this was a rhegmatogenous retinal detachment.