| BackgroundThe human retina and choroid,comprised approximately a dozen layers of tissue packed together such as neurons,supporting cells and capillaries,are important ocular structures of the posterior segment.Retinal and choroidal pathologies are known to have significant role in various visual impairment and blindness,such as glaucoma,age-related macular degeneration(AMD),macular edema,diabetic retinopathy and others.Given the irreversible character of these illnesses,understanding more about the structural and functional subunits of retina and choroid has long since been a topic of interest.Qualitative and quantitative analyses of these laminar structures are essential,not only for understanding the pathophysiology of choroidopathy and retinopathy,but more importantly to assess the efficacy of preventative therapies and new treatments.In parallel,sharing similar anatomical features and physiological properties,the retinal vessels offer a unique site for studying the overall microvasculature in vivo.Histopathologic studies have suggested that retinal vascular signs are closely related to pathological microvascular changes in other organs.What's more,changes to the retina can occur in some chronic diseases years before other signs become apparent.Detailed assessment of morphological characteristics and microvasculature changes of retina is critical in the diagnosis and management of not only ocular but also systemic diseases.Since retina can be visualized directly and monitored repeatedly using optical techniques,there have been various studies to exploit image processing and analysis devices to evaluate morphometric variations in the macular layers and microvasculature.Among these methods,fundus camera imaging and ultrasonography have been used in the diagnosis and serial monitoring of retinal diseases noninvasively;techniques include fluorescein and/Indocyanine green angiography can give useful information about the ocular circulation.Numerous data from substantial,epidemiological and clinical studies have documented the macular manifestations related to ocular diseases.Moreover,several prospective,population-based cohort studies have convincingly shown links between characteristic fundus features,such as retinal arteriolar narrowing,retinal arteriolar macroaneurysm formation and changes of retinal vascular geometric parameters,may be linked to the incidence and development of hypertension.Furthermore,it has been long recognized that mild retinopathy signs were correlate with increased risk of cardiovascular disease(CVD)mortality,independent of traditional cardiovascular risk factors.However,traditional investigations such as fundus photography,fluorescein angiography and ultrasonography had limited utility as tools to display the retinal anatomy in sufficient detail,because they can only provide qualitative and prospective information.Optical coherence tomography(OCT)is an exciting imaging modality revolutionizing both basic retina research and clinical practice.The introduction of OCT has made it possible to produce cross-sectional images of the living human retina quantitatively and noninvasively with high resolution.Because OCT is easy to use,lacks ionizing radiation,ensures patient comfort,and is economical,it has been used extensively to evaluate and manage a variety of ocular disease.Spectral domain-OCT(SD-OCT)is an advanced modification of original time-domain OCT that provides higher spatial resolution,increased density of three-dimensional(3D)scans,better reproducibility for image acquisition,and more excellent visualization of the architectural morphology of the internal retinal layers,including those of the photoreceptor layer.In addition,a functional extension of OCT technology known as OCT angiography(OCTA)has evolved within the past decade.The development of OCTA offers the possibility of acquiring depth-resolved images of the microcirculation in different retinal layers and choroid as well as the radial peripapillary capillary network that has never been available before.Moreover,OCTA data simultaneously displays en face structural OCT images and co-registered microvasculature within the eye.With the creation of novel OCT-based methods,OCTA gradually become the dominant modality for diagnosis,assessing progression and treatment response of diseases,especially as it pertains to microvascular dysfunction.In conclusion,with more detailed quantitative and qualitative assessment of retinal and choroidal tissue structure,SD-OCT and OCTA can provide powerful insight into the precise morphologic and subtle microvascular changes associated with risk stratification and disease progression of ocular as well as systemic conditions.Research Purpose1.To assess the effect of age on the thickness of individual macular retinal layers of the Early Treatment Diabetic Retinopathy Study(ETDRS)area and subfoveal choroidal vascular layers in ophthalmologically healthy Chinese subjects using SD-OCT.2.To quantify early changes of macular microvascular density,skeleton density,vessel diameter,branching complexity,foveal avascular area and peripapillary vessel caliber in systemic hypertension(HTN)without retinopathy using OCTA.Materials and Method1.In this prospective observational study,525 ophthalmologically healthy Chinese subjects aged between 20 and 87 years old were included.One eye was randomly selected for each patient.Macular thickness profiles of RT and eight individual retinal layers in the standard ETDRS grid were automatically segmented and measured using SD-OCT Subfoveal choroidal vascular layers' thickness was measured using enhanced depth imaging mode.Each enhanced depth imaging SD-OCT image was analyzed to determine the choroidal thickness,large choroidal vessel layer thickness,and medium choroidal vessel layer thickness.The correlation of layer thickness with age was accessed.2.This prospective observational study involved HTN(137 eyes,77 individuals)and healthy eyes(79 eyes,43 individuals)as control to assess retinal microvascular changes in segmented OCTA images.Indices of the microcirculation included mean vessel density(VD),skeleton density(SD),vessel diameter index(VDI),fractal dimension(FD)and foveal avascular zone(FAZ)of superficial retinal layer(SRL)and deep retinal layer(DRL),and peripapillary vessel caliber.The correlation of these indices with mean arterial pressure(MAP)and ocular perfusion pressure(OPP)was analyzed.Research results1.No age-associated variation was found on retinal thickness(RT)in the fovea;however,the foveal thickness of outer nuclear layer(ONL),retinal pigment epithelium(RPE)and vascular sublayers of the choroid decreased significantly with aging in this area(P<0.05,respectively).Significant age-related reduction was seen in RT in the pericentral and peripheral rings(P<0.05,respectively).The significant variation in thinning of the ganglion cell layer,inner plexiform layer,and ONL with aging is thought to be the main determinant of these results(P<0.05,respectively).On the contrary,the RPE layout showed age-related thickening(P<0.05,respectively)in the pericentral and peripheral regions.2.HTN eyes have decreasing macular capillary density,branching complexity,and narrowing peripapillary vascular caliber compared with control eyes.Mean VD of DRL,SD of SRL and DRL,FD of SRL and DRL was significantly reduced in the macula of HTN eyes(all P<0.01).Meanwhile,HTN eyes had margin results of narrower peripapillary arteries(P = 0.04).No significant findings were demonstrated on VD of SRL,VDI and FAZ of SRL and DRL,peripapillary total vascular caliber and peripapillary venal caliber(all P>0.05).SD and VD of the DRL correlated negatively with MAP(both R =-0.152,p=0.03).Conclusions1.The thickness of individual layers of the macular may be determinants of the age-related variations observed in the ophthalmologically healthy Chinese cohort,as assessed by SD-OCT examination.2.Vascular changes in HTN eyes can be objectively and reliably characterized with vascular metrics by OCTA.OCTA algorithms may provide an additional inexpensive tool to aid in the preclinical assessment of HTN subjects. |
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