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Myopia is the most common type of refractive error. At present, the characteristics of the low age and rapid growth of myopia in our country are obvious, and the myopia of adolescents and children has become a public health problem of concern to the whole society. Visual experience guides the development of children's refractive state and emmetropization. The occurrence and development of myopia is accompanied by changes in the structure of the eyeball, and the choroid has a thinning trend. The thickness change of the choroid may be determined by blood flow perfusion. Decreased choroidal blood flow perfusion may lead to scleral ischemia and hypoxia, and hypoxia induces scleral matrix remodeling and axial length growth. This article reviews the relationship between choroidal blood flow and myopia, and suggests the significance of paying attention to choroidal changes in the prevention and control of myopia.
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Myopia is the most common ametropia. High myopia, especially pathological high myopia, is often accompanied by a series of fundus pathological changes, such as Fuchs spot and choroidal neovascularization(CNV), etc, which can lead to serious damage of visual function. In recent years, it has been found that the changes of choroidal thickness and blood flow play a considerable role in the progression of high myopia. The change of choroidal thickness can directly reflect the abnormality of its structure and function. The choroidal thickness in high myopia is significantly thinner than that in normal people, and the thinning degree varies in different regions. At the same time, the choroid is the main source of blood supply to the eyes, and its blood flow directly determines whether the blood supply is sufficient to the eyes. Therefore, observing the changes of choroidal thickness and blood flow in high myopia is of great significance to explore the progress of myopia or observe its pathological changes. This review illustrates the choroidal structure, thickness and choroidal blood flow changes of high myopia. At the same time, it analyzes and discusses the new research progress and main existing problems in recent years, the new challenges and future research directions, hoping to provide help for clinical monitoring of the occurrence and progression in high myopia.
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@#AIM:To observe the changes of the vessel density of choriocapillaris in lens-induced myopia in guinea pigs, and to explore choroidal endothelin-1(ET-1), endothelin receptor A(ETAR)and receptor B(ETBR)expression changes and the effect of electroacupuncture. <p>METHODS: Fifty-four guinea pigs were randomly divided into normal control(NC), lens-induced myopia(LIM)and LIM+electroacupuncture(LIM+EA). The NC group was fed normally without intervention and the right eye in LIM group and LIM+EA group was coverd with a -6.00D lens to establish a myopia model. At 2 and 4wk, the refraction, axial length and the vessel density of choriocapillaris in groups were measured. The expression and protein content of ET-1, ETAR and ETBR mRNA in groups were detected by the real-time fluorescent quantitative PCR(quantitative polymerase chain reaction, q-PCR), enzyme-linked immunosorbent assay(ELISA)and immunohistochemistry. <p>RESULTS: At 2 and 4wk, compared with the the NC group, refraction and axial length in LIM group and LIM+EA group had significantly increased(all <i>P</i><0.001). Compared with the LIM group, the refraction and axial length in LIM+EA group were decreased(all <i>P</i><0.05). At 2 and 4wk, compared with the NC group,the vessel density of choriocapillaris was decreased(<i>P</i><0.001)and the ET-1, ETAR and ETBR mRNA and protein levels in choroid were increased(all <i>P</i><0.05)in LIM group. At 2 and 4wk, compared with the LIM group,the vessel density of choriocapillaris was decreased(<i>P</i><0.01)and the ET-1, ETAR and ETBR mRNA and protein levels in choroid were increased in LIM+EA group.<p>CONCLUSION:In LIM guinea pigs, the choroidal blood flow decreased with the increased of refraction and axial length, which may affect ET-1 and its receptors through vascular shear force during the development of myopia. At the same time, electroacupuncture can improve choroidal blood flow through neuromodulation and affects the vascular shear stress to down-regulate the content of ET-1 and its receptor to delay the development of myopia.
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PURPOSE: To evaluate choroidal blood flow changes in eyes with high myopia according to the pulsatile components of ocular blood flow analysis. METHODS: A total of 104 subjects (52 males and 52 females) were included in this study. One eye of each participant was randomly selected and assigned to one of four refractive groups, designated as, hyperopes (n = 20; refractive error, > or =+1.00 diopter [D]), emmetropes (n = 28; refractive error, +/-0.75 D), lower myopes (n = 33; refractive error, -1.00 to -4.75 D), and high myopes (n = 23; refractive error, < or =-5.00 D). Components of pulse amplitude (OBFa), pulse volume (OBFv), pulse rate (OBFr), and pulsatile ocular blood flow (POBF) were analyzed using a blood flow analyzer. Intraocular pressure and axial length were measured. RESULTS: Pulsatile components of OBFa, OBFv, and POBF showed positive correlations with refractive error and showed negative correlations with axial length (r = 0.729, r = 0.772, r = 0.781, respectively, all p < 0.001; r = -0.727, r = -0.762, r = -0.771, respectively, all p < 0.001). The correlations of refractive error and axial length with OBFr were irrelevant (r = -0.157, p = 0.113; r = 0.123, p = 0.213). High myopes showed significantly lower OBFa, OBFv, and POBF than the other groups (all p < 0.001). CONCLUSIONS: Axial length changes in high myopes potentially influence choroidal blood flow, assuming the changes are caused by narrowing of the choroidal vessel diameter and increasing rigidity of the choroidal vessel wall. These finding explains the influence of axial length on OBFa, OBFv, and POBF, but not on OBFr. Thus, changes in axial length and the possible influence of these changes on the physical properties of choroidal vessels is the mechanism believed to be responsible for putting high myopes at risk for ocular vascular diseases.
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Adult , Female , Humans , Male , Young Adult , Axial Length, Eye , Choroid/blood supply , Myopia/diagnosis , Regional Blood Flow/physiologyABSTRACT
AIM: To study the effects of Tetramethylpyrazine (TMP) on retinal pigment epithelium (RPE) degeneration, choroidal blood flow and oxidative stress of RPE cells.METHODS: The 35mg/kg NaIO3-induced RPE degeneration rat eyes was given 25μg 1% TMP eye drops 3 times a day for 7 days before NaIO3 injection, and then 2 to 4 weeks after NaIO3 injection. RPE function was measured with c-wave of electroretinogram (ERG). Colored microsphere technique was used for in vivo experiments to determine the choroidal blood flow in ocular hypertensive (40mmHg) rabbit eyes. Methylthiazoltetrazolium (MTT) assay was used to study in vitro effect of TMP on various oxidants induced injury in the hRPE (ARPE-19 (ATCC, Manassas, VA, USA)) . RESULTS: Two weeks after NaIO3 injection, the amplitude of ERG c-wave fell markedly in NaIO3 group to 36% of control group (P<0.01). No apparent difference was observed in TMP+NaIO3 group. Four weeks later, the NaIO3 group fell to 46% of control group (P<0.01), while the TMP+NaIO3 group fell to only 77% of control group (P<0.01). There was a 67% reversal of the ERG c-wave by TMP as compared to NaIO3 group (P<0.01). The choroidal blood flow was significantly increased at all time points (at 30, 60 and 120 minutes after TMP instillation) as compared with corresponding controls. TMP had no effect on hypoxia-(1%O2), t-BHP- and H2O2-induced damage in RPE cells. 10μg/mL TMP could reverse 1 and 3mmol/L NaN3-induced loss of viability of RPE by 18.5% (P<0.01) and 23% (P<0.01), respectively. 30μg/mL TMP could reverse 30 and 100mmol/L NaIO3 induced loss of viability of RPE by 18.1% (P<0.05) and 16.8% (P<0.01), respectively.CONCLUSION: TMP can significantly protect RPE from NaIO3 induced degeneration in vivo and oxidative stress in vitro and can increase choroidal blood flow markedly in vivo .
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· Age-related macular degeneration (AMD) is the leading cause of legal blindness in individuals aged over 65 in the United States and other industrialized nations. Till now, we have limited choices of treatment for this kind of disease. Treatment available can be grouped into two major categories: physical and pharmacological therapies. The former received extensive attention with little success whereas the latter attract new attention with great hope of success. The pharmacological therapies indude photodynamic therapy (PDT), steroids, vascular endothelial growth factor (VEGF) inhibitors, extracellular matrix (ECM) modifiers, gene therapy, nutrition supplements, choroidal blood flow facilitators and the like. PDT treatment is the only available effective treatment for certain forms of neovascular AMD. Anecortave acetate,as a synthetic derivative of cortisol, might stabilize vision in patients with predominantly classic subfoveal choroidal neovascularization (CNV) for up to 6mo through subtenon juxtascleral depot application. Intravitreous injection of VEGF aptamer stabilized or improved vision in 87.5% of patients with subfoveal CNV 3mo after treatment. Malfunction of choroidal blood flow is found in early stage of AMD. Elevation of intravascular pressure is the crucial hemodynamic factor in age-related macular degeneration, resulting in a decrease of the blood flow of choriocapillaries. Chain reactions are triggered which lead to retinal pigment epithelium (RPE) degeneration,Bruch's membrane breakdown, CNV formation, AMD and blindness in the end. Therefore, specific drugs that can increase the choroidal blood flow could be very useful to prevent the AMD from developing and worsening. Although most of them are still in the experimental stage,it is hopeful to find a way to treat AMD at the early stage and to prevent the disease to be triggered and developed.
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The effect of electroacupuncture (EA) stimulation on tissue circulation in the human ocular fundus (choroidal blood flow) was studied in 11 adult healthy volunteers (6 males and 5 females, age 31.5±5.7y) who had no physical or ocular disease. Using the laser speckle method, normalized blur (NB) values, a quantitative index for tissue blood flow, were measured over an area of choroid between the macula and the optic nerve papilla with no discrete visible vessel. The EA stimulation was applied between BL 10 and GB 20 and between GB 21 and SI 13 on the right side for 15 minutes at 1Hz with an intensity which cause slight muscle contraction. The NB value and intraocular pressure (IOP) in both side eyes, blood pressure (BP) and pulse rate (PR) were measured at baseline time, immediately after EA, and every 5 minutes after EA up to 15 minutes. These procedures were repeated on the same subjects as a control trial on another day. The NB value of choroid on the stimulated side significantly increased following EA stimulation compared with the control value, while that in the unstimulated side showed no significant change. No significant change was observed in BP, IOP or ocular perfusion pressure throughout the experimental period.