as a vital part of visual pathway , retina plays an important role in the generation and maintenance of vision . normal perfusion of retinal vessels is the essential requirement for retina to maintain its normal function . as we all know , a variety of instruments and techniques have been used to measure retinal perfusion , such as laser speckle imaging , laser doppler flowmetry , and doppler optic coherence tomography . however , these are limited in terms of clinical applications and research as they are nonquantitative and/or invasive . recently , a method for measuring local circulation has been developed using high - speed optical coherence tomography ( oct ) to perform quantitative angiography . using a split - spectrum amplitude de - correlation angiography ( ssada ) algorithm , flow in the optic disc and macula although the reproducibility of optic disc and macular flow perfusion parameters in normal people has been previously reported , the reproducibility of flow perfusion parameters in the optic discs and maculae of ocularly normal monkeys is unclear . the reproducibility of a technique is of primary importance when addressing its suitability for use in detecting disease . therefore , the current study was conducted to evaluate the reproducibility of optic disc and macular flow perfusion parameters in normal rhesus monkeys as measured by oct . a total of 18 normal adult male rhesus monkeys ( macaca mulatta ) were studied . the animal production license number is scxk ( beijing ) 2010 - 0007 , with a mean age of 6.5 years ( range 5.57.5 years ) and a mean weight of 7.7 kg ( range 7.08.7 kg ) . this study was also evaluated and approved by the institutional animal care and use committee of capital medical university . the rhesus monkeys involved in this study were all purchased from beijing institute of xieerxin biology resource , which was the largest nonhuman primate center in the north part of china and specialized in breeding laboratory nonhuman primate . then , the rhesus monkeys were housed and monitored at the large animal room of capital medical university according to the national standard of china , which was named as laboratory animal institutions general requirements for quality and competence ( gb / t 27416 - 2014 ) during the 3 years after the point of experimental implantation . injection of ketamine hcl ( 20 mg / kg ) + midazolam ( 0.2 mg / kg ) . monkeys had not undergone any interventions and had not been involved in any previous studies . tropicamide phenylephrine eye drops ( 0.5% , santen - china , beijing , china ) were administered topically to both eyes to dilate the pupils . a rigid plano contact lens was placed onto the corneal surface during the in vivo imaging . artificial tears ( refresh plus , allergan , irvine , ca , usa ) were used to maintain corneal moisture . both eyes of each monkey were scanned using the rtvue xr with angiovue ( software version 2014.0.1.68 ; optovue , inc . , fremont , ca , usa ) , with a light source centered at 840 nm , a bandwidth of 45 nm , and an a - scan - rate of 70,000 scans / s . scans of both the optic disc and macular areas were acquired . the scan sizes of optic disc and macular area were 4.5 mm  4.5 mm and 3.0 mm  3.0 mm , respectively . in detail , optic disc area was divided into four layers , which were optic nerve head ( onh ) ( all above retinal pigment epithelium layer ) , vitreous , radial peripapillary capillary ( rpc ) ( between the nerve fibers ) , and choroid layers . macular area was also divided into four layers , which were superficial retina ( upper line : internal limiting membrane with offset of 3 microns ; lower line : inner plexiform layer with offset of 15 microns ) , deep retina ( upper line : inner plexiform layer with offset of 15 microns ; lower line : inner plexiform layer with offset of 70 microns ) , outer retina ( upper line : inner plexiform layer with offset of 70 microns ; lower line : retinal pigment epithelium reference layer with offset of 30 microns ) , and choroid layers ( upper line : retinal pigment epithelium reference layer with offset of 30 microns ; lower line : retinal pigment epithelium reference layer with offset of 60 microns ) . all images were taken by the same trained examiner ( jing li ) and all measurements were repeated 3 times during the first examination and once at each of the two following examinations . flow index , which is the key parameter of perfusion , was calculated automatically using the above software and was defined as the average de - correlation value as previously described . all statistical analyses were performed by using spss statistics version 19.0 ( spss , inc . , the intra - session repeatability was calculated with three continuous results obtained during the first visit . icc values of 0.81.00 indicate almost perfect agreement between measurements and values < 0.50 indicate poor to fair agreement . we also performed an analysis of variance and calculated the p value to evaluate the difference between the measurements during three visits . this study was also evaluated and approved by the institutional animal care and use committee of capital medical university . the rhesus monkeys involved in this study were all purchased from beijing institute of xieerxin biology resource , which was the largest nonhuman primate center in the north part of china and specialized in breeding laboratory nonhuman primate . then , the rhesus monkeys were housed and monitored at the large animal room of capital medical university according to the national standard of china , which was named as laboratory animal institutions general requirements for quality and competence ( gb / t 27416 - 2014 ) during the 3 years after the point of experimental implantation . injection of ketamine hcl ( 20 mg / kg ) + midazolam ( 0.2 mg / kg ) . monkeys had not undergone any interventions and had not been involved in any previous studies . tropicamide phenylephrine eye drops ( 0.5% , santen - china , beijing , china ) were administered topically to both eyes to dilate the pupils . a rigid plano contact lens was placed onto the corneal surface during the in vivo imaging . artificial tears ( refresh plus , allergan , irvine , ca , usa ) were used to maintain corneal moisture . both eyes of each monkey were scanned using the rtvue xr with angiovue ( software version 2014.0.1.68 ; optovue , inc . , fremont , ca , usa ) , with a light source centered at 840 nm , a bandwidth of 45 nm , and an a - scan - rate of 70,000 scans / s . the scan sizes of optic disc and macular area were 4.5 mm  4.5 mm and 3.0 mm  3.0 mm , respectively . in detail , optic disc area was divided into four layers , which were optic nerve head ( onh ) ( all above retinal pigment epithelium layer ) , vitreous , radial peripapillary capillary ( rpc ) ( between the nerve fibers ) , and choroid layers . macular area was also divided into four layers , which were superficial retina ( upper line : internal limiting membrane with offset of 3 microns ; lower line : inner plexiform layer with offset of 15 microns ) , deep retina ( upper line : inner plexiform layer with offset of 15 microns ; lower line : inner plexiform layer with offset of 70 microns ) , outer retina ( upper line : inner plexiform layer with offset of 70 microns ; lower line : retinal pigment epithelium reference layer with offset of 30 microns ) , and choroid layers ( upper line : retinal pigment epithelium reference layer with offset of 30 microns ; lower line : retinal pigment epithelium reference layer with offset of 60 microns ) . all images were taken by the same trained examiner ( jing li ) and all measurements were repeated 3 times during the first examination and once at each of the two following examinations . flow index , which is the key parameter of perfusion , was calculated automatically using the above software and was defined as the average de - correlation value as previously described . all statistical analyses were performed by using spss statistics version 19.0 ( spss , inc . , the intra - session repeatability was calculated with three continuous results obtained during the first visit . icc values of 0.81.00 indicate almost perfect agreement between measurements and values < 0.50 indicate poor to fair agreement . we also performed an analysis of variance and calculated the p value to evaluate the difference between the measurements during three visits . a total of 18 eyes of 18 adult male rhesus monkeys were included in the study . the average flow indexes of four optic disc layers were 0.171  0.009 for the onh layer , 0.015  0.004 for the vitreous layer , 0.052  0.009 for the rpc layer , and 0.167  0.011 for the choroid layer . the average flow indices of the four macula layers were 0.044  0.011 for the superficial retinal layer , 0.036  0.011 for deep retinal layer , 0.016  0.009 for outer retinal layer , and 0.155  0.013 for choroid layer . flow indices of the four optic disc layers and four macula layers at three visits had no statistical difference ( each p > 0.05 ) [ table 1 and figures 1 , 2 ] . normal values of flow index in normal monkey eyes onh : optic nerve head ; rpc : radial peripapillary capillary ; sd : standard deviation . optical coherence tomography angiograms of optic disc area ( 4.5 mm  4.5 mm ) in normal monkey eyes . optical coherence tomography angiograms of macular area ( 3.0 mm  3.0 mm ) in normal monkey eyes . intra - visit ( icc values : 0.8210.954 ) and inter - visit ( icc values : 0.8440.899 ) repeatability were both high . the highest intra - visit icc value in optic disc area was in the rpc layer ( 0.931 ) and the highest intra - visit icc value in macular area was in the choroid capillary layer ( 0.954 ) . correspondingly , the highest inter - visit icc value in optic disc area was in the vitreous layer ( 0.892 ) and the highest inter - visit icc value in macular area was in the outer retinal layer , which was 0.899 [ tables 2 and 3 ] . intra - visit reproductivity of flow index measurements in normal monkey eyes onh : optic nerve head ; rpc : radial peripapillary capillary ; icc : intraclass correlation coefficient ; ci : confidence interval . inter - visit reproductivity of flow index measurements in normal monkey eyes onh : optic nerve head ; rpc : radial peripapillary capillary ; icc : intraclass correlation coefficient ; ci : confidence interval . this study establishes a normative database for perfusion of the optic disc and macular areas in healthy nonprimates . in our study , average flow index of four layers of optic disc area were 0.171 for onh layer , 0.015 for vitreous layer , 0.052 for rpc layer , and 0.167 for choroid layer , respectively . average flow index of four layers of macula area were 0.044 for superficial retina layer , 0.036 for deep retina layer , 0.016 for outer retina layer , and 0.155 for choroid layer . oct angiography , which was first described in 2012 , has now made it possible to study and quantify perfusion of both the optic disc and the macula . there are a growing number of researches that focus on the new technique to study the changes of optic and macular perfusion in various ocular diseases , such as glaucoma , age - related macular degeneration ( amd ) , diabetic retinopathy , retinal vein occlusion , and so on . results of this study found that both intra - visit ( icc values : 0.8210.954 ) and inter - visit ( icc values : 0.8440.899 ) reproducibility of flow index measurements were high . wei et al . found that this technique could be used to measure macular perfusion in normal people and had high repeatability ( 1.3% intra - visit and 2.1% inter - visit coefficients of variation ) . yu et al . investigated macular perfusion in healthy chinese individuals using the spectral - domain system rtvue - xr avanti and found that the mean icc between two measurements from 15 human eyes was 0.910 for vessel area density and 0.925 for the flow index , which were all higher than results in the current study . one reason might be that the monkeys were anesthetized with ketamine hcl and midazolam , and thus lacked of ability to fixate on a target , as the humans did . in addition , there was some slight eye movement in the anesthetized monkeys , which was difficult to avoid . in other words , the actual flow index of the optic disc and macular areas in rhesus monkeys might be higher than indicated in the current study . second , these results might be valid for rhesus monkeys ; however , it is not clear whether the results regarding the reproducibility of the flow index measurements are applicable in other species . third , the ssada technique does not directly measure the perfusion of optic disc ; however , measures the peri - onh region , which reflects perfusion of the onh . finally , since our results were obtained on normal eyes , caution must be exerted if the results are applied to monkeys with ocular diseases , such as glaucoma or amd . in conclusion , this is a rare study of normal values and reproducibility of flow indexes using rtvue xr with angiovue to perform quantitative angiography in normal monkey eyes . there was a high reproducibility of rtvue xr with angiovue - assisted measurements of the flow index measurements in normal monkey eyes . these results suggest that the rtvue xr with oct angiography technique might be suitable and creditable to assess changes during follow - up examinations of experimental ocular diseases , particularly diseases in the optic disc and macula areas . this project was supported by a grant from national natural science foundation of china ( no . this project was supported by a grant from national natural science foundation of china ( no .
background : optical coherence tomography ( oct ) angiography is a novel technique by which we can detect the local perfusion of fundus directly . the aim of this study was to evaluate the reproducibility of optic disc and macular flow perfusion parameters in rhesus monkeys using oct angiography.methods:eighteen healthy monkeys ( 18 eyes ) were subjected to optic disc and macula flow index measurements via a high - speed and high - resolution spectral - domain oct xr avanti with a split - spectrum amplitude de - correlation angiography algorithm . 
 right eye was imaged 3 times during the first examination and once during each of the two following examinations . 
 the intra - visit and inter - visit intraclass correlation coefficients ( iccs ) were both determined.results:the average flow indices of the four optic disc area layers were 0.171  0.009 ( optic nerve head ) , 0.015  0.004 ( vitreous ) , 0.052  0.009 
 ( radial peripapillary capillary ) , and 0.167  0.011 ( choroid ) . 
 average flow indices of the four macula area layers were 0.044  0.011 ( superficial retina ) , 0.036  0.011 ( deep retina ) , 0.016  0.009 ( outer retina ) , and 0.155  0.013 ( choroid ) . 
 intra - visit ( icc value : 0.8210.954 ) and inter - visit ( icc value : 0.8440.899 ) repeatability were both high.conclusions:the study is about the reproducibility of optic disc and macular perfusion parameters as measured by oct angiography in healthy rhesus monkeys . 
 flow index measurement reproducibility is high for both the optic disc and macula of normal monkey eyes . 
 oct angiography might be a useful technique to assess changes when examining monkeys with experimental ocular diseases .