| Purpose: Retinal thickness and retinal vessel density(VD)measurements are often used as indicators for the early evaluation of glaucoma.Due to individual differences in the size of optic disc in the population,some studies have found that the size of optic disc is correlated with retinal thickness and retinal VD,but the conclusion is still controversial.The aim of this study was to measure the parameters of optic disc,retinal thickness and retinal VD using fundus stereography and optical coherence tomography angiography(OCTA),and to study the effects of optic disc size on retinal thickness and retinal VD measurements in healthy eyes.The systemic and ocular influencing factors of the two were analyzed to find out the more suitable diagnostic indicators for early glaucoma in patients with different optic disc sizes.Methods: The first part examines the effect of optic disc size on measurements of retinal thickness,which mainly includes peripapillary retinal nerve fiber layer(p RNFL)and macular ganglion cell complex(m GCC).Use OCT to measure the thickness of p RNFL and m GCC in healthy eyes,including the whole,superior,inferior,nasal and temporal p RNFL thickness and the thickness of m GCC in the average,superior and inferior.KOWA nonmyd WX fundus stereoscopic camera was used to image the fundus retina,and KOWA VK-2 WX 3D analysis software was used for quantitative analysis of the optic disc.Optic disc parameters includes vertical cup disc ratio(VCDR),cup area,disc area,disc rim area and maximum cup depth(MCD).Biological measurements such as central corneal thickness(CCT),anterior chamber depth,lens thickness,and axial length(AL)are performed using lenstar.According to the disc area,the subjects were divided into three groups: large,medium and small optic disc group,and the thickness of p RNFL and m GCC in each quadrant of the three groups were compared by the analysis of variance or the Kruskal-Wallis test.Univariate and multifactorial linear regression models were used to evaluate systemic and eye-related influencing factors for p RNFL thickness and m GCC thickness measurements.The second part examines the effect of optic disc size on retinal VD measurements,which mainly includes VD in disc region and macular region.OCTA was used to measure VD in the disc region and macular region in healthy eyes.VD in the disc region includes whole vessel density(w VD),inside disc vessel density(id VD),peripapillary vessel density(pp VD)and on the superior and inferior hemispheres of Garway Heath(GH).The VD in macular region included superficial vessel density(SVD)and deep vessel density(DVD),SVD and DVD include Parafoveal and Perifoveal.KOWA nonmyd WX fundus stereoscopic camera was used to image the fundus retina,and KOWA VK-2 WX 3D analysis software was used for quantitative analysis of the optic disc.Optic disc parameters includes VCDR,cup area,disc area,and rim area.Biological measurements such as CCT,anterior chamber depth,lens thickness,and AL are performed using lenstar.According to the disc area,the subjects were divided into three groups: large,medium and small optic disc group.Analysis of variance or the Kruskal-Wallis test was used to compare the VD in the disc region and macular region in different optic disc groups.Univariate and multifactorial linear regression models were used to evaluate ocular and systemic correlation factors of pp VD and macular VD.Results: In the first part of the study,a total of 366 healthy eyes met inclusion and exclusion criteria for 366 subjects,including 93 males(25.4%)and 273 females(74.6%).The mean age was 60.39±6.15 years(range 50 to 82 years),the mean AL was 22.82±0.82mm(range 20.81 to 25.20mm),and the average area of optic disc was 2.56±0.51mm2(range 1.45 to 4.22 mm2).The average thickness of p RNFL and m GCC were 112.82±12.29μm and 96.68±7.10μm,respectively.In the three groups,the thickness of p RNFL was thicker in the inferior quadrant than the superior quadrant,followed by the nasal quadrant and the temporal quadrant.There were significant differences in p RNFL thickness in the global,temporal and superior quadrants among the three groups(P=0.035,0.034 and 0.013,respectively),and differences between small and large optic disc groups after correction by Bonferroni method(P=0.031,0.072 and 0.017,respectively),while there were no significant differences between the other groups(all P values > 0.05).There were no significant differences in p RNFL thickness in nasal and inferior quadrants and m GCC thickness in each quadrant among the three groups(all P values > 0.05).In univariate and multivariate linear regression analysis,age(B=-0.300,P=0.003),sex(B=3.403,P=0.018),disc area(B=5.442,P < 0.001),VCDR(B=-36.294,P < 0.001)and MCD(B=-0.060,P=0.007)was an independent factor of p RNFL thickness measurements.The independent influencing factors of m GCC thickness measurements were age(B=-0.144,P=0.018),best-corrected visual acuity(BCVA)(B=-5.903,P=0.023),and VCDR(B=-13.418,P=0.002).In the second part of the study,a total of 341 healthy eyes met the inclusion and exclusion criteria of 341 subjects,including 84 males(24.6%)and 257 females(75.4%).The mean age of the subjects was 60.48±6.29 years(ranging from 50 to 82 years).The mean AL was 22.83±0.81mm(range 20.81 to 25.20mm),and the average disc area was 2.57±0.51mm2(range 1.45 to 4.22 mm2).In addition,the mean values of w VD,id VD and pp VD were 49.86±2.76(%),49.13±4.67(%)and 52.71±3.24(%),respectively.The mean parafoveal and perifoveal in macular SVD were 50.87±4.40(%)and 50.08±3.35(%),respectively.The mean parafoveal and perifoveal of DVD in macular region were 54.50±4.06(%)and 51.67±5.78(%),respectively.GH S-Hemi VD,GH I-Hemi VD and pp VD in the optic disc region were significantly different among the three groups(P=0.046,0.020 and 0.024,respectively),and differences between small and middle optic disc groups(P=0.039,0.028 and 0.021,respectively)after correction by Bonferroni method,while there were no significant differences between the other groups.In addition,there were no significant differences in SVD and DVD in macular region among the three groups(all P > 0.05).Univariate and multivariate linear regression analysis of pp VD showed that age(B=0.055,P=0.010),sex(B=0.914,P=0.003)and p RNFL thickness(B=0.166,P < 0.001)were independent influencing factors of pp VD.However,the effect of disc area on pp VD was not statistically significant(P > 0.05).In univariate and multivariate linear regression analysis of VD in macular region,it was found that the independent influencing factors of SVD in macular region were p RNFL thickness(parafoveal and perifoveal area B=0.057 and 0.077,all P values < 0.001)and SSI(parafoveal and perifoveal area B=0.342 and 0.283,all P values < 0.001).The independent influencing factors of DVD in macular region were sex(parafoveal B=1.180,P=0.004),age(parafoveal and perifoveal area B=-0.100 and-0.090,P=0.001 and 0.010,respectively,)and SSI(parafoveal and perifoveal area B=0.320 and 0.594,all P values < 0.001),the effect of disc area on VD in macular region was not statistically significant(all P values > 0.05).Conclusions: In this study,it was found that optic disc size was an independent factor influencing p RNFL thickness measurements,while had no statistical significance on the thickness of m GCC,the VD of optic disc and macular region.Therefore,when using retinal thickness to evaluate early glaucoma in patients with different optic disc size,m GCC thickness should be the main assist measurements.When retinal VD is used,both optic disc and macular VD can be used for the diagnosis of early glaucoma in patients with different optic disc size,but the diagnostic accuracy of both needs to be further studied.In addition,this study also found that age is an important influencing factor of retinal thickness and retinal VD,sex and p RNFL thickness are the influencing factors of VD in the optic disc region,while sex,age,p RNFL thickness and SSI are the influencing factors of VD in the macular region.Therefore,the above factors should be considered in the measurement of retinal thickness and retinal VD. |
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