视网膜分枝静脉阻塞发病的解剖学因素

为了评价动静脉交叉在视网膜分枝静脉阻塞(BRVO)发病中的作用,我们对50名BRVO患者的FFA负片进行了分析,并以同一患者的同一眼的对侧血管弓及对侧眼的相同象限的相应的动静脉交叉作为对照组.结果发现:本组BRVO患者有80%发生在颞上象限,16%发生在颞下象限,4%发生在鼻上象限.且阻塞点均位于动静脉交叉处,而动静脉交叉处动脉位于静脉之前且交叉与视盘距离近是BRVO发病的解剖学方面的危险因素.     

正常视网膜血管直径的非对称性研究

目的:利用IMAGEnet软件对眼底血管造影数字图像进行视网膜血管直径测量以探讨正常眼视网膜血管直径是否存在差异。方法:利用IMAGEnet软件对眼底血管造影数字图像进行放大和对比度调整,测量4个象限近视盘周围1PD范围内的视网膜动脉直径(RAD)和静脉直径(RVD),计算视网膜动静脉比值(A/V)并检验该测量方法的可重复性。结果:左右眼对应象限之间的RAD,RVD和A/V比值差异无统计学意义,但对单眼而言,颞侧与鼻侧象限的RAD和RVD以及A/V比值有着显著性差异。可重复性检验以类内相关系数(intraclass correlation coefficient,ICC)来表示,RAD的者内信度为0.97(P<0.01),RVD为0.986(P<0.01);RAD的者间信度为0.976(P<0.01),RVD为0.975(P<0.01)。结论:正常双眼对应象限的视网膜血管直径没有差异,但单眼不同象限的视网膜血管直径存在差异,利用IMAGEnet软件对视网膜荧光造影血管直径进行测量是可行和可靠的。     

基于荧光眼底特征探讨视网膜分支静脉阻塞的临床分型

目的:分析视网膜分支静脉阻塞(branch retinal vein occlu-sion,BRVO)的荧光素眼底血管造影特征,探讨视网膜分支静脉阻塞进一步分型的必要性。方法:回顾荧光素眼底血管造影检查1450例BRVO患者,依荧光眼底像确定患者阻塞点位于动静脉交叉处2～3级以上者56例56眼,对其视网膜无灌注区大小,新生血管等情况进行观察。结果:患者56例56眼,占BRVO患者总眼数的3.9%,其中视网膜2级动静脉交叉阻塞者29眼,3级动静脉交叉阻塞者18眼,3级以上动静脉交叉阻塞者9眼。荧光视网膜像显示56眼中42眼存在阻塞所属区域小片无灌注区低荧光,16眼有新生血管性高荧光,未见玻璃体积血,增生性视网膜病变及牵拉性视网膜脱离等并发症发生。结论:临床视网膜动静脉交叉处2～3级以上BRVO者有别于常见的BRVO,其视网膜损害范围轻,出血范围小,程度轻,且无灌注区面积小,发生新生血管密度低,此类患者有必要单独列出,BRVO值得进一步分型,以促进临床的诊治。     

玻璃体腔注射Avastin治疗视网膜分支静脉阻塞

视网膜分支静脉阻塞（branch retinal vein occlusion,BRVO）是影响50岁以上人群的常见视网膜血管疾病。其相关危险因素包括：老龄、动脉高压、动脉硬化、糖尿病、高血脂症和吸烟史。眼底表现为沿某视网膜分支血管（主要为颞侧）的象限性视网膜出血及水肿,可以合并棉絮斑。     

视网膜分支静脉阻塞与动—静脉交叉的关系

视网膜分支静脉阻塞（BRVO）的阻塞部位多位于动—静脉交叉处。但迄今有关交叉处的动、静脉解剖位置与BRVO的关系仍不十分明了．为了探讨BRVO与动—静脉交叉的关系，作者研究了82眼（76例）BRVO和82眼（82例）无BRVO者的眼底彩色照片和眼底荧光血管造影片发现：BRVO多发生于颞侧（90．3％），尤其是颞上象限（54．95％），且在阻塞处，静脉后位交叉为100％（82／82）；而在三个不同对照组的动—静脉交叉处，静脉后位交叉分别为：B组67．1％（55／82），C组70．0％（49／70），D组74．4％（61／82）。阻塞组分别与三个不同对照组比较有显著差异（P均＜0．001）。提示：静脉后位交叉可能为BRVO的主要危险因素；动脉对静脉的机械压迫可能是BRVO的主要原因之一。此外，还对动—静脉交叉在各象限的分布和类型进行探讨。     

高度近视患者后极部视网膜血管曲折度及分叉角变异

目的 观察高度近视患者后极部各个象限视网膜动静脉曲折度及分叉角的变异.方法 对比分析高度近视患者32例52只眼以及正常人22例30只眼后极部不同象限视网膜血管曲折度及分叉角大小,并比较高度近视后极部视网膜血管与正常眼的差异.多变量方差分析对结果 进行分析,P<0.05为差异有统计学意义.结果 高度近视眼由视盘发出平行走向黄斑的血管,动脉曲折度分别为(1.29±1.10)×10-4、(5.39±1.93)×10-5;正常眼分别为(4.15±2.38)×10-4、(9.75±4.99)×10-5,两组差异均有统计学意义(t=1.99,2.00;P<0.05).高度近视眼视网膜动脉鼻上鼻下分叉角分别为(66.17±14.04)°、(61.20±11.02)°,正常眼分别为(77.66±14.12)°、(85.86±16.45)°,两组差异均有统计学意义(F=0.77,0.83;P<0.05).高度近视眼视网膜静脉颞上颞下分叉角分别为(92.39±20.36)°、(83.56± 23.50)°,正常眼分别为(79.45±15.94)°、(70.59±17.27)°,两组比较差异均有统计学意义(F=2.34,1.83;P<0.05).结论高度近视眼视网膜动脉及从视盘发出平行走向黄斑的血管曲折度变小,与动脉相应静脉曲折度变化不明显;高度近视眼底血管动脉鼻上鼻下分叉角较正常眼较小,高度近视眼底静脉颞上颞下分叉角较正常眼增大.     

视网膜静脉阻塞中心凹周围视网膜厚度的OCT观察

目的：分析视网膜静脉阻塞患者中心凹两侧视网膜的光学相干断层成像(OCT)特征。方法：40例视网膜静脉阻塞患者(40眼)行OCT检查。其中CRVO30例，BRVO10例。结果：CRVO中心凹鼻侧视网膜厚度大于颞侧，BRVO中心凹阻塞侧视网膜厚度大于对侧。阻塞远端的视网膜结构变化较小，阻塞近端的视网膜结构变化较大。结论：OCT可以有效地观察视网膜静脉阻塞患者后极部中心凹两侧视网膜的变化，静脉阻塞近端的视网膜结构损害比远端更加严重。     

无早期症状的视网膜分支静脉阻塞临床特点

目的观察视网膜分支静脉阻塞(BRVO)中,因不参与引流黄斑区血液,而阻塞早期无症状病例的临床及荧光素眼底血管造影(FFA)特点。方法回顾性分析BRVO病例中因合并玻璃体积血就诊及FFA检查时偶然发现的66例(70只眼)临床资料。结果 66例BRVO病例中,右眼26例,左眼36例,双眼4例。颞上周边支阻塞45只眼,占68.18%;颞下周边支5只眼,占7.58%;鼻上支8只眼,占12.12%;鼻下支12只眼,占18.18%。FFA检查时偶然发现17例,占25.76%;继发玻璃体积血49例,占74.24%。70只眼均发现大小、数量不等的视网膜新生血管。伴增生膜5只眼,占7.58%。合并视盘新生血管3只眼,占4.55%。黄斑前膜4只眼,占6.06%;视网膜裂孔、并继发视网膜脱离6只眼,占8.57%。结论无早期症状BRVO病例,均为BRVO后期并发症,与其它类型BRVO有所不同。     

应用炫彩成像技术观察视网膜分支静脉阻塞患者动静脉交叉压迫点的临床意义

目的　探讨利用炫彩视网膜成像技术观察视网膜分支静脉阻塞（BRVO）患者动静脉交叉压迫点的可行性及其临床意义。方法　前瞻性研究。纳入2019年7月至2020年10月就诊于遵义医科大学第二附属医院眼科门诊的BRVO患者49例49眼。散瞳后分别行传统彩色眼底照相、基于共焦扫描激光检眼镜的海德堡炫彩成像（MultiColor）以及荧光素眼底血管造影（FFA）检查,以FFA图像为依据观察动静脉交叉压迫点,利用Spectralis HRA-2炫彩成像对压迫点所处的血管进行分级评分并测量压迫点距视盘血管发出区的距离。根据FFA结果将BRVO患者分成缺血型组和非缺血型组,对比两组患者上述指标差异。 结果　炫彩成像观察到的BRVO患者动静脉交叉压迫点与FFA图像结果一致,49例患者均为视网膜颞侧分支静脉阻塞,颞上分支阻塞者33例,颞下分支阻塞者16例,缺血型组与非缺血型组患者阻塞部位相比差异无统计学意义（P＝0.289）。缺血型组患者压迫点血管分级评分平均为1.0分,与非缺血型患者的血管分级评分平均2.5分相比,差异有统计学意义（P=0.001）。压迫点距视盘血管发出区的距离缺血型组为（2543.00±769.06）μm,非缺血型组为（3505.44±1125.42）μm,两组比较差异有统计学意义（P＝0.002）,压迫点血管分级评分与BRVO是否发生缺血相关（P=0.003）。结论　基于共焦扫描激光检眼镜的海德堡炫彩成像技术可以直观地观察BRVO患者动静脉交叉压迫点而不受出血的影响,并可以对压迫点血管进行分级评分,有助于为BRVO患者的治疗及预后评估提供更全面准确的信息。     

糖尿病患者视网膜血管血氧饱和度变化研究

目的 观察糖尿病患者与健康人群视网膜血管血氧饱和度的差异.方法 临床确诊为糖尿病的71例(71眼)患者和91名(91眼)健康者分别纳入糖尿病组和正常组.采用视网膜血管血氧饱和度测量仪检测两组受检者,并应用仪器配套软件分析距离视盘中心1.5-3.0个视盘直径的视网膜动脉、静脉血氧饱和度值.结果 71例糖尿病患者中,男性与女性、各个年龄段、不同糖尿病病程间比较,视网膜动脉、静脉及其各象限分支动脉、静脉的血氧饱和度差异均无统计学意义(均为P ＞0.05).糖尿病组视网膜动脉血氧饱和度较正常组显著升高(P=0.00);糖尿病组视网膜动脉各象限的血氧饱和度均较正常组高,其中颞上分支、颞下分支与正常组相比差异均有统计学意义(均为P ＜0.05).糖尿病组视网膜静脉血氧饱和度较正常组有升高的趋势,但差异无统计学意义(P＞0.05);糖尿病组视网膜静脉血氧饱和度颞上分支、颞下分支较正常组高,鼻下分支较正常组低,差异均有统计学意义(均为P ＜0.05).糖尿病组视网膜动静脉血氧饱和度差值较正常组显著升高(P=0.00).结论 糖尿病患者视网膜血管血氧饱和度与健康人群存在显著差异;糖尿病患者不同象限的血管血氧饱和度存在不同程度的改变,提示视网膜氧代谢异常程度在各象限的分布并不均匀.     

Systemic hyperoxia and retinal vasomotor responses

PURPOSE: Several studies have investigated the changes in retinal vessel diameter during physiological stress or pathologic conditions. These studies were principally based on individual fundus photographs and as such did not allow the evaluation of vessel dynamics over time. The research objective was to detail the time course and amplitude changes in the diameter of arteries and veins across all retinal quadrants, during and after hyperoxic vascular stress. METHODS: The dynamics of changes in retinal vessel diameter were quantified with a retinal vessel analyzer, which digitizes fundus images in real time and simultaneously quantifies vessel diameter. The arterial and venous diameters within one disc diameter of the optic nerve head in each quadrant were studied. Twenty young adults participated in this study in which the vessel diameters were measured during successive phases of breathing either room air or pure oxygen. The oxygen saturation level (SaO(2)), end-tidal carbon dioxide (EtCO(2)), pulse rate (PR), respiratory rate (RR), and blood pressure (BP) were also monitored throughout testing. RESULTS: Breathing 100% O(2) caused an increase in SaO(2) and a decrease in the EtCO(2). All other systemic parameters measured (PR, RR, BP, and ocular perfusion pressure [OPP]) remained unchanged. However, the retinal veins and arteries constricted by approximately 14% and approximately 9% respectively, in all retinal quadrants. After experimental hyperoxia, inhalation of room air was associated with a progressive increase in the caliber of vessels toward their pretest size. The amplitude and overall profile of vessel reactivity to and recovery from hyperoxia was the same across retinal quadrants. CONCLUSIONS: These data indicate that, during systemic hyperoxic stress, the retinal vessels change in caliber uniformly across retinal quadrants in healthy young adults. This type of physiological vascular provocation could be used to investigate the quality of vascular regulation during aging and in vascular diseases of the eye.     

10-year fundus tessellation progression and retinal vein occlusion

AIM: To access the 10-year fundus tessellation progression in patients with retinal vein occlusion. METHODS: The Beijing Eye Study 2001/2011 is a population-based longitudinal study. The study participants underwent a detailed physical and ophthalmic examination. Degree of fundus tessellation was graded by using fundus photographs of the macula and optic disc. Progression of fundus tessellation was calculated by fundus tessellation degree of 2011 minus degree of 2001. Fundus photographs were used for assessment of retinal vein occlusion. RESULTS: The Beijing Eye Study included 4403 subjects in 2001, 3468 subjects was repeated in 2011. Assessment of retinal vein obstruction and fundus tessellation progression were available for 2462 subjects (71.0%), with 66 subjects fulfilled the diagnosis of retinal vein occlusion. Of the 66 participants, 59 participants with unilateral branch retinal vein occlusion, 5 participants with unilateral central retinal vein occlusion, 1 participant with bilateral branch retinal vein occlusion, and 1 participant with branch retinal vein occlusion in one eye and central retinal vein occlusion in the other eye. Mean degree of peripapillary fundus tessellation progression were significantly higher in the whole retinal vein occlusion group (0.33±0.39, P<0.001), central retinal vein occlusion group (0.71±0.8, P=0.025) and branch retinal vein occlusion group (0.29±0.34, P=0.006) than the control group (0.20±0.26). After adjustment for age, prevalence of tilted disc, change of best corrected visual acuity, axial length, progression of peripapillary fundus tessellation was associated with the presence of retinal vein occlusion (P=0.004; regression coefficient B, 0.094; 95%CI, 0.029, 0.158; standardized coefficient B, 0.056). As a corollary, after adjusting for smoking duration, systolic blood pressure, anterior corneal curvature, prevalence of RVO was associated with more peripapillary fundus tessellation progression (P<0.001; regression coefficient B: 1.257; OR: 3.517; 95%CI: 1.777, 6.958). CONCLUSION: Peripapillary fundus tessellation progresses faster in individuals with retinal vein occlusion. This may reflect the thinning and hypoperfusion of choroid in patients with retinal vein occlusion.     

Differences by quadrant of retinal nerve fiber layer thickness in healthy eyes

PURPOSE: The purpose of this study was to determine the distribution of retinal nerve fiber layer thickness by quadrant in healthy eyes. PATIENTS AND METHODS: Forty subjects with healthy eyes were included in the study. A complete ophthalmic examination was performed, including determination of visual fields by automated perimetry. The subjects had no family history of retinal disease or glaucoma. Forty right eyes and 40 left eyes were measured. Retinal nerve fiber layer thickness was measured using simultaneous stereophotographs with stereophotogrammetry at the disc margin. For the total disc and four quadrants, absolute retinal nerve fiber layer thickness and optic disc area was determined using a magnification correction formula. RESULTS: Comparison of the quadrants showed that the retinal nerve fiber layer thicknesses of the superior, inferior, and nasal quadrants were significantly thicker than the temporal quadrant (P = 0.00006 for right and left eyes). No significant differences were observed between the superior, inferior, and nasal quadrants in the right eye. In the left eye, the superior retinal nerve fiber layer thickness was significantly greater than the inferior (P = 0.028) and nasal retinal nerve fiber layer thicknesses (P = 0.00006), while the inferior was not significantly different from the nasal. No significant difference in quadrant retinal nerve fiber layer thickness was noted between eyes. CONCLUSIONS: Measurements of retinal nerve fiber layer thickness in healthy eyes show the thinnest quadrant to be the temporal, with the other three quadrants having similar thicknesses. This pattern corresponds to the histologic measurements of retinal nerve fiber layer thickness.     

视网膜分支静脉阻塞合并视网膜脱离的临床分析

目的 分析视网膜分支静脉阻塞(BRVO)合并视网膜脱离(RD)的临床特征及有效的治疗方法.方法 收集2004年11月至2007年10月治疗的有完整随访观察资料的18例(18只眼)BRVO合并RD的病例,采用常规三通道闭合式玻璃体切割手术,其中6例联合白内障超声乳化吸出术,合并黄斑裂孔的患眼行内界膜剥离,术后1、2周,1、2、3、6月随访,平均随访4.8月,观察患者的视力、眼底、眼压、玻璃体后脱离,术中术后并发症、及术后视网膜复位等情况.结果 全部病例于术中均发现裂孔,单个孔、多发孔各9例,孔源性视网膜脱离17例,牵引性视网膜脱离1例,黄斑孔5例,黄斑孔中合并黄斑囊样水肿1例,合并黄斑前膜2例.18例中发现纤维血管膜生长的15例,玻璃体不完全性后脱离粘连牵拉视网膜的12例,黄斑水肿6例,其中合并黄斑前膜2例.BRVO发生于颞上的6例,鼻上6例,上半侧3例,颞下2例,颢上合并颞下1例.18例中术后视力提高12例,视力稳定3例,视力下降3例,术后最佳矫正视力HM3例、0.1-0.39例、0.3以上6例.一次手术视网膜复位的16例,2例于硅油取出时发现局限性视网膜脱离,再次填充C3F8后视网膜复位.结论 视网膜分支静脉阻塞合并视网膜脱离的临床表现较复杂,术前眼底情况不明确,视网膜裂孔及多发性裂孔的发生率较高,多数病例玻璃体后脱离不完全粘连牵拉视网膜,且合并纤维血管膜的增生,玻璃体手术或联合手术是适合的治疗方法,可取得较好的临床疗效.     

基于深度学习的双模态眼底照相机视网膜分支静脉阻塞的血氧饱和度及血管形态学研究

目的基于深度学习的双模态眼底照相机研究视网膜分支静脉阻塞(BRVO)患眼视网膜血氧饱和度及血管形态变化。方法前瞻性研究。2020年5~10月于温州医科大学附属眼视光学院检查确诊的BRVO患者31例31只眼(BRVO组)和性别年龄匹配的健康志愿者20名20只眼(对照组)纳入研究。BRVO组31例31只眼中,既往接受1次玻璃体腔注射抗血管内皮生长因子药物治疗20例20只眼,未接受任何治疗11例11只眼;并据此分为治疗组、未治疗组。应用双模态眼底照相机采集视网膜图像;利用深度学习方法在黄斑感兴趣区域(MROI)分割动静脉;使用光密度比计算对照组受检眼、BRVO组患者受累侧和非受累侧视网膜血氧饱和度(SO₂),并计算MROI内动静脉直径、曲率、分形维数及密度。组间定量资料比较采用单因素方差分析。结果BRVO组患眼、对侧眼及对照组受检眼MROI内动脉SO₂(SO₂-A)比较,差异有统计学意义(F=4.925,P<0.001);静脉SO₂(SO₂-V)比较,差异无统计学意义(F=0.607,P=0.178)。未治疗组患者受累侧、非受累侧MROI内SO₂-A较对照组升高,差异有统计学意义(F=4.925,P=0.012);SO₂-V比较,差异无统计学意义(F=0.607,P=0.550)。治疗组受累侧、非受累侧和对照组受检眼MROI内SO₂-A、SO₂-V比较,差异均无统计学意义(F=0.159、1.701,P=0.854、0.197)。治疗组、未治疗组受累侧和对照组受检眼MROI内SO₂-A、SO₂-V比较,差异无统计学意义(F=2.553、0.265,P=0.088、0.546)。未治疗组、治疗组患眼和对照组受检眼动脉直径、动脉曲率、动脉分形维数、静脉分形维数、动脉密度、静脉密度比较,差异均有统计学意义(F=3.527、3.322、7.251、26.128、4.782、5.612,P=0.047、0.044、0.002、<0.001、0.013、0.006);静脉直径、静脉曲率比较,差异无统计学意义(F=2.132、1.199,P=0.143、0.321)。结论BRVO患者SO₂-A较健康眼升高,抗血管内皮生长因子药物治疗后降低;SO₂-V不变。     

Retinal vessel oxygen saturation in healthy subjects and early branch retinal vein occlusion

AIM: To measure the retinal oxygen saturation in healthy subjects and early branch retinal vein occlusion (BRVO) in Chinese population. METHODS: The retinal vessel oxygen saturation of the healthy subjects and BRVO patients were measured by a noninvasive retinal oximeter (Oxymap ehf., Reykjavik, Iceland). RESULTS: The study included 22 patients with unilateral BRVO (mean age: 55.1±8.8y) in the study group and 91 healthy participants (mean age: 37.5±14.0y) in the control group. In the healthy individuals, mean arterial and venous oxygen saturation were significantly (P<0.001) higher in the superior nasal quadrant (98.5%±10.1% and 57.3%±8.7%, respectively) than in the inferior nasal quadrant (94.2%±9.0% and 54.1%±9.6%, respectively), followed by the superior temporal quadrant (89.1%±10.1% and 51.9%±8.9%, respectively) and the inferior temporal quadrant (86.4%±9.4% and 46.6%±9.6%, respectively). In patients with ischemic BRVO, arterial oxymetric values were significantly higher and venous measurements significantly lower for the affected vessel (107.5%±9.7% and 46.4%±14.2%, respectively) than the unaffected vessel in the same eye (99.2%±12.2% and 55.5%±7.9%, respectively) and as compared to the vessel in the unaffected fellow eye (93.1%±6.9% and 55.7%±6.8%) (P=0.005 and P=0.02, respectively). In the patients with non-ischemic BRVO, mean venous oxygen saturation was lower in the affected vein (39.8%±12.2%) than in the unaffected vessels of the same eye (50.8%±10.5%) and in the fellow eye (58.21%±5.7%) (P=0.03). Mean arterial oxygen saturation did not differ significantly (P=0.42) between all three groups. CONCLUSION: In patients with BRVO, the venous oxygen saturation in the affected vessels is decreased potentially due to decreased blood velocity and flow. Interestingly, the arterial oxygen saturation in eyes with ischemic BRVO is increased in the affected arteries.     

The role of a second isolated retinal artery in branch retinal vein obstruction

PURPOSE: To evaluate the prevalence of a second isolated retinal artery in eyes with and without branch retinal vein obstruction (BRVO). METHODS: A retrospective study of the color photographs and fluorescein angiograms of 100 patients with unilateral BRVO (64 superotemporal and 34 inferotemporal) and a control group of 33 patients (66 eyes) with different ailments was made. The prevalence of a second isolated retinal artery, which coursed closer to the macular region, in BRVO eyes, fellow eyes and eyes of the control group was evaluated. The types and sites of arteriovenous crossings were also recorded for comparison. RESULTS: The eyes with BRVO, which involved the superotemporal quadrant, had significantly larger numbers of arteriovenous crossings than did fellow eyes (p = 0.02) and control eyes (p = 0.001). In the superotemporal quadrant, a significantly higher percentage (35 of 66, 53%) of the control eyes had a second isolated retinal artery than did BRVO eyes (16 of 64 cases, 25%, p = 0.001). CONCLUSIONS: The second isolated retinal artery, which has not been previously mentioned in the literature, may lower the chance of arteriovenous crossings and play a protective role in BRVO.     

Laser treatment and the mechanism of edema reduction in branch retinal vein occlusion

PURPOSE: To test a hypothesis on the physiological mechanism of the disappearance of macular edema after laser treatment. The hypothesis is based on the effect grid laser treatment has on retinal oxygenation and hemodynamics. It predicts that laser-induced reduction of macular edema is associated with shortening and narrowing of retinal vessels in patients with branch retinal vein occlusion (BRVO). METHODS: The study included 12 subjects, treated with argon laser photocoagulation for BRVO and macular edema. Fundus photographs taken at the time of diagnosis and again after laser treatment, were digitized, and diameter and segment length of retinal vessels was measured using NIH-Image program. RESULTS: Macular edema disappeared or was dramatically reduced in all cases after laser treatment. The diameter of occluded venules constricted to 0.81+/-0.02 (mean +/- SD, P = 0.019) of the prelaser diameter and adjacent arterioles constricted to 0.78+/-0.01 (P = 0.008). The laser treatment also led to shortening of the affected vessels. The final segment length of the occluded venules was 0.95+/-0.17 (P = 0.005) of the length before treatment. The corresponding value for the adjacent arterioles is 0.95+/-0.14 (P = 0.008). Control arterioles and venules in the same fundus did not change in either length or width. CONCLUSIONS: These results do not reject the authors' hypothesis that the disappearance of macular edema in BRVO can be explained by the effect the laser photocoagulation has on retinal oxygenation. Increased oxygenation causes vessel constriction and shortening and lower intravascular pressure, which reduces edema formation according to Starling's law.