近视可防止糖尿病视力减退


  【24drs.com】根据研究样本为630只眼睛的纵向研究结果,近视者的较长视轴(AL)可防止糖尿病视网膜病变和糖尿病黄斑部水肿。
  
  在线刊载于5月23日眼科学期刊的一篇文献,墨尔本大学、Royal Victorian眼耳科医院、澳洲眼科研究中心Ryan Eyn Kidd Man等人,对有严重视网膜病变和糖尿病黄斑部水肿的367名18岁以上第1型、第2型糖尿病患,分析了视轴、等效球镜(SE)折射、角膜曲率(CC)和前房深度(ACD),视网膜病变分级是依据2度视野视网膜相片和眼底黄斑部水肿相片,经光学相关断层扫描证实。
  
  研究团队发现,视轴较长的眼睛比较不会发生轻微(胜算比[OR]),0.58;95%信心区间[CI],0.41 - 0.83;P = .006 (视轴每增加1 mm时)、中度(OR,0.73;95% CI,0.60 - 0.88;P = .002)或严重(OR,0.67;95% CI,0.53 - 0.85;P = .01)糖尿病视网膜病变(DR)。研究结果也显示,糖尿病黄斑部水肿(DME)的轻微(OR,0.70;95% CI,0.56 - 0.86;P < .001)和中度(OR,0.72;95% CI,0.56 - 0.93;P = .002)风险降低,严重者则无。糖尿病视网膜病变与SE、ACD及CC则无关联。
  
  作者们写道,这些结果认为,视轴延长但是屈光没有改变,可能是稍早之研究所提的近视对糖尿病视网膜病变之保护关联的原因。
  
  该研究为发现近视对糖尿病视网膜病变有保护效果,但是并未指出近视的哪里个因素造成差异之临床观察试验和稍早的研究提供了强烈支持。
  
  密西根大学、Kellogg眼科中心眼科与视力科学教授Thomas W. Gardner医师表示,那篇临床观察已经是30多年前,但是没人真的相信;这次的研究强度在于,使用许多病患的实际资料,这次的研究样本数,而且是前瞻型式,更进一步地强化研究结果。
  
  Louisville大学眼科与视力科学系糖尿病视网膜病变服务小组主任Shlomit Schaal博士表示同意,她指出,这篇研究强化了视轴长度对于近视和糖尿病视网膜病变之保护关联而言是一重要因素的理论。
  
  Schaal博士写道,研究强度包括,临床样本数多且涵盖各种程度的糖尿病视网膜病变、使用视网膜相片评估糖尿病视网膜病变且依据标准分及规范,且有详细而完整的临床检查规范。不过,研究者应使用标准化体积变化指数(SVCI)取代状态OCT(optical coherence tomography),因这仅在中央黄斑部厚度时考虑使用。
  
  Schaal博士写道,SVCI纳入所有由OCT扫描的区域,包括黄斑体积,而不仅是厚度。
  
  Gardner医师指出,这篇研究对病患照护不太可能有太多影响。视轴长度只是少数保护关联之一,但是,在实务上,不知道如何实际应用。我们不知道如何把所有这些危险因素汇集成某些单位化的整合风险分数。如果有人近视相当深,可能比较不会发生视网膜病变,但是,这对于我们照护病患有何影响,我们可能还了解不够。
  
  作者们表示,尽管如此,视轴和出现糖尿病视网膜病变与严重度和DME有关。这些结果认为,视轴变长对预防近视扮演重要角色。需要后续研究评估糖尿病视网膜病变和DME与视轴的纵向关联。最大的问题依旧是为何视轴有保护性。
  
  研究限制包括,横断面设计,排除了因果关系和时序关联方面的结论,可能有选样偏差,纳入了进行雷射光凝疗法治疗DME的病患,未评估晶体生物识别。
  
  Schaal博士写道,视轴延长对于发生糖尿病视网膜病变和黄斑部水肿之保护效果的实际机转仍有待确认,理论上,视轴长度增加而降低血流可能与此关联有关。这篇研究并未探讨机转,只是显示有关联。
  
  资料来源:http://www.24drs.com/professional/list/content.asp?x_idno=6838&x_classno=0&x_chkdelpoint=Y
  

Myopia Protects Against Diabetic Vision Loss

By Jenni Laidman
Medscape Medical News

May 31, 2012 — The longer axial length (AL) of myopia appears protective against diabetic retinopathy and diabetic macular edema, according to results from a longitudinal study involving 630 eyes.

In an article published online May 23 in Ophthalmology, Ryan Eyn Kidd Man, BSc, from the Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, analyzed measurements of AL, spherical equivalent (SE) refraction, corneal curvature (CC), and anterior chamber depth (ACD) against the presence and severity of retinopathy and diagnosed diabetic macular edema in 367 adults aged 18 years and older with type 1 and type 2 diabetes. The retinopathy was graded from 2-field retinal photographs and the macular edema from fundus photographs confirmed by optical coherence tomography.

The research team found that eyes with longer AL were less likely to have mild (odds ratio [OR], 0.58; 95% confidence interval [CI], 0.41 - 0.83; P = .006 per mm increase in AL), moderate (OR, 0.73; 95% CI, 0.60 - 0.88; P = .002), or severe (OR, 0.67; 95% CI, 0.53 - 0.85; P = .01) diabetic retinopathy. The results also showed a decreased risk for mild (OR, 0.70; 95% CI, 0.56 - 0.86; P < .001) and moderate (OR, 0.72; 95% CI, 0.56 - 0.93; P = .002), but not severe, diabetic macular edema (DME). There was no association for SE, ACD, and CC with DR.

"These findings suggest that axial elongation, and not changes in the refractive component, may contribute most to the protective relationship of myopia with DR demonstrated in earlier studies," the authors write.

The study provides strong support for well-known clinical observations and earlier studies, which have seen a protective effect of myopia on DR without pinpointing just what component of nearsightedness made the difference.

"This clinical observation has been around more than 30 years, but nobody's really pursued it before," Thomas W. Gardner, MD, professor of ophthalmology and visual sciences at the Kellogg Eye Center at the University of Michigan, Ann Arbor, told Medscape Medical News. "The strength here is this uses real data from a large number of patients," he said. The size of the study, and the fact that it was prospective rather than retrospective, further bolsters the finding, he added.

Shlomit Schaal, MD, PhD, director, Diabetic Retinopathy Service, Department of Ophthalmology and Visual Sciences, University of Louisville, Kentucky, agrees. "This study strengthens existing theories that axial elongation is an important factor to the protective association of myopia with diabetic retinopathy," she wrote in an email to Medscape Medical News.

"Study strengths include the large clinical sample of patients with differing levels of diabetic retinopathy, the assessment of diabetic retinopathy using retinal photographs following standardized grading protocols, and the detailed and comprehensive clinical examination protocol," Dr. Schaal wrote. However, she said investigators should have used the Standardized Volumetric Change Index (SVCI) instead of Status OCT (optical coherence tomography), which took into consideration only the central macular thickness.

The SVCI "takes into considerations all zones scanned by the OCT, and also the macular volume, not just the thickness parameter alone," Dr. Schaal wrote.

The study is unlikely to have much effect on patient care, Dr. Gardner added. "Axial length is one of the few protective associations we have in general, but in terms of actual practice, I'm not sure how one actually applies it. We don't know how yet to put together all these risk factors into some unitized, integrated risk score. I think if somebody is pretty myopic it makes it less likely they'll get retinopathy, but how that influences how we take care of patients, I don't think we understand that yet."

Nonetheless, the authors conclude "that AL is associated with the presence and severity of DR and DME." They continue, "[t]hese results suggest that an elongated globe plays a major role in the protective influence of myopia.... Future studies assessing longitudinal associations between axial dimensions with DR and DME are needed." The big question remaining is just why AL is protective.

There are study limitations including the cross-sectional design, which precludes conclusions about causality and temporal sequence of the associations, potential selection biases, inclusion of patients who underwent laser photocoagulation for DME, and lack of assessment of lens biometry.

"The exact mechanisms by which axial elongation exerts a protective effect for the development of diabetic retinopathy and cystoid macular edema [remain] to be determined," Dr. Schaal wrote. "The theory is that the decrease in blood flow with increasing axial length may play a role in this association. This study did not investigate the mechanism, it just demonstrated the association."

The Centre for Eye Research Australia receives support from the Victorian Government. This study is supported by an Australian Research Council linkage grant and by the National Health and Medical Research Council Centre for Clinical Research Excellence. The funding organizations had no role in the design or conduct of this research. The authors, Dr. Gardner, and Dr. Schaal have disclosed no relevant financial relationships.

Ophthalmology. Published online May 23, 2012.

    
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