推荐回答(5个)
太阳镜可能给眼睛造成哪些伤害
1.可诱发青光眼的急性发作。因为戴了太阳镜后,进入眼内的可见光减少,瞳孔会自然开大,造成前房角狭窄,导致房水引流不畅,时间长了,易诱发闭角型青光眼急性发作。患者会出现眼红、眼痛、头痛、视力急剧下降,甚至伴有恶心、呕吐等全身症状。所以青光眼病人或怀疑患有青光眼的人不宜戴太阳镜。
2.可导致弱视。6岁以下儿童的视觉功能还未发育成熟,戴太阳镜时间长了,眼底黄斑区不能得到有效的刺激,会影响视觉的进一步发育,甚至形成弱视。所以6岁以下儿童不宜戴太阳镜。
3.可引起视觉疲劳。有些人不分时间和场合,不管在户外还是室内,不论太阳光强弱,甚至在黄昏、傍晚以及在看电影、电视时也戴着太阳镜。这样做会加重眼睛的负担,引起眼肌紧张,视物模糊,严重时还会出现头晕眼花、不能久视等症状。
4.可引起太阳镜综合征。患太阳镜综合征的多见于赶时髦的年轻人,他们偏爱戴边宽、架厚、分量重的大框架太阳镜。这类眼镜连续戴1~2周后,戴镜者会出现眼眶或两面颊之间部位麻木、知觉迟钝等症状,呼吸时有鼻部不适的感觉,就像患了感冒。还有人感到像有小虫子在脸上爬行,上颌牙龈麻木,上门牙感觉不适,眼睛酸胀。这是由于人的面部感觉主要是由三叉神经支配,三叉神经的眶下支是经眼眶下缘的眶下孔穿出的,厚架、宽边、分量重的太阳镜往往会压住三叉神经眶下支,因而引发上述症状。
选择太阳镜应注意哪些问题
太阳镜选择很有学问,选择不当容易对眼睛造成损害,在选择太阳镜时应注意的问题有:
●应到正规眼镜店选择正规厂家生产的具有防紫外线功能的太阳镜。街边小摊儿、小贩出售的眼镜,往往不能达到防紫外线的标准,最好不要选购。
●选择时注意镜片表面要光滑,无波纹、无瑕疵、无气泡、无磨痕。要将镜片平放,从水平方向观察镜片有无翘曲。凹凸不平或有痕迹、气泡的镜片不宜选购。
●镜片的颜色选择,应以戴上后看周围环境的颜色不失真,物体的边缘清晰,能有效识别不同颜色信号灯为原则。镜片颜色深浅的选择,应视活动场所而定,一般以中等深度为好,如淡灰色、淡茶色、淡绿色等,这些颜色的太阳镜对红外线、紫外线吸收较好。当然,如果要求遮光效果很强,就应选择颜色较深的镜片。但骑车或驾车者不能选择颜色太深的镜片,否则不能有效识别不同颜色的交通信号灯。
●选购太阳镜还得考虑它与眼睛大小、脸形、眉毛、鼻子之间的匹配关系。大眼睛的人要选择大镜框的太阳镜,眼睛小一些的选择小一些镜框的太阳镜,胖圆脸形的人适合戴粗大框架的太阳镜,瘦长脸形的人适合圆形镜框的太阳镜,扁圆形脸的人宜选用上下略窄的方形框架的太阳镜。
俗H0
Xg在主流的太阳镜排行中 性价比很不错的
http://FwPtKwHfXc-i.chen.gouwu6.org/byaj?xSjWoLePj--CpJuTiUeIcVu--GtUcTdXi--GcSqRsFe--QnVfDhNa--XdDaSvLp--FhFdVePa--AfDeVwQa--CeKnEuTw--HjVjCmFf--JxHtImIb.html
.E
Ij太阳镜n(A/2)=√((1-cosA)/
((1 cosA)) tan(A/3)
=-√((1-cosA)/((1 cosA))
享支持LAN Optimizer (智拿型网络带宽优化吼理工具)
b(a-b)=-(b-a/2)^2 a^2/4 ab
-b^2=-(b-a/2)^2 a
^2/4 且a>b>0 所以0≤ab-b^2≤a^2/4
http://baike.baidu.com
所以16/(ab-b^2)≥64/a^2 所以a^2
16/(ab-b^2)≥a^2 64/a^2≥2
根号64=2*8=16 所以最
小值为16 当b=a/2,
且a=4,即a=4,b=2时,能取到最小值19
MT太阳镜press7.3)
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