厂址选择的技术经济分析方法有（）A、方案比较法 B、分级计分法 C、最小运输费用法 D、规
题型：多项选择题
问题：
厂址选择的技术经济分析方法有（）
A、方案比较法
B、分级计分法
C、最小运输费用法
D、规模曲线法
题型：多项选择题
Myopia
The fact that around one in four people around the world suffer from myopia has resulted in a lot of research being done into the causes and development of this eye disease. Despite all the theories, there have been no conclusive answers, which means a quarter of the population still live with the inconvenience and hassle of wearing glasses or contact lenses to correct their vision impairment. So what do we know
Myopia, also known as nearsightedness or shortsightedness, results from the resting eye focussing on objects in the distance. For the eye to look at objects close to the subject, the lens must increase in thickness and in the radius of curvature. Subjects with this condition often have excessively long eyes which results in the image forming in front of the retina as opposed to on it. The main culprit of this deformation impairment is excessive postnatal eye growth. Although some cases arise in early adulthood, the majority are formed in the early school years. Around 5% of cases lead to blindness and it predisposes shortsighted people to retinal detachment, retinal degeneration and glaucoma.
As mentioned earlier, who is actually prone to this illness has not yet been fully determined. However, those more likely to develop the impairment are children with myopic parents or those doing ’near work’. If you suffered childhood illnesses, low birth weight, used night lights as a child or have nearsighted siblings, you may also be more susceptible to the condition. Thus it can be seen that researchers are divided as to whether the disease is caused by genetic or environmental factors. There are two main points supporting the genetic argument. Firstly, there is evidence to suggest that myopia may be due to a dominant gene that is inherited by the child from the parents. Secondly, it is also thought that myopia may be caused by influences from the nervous system that are not normal and have a negative impact on the developing eye. Although there is ample evidence to support the fact that myopia runs in families, this evidence has not been directly linked as a definite cause for the disease’s development. Moreover, this is not to say that the case for environmental factors shows no validity.
Researchers have split environmental factors up into two main contributors. One is that too much ’close work’ is attributed to the development of myopia. The other is a theory which states that night lights may be responsible for myopia in infants. For the former, experiments have been conducted on both monkeys and chicks to prove its validity. They were forced to view objects at a close distance. By limiting their visual field, there were definite and extreme changes in their ocular refraction which led to the animals becoming myopic. For the latter, tests conducted on infants concluded that those who were exposed to a night light had a greater tendency to develop myopia. In fact, the more light they were exposed to, the more prevalent nearsightedness became.
However, much more study is needed to verify the results of this research on night lights. There are still some question marks over the tests’ validity. Some believe that myopic parents are more likely to light the rooms of their children, making it a genetic and not an environmental factor. Some have suggested that research hasn’t been extended to all ethnic groups, especially Asians in whom the incidence of myopia tends to be higher. Others have asked how an infant’s eye carl recall the damage it received earlier in life when the impairment doesn’t manifest itself till later in life. Finally the research is also reliant on parents’ recollection of their child’s earlier childhood events being accurate. This essentially means that you do not need to go and start throwing out your children’s night lights just yet.
With the lack of concrete evidence on how myopia is caused, it is hard to determine a way of preventing the condition. Cures are available to some. The most popular is probably Lasik eye treatment. This is where lasers are used to correct one’s vision. However, this is not a miracle cure as it can have side effects and even be quite dangerous for some. So for now around 25% of the population continues to power on through challenges with their glasses or contact lenses regardless of how it may affect their lifestyle.