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In glasses with powers beyond ±4.00D, the vertex distance can affect the effective power of the glasses. [4] A shorter vertex distance can expand the field of view, but if the vertex distance is too small, the eyelashes will come into contact with the back of the lens, smudging the lens and causing annoyance for the wearer.
The number of people globally with refractive errors has been estimated at one to two billion. [4] Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected. [4] Near-sightedness is the most common disorder. [5] Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%. [6]
Using a phoropter to determine a prescription for eyeglasses. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.
[2] [4] Rates vary significantly in different areas of the world. [2] Rates among adults are between 15% and 49%. [3] [19] Among children, it affects 1% of rural Nepalese, 4% of South Africans, 12% of people in the US, and 37% in some large Chinese cities. [2] [3] In China the proportion of girls is slightly higher than boys.
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment The human eye can detect a luminance from 10 −6 cd/m 2 , or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
In the Rich Text Format specification, language code 4 is for the Chinese language. Codes for regional variants of Chinese are congruent to 4 mod 256. Credit card machines have four-twelve function keys. On most phones, the 4 key is associated with the letters G, H, and I, [85] but on the BlackBerry Pearl, it is the key for D and F.
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