Overall, it is cheap, easy, and quick to implement the distributed backbone network. Collapsed backbone. This type of backbone uses single, powerful router as the central connection point for multiple subnetworks. As Figure 4 shows, the central device is the highest level of the backbone.arallel backbone. Parallel backbone is a variation of the collapsed backbone, where devices are having more than one connection between them. As Figure 5 shows, there are multiple connections between the high level routers and the network segments.
The most common method to measure visual acuity is the Snellen eye chart. Like all eye charts, the Snellen chart tests a patient's ability to resolve high-contrast letters and is satisfactory if their vision is good. Unfortunately, the chart does not have enough sensitivity for patients with poor vision.
Reading charts are often used to measure visual acuity. Visual acuity measurements evaluate how clearly each eye is seeing. As part of the testing, you are asked to read letters on distance and near reading charts. The results of visual acuity testing are written as a fraction such as 20/40.When testing distance vision, the top number in the fraction is the standard distance at which testing is done, twenty feet. The bottom number is the smallest letter size you were able to read.A person with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen at 40 feet in order to see it clearly. Normal distance visual acuity is 20/20.Preliminary testing may include evaluation of specific aspects of visual function and eye health such as depth perception, color vision, eye muscle movements, peripheral or side vision, and the way your pupils respond to light.eading charts are often used to measure visual acuity. Visual acuity measurements evaluate how clearly each eye is seeing. As part of the testing, you are asked to read letters on distance and near reading charts. The results of visual acuity testing are written as a fraction such as 20/40.