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.
The testing parameter that varies least from state to state is visual acuity. All states have visual acuity requirements for licensure, and all but 3 have set the minimum best corrected visual acuity (BCVA) requirement at 20/40 in the better eye. Georgia requires a BCVA of at least 20/60 in at least one eye; for New Jersey and Wyoming the requirement is 20/50.