edge clearance


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edge clearance

A small, peripheral gap between the edge of a rigid contact lens and the cornea. It is important as it allows tear exchange and eases lens removal. The absence of edge clearance in rigid contact lenses may lead to superficial corneal damage.
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3 and 9 o'clock staining (see Figure 2) will often be evident in patients having both 'with' and ' against the rule' astigmatism, due to a lack of lens movement caused by reduced edge clearance
Choosing a lens with smaller total diameter will help to minimise the exaggeration between the two different meridians on the corneal surface, which in turn will help to avoid the excessive edge clearance in the steeper meridian.
The edge clearance on top and bottom of PCB must be 3 mm.
Keep the holes outside the 3 mm edge clearance area and keep a free space of 8 mm diameter around these holes.
Offers 3 mm and 5 mm edge clearance changeover without additional parts and an adjustable stencil shelf for maximum flexibility.
The non-magnetic packaging and small edge clearances are ideal for building larger arrays for use in the high magnetic field environment of PET/MRI scanners, which are used to monitor the vital processes of human and animal bodies or body parts.
Tooling and registration holes, edge clearances, component lead-hole sizes, physical component size and assembly angles were all standardized to optimize component packaging, board design and insertion throughputs.