Lens Shape
Corrective lenses can be produced in many different shapes, from a simple circular lens, to wide, squat rectangular fashion glasses, to full eye lenses that cover as much of the visual space as possible.
For lower power lenses, the wearer may choose a lens shape that is limiting in the corrective capability but which allows for trendy fashion shapes.
Higher power patients with naturally poor vision may opt for a larger full-eye lens simply because without the lens they cannot see clearly, and a small lens leads to tunnel vision with blurriness in the surrounding space beyond the edges of the lens.
Bifocal, trifocal, and progressive lenses generally require a tall lens shape to accommodate the different bands of lens focus. If the lens is too squat these bands form very narrow strips, as if looking at the world through a clearly focused mailbox slot within the bands of focus.
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