Corrective lenses can be produced in many different shapes from a circular lens called a lens blank. Lens blanks are cut to fit the shape of the frame that will hold them. Frame styles vary and fashion trends change over time, resulting in a multitude of lens shapes. For lower power lenses, there are few restrictions which allows for many trendy and fashionable shapes. Higher power lenses can cause distortion of peripheral vision and may become thick and heavy if a large lens shape is used. However, if the lens becomes too small, the field of view can be drastically reduced.
photopsia Flashes of light often noticed in the edges of the visual field. Photopsia can have many causes, including mechanical (rather than visual) stimulation of light-sensitive cells (photoreceptors) in the retina. For example, a detached retina can cause photopsia when the retina pulls away or detaches from tissue in the inner back of the eye. A vitreous detachment with accompanying photopsia can occur when the eye's gel-like interior begins to shrink and pull against the retina. Photopsia can be accompanied by a shower of spots and floaters .
The global production of CA materials was over 800,000 tonnes (790,000 long tons; 880,000 short tons) per year in 2008. Many products are disposed of as litter or into compost. While it was initially believed that CA was virtually non- biodegradable , it has been shown that initial partial deacetylization the polymer’s cellulose backbone is readily biodegraded by cellulase enzymes. In biologically highly active soil , CA fibers are completely destroyed after 4–9 months. Photodegradation is optimal with 280 nm or shorter wavelength UV-irradiation and enhanced by TiO2 pigment.  CA cigarette filters take years to be broken down in the open.