Top focus deviation
The nominal apex value of the sunglasses should be 0.00D. The deviation of the lens manufacturing or the lens and the assembly of the frame may cause deviation of the apex power (ie with positive or negative apex). If it exceeds a certain range, the wearer may feel that the object is deformed, and the serious one may affect the wearer's vision health. Corresponding to the national standard table 1 of GB10810.1 "Spectacle lens part 1 : single light and multifocal lens", the spherical lens top power tolerance is ±0.12D; the cylindrical lens top power tolerance is ±0.09D.
The prism of the sunglasses should be 0.00 Δ. If the lens has a prismatic degree, the focus will be shifted. If it exceeds the standard allowable range, the binocular vision may not be combined, or the imbalance may be caused. The eye muscles and optic nerves are disorderly regulated, and severe neurological disorders or strabismus may occur. According to the requirements of Table 4 of GB10810.1, the prism degree tolerance is 0.25 Δ.
For light-colored sunglasses, the light transmittance should be >40%; for sunshades, the light transmittance range is 8% to 40%. The light transmittance project is an important indicator of the function of sunglasses. According to the current Chinese standard, sunglasses are divided into three categories: sun visors, light-colored sunglasses and special-purpose sunglasses, while European standards and international standards divide them into five categories.