The forward tilt angle, also called the tilt angle, refers to the angle between the plane line and the vertical line of the lens, which is generally 10~15°.

Since people naturally look forward less frequently in the horizontal position, they are often used to looking at the target with their heads slightly downward, so the horizontal line of sight and the usual habitual line of sight form an inclination angle.

In this way, the position and angle of the lens in front of the eyes must match and adapt to this tilt angle, and cannot deviate from this structure.