Where is the inner buckle line? What is its essence? What is the function?

The inner buckle line is located in the pupil and surrounds the circumference of the pupil and extends toward the center of the pupil. Its composition is a melanin layer whose shape is the result of the melanin layer extending toward the pupil. Its function is to protect against light damage.

①What is the shape of the inner buckle line in the evaluation system?

In the evaluation system, we divide the shape of the inner buckle line into two types, one is a circular ring and the other is a non-circular ring.

②How to distinguish the width of the inner buckle line?

Under normal circumstances，We call it wide when the width of the inner buckle line is large or equal to 1/15 of the pupil radius. We call it narrow when the width of the inner buckle line is less than 1/15 of the pupil radius. When the pupil is elliptical, the radius should be chosen according to the short side and the ratio is still determined by 1/15 mentioned above.

③How to judge the elasticity of the inner buckle line?

Judging the elasticity of the inner buckle line, we usually decide in two cases: under the strong sunlight, the inner buckle line is pulled with the contraction of the pupil, and the width of the inner buckle line is obviously increased. In the case of insufficient light, the inner buckle line expands as the pupil expands and the width of the inner buckle line is significantly reduced due to the expansion of the pupil. The evaluation system calls these two distinct functions "elastic."

④How to judge whether the elasticity of the inner buckle line is strong or weak?

The strength or weakness of the inner buckle line is judged according to the frequency and amplitude of the pupil contraction and expansion. Whether it is under strong light or dim light, the inner buckle line contraction and expansion must have both amplitude and frequency. It is strong. Otherwise it is weak.