There are many factors affecting contrast sensitivity (CS), among which glare, age, pupil diameter, spatial frequency and refractive status are the most important.

① Relationship between contrast sensitivity (CS) and glare

Glare refers to a phenomenon that the sensitivity of the retina is reduced in whole or in part when the eye is faced with dazzling light, which affects the eye's ability to distinguish targets. It is caused by the scattering of stray light in the eye. There are mainly three types of glare: disabling glare, adaptive glare and adaptive glare.

Incapacitating glare is the decrease of visual function caused by external glare light source. The most common example is the decrease of visual acuity caused by illumination on the dusty front windshield of the car; Inadaptable glare refers to the uncomfortable feeling under bright light, and there is light in the fixed high brightness area. For example, if reading under strong direct light causes discomfort, visual avoidance can be used to avoid vision loss; Light adaptive glare refers to the visual acuity decline when the human eye changes from dark environment to bright environment, because the afterimage of the glare source produces a central dark spot, which still exists when the glare source is removed. This kind of glare is due to the light adaptation of photoreceptors, which will be obvious when suffering from macular disease.

In a bright environment, when the contrast sensitivity (CS) value under glare is greater than that without glare, the contrast sensitivity (CS) value of human eyes can be increased. In the dark environment, the contrast sensitivity (CS) of the retina decreased significantly, resulting in a decline in the resolution of the human eye. Therefore, the contrast sensitivity (CS) of the eye to distinguish all spatial frequency targets is reduced in the glare environment, and the detected contrast sensitivity (CS) in the non glare state is greater than that in the glare state.

② Relationship between contrast sensitivity (CS) and pupil diameter

Pupil size directly affects the brightness of retina and the clarity of retinal image, thus affecting the contrast sensitivity (CS) value. Studies have shown that when the pupil diameter is less than 2.5mm, the stray light generated by the incident light at the pupil edge will interfere with the retinal imaging quality and reduce the contrast sensitivity (CS). When the pupil diameter is too large, the aberrations of human eyes increase, which also interferes with the contrast sensitivity (CS).

③ Relation between contrast sensitivity (CS) and spatial frequency

The contrast sensitivity (CS) function graph of normal human eyes presents an inverted "U" shape (the shaded area of the contrast sensitivity (CS) visual acuity chart), which is the highest at the middle spatial frequency. The "low frequency area" at one end mainly reflects the visual contrast, and the "high frequency area" at the other end mainly reflects the visual sensitivity. The higher contrast sensitivity (CS) in the middle spatial frequency region is because the activity of human visual system mainly depends on the middle frequency region. At the high spatial frequency end, the curve extrapolation and axis intersect at one point, indicating that only when the contrast is 100%, the sine wave grating can be distinguished by the human eye, which corresponds to the visual acuity of the visual acuity chart. Therefore, the visual acuity chart is only a point on the contrast sensitivity (CS) curve, so the contrast sensitivity (CS) can evaluate visual function more comprehensively and objectively than vision.

④ Relationship between contrast sensitivity (CS) and refractive status

The low vision of amblyopia is first manifested in the decrease of low-frequency contrast sensitivity (CS), and the visual rehabilitation process of amblyopia is first manifested in the increase of contrast sensitivity (CS), followed by the increase of vision, which is very important for the early diagnosis of amblyopia. The contrast sensitivity (CS) of high myopia was also abnormal with the increase of myopia degree.

⑤ Relationship between contrast sensitivity (CS) and age

The contrast sensitivity (CS) of children aged 3 ~ 5 years old is close to that of adults, but the spatial frequencies are slightly lower. With the increase of age, the contrast sensitivity (CS) continues to increase, and starts to decline from about 40 years old. The peak value of contrast sensitivity (CS) function curve (CSF) moves from high spatial frequency to low spatial frequency with the increase of age.