As is well known, the human eye is a complex refractive system, with the highest refractive index being the crystalline lens. You can imagine it as a built-in lens. If you choose the cheapest eyeglasses lens with the same Abbe number as the human eye, the imaging quality is optimal, resulting in minimal visual fatigue and excellent contrast vision.

Currently, most high Abbe number cheapest eyeglasses lenses have extremely low refractive index, making them a good choice for people with low refractive index (below 300 degrees).

But for people with a height of over 600 degrees, low refractive index lenses are very thick and can easily produce prism effects, affecting the visual effect.

So for these people, the first choice is to choose lenses with higher refractive index to reduce lens thickness and weight, but such a choice will also result in a certain degree of clarity loss.

When the Abbe number is above 50, it is in high-definition mode, which is most comfortable for the human eye. When the refractive error is below 300 degrees and not above 400 degrees, this type of cheapest eyeglasses lens can be selected.

When the Abbe number is between 49 and 40, it is in a clear and comfortable state. For the human eye, the imaging quality is excellent and the comfort is good. When the refractive error is higher than 250 degrees and lower than 600 degrees, this type of lens can be used.

When the Abbe number is between 39 and 36, the clarity and comfort are generally acceptable to the human eye, and the visual performance is still good. The impact on the human eye is limited, and there is very little harm to the eyes. For those with high refractive errors, this type of lens is still acceptable.