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First, what is the distance between the prescription lens and the cornea? And why should we be concerned about this distance? The distance between the prescription lens and the cornea is the distance between the optical center of the inner surface of a lens of prescription eyeglasses and the vertex of the cornea, or VD for short.

distance between prescription lens and cornea

After understanding what "VD" is, let's talk about the relationship between this distance and wearing glasses.

The lens-eye distance of contact lenses is 0. Because it is attached to the cornea's surface, the contact lens is as many degrees as it is effective. As a result, the eye looks through the optical center point to the maximum extent possible. It has apparent features: visual effect with slight shrinkage and distortion; closest to natural imaging effect. The field of view is open, just like the naked eye.

Not everyone is suitable for contact lenses, so most people still wear prescription eyeglasses, that will exist VD. According to tests, there is a relationship between this VD and effective lens prescription. For example, the VD of a typical eyeglass frame is 12 mm. If it is reduced to 8 mm, the effective prescription may increase by about 10-15 degrees; similarly, if it is increased to 16 mm, the effective prescription may decrease by 10-15 degrees.

Normal optometry, comprehensive optometry, and trial eyeglass frames have defaulted to 12 mm VD. However, most acetate glasses frames are supposed to be less than 12mm lens-eye distance when worn on the face because of the one-piece nose rest. Metal glasses are generally larger than acetate frames because they have adjustable nose pads.

After our continuous observation, using the same prescription eyeglass lenses, wearing acetate frames is more comfortable than metal frames! If the old glasses are acetate frames and change to metal frames, and the customer has sensitive eyes, there is a greater chance that they will need to adapt upfront. On the other hand, if the old glasses are metal frames replaced with acetate frames, most customers are satisfied with the new glasses without having to adapt. Why are acetate frames more comfortable?

1) Contact lenses do not have a phase difference problem; even if the difference between the two eyes is vast, you can still wear them comfortably. This is because VD is almost 0, which means infinitely tiny. Especially for those who have a big difference in the prescription of both eyes, people with refractive disparity will be more comfortable with acetate frames than metal frames because the VD is small and the phase difference is slight.

2) If we look outside close to the window, the field of view will be significant, and the edge of the window can not be seen. If we take two steps back, the field of view outside will be reduced, and the window frame will be seen. Wearing glasses is the same reason; acetate glasses frame mirror VD small, the field of view will be more open, more through the optical center point to see, naturally will be more comfortable. Can imagine the state of VD infinitely small, can only see through the center point.

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