There are four points to pay attention to when choosing contact lenses

There are four points to pay attention to when choosing contact lenses

In fact, there are many aspects that need to be paid attention to in the selection of contact lenses, such as corneal coverage, center positioning, lens mobility, etc., the following small series will tell you in detail about the four points that need to be paid attention to in the selection of contact lenses, and take you together to scientifically and standardize optometry and glasses. 1. Corneal coverageCorneal coverage refers to the degree to which the lens covers the cornea. In the picture on the right, the edge of the nasal lens does not completely cover the cornea, and part of the edge of the iris is not covered, while the temporal side can see that part of the edge of the lens covers the bulbar conjunctiva, which belongs to poor corneal coverage, so the first step is to evaluate the corneal coverage, it is necessary to see whether the lens completely covers the cornea, because when choosing the diameter of the contact lens lens, the first thing is to measure the customer's horizontal visible iris diameter, and on this basis, add 2mm to get the most suitable contact lens diameter for the customer. Therefore, the diameter of the contact lens must be greater than the diameter of the cornea, which is mainly for soft lenses, and it is necessary to ensure that the entire lens completely covers the cornea, and then configure it. 2. Center positioningCenter positioning refers to the pupil heart evaluation of the lens and cornea. Because there is a small black circle in the middle of the cornea of the human eye, that is, the pupil, for the lens, whether it is colored or transparent, in fact, there is such a small circle in the center, called the optical area of the lens, and the most ideal state is to align the corneal pupil with the optical area of the lens, so that it is called good center positioning. As you can see from the image above, the left lens completely covers the cornea, and the 360-degree distance between the lens and the limbus is very uniform, so the center of this lens is well positioned. In the image on the right, you can see that the edge of the lens is tangential to the limbus from the lower side of the nose, and the edge of the lens is much more than the bulbar conjunctiva above the temporal side, and the lens is offset towards the upper temporal area of the customer, so the customer's pupil is not aligned with the optical area of the lens. We should also pay attention to this item when choosing contact lenses, to see whether the lens completely covers the cornea, and then observe whether the 360-degree distance of the extra edge is uniform, if it is uniform, it means that the optical area of the pupil and the lens is a concentric circle, if the extra area is uneven, it means that the lens is offset, and its center positioning is not particularly good. 3. Lens mobility The lens movement refers to the degree to which the relative position of the lens changes due to the eyelid force, that is, the upper eyelid conjunctiva will rub against the lens every time the human eye blinks, and there is friction between the two. In the picture on the left, there is some deviation of the lens after blinking, but the lower edge of the lens does not exceed the limbus after it is moved, so this movement is good mobility. In the picture on the right, the lens has run to a very high position after blinking, and the lower edge of the lens has exceeded the corneal limbus below, and the distance exceeded is very large, so if you see this happening to the glasses, you can assume that the movement of the lens is too large, and we usually have to experience it when we buy contact lenses. 4. Tightness Tightness refers to the tightness of the lens and the cornea with the method of passing, in fact, there is a very famous experiment called the lower eyelid push up experiment, this method is to use the thumb to push the lower eyelid margin, and then let the lower eyelid margin to push the lower edge of the contact lens lens, in the process of pushing, you can feel the tightness between the lens and the cornea, if you find that there is no resistance when pushing up, the lens can be pushed up well, and then because of gravity slowly and uniformly slide, If the sliding distance is about 2mm, you can think that the tightness is normal, if the tightness is tight, you will feel that the resistance to push up is particularly large, and the cornea seems to be stuck with the lens.