What Are Prescription Safety Glasses?

Aspheric glasses have a different surface curvature than ordinary spherical lenses. In order to pursue the thinness of the lens, the curved surface of the lens needs to be changed. In the past, spherical design was used to increase aberrations and distortion. As a result, obvious image blur and visual distortion occurred. , Narrow field of vision and other adverse phenomena. The current aspheric design has corrected the image and solved the problem of distortion of vision. At the same time, the lens is lighter, thinner and flatter. Moreover, it still maintains excellent impact resistance, making it safe for the wearer to use.

Aspheric glasses

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Aspheric glasses have a different surface curvature than ordinary spherical lenses. In order to pursue the thinness of the lens, the curved surface of the lens needs to be changed. In the past, spherical design was used to increase aberrations and distortion. As a result, obvious image blur and visual distortion occurred. , Narrow field of vision and other adverse phenomena. The current aspheric design has corrected the image and solved the problem of distortion of vision. At the same time, the lens is lighter, thinner and flatter. Moreover, it still maintains excellent impact resistance, making it safe for the wearer to use.

Chinese name

Aspheric glasses

Solve the problem

Vision distortion

Definition

Glasses made with aspheric lenses

Advantages

Reduced lens aberrations

Glasses made with aspherical lenses are called aspheric glasses. This is a concept opposite to ordinary spherical glasses.

Aspheric glasses have a different surface curvature than ordinary spherical lenses. In order to pursue the thinness of the lens, the curved surface of the lens needs to be changed. In the past, spherical design was used to increase aberrations and distortion. As a result, obvious image blur and visual distortion occurred. , Narrow field of vision and other adverse phenomena. The current aspheric design has corrected the image and solved the problem of distortion of vision. At the same time, the lens is lighter, thinner and flatter. Moreover, it still maintains excellent impact resistance, making it safe for the wearer to use.

In the case of refractive error correction, the quality of the spectacle lens is directly related to the clarity and comfort of the human eye. For spherical lenses, the aberrations cannot be corrected with the combination of lenses. Find out ways to reduce aberrations and improve sharpness, such as reducing the vertex distance (VD) and reducing the interference of magnification; the lens is as thin as possible; choosing the best base curve and other methods to control the aberrations in a small range

Modern spectacle lenses have been designed with computers. Computers can make very accurate optical path traces to find the best form of lenses. In the 19th century, the best shape of the best curved spectacle lenses could be calculated manually. The lens is called a point-focus lens. In 1904, Tschelning, a great vision optics expert, calculated according to the third-order theory of aberrations. The best lens form for various lens powers was calculated according to Tschelning. This series of the best curved figures with different degrees of vision form an ellipse. Although this ellipse was not proposed by Czerning, future generations still call it Tschelning Ellipse Park. According to the design of Czerning, the lenses cannot reach The purpose of complete aberration. According to the lens designed by Czerning Ellipse, there are two disadvantages:

1. The lens designed according to Czerning ellipse can form a point focus lens and reduce the aberrations in the range of + 7.00--22.00D. If you can control the aberrations beyond this range, you can't do anything but use an aspheric design method to eliminate them. Aberration

2. According to Czerning s best curved design lens, its curvature is large, that is, the lens base arc is steeper, and the lens is thicker and less beautiful. For example: + 3.00DS, the best base curve is + 8.83D. Can not meet patients' requirements for light and thin ophthalmic lenses

In recent years, some lens designers have tried to adopt a very flat design for the base lens of the spectacle lens in order to cater to the preferences of patients. Although the flat lenses look thinner and more beautiful, they cannot avoid optical defects and make certain aberrations out of range. The lens that affects the clarity and comfort of the vision may be acceptable in the 30-degree fixation range. Outside the 30-degree fixation range, the peripheral vision and dynamic vision of the wearer are significantly affected. In order to make the lens flat and obtain Clear image quality, researchers used optimized aspheric lenses that minimize optical defects in lenses

Strictly speaking, all lenses with refractive surfaces that are not spherical or aspherical include: cylindrical lenses, progressive multifocal lenses, and top-peripheral aspheric lenses, all of which are modern achromatic aspheric lenses, which actually refer to the top-periphery Aspheric lens This lens gradually increases the radius of curvature from the lens center to the periphery (the lens surface is gradually flat). The refractive surface of the lens is calculated based on the selected base arc. The aspheric curve is close to the ideal aspheric curve. Light enters the lens, regardless of paraxial or far-axis light can be converged to a point

In order to make the glasses look beautiful, the aspheric lens is designed as flat as possible but the lens has a flat base curve, even if the aspheric design is used, its optical performance will decrease rapidly, such as: n = 1.6 resin lens, aspheric design, +1.5 The lens of D has a base angle of + 3.25D and a field angle of 30 degrees. Its field curvature is 0.02D and astigmatism is 0.10D. The image quality is good. If you use a flatter + 2.00D base curve, the field curvature is 30 degrees. 0.55D, astigmatism 0.71D, the image clarity decreases, and the image quality is worse

Optometry with aspheric lenses and glasses, using standard optometry requirements: accurate optometry, reasonable prescription

1. Requirement for measuring monocular PD level: The eye must be horizontally aligned with the aspheric lens optical center (the center of the concentric circle)

2. Pupil height and vertical requirements: The starting point of the pupil height (pupil height) on the template of the frame must be related to the forward angle of the frame (the angle between the front frame of the glasses and the temples) (Figure 7) , For every 2 degrees of anteversion (88 degrees of anteversion), the starting point of the pupil height drops by 1mm, up to 5mm

3, adjust the frame: adjust the frame in advance to make the frame flat, the length of the mounting ears is appropriate, the volt is attached, and the comfortable forward tilt angle is 80-85 degrees

4. Point pupil height method: In addition to the frame forward tilt angle compensation, the patient's head can be tilted back slightly, so that the front frame of the glasses is perpendicular to the ground. Use a waterproof pen to point at the center of the pupil and directly point on the frame plate.

80-850

Figure 7 Forward angle

Figure 8 Pupil height position

Optimized design of aspherical lenses can obtain the best optical performance and thin and beautiful wearing effect. However, the assembly of spectacle lenses is different from spherical lenses, and assembly errors are not allowed. If the processing of spherical lenses is slightly problematic, generally not Affects the use of lens wearers (of course, the assembly should be standardized), but the processing of spherical lenses is slightly negligent, and its optical performance is worse than spherical lenses. It is often reflected clinically: the original spherical lens was worn, and a pair of aspheric glasses was replaced. There is no clear and comfortable explanation by the optometrist. The spherical lens may have been used to before. The aspheric lens has just been changed. Patients who need a process of adaptation may even want to replace the spherical lens. The main reason is that the optician's assembly is wrong.

The assembling of aspherical lens should pay attention to the following points:

1. Ensure that the horizontal distance of the pupil center is equal to the center distance of the concentric circle of the aspheric lens. The starting point of the pupil height is within 1-5mm below the pupil center.

2. The marked line of pupil height is shown in Figure 8. The marked line should be kept until the patient tries on successfully.

3. When the geometric center distance and interpupillary distance of the frame are not equal, you need to move the center to the required position. For example, if the frame mark is 54-16, PD66mm, then the optical center needs to be moved 2mm inward. Same as the spherical mirror processing method.

4. It is forbidden to shift the prism in the prescription, or if there is a prism in the grinding prism prescription, it is not suitable to prepare aspherical lenses. If a prism is required in the prescription, the lens must be moved, or the aspheric lens of the polished prism, the optical center of the aspheric lens. It will deviate from the geometric center, and make the pupil deviate from the optical center. When the eye looks in one direction, it may reach the optical center quickly; when the eye turns to look in the other direction, it does not reach the optical center fast enough, so that the patient sees something. An unpleasant feeling and even vision loss

5, template production: template size is accurate, the movement of the optical center, pupil height, marked on the template

6, cut edges, chamfers, slotting, drilling, testing, etc., the same as spherical lenses

1, adjust the frame to be flat, comfortable to wear on the face, fold fit ears are properly curved, the two temples are symmetrically positioned on the front frame plane

175-1800, forward tilt 80-850

2, check the visual acuity of monocular and binocular correction vision should be the same as or slightly better than the optometry

3, put on glasses to walk, see if there is any abnormal feeling reading with no obstacles, no response, the end of the optician

Nine, prognosis description: Before the end of the optician need to communicate with the patient a few words

1. It may be a bit uncomfortable to wear glasses for the first time.

2, common sense using glasses

3. Methods for protecting eyes

4. Review time

X. Complaint Handling

1. Check the prescription

2. Check the pupil height and optical center distance

3, new optometry

: Adaptation Guide (from Optics)

1. Measuring monocular PD

2. According to the customary method, measure the height of the main reference point (pupil height). According to the forward tilt angle, it is less than 20.

3. Another method for determining the main reference point: Make the optician wear the frame, tilt the head slightly backward, make the front frame of the frame perpendicular to the ground, and then measure the main reference point at this position

4. For aspheric lenses, it is strictly forbidden to grind prisms to move the center of light away from the center of the aspheric lens area, which will destroy the optical advantages of aspheric lenses