WO2023216540A1

WO2023216540A1 - Scleral contact lens based on phase modulation technology

Info

Publication number: WO2023216540A1
Application number: PCT/CN2022/131983
Authority: WO
Inventors: 曹立; 张艳; 赵紫微; 霍胜彬
Original assignee: 天津世纪康泰生物医学工程有限公司
Priority date: 2022-05-09
Filing date: 2022-11-15
Publication date: 2023-11-16
Also published as: CN114779497A

Abstract

Provided in the present invention is a scleral contact lens based on phase modulation technology. By superposing a modulation/demodulation phase on an optical surface of the front surface of the scleral contact lens, the total wavefront aberration is modulated in a customized mode, thus satisfying requirements on the human eye wavefront aberration during designing, accurately compensating various types of wavefront distortions of the front surface of corneas of a patient, and greatly improving the eyesight level and the visual quality of the patient.

Description

A scleral contact lens based on phase modulation technology

This application claims priority to the Chinese patent application filed with the China Patent Office on May 9, 2022, with application number 202210500567. incorporated in this application.

Technical field

The present invention relates to the technical field of scleral contact lenses, and in particular to a scleral contact lens based on phase modulation technology.

Background technique

Scleral lenses are a specially designed rigid gas-permeable contact lens. They are named for their large diameter, no contact between the lens and the cornea, the lens spanning the entire cornea, the lens landing in the scleral area, and the middle of the cornea being filled with preservative-free saline. . Large-diameter contact lenses allow the lens to be positioned outside the edge of the cornea, making it considered the best way to correct vision for patients with irregular corneas. For the cornea, only wearing scleral lenses has a real gap without any mechanical friction. . Try to avoid any contact between the lens and the cornea, so that the lens spans the cornea like a bridge, as shown in Figure 1. From a technical point of view, these lenses are not contact lenses, at least they do not come into contact with the corneal surface, and the comfort of the cornea is greatly improved, which is one of the biggest advantages of large-diameter contact lenses.

In recent years, scleral lenses have become increasingly popular in Europe and the United States. Due to their personalized design, they have certain advantages in the treatment of refractive correction, irregular cornea, and dry eye. According to the diameter of scleral lenses, they can be divided into corneoscleral lenses (diameter 12.5mm-15mm, contacting part of the cornea), mini scleral lenses (diameter 15mm-18mm, completely touching the sclera) and full scleral lenses (18mm-25mm, completely touching the sclera). ), because mini scleral lenses usually have a small tear storage capacity, good oxygen permeability and visual quality, and have a good corneal apex gap, which can reduce mechanical friction on the central cornea.

Scleral lenses use rigid gas-permeable scleral contact lens materials, that is, through highly oxygen-permeable RGP materials, materials with different oxygen permeability coefficients are gradually improved. The current lens materials mainly come from BOSTON, Menicon and CONTAMAC. BOSTON material is currently the most used, most commonly used, and most used material in the world. It has high oxygen permeability and moisture content, and has good comfort. Among them, BOSTON XO2 material has a wetting angle of 38 and an oxygen permeability coefficient of 141. It has a high With Dk value, good dimensional stability and processability, this material has been applied to rigid gas-permeable contact lenses for orthokeratology. Its safety and effectiveness have been verified. Its high oxygen permeability and balanced processability properties and become an ideal material for preparing scleral lenses. Scleral lenses need to use high Dk materials, and there should not be too much tear fluid in the lens-corneal space to prevent hypoxia. Studies have shown that there are currently no studies confirming that wearing modern scleral lenses causes corneal hypoxia.

The clinical application of scleral lenses generally uses try-on lenses and trial-on evaluation technology. The main fitting process is: first, perform corneoscleral topography, slit lamp examination, and OCT anterior segment examination. Obtain the sagittal height from the corneal apex to the landing zone and the corresponding sagittal height difference, and select a suitable trial piece for trial fitting evaluation; use a suction stick to hold the lens before wearing it, fill the lens with physiological saline and fluorescein sodium, and instruct the patient to lower his head vertically. Look at the ground, use your hands to open the upper and lower eyelids as much as possible to expose the eyeball. The doctor helps the patient put on the lens and observe whether there are any bubbles under the lens. If there are bubbles, remove them and wear them again. There is almost zero lens movement when wearing scleral lenses, and there is almost no tear exchange. The ideal vertex tear film gap is about 300 microns. There will be a slight depression when the edge of the lens lands on the sclera. The thickness of the tear layer is significantly reduced after wearing (120-170 microns). Therefore, the fit evaluation should be carried out half an hour after wearing the glasses. To evaluate the tear thickness between the lens and the cornea, you can use a slit lamp and use light sectioning to observe the tear thickness under the lens at a 45-degree angle (fluorescent staining can optionally be used). The corneal limbus should be 360-degree full of fluorescence when observed under a slit lamp. Direct contact between the lens and the corneal limbus should be avoided. The edge of the lens should not compress the bulbar conjunctival blood vessels. The limbus is very important for corneal health, especially because stem cells are responsible for producing new epithelial cells, which are dispersed throughout the cornea. The tear fluid between the lens and the limbus is very important for the fragile stem cells in the limbus. When fitting, try to ensure that there is about 100 microns of space in the limbus. It is recommended to use OCT as an auxiliary tool during fitting. Accurately evaluate the tear thickness that should be retained at each position from the central apex to the limbus to improve the accuracy of fitting.

It is also important to assess the pressure exerted by the lens positioning arc on the bulbar conjunctiva. If the positioning area compresses the conjunctiva excessively, the blood in the compressed area of the conjunctiva will not be able to pass through the blood vessels, causing the conjunctival blood vessels under the lens to become white. In addition, scleral lenses also need to be tilted to help tear circulation. However, the warp angle should not be too high. An excessively high warp angle will increase the foreign body sensation and make it easy to feel uncomfortable when wearing it, affecting the wearing comfort. The warp angle can be adjusted by changing the angle of the positioning area. Finally, subjective refraction and visual acuity examination after wearing glasses are performed to determine the lens diopter.

In general, rigid scleral contact lenses have the following unique advantages: (1) High oxygen permeability ensures that the surface of the eye receives sufficient oxygen, which greatly reduces complications compared with ordinary soft lenses. It is one of the safest contact lenses currently worn. 1; (2) It has good shaping effect and good optical performance, ensuring that you get clear vision, even high astigmatism, irregular astigmatism, and aphakia will be well corrected; (3) In addition, the adaptation of scleral lenses The symptoms are quite extensive: general myopia, hyperopia, astigmatism, and anisometropia; especially high myopia, high hyperopia, high astigmatism, and irregular astigmatism; patients with keratoconus or presbyopia, due to various refractive corneal surgeries (such as RK, PRK, LASIK), keratoplasty, corneal diseases (such as corneal trauma, keratitis) causing irregular corneal astigmatism; all those who are unable to give up wearing contact lenses due to various complications caused by wearing contact lenses. The wearer.

Compared with soft lenses and frame glasses, the key reason why scleral contact lenses can significantly improve the visual quality of the human eye is that a tear layer of several hundred microns is formed between the front surface of the cornea and the back surface of the scleral lens. The tear layer The refractive index is similar to the refractive index of the cornea itself. Therefore, it can significantly reduce the changes in wavefront aberration caused by various defects and deformations on the front surface of the cornea and improve the patient's visual quality. However, due to the current majority of The optical zone of scleral contact lenses is a simple spherical design. Although it improves the visual quality to a certain extent, many patients still experience glare and unclear vision after wearing them, especially when their pupils become enlarged at night. , the main reason is that patients who wear scleral lenses generally have poor corneal conditions, with irregular astigmatism or regular high-level astigmatism, and some even have coma, clover and other higher-order aberrations. These The existence of high-order aberrations greatly limits the further improvement of patients' visual quality. Therefore, there is an urgent need to develop a scleral contact lens based on phase modulation technology to solve the above technical problems.

In view of this, the present invention is proposed.

Contents of the invention

The purpose of the present invention is to provide a scleral contact lens based on phase modulation technology. First, a three-dimensional sagittal height distribution model of the front surface of the human cornea is established. Secondly, based on the classic LB human eye model, the human eye optical system after wearing the scleral contact lens is established. Model, again, the rear surface of the scleral lens adopts a spherical design, which mainly matches the curvature radius of the front surface of the human eye. Finally, based on the actual wavefront aberration of the whole eye, the phase modulation function is superimposed on the optical area of the front surface of the scleral lens, and each incident field of view is The specific optical aberration is modulated to achieve the balance or correction of the target aberration.

In view of the above-mentioned problems existing in the prior art, the present invention provides a scleral contact lens based on phase modulation technology. The inner surface of the scleral contact lens (the surface in contact with the cornea) can be generally divided into three parts from the middle to the outside. Part: middle optical zone D1, transition zone D2 and landing zone D3, the middle optical zone spans the cornea and does not contact the cornea to correct vision; the transition zone connects the optical zone and the landing zone, is located at the edge of the cornea, and is divided into two areas : Edge adaptation area and limbus area. The limbus area is located at the edge of the cornea and maintains a certain gap with the edge of the cornea. The edge adaptation area is used to adjust the sagittal height of the scleral lens and compensate for the sagittal height; the landing zone is the load-bearing area of the entire lens. , should be consistent with the curvature of the sclera, and contact the sclera tangentially, so that the scleral contact lens can be well fixed on the sclera, and the landing area forms an angle with the cornea, which is conducive to the exchange of tears.

The front surface optical zone of the scleral contact lens and the inner surface optical zone of the scleral lens jointly provide optical imaging characteristics. The front surface optical zone has a base shape similar to the standard surface type (flat, spherical, quadratic surface) plus Additional phase term defined by Zernike standard coefficients. When light passes through this surface, the additional phase term deviates and increases the optical path of the light. This surface type actually adds phase modulation on the basis of the standard surface type. The additional phase of the surface is defined as:

This phase function describes how to modulate the phase by adding modulation phase at any radial wavelength position based on the standard curved surface. The standard surface shape (base shape) of the front surface optical zone of the scleral contact lens adopts a biquadric surface design with higher-order terms, which is expressed by the following formula:

in,

In addition to the base radius, the _higher -order coefficients of the conic _coefficients in the , Kx and Ky.

The surface shape of the front surface optical zone of the scleral contact lens, that is, the surface shape distribution after phase modulation, is expressed as:

The first item is the basal surface profile distribution, which together with the rear surface of the scleral lens provides the optical power of the scleral contact lens. The next two items are the higher-order aspherical coefficients in the x and y directions. The last term is superimposed on the basic surface profile. The phase modulation term above.

For the scleral contact lens, the surface shape distribution of the human cornea is measured with a corneal topograph, and the sagittal height distribution map of the front surface shape of the cornea is obtained. The equivalent radius of curvature and cone coefficient are fitted, and the sagittal height difference is measured using Zenico. Sagittal height coefficient expansion:

With the scleral contact lens, the discretely sampled surface shape of the front corneal surface can also be directly converted into a phase plane. The conversion method is as follows:

The sagittal height distribution of the anterior corneal surface is discretized on the two-dimensional xy plane. Δy is the sagittal height of the anterior corneal surface at the Δx displacement interval, and the sagittal height distribution can be directly transformed into the phase.

After the scleral contact lens is simulated to be worn, the imaging optical system of the human eye after wearing the lens is established, and the ray tracing method is used to calculate the retinal defocus distribution when the on-axis field of view and the off-axis field of view are incident, based on multiple retinal positions. The size of the weighted sum of the RMS values of the field of view diffuse spots is used as the evaluation function. The smaller the value, the better the imaging quality, that is:

The scleral contact lens is characterized in that the entire lens is treated with plasma to improve surface hydrophilicity, making it more comfortable to wear, and the plasma power is 10-2000W.

The refractive index range of the scleral contact lens is between 1.4-1.6, and the oxygen permeability coefficient is (80-200)*10 ^-11 (cm ² /s) [mlO ₂ /(ml×mmHg)].

The total diameter of the scleral contact lens ranges from 12.5mm to 24mm, and the radius of curvature of the rear surface ranges from 6.4mm to 9.2mm.

Design method:

(1) Use a corneal topograph to obtain information such as the front and rear surface curvature, thickness, and anterior chamber depth of the human cornea. The most important thing is to obtain the aspherical coefficient Q of the human cornea on a personalized basis.

(2) Based on the sagittal height distribution data of the anterior corneal surface obtained by the corneal topograph, a model of the sagittal height distribution of the anterior corneal surface of the human eye is established, and a fitting algorithm is used to obtain the difference between the actual surface sagittal height and the fitted sagittal height, and the residual is calculated The Zenico polynomial is expanded, and finally the expression of the front surface sagittal height is obtained.

(3) Convert the sagittal height of the anterior corneal surface into phase distribution data, import it into the personalized human eye model, and establish a complete personalized human eye model including the actual anterior corneal surface.

(4) Based on the personalized human eye model, establish a human eye optical system model after wearing scleral contact lenses, establish on-axis and off-axis rays, and perform ray tracing.

(5) The rear surface of the scleral lens is matched with the front surface of the human cornea, and a radius slightly flatter than the average curvature radius of the front cornea surface is used. A spherical design is adopted to match the curvature radius of the front surface of the human cornea.

(6) Through personalized human eye ray tracing, the wavefront aberration distribution characteristics and amplitude of the whole eye under different pupil conditions are obtained, and aberration values for targeted phase modulation and compensation are given according to the actual needs of the patient;

(7) In view of the actual wavefront aberration of the whole eye, the phase modulation function is superimposed on the optical area of the front surface of the scleral lens to modulate the specific optical aberration of each incident field of view to achieve the balance or correction of the target aberration.

(8) Determine the final contour of the front surface of the scleral lens.

(9) Lathe and polishing processing. The raw material used for processing is a highly oxygen-permeable material, which reaches a glassy state at room temperature. Diamond single-point turning processing technology is used to turn the front and rear surfaces. Single-end polishing removes driveway lines and minor scratches.

(10) After plasma treatment, the surface hydrophilicity is improved, making it more comfortable to wear. The plasma power is 10-2000W.

The present invention provides a scleral contact lens based on phase modulation technology. By superimposing the modulation/demodulation phase on the optical surface of the front surface of the scleral contact lens, the wavefront aberration of the whole eye is personalizedly modulated, and has the following beneficial effects. :

1. Meet the design requirements for human eye wavefront aberration.

2. Accurately compensate for various wavefront distortions on the front surface of the patient's cornea.

3. Significantly improve the patient’s vision level and visual quality.

Instructions with pictures

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the drawings of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram of a human eye wearing a scleral contact lens;

Figure 2 is a schematic structural diagram of a scleral contact lens;

Figure 3 is a light tracing diagram of the human eye with a scleral contact lens;

Figure 4 is a design flow chart of scleral contact lenses based on phase modulation technology;

Figure 5 Comparison of the Zernike coefficient before and after modulation of the central field of view under a 6mm pupil, the spherical surface is before modulation and the aspheric surface is after modulation;

Figure 6 Comparison of the Zernike coefficient before and after modulation of the 5-degree field of view under a 6mm pupil, the spherical surface is before modulation and the aspheric surface is after modulation;

Figure 7 Comparison of the Zernike coefficient before and after modulation of the 10-degree field of view under a 6mm pupil, the spherical surface is before modulation and the aspheric surface is after modulation;

Figure 8 is a comparison of MTF before and after 6mm pupil, 0 degree field of view modulation;

Figure 9 is a comparison of MTF before and after 5-degree field of view modulation for a 6mm pupil;

Figure 10 is a comparison of MTF before and after -5 degree field of view modulation with a 6mm pupil.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments and drawings to help understand the content of the present invention.

Example 1

As shown in Figure 2, which is a schematic structural diagram of a scleral contact lens, the inner surface of the scleral contact lens (the surface in contact with the cornea) can be generally divided into three parts from the middle to the outside: the middle optical zone D1, the transition zone D2 and the landing zone. In area D3, the front surface optical area of the scleral contact lens and the inner surface optical area of the scleral lens jointly provide optical imaging characteristics.

The preparation steps of the scleral contact lens are as follows, and the design flow chart is shown in Figure 4:

(4) Based on the personalized human eye model, establish the human eye optical system model after wearing scleral contact lenses, establish on-axis and off-axis rays, and perform ray tracing, as shown in Figure 3.

(5) The back surface of the scleral lens is matched with the front surface of the human cornea. The radius is flatter than the average curvature radius of the front cornea surface, and a spherical design is adopted to match the curvature radius of the front surface of the human cornea.

(6) Through personalized human eye ray tracing, the wavefront aberration distribution characteristics and amplitude of the whole eye under different pupil conditions are obtained, and aberration values for targeted phase modulation and compensation are given according to the actual needs of the patient.

(8) Determine the final contour of the front surface of the scleral lens, lathe and polish it. The raw material used for processing is a highly oxygen-permeable material, which reaches a glassy state at room temperature. Diamond single-point turning processing technology is used to turn the front and rear surfaces. Single-end polishing removes driveway lines and minor scratches.

(9) After plasma treatment, the surface hydrophilicity is improved, making it more comfortable to wear. The plasma power is 10-2000W.

Results analysis and discussion:

Using ray tracing software, combined with the established personalized human eye model, the distribution of on-axis and off-axis light in the retina of the human eye is obtained. As shown in Figure 3, it can be seen that the diopter error of the on-axis point has been obtained. Correction, the light is focused on the retina, and then the off-axis light is focused in front or behind the retina. The Zernike terms of the target modulation are the astigmatism terms Z5 and Z6 of the 6mm pupil, the coma aberration terms Z7 and Z8, and the spherical aberration term Z11. For patients with scleral lenses, even in the on-axis field of view, there will be astigmatism and coma due to corneal irregularity and deformation. For off-axis rays, coma is very important for patients with keratoconus. Obvious aberrations, this example is intended to demonstrate targeted aberration modulation capabilities.

Figure 5 Comparison of the Zernike coefficient before and after modulation of the central field of view under a 6mm pupil. The spherical surface is before modulation and the aspheric surface is after modulation.

Figure 6 Comparison of the Zernike coefficient before and after modulation of the 5-degree field of view under a 6mm pupil. The spherical surface is before modulation and the aspheric surface is after modulation.

Figure 7 Comparison of the Zernike coefficient before and after modulation of the 10-degree field of view under a 6mm pupil. The spherical surface is before modulation and the aspheric surface is after modulation.

A corneal topograph was used to test the basic parameters of the personalized human eye, and a human eye model was established. The front surface of the cornea was fitted with a spherical average curvature radius. After ray tracing, the aberration distribution under different fields of view was obtained. For the convenience of comparison, a 6mm pupil is uniformly used. At this time, the difference in aberration of the human eye is obvious. The aspheric surface refers to the average curvature radius of the front surface of the human cornea obtained by using the corneal topography map. After fitting, the remaining sagittal heights are calculated. The Zenico polynomial is expanded to obtain the final surface distribution model, after ray tracing and modulation compensation. After obtaining the Zenico aberration value, the aberration distribution of different fields of view before and after modulation is shown in Figure 5-Figure 7. It can be clearly seen that the aberration has been significantly reduced before and after modulation, reaching the phase modulation purposes.

Figures 8 to 10 are the MTF comparison diagrams before and after modulation of the 0-degree field of view, the 5-degree field of view, and the -5-degree field of view under the 6mm pupil. It can be seen that since the aberration has been significantly reduced, the corresponding field of view The modulation transfer function (MTF) has also been significantly improved.

Since the phase modulation function can be directly superimposed on the optical area of the front surface of the scleral lens, it facilitates later lathe processing and molding. This phase modulation technology can specifically modulate and compensate the actual detected human eye aberrations. Has wider adaptability and universality.

Specific examples are used in this article to elaborate the inventive concept in detail. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be pointed out that for those of ordinary skill in the art, any obvious modifications, equivalent substitutions or other improvements made without departing from the concept of the invention should be included in the protection scope of the present invention.

Claims

A scleral contact lens based on phase modulation technology, characterized in that the inner surface of the scleral contact lens, that is, the surface in contact with the cornea, is generally divided into three parts from the middle to the outside: a middle optical zone, a transition zone and Landing zone; the optical zone spans the cornea and does not contact the cornea to correct vision; the transition zone, connecting the optical zone and the landing zone, is located at the edge of the cornea and is divided into two areas: the edge adaptation zone and the limbus Area, limbal area, is located at the edge of the cornea and maintains a gap with the edge of the cornea; the edge adaptation area is used to adjust the sagittal height of the scleral lens and compensate for the sagittal height; the landing zone is the load-bearing area of the entire lens and must be consistent with the curvature of the sclera. It is in tangential contact with the sclera, so that the scleral contact lens can be well fixed on the sclera, and the landing area forms an angle with the cornea, which facilitates the exchange of tears.
A scleral contact lens based on phase modulation technology according to claim 1, characterized in that the front surface optical zone of the scleral contact lens and the inner surface optical zone of the scleral lens jointly provide optical imaging characteristics, and the front surface optical zone has an The base shape is similar to the standard surface type (plane, spherical, quadratic surface) plus an additional phase term defined by the Zernike standard coefficient. When the light passes through the surface type, the additional phase term deviates and the optical path of the light increases. , this surface type actually adds phase modulation on the basis of the standard surface type. The additional phase of the surface is defined as:

Here, N is the number of Zernike coefficients in the series, A i is the coefficient in the Zernike polynomial, ρ is the normalized radial ray coordinate value, ψ is the angular coordinate value of the ray, and D is the diffraction order, This phase function describes how to modulate the wavefront by adding modulation phase at any radial wavelength position based on the standard curved surface. A i is in wavelength units, and λ corresponds to a phase shift of 2π.
is the wave surface distribution in the polar coordinate system.
A scleral contact lens based on phase modulation technology according to claim 2, characterized in that the standard surface shape (base shape) of the front surface optical zone of the scleral contact lens adopts a biquadric surface design with higher order terms. , expressed by the following formula:

in,

In addition to the base radius, the higher-order coefficients of the conic coefficients in the , Kx and Ky.
A scleral contact lens based on phase modulation technology according to claim 3, characterized in that the surface shape of the front surface optical zone of the scleral contact lens, that is, the surface shape distribution after phase modulation is:

The first item is the basal surface profile distribution, which together with the rear surface of the scleral lens provides the optical power of the scleral contact lens. The next two items are the higher-order aspherical coefficients in the x and y directions. The last term is superimposed on the basic surface profile. The phase modulation term above.
A scleral contact lens based on phase modulation technology according to claim 4, characterized in that the surface shape distribution of the human cornea is measured with a corneal topograph to obtain the sagittal height distribution map of the front surface of the cornea, and the fitting The equivalent radius of curvature and cone coefficient are obtained, and the sagittal height difference is expanded with the Zenico sagittal height coefficient:

Among them, k is the cone coefficient of the best-fitting surface of the anterior corneal surface, c is the reciprocal of the radius of curvature, N is the number of Zernike terms, B i is the Zernike coefficient value, and ρ is the normalized radial ray coordinate value, ψ is the angular coordinate value of the light.
A scleral contact lens based on phase modulation technology according to claim 5, characterized in that the discretely sampled surface shape of the front surface of the cornea is directly converted into a phase plane, and the conversion method is as follows:

The sagittal height distribution of the anterior corneal surface is discretized on the two-dimensional xy plane. Δy is the sagittal height of the anterior corneal surface at the Δx displacement interval, and the sagittal height distribution can be directly transformed into the phase.
A scleral contact lens based on phase modulation technology according to claim 6, characterized in that after the scleral contact lens is simulated to be worn, the human eye imaging optical system after wearing the lens is established, and the ray tracing method is used to calculate the on-axis visual acuity. When the field and off-axis fields of view are incident, the defocus distribution of the retina is based on the weighted sum of the RMS values of multiple fields of view at the retinal position as the evaluation function. The smaller the value, the better the imaging quality, that is:

Among them: S i is the weighting coefficient, RMS i is the diffuse spot RMS value of i field of view, and T is the total number of fields of view participating in the calculation.
A scleral contact lens based on phase modulation technology according to claim 7, characterized in that the entire lens is treated with plasma to improve surface hydrophilicity and make it more comfortable to wear, and the plasma power is 10-2000W.
A scleral contact lens based on phase modulation technology according to claim 8, characterized in that its refractive index range is between 1.4-1.6, and its oxygen permeability coefficient is (80-200)*10 -11 (cm 2 / s)[mlO 2 /(ml×mmHg)].
A scleral contact lens based on phase modulation technology according to claim 9, characterized in that its total diameter ranges between 12.5mm and 24mm, and its rear surface curvature radius ranges between 6.4mm and 9.2mm.