System and method for detecting the refractive power of dry ophthalmic lenses

Abstract

The present invention relates to a system for testing the refractive power of a dry ophthalmic lens to be tested, the system comprising: a) a top camera (10) for observing an ophthalmic lens (40) through an optical module (25); b) an optically transparent surface (30) for positioning the ophthalmic lens (40) for testing; c) a precisely calibrated glass target (50) appropriately positioned on a transparent plate (60) and arranged to obtain an image of the ophthalmic lens (40) that overlaps an image of a pattern on the target (50); and d) at least one light source having LEDs of multiple wavelengths to capture different images under multiple lighting conditions.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for detecting the refractive power of an ophthalmic lens, and more particularly to an apparatus and method for detecting the refractive power of a dry contact lens, which is suitable for integration into an online detection system at an automatic contact lens production machine. Background Art

[0002] The manufacture of ophthalmic lenses, in particular single-wear soft contact lenses, can be manufactured in fully automated production lines with the aid of reusable molds. In order to ensure top quality of said contact lenses, optical inspection systems are essential to guarantee high quality for customers. Ophthalmic lenses or contact lenses are produced in different categories of refractive power, which makes it essential to ensure that they are inspected according to the manufacturing specifications of the ophthalmic lenses or contact lenses. Manual methods are slow and the selective sampling inspection of lenses creates the problem of insufficient quality inspection associated with these methods. Therefore, it is an essential and important requirement for contact lens manufacturers to ensure that 100% of the products produced are inspected and separated according to their characteristics. Fast, reliable and consistent inspection methods must be deployed to guarantee reliable product quality.

[0003] Ophthalmic lenses are manufactured to accommodate different types of eye characteristics. Contact lenses need to be properly sorted according to their refractive power before distribution. There are several prior art systems for measuring refractive power, but one of the most popular systems involves the use of a motorized indexing system that relies on focus on the top and bottom surfaces of the contact lens. However, such equipment cannot be integrated into high-speed automated manufacturing systems because the time required to inspect each lens makes these devices unsuitable for such a purpose. Another type of inspection system for detecting the refractive power of contact lenses involves the use of a motorized zoom lens to focus on different points on the contact lens and applying certain algorithms to match the changes in zoom factor values ​​to determine the refractive power of the lens. Here again, these systems cannot be integrated into high-speed production lines for manufacturing contact lenses due to the time required to perform the process.

[0004] Manual inspection systems that require human intervention are not practical for high-speed production because such manual inspection systems are too slow, because human inspectors are prone to biased judgments, and because inspection results are inconsistent between different inspectors.

[0005] The main difficulty in inspecting contact lenses is that the inspection must be performed immediately after the contact lenses are molded. If the inspection of the contact lenses for their refractive power can be performed immediately after they are molded, any process-related problems or defects can be quickly resolved. The manufacture of a large number of defective contact lenses can be prevented. The typical process of contact lens inspection is traditionally performed offline in the final manufacturing process, where the lenses are suspended in a saline solution and their refractive properties must be taken into account when calculating or determining the actual refractive power of the contact lenses being inspected. Defects discovered at this final inspection stage make it difficult for manufacturers to analyze the problem and introduce steps in the correction process during the molding process. In addition, delayed identification of problems can result in significant losses in material and output to customers.

[0006] Therefore, the object of the present invention is to overcome the above-mentioned shortcomings of the prior art and to provide a method for greatly improving the efficiency of testing the refractive power of a lens, which method is suitable for integration into an automated system or device for fast, reliable and accurate testing. Summary of the invention

[0007] According to one aspect of the present invention, a system and method are provided for automatically determining the refractive power of an ophthalmic lens on-line in an automated production line for ophthalmic lenses, such as soft contact lenses, before the ophthalmic lenses are sent to a final stage packaging process.

[0008] The method comprises the following steps:

[0009] Providing an inspection platform including an optically transparent bottom having a flat surface, wherein the ophthalmic lens is placed on the flat surface with the convex side facing upward; and positioning the platform in a predetermined position below the inspection module;

[0010] providing a calibration glass target having a pre-etched pattern of accurately placed black and white squares. The glass target is positioned beneath the contact lens holder to create a grid pattern and a superimposed image of the contact lens at the camera detector;

[0011] A light source and a high-resolution digital camera are provided for receiving light from the light source that passes through a calibrated glass target and an ophthalmic lens mounted on a transparent surface of the platform and impinges on a camera detector, thereby generating a signal at an output of the camera.

[0012] The signal generated at the detector is measured and a table of parameter values ​​is created, which is related to the refractive power (in pixels) of several contact lenses with known refractive power. These values ​​are generated using several superimposed images of several contact lenses with known refractive power or otherwise known as standard samples; and the distances between several adjacent squares within a predetermined optical area of ​​each contact lens image are then measured and the results are tabulated to form a reference table. The standard sample includes a series of positive and negative refractive power contact lenses.

[0013] The determination of the refractive power of the ophthalmic lens is performed when the ophthalmic lens is placed on the transparent plate. The term "optical power" as used herein should be understood in a very general sense, such as one or a combination of refractive properties of an ophthalmic lens, such as, for example, the spherical refractive power of a spherical soft contact lens, the cylindrical refractive power of a toric contact lens, the orientation of the cylinder axis, aberrations, etc.

[0014] The present invention provides an innovative method for testing the optical power of a contact lens, which begins by acquiring an image of the contact lens superimposed with an image of a pattern in a calibration glass target. The process is repeated for several contact lenses of known optical power, otherwise known as standard samples.

[0015] The present invention also provides an innovative process for testing the refractive power of a contact lens, the process comprising a means for creating a reference or calibration table of refractive power values ​​proportional to the average distance (measured in pixels) between four adjacent squares calculated and tabulated for each and every square in the optical zone of the contact lens image. The process is applied to each individual image acquired for each individual standard sample. The proportional refractive power of the lens is obtained by applying a certain formula to the average distance value in pixels for each value in the table. As an example, a square of a 7x7 area in the center of the optical zone of the contact lens is selected. Depending on the complexity or specifications required by the customer, the areas identified in the optical zone can be increased or decreased.

[0016] The present invention also provides an innovative method for generating an extrapolated graphical line graph, wherein the average distance value in pixels represents the X-axis and the refractive power in diopters represents the Y-axis.

[0017] Therefore, the aforementioned method according to the present invention is particularly effective for dry contact lenses, because the refractive power measured or detected during the production process of the contact lens is improved by using the interpolation map. The final refractive power determined using the graph or table can also be transmitted electronically to enable integration into third-party equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A complete understanding of the present invention may be gained by considering the following detailed description in conjunction with the accompanying drawings, in which:

[0019] Figure 1 A preferred embodiment of the invention is shown. The apparatus comprises a high resolution camera 10, an optical lens 20 for viewing a lens 40 located on a glass platform 30, a calibration glass target 50 suitably positioned on another glass platform 60, and a light emitting diode (LED) based illumination module 70 for directing illumination 65 towards the contact lens 40, all of which are suitably aligned with the optical axis 25 of the apparatus. The illumination module 70 is controlled by a programmable strobe controller (not shown) for controlling the illumination trigger pulse width and the intensity of the LED segments.

[0020] Figure 1a An isometric view of an optical assembly is shown showing some of the different parts of the invention.

[0021] Figure 2 Shows the positioning Figure 1a A sample of a precision glass-based calibration target 50 is placed within the holder 60 .

[0022] Figure 3 A diagram showing an image 95 of a precise target glass 50 is shown. Figure 1 An image of a contact lens 40 of known refractive power is superimposed in FIG. 9 , and the rectangular area enclosed by frame 90 illustrates the optical region of interest for the present invention.

[0023] Figure 4 Shows Figure 3 90 , wherein most of the squares in the optical area are clearly visible, wherein a selected set of 7×7 squares in the center of the optical area 90 are enclosed by a frame 97 .

[0024] Figure 5 Pictured Figure 4 The following area 97 is defined in the figure: In this area 97 the actual refractive power of the contact lens 40 is to be detected.

[0025] Figure 6 yes Figure 5 An enlarged view of a 7×7 square frame in the area 97 of (eg, a lens with a diopter of 9.375), wherein each frame preferably contains 166 pixels. Figure 6 For each box in , the horizontal axes are labeled A, B, C, D, E, F&G, and the vertical axes are labeled 1, 2, 3, 4, 5, 6, and 7.

[0026] Figure 7 Shown in Figure 6 A table of the average distances in pixels measured between adjacent squares.

[0027] Figure 7a A formula is shown for matching the distance to the known power of a contact lens.

[0028] Figure 8 Shows that Figure 7 The distance values ​​in are applied to Figure 7a Following the formula in , there is a table with values ​​in diopters (optical power).

[0029] Fig. 9 It is a reference table of distance and diopter values ​​for a set of preselected contact lenses or standard samples with known refractive power.

[0030] Fig.10 is based on Fig. 9 An extrapolation graph is drawn from the values ​​in the reference table, where the X-axis represents the average distance value and the Y-axis represents the proportional diopter value (refractive power). DETAILED DESCRIPTION

[0031] Figure 1 The embodiment of the first aspect of the present invention is shown, which is a detection device or apparatus for detecting the refractive power of a dry contact lens. The preferred embodiment includes the following parts.

[0032] A high-resolution camera 10 coupled to an optical lens 20 is focused on a high-precision calibration glass target 50 mounted on another glass platform 60. An LED-based illumination source 70 is arranged to direct light 65 through the transparent bottom 60 and the glass calibration target 50, all of which are suitably positioned in line with the optical axis 25. The LED light further illuminates an ophthalmic lens 40 located on a glass platform 30, wherein the convex surface of the ophthalmic lens faces the optical lens 20. The light that has passed through the contact lens 40 and carries the lens information is captured by the camera 10 after being focused by the optical lens 20, and the lens information is superimposed with the pattern etched or printed on the calibration glass target 50. Figure 1a The picture shows Figure 1 A stereogram of the present invention in FIG.

[0033] exist Figure 2 In FIG. 5 , a typical glass target 50 or calibration glass plate having a pattern consisting of alternating black and white squares that can be etched or printed is shown. The pattern size is very precise and the pattern is one of the key elements of the device that plays a major role in determining the refractive power of the contact lens. The calibration glass target 50 is commercially available with patterns etched or printed with different designs. Different calibration target patterns can be selected depending on the inspection type and the inspection accuracy required by the customer.

[0034] exist Figure 3 , an image 95 is shown, which represents the Figure 1The camera 10 in FIG. 1 captures overlapping images of the calibration target and the invisible lens. Figure 3 The area enclosed by rectangle 90 in FIG. 9 represents the optical region of interest.

[0035] exist Figure 4 In the image region 90, a smaller image region 97 is preferably selected in the center, the image region 97 being composed of 7×7 square frames, and each square frame being composed of approximately 166 pixels. As a first step, the region 90 is processed by an image processing algorithm to detect the edges of all 49 squares. In the next step, each square is filled with a predetermined gray value to clearly separate each square from the adjacent squares.

[0036] Figure 5 An example of the final result after image analysis and processing is illustrated, wherein each square box is filled with the same grayscale value to clearly distinguish each square box itself from its adjacent square boxes, wherein the horizontal rows are labeled A, B, C, D, E, F&G, and the vertical rows are labeled 1, 2, 3, 4, 5, 6, and 7.

[0037] Area 97 is determined by the user during a teaching process which will not be described in detail as it is outside the scope of the present invention. Figure 4 As will be apparent from the illustration of FIG. 9, region 97 is a 7×7 square region located in the center of region 95 and is the most important location for determining the power of the contact lens. Although the remainder of this region is also important for understanding the distribution of power around the entire contact lens, it is beyond the scope of the present invention and is therefore not discussed in detail.

[0038] exist Figure 6 , area 97 is magnified to show the 7×7 pixels at the center of the optical area. Area 97 is further analyzed to determine the refractive power of the contact lens. As a first step, the center of all pixels is located and the distances between all adjacent horizontal and vertical pixels in the center are measured. For example, Figure 6 , nine boxes are shown, starting with square box 4D and surrounded by boxes 4C, 3C, 3D, 3E, 4E, 5E, 5D, and 5C. The distance in pixels is measured from the center of box 4D represented by position 98 to the center of boxes 4C, 3D, 4E, and 5D. For high accuracy and repeatability of the distance measurement between the centers of pixels, a sub-pixelation algorithm is implemented. Subsequently, the average of all four distances in pixels, i.e., the distances between 4D and 3D, 4D and 4C, 4D and 5D, and 4D and 4E, is input to the distances between 4D and 3D, 4D and 4C, 4D and 5D, and 4D and 4E. Figure 7 The position indicated by box position 4D in the table in Figure 7 The position in XY is denoted and is also called the central reference position. It is important to note that Figure 6 The distance of all boxes in the positive direction is moved to the right and top of position XY, and the negative direction is moved to the left and bottom of position XY. For example: Figure 6 The distance value in pixels of frame 1A is given by Figure 7 The above process is then applied to Figure 6 All boxes in the , and their respective values ​​are entered into Figure 7 In this example, Figure 7 The resulting table shown in Figure 6 A complete list of average distances for the matrix of 7×7 boxes in box 97 represents a contact lens or standard sample with a known refractive power of 9.37 (refractive power in diopters).

[0039] With known refractive power, and using Figure 7 Using the table in , a formula is derived to match the distance to the known power of the contact lens. A typical resulting formula is as follows:

[0040] Y=-9E-07x 4 +0.0005x 3 -0.1281x 2 +14.204x-630.16

[0041] It is important to note that the above formula is illustrated for purposes of understanding and that one skilled in the art will be able to change or modify the formula to suit different manufacturers' contact lens materials, designs and processes.

[0042] Will Figure 7a The formula in applies to Figure 7 For each value in the table, we can get Figure 8 New table of diopter (optical power) values ​​shown in . Figure 8 The average of all the diopter values ​​in represents the diopter value or refractive power of the contact lens.

[0043] In a subsequent step, different contact lenses with known refractive power are used to obtain a similar Figure 7 and Figure 8 The new table shown in Fig. 9 In the table shown in , a total of six contact lenses were used, which are also otherwise referred to as standard samples. Fig. 9 As shown in the reference table in , each contact lens represents a different refractive power and their respective average distances between the selected 7×7 boxes. Fig. 9 A series of contact lenses, or reference samples, are carefully selected to cover the wide range of refractive powers commonly manufactured in the industry.

[0044] In the final step, Fig. 9 The table in the plot is as follows Fig.10 In the graph shown in , where the X-axis represents the average distance and the Y-axis represents their respective diopter values. Fig.10 A simple analysis of the graph in shows shorter distance values ​​for contact lenses with negative refractive power and gradually increasing distances for contact lenses with positive refractive power. Fig.10 The charts and Fig. 9 The tables in are illustrative and Fig.10 The extrapolation line in can be obtained by Fig. 9 More standard samples are included during creation of the reference or calibration tables to further smooth out the process to achieve better accuracy in testing the refractive power in contact lenses in normal production.

Claims

1. A system for online detection of the refractive power of a dry ophthalmic contact lens under inspection, the system comprising: a) a top camera (10), the top camera (10) being arranged to observe the dry ophthalmic contact lens (40) through an optical module (25); b) an optically transparent surface (30) for positioning the dry ophthalmic contact lens (40) for inspection; c) a precisely calibrated glass target (50) appropriately positioned on a transparent plate (60) and arranged to obtain an image of the dry ophthalmic contact lens (40) superimposed with an image of the pattern on the glass target (50); d) at least one light source having light emitting diodes of multiple wavelengths to capture different images under various lighting conditions, wherein the refractive power is determined based on a grayscale value applied to each square in a selected 7×7 square area of ​​the captured image; The system is arranged to measure the average distance between adjacent squares and a central pixel in the selected 7×7 square area; wherein the adjacent square is adjacent to the central pixel; The system is further arranged to calculate a diopter value of the dry ophthalmic contact lens for each of the measured average distances; And thus the refractive power of the dry ophthalmic contact lens is determined by comparing the diopter value with calibration tables and graphs.

2. The system according to claim 1, wherein: The glass target includes a precisely etched pattern of equally spaced squares of varying contrast.

3. The system according to claim 1, wherein: The calibration involves multiple known power contact lenses or standard samples that are selected to plot graphs over the entire range of power and create tables for comparison during normal production and inspection.

4. The system according to claim 1, wherein: The calibration tables and charts are generated from the cylindrical power data points and the spherical power data points, and the calibration tables and charts include both positive power contact lenses and negative power contact lenses.

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