Automatic eye refractive power measuring apparatus

Abstract: Automatic eye refractive power measuring apparatus for automatically measuring refractive power of an eye under test by means of objective measurement. It comprises a projection system (1) for projecting a measuring target image to a retina of the eye (6) under test by invisible light; an imaging optical system (2) for imaging a reflection image of the measuring target image projected to the retina and reflected by the retina; an opto-electric detector (29) having a photosensitive surface (29a) disposed at imaging position and adapted to output electrical signal corresponding to the measuring target image formed on the photosensitive sur­ face; display means (44) for displaying the measuring target image reflected on the retina based on the electrical signal as a visible image; and an auto-measuring portion adapted to detect focussing state of the measuring target image (46) projected to the retina based on the electrical signal and automatically calculate refractive power of the eye under test from the electrical signal.

Description: FIELD OF THE INVENTION This invention relates to an automatic eye refractive power measuring apparatus for automatically measuring refractive power of an eye under test, and more particularly to an automatic eye refractive power measuring apparatus for detecting focussing state of a measuring target image projected to a retina of the eye under test by an opto-electric detector, indicating the focussing state of the measuring target image by electrical signal outputted from the opto-electric detector, and measuring refractive power of the eye under test. BACKGROUND OF THE INVENTION There has been known an automatic eye refractive power measuring apparatus for projecting a measuring target image to the retina of an eye under test by using infrared light as invisible light and automatically measuring focussing state of the measuring target image. In this type of automatic eye refractive power measuring apparatus, the anterior portion of the eye under test is collimated by a television monitor, etc. in order to position the eye under test. In the conventional automatic eye refractive power measuring apparatus, the measuring target image is projected on an opto-electric element for detecting only focussing state and no means is provided for a tester himself to observe the measuring target image directly. Therefore, in the conventional automatic eye refractive power measuring apparatus, even when an adverse affection is exerted on the measuring target image by reflection of the cornea and crystal body, or by reflection light reflected on the eyelashes and eyelid, the tester himself cannot recognize it. Accordingly, the test result lacks dependability. Also, even when accommodation is acted on the eye under test, it is required to be judged from the result of the measurement. Therefore, in order to increase dependability, a high eyesight art of the tester himself is required. EP-A-0 177 005 which is an intermediate document (date of priority : October 2, 1984 ; date of publication : April 9, 1986) describes an eye examining apparatus which is capable of the accurate detection of any abnormality in the optical system of a patient's eye which might exist at any position of the eye, and also which is capable of providing easy measurement of the degree of refraction of the patient's eye. The apparatus comprises a target projecting system for projecting onto a retina a target image to be measured ; focalizing means for detecting the focus of the target to be measured and for focalizing it on the retina ; and an optical transfer function measuring system for detecting the contrast of the target image to be measured, which is focalized on the retina, and thereby measuring the optical transfer function of the patient's eye. OBJECT OF THE INVENTION It is therefore a first object of the present invention to provide a highly dependable automatic eye refractive power measuring apparatus, wherein a measuring target image is made as a visible image so that the tester himself can observe it and the tester can always confirm the state of the measuring target image on the retina of the eye under test during the automatic measurement of refractive power of the eye under test. A second object of the present invention is to provide an automatic eye refractive power measuring apparatus, wherein a measurement application scope can be improved by avoiding inability of measurement due to level down of light quantity of the measuring target image on the retina which is occurred in such cases as when the eye under test is suffered from a disease such as cataract, the diameter of the pupil of the eye under test is small and the like. SUMMARY OF THE INVENTION In order to achieve the above objects, the invention describes an automatic eye refractive power measuring apparatus for automatically measuring the refractive power of an eye under test by measuring objectively the focusing state of a measurement target projected onto the retina of the eye under test, comprising: a target image projection system for projecting with invisible tight the image of a measuring target onto the retina of the eye under test; an imaging optical system for imaging at an imaging position a reflection image of the measuring target image reflected by the retina; an opto-electric detector having a photosensitive surface disposed at said imaging position and arranged to output an electrical signal corresponding to the reflection image of the measuring target image formed on the photosensitive surface; display means for converting the reflection image of the measuring target image to a visible image in accordance with said electrical signal and for displaying the converted visible image; and computer means for calculating the refractive power of the eye under test in accordance with said electrical signal; wherein the computer means are arranged to be selectively operable in either an automatic measurement mode or a manual measurement mode, where in said automatic measurement mode the focusing state of the measuring target image projected onto the retina is determined in accordance with said electrical signal and the refractive power of the eye under test is automatically calculated based on said focusing state, and where in said manual measurement mode a manual measurement means is activated for measuring the refractive power of the eye under test by an operator directly observing the focusing state of the measurement target image on said display means and manually activating said computer means to calculate the refractive power of the eye under test in accordance with said electrical signal describing the observed focusing state of the measurement target image; and measurement mode switching means , for selectively activating said automatic measurement mode and said manual measurement mode, are automatically selectively activated by said computer means depending on the light intensity of the reflection image of the measuring target image detected by the opto-electric detector. In one embodiment of the invention the computer means automatically activate said measurement mode switching means to switch to the manual measurement mode when the detected light intensity of the reflection image of the measuring target image is less than a predetermined value. Advantageously the invention apparatus may also comprises : a measurement finish switch for storing the measured focusing state at a first predetermined meridian in the computer means when said switch is activated during the manual measurement mode; and means for rotating said measuring target relative to the eye under test to measure the focusing state of the measuring target image along a second predetermined meridian Since the invention is such constituted as mentioned above, a measuring target image projected to the retina of the eye under test is detected by an opto-electric detector, the measuring target image is indicated based on electrical signal outputted from the opto-electric detector, and such information as slit space of an image showing its focussing state is automatically measured. Accordingly, the tester can know whether the measuring target image projected to the retina of the eye under test is affected by something and judge dependability of the measurement result. That is, according to this automatic eye refractive power measuring apparatus, a comparatively more accurate eyesight test can be carried out. Further, according to the constitution of the invention, the slit space, etc. indicating focussing state of the measuring target image projected to the retina of the eye under test is measured by using electrical signal outputted from the opto-electric detector. Accordingly, an opto-electric detector as a detecting portion for measurement and an opto-electric detector for indicating an image are not required to provide separately. Thus, a simple constitution of the apparatus is obtainable. According to the constitution of the invention, not only auto-measurement but also manual measurement in which the tester observes the measurement target image of the display means can be effected. Accordingly, even if such an instance should arise as inability of measurement due to shortage of light quantity of the measuring target image projected on the retina caused by disease or the like of the patient, manual measurement can be easily carried out by simply switching the measuring mode without using additional measuring apparatuses. Accordingly, the measurement applicable scope can be enlarged. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic constitution of an optical system of an automatic eye refractive power measuring apparatus according to the present invention; Fig. 2 is a perspective view of a target plate constituting the optical system; Fig. 3 is a plan view of a chart plate constituting the optical system; Figs. 4 through 6 are schematic views showing various types of imaging state of a measuring target image formed by the optical system; Fig. 7 15 a measurement circuit for actuating the automatic eye refractive power measuring apparatus; and Figs. 8(a) through 8(c) are flow charts for running a program by the measurement circuit. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates an optical system of an automatic eye refractive power measuring apparatus according to the present invention. In Fig. 1, 1 denotes a target image projection system, 2 denotes an imaging optical system, 3 denotes a common use optical system commonly used for both the target image projection system 1 and the imaging optical system 2, 4 denotes a chart projection system, 5 denotes a sighting optical system, 6 denotes an eye under test, and 7 denotes an anterior portion. The target image projection system 1 has such a function as to form a target image on a retina 8 by projecting target light to the retina 8 of the eye 6 under test through the common use optical system 3. The target image projection system 1 generally comprises a luminous element 9, a condenser lens 10, a target plate 11, reflection prisms 12, 13, a relay lens 14, a reflection prism 15, and a half moon diaphragm plate 16. In this embodiment, the luminous element 9 emits infrared light as invisible light. The infrared light becomes parallel bundle of rays by the condenser lens 10 to illuminate the target plate 11. The target plate 11, as shown in Fig. 2, is formed with slits 11a through 11d and attached with four deflection prisms 11e through 11n. Due to the foregoing, the target plate 11 is illuminated by the infrared light to form measuring target light. At this time, the deflection prisms 11e through 11h deflects the measuring target light to a direction perpendicular to the longitudinal direction of the slits. The common use optical system 3 comprises a slit prism 17, an image rotator 18, an objective lens 19, and a beam splitter 20. The measuring target light from the target plate 11 is reflected by the reflection prisms 12, 13, 15, guided to the half moon diaphragm plate 16, passes through half moon holes 16a, 16b, and reflected on a reflection surface 17a of the split prism 17. The measuring target light reflected on the reflection surface 17a passes the pupil of the eye 6 under test through image rotator 18, objective lens 19 and beam splitter 20, and is projected on the retina 8. The half moon diaphragm 16 is disposed in such a manner as to be in a conjugate relation with the pupil position of the eye 6 under test in a proper position with respect to the objective lens 19. The half moon diaphragm 16 is adapted to block harmful reflection light for measurement from the anterior portion 7 of the eye 6 under test and enter the target light to the eye 6 under test. The image rotator 18 is adapted to rotates the measuring target image formed on the retina 8 by angle ϑ in the meridian direction of the eye 6 under test by rotating it about an optical axis ℓ of the common use optical system 3 by angle of ϑ/2. The reflection light of the measuring target image projected on the retina 8 is guided to the imaging optical system 2 through beam splitter 20, objective lens 19, slit hole 17a of the slit prism 17, an opening 21a formed in the central portion of an opening diaphragm plate 21, relay lens 22 and reflection prism 23. The opening diaphragm 21 is disposed in a conjugate position with the pupil of the eye 6 under test and adapted to guide the reflection light passing through the central portion of the pupil to the relay lens 22. The imaging optical system 2 generally comprises a reflection mirror 24, a movable lens 25, a reflection mirror 26, a half mirror 27, and an imaging lens 28. The imaging optical system 2 is adapted to guide the reflection light of the measuring target image formed on the retina 8 to a photosensitive surface 29a of a photosensitive apparatus 29 as an opto-electric detector and forms a measuring target image thereon. In this embodiment, if the image rotator 18 is rotated about the optical axis ℓ by angle of ϑ/2 as mentioned above, the measuring target image is rotated by angle of ϑ in its rotating direction. However, since the reflection light reflected on the retina 8 passes through the image rotator 18 again, it causes the measuring target image to rotate by angle of ϑ in the opposite direction with respect to the rotating direction of the image rotator 18 and the photosensitive surface 29a of the image pick-up apparatus 29 is formed with a measuring target image facing toward a predetermined direction irrespective of the rotation of the image rotator 18. The chart projection system 4 generally comprises a tungsten lamp 30 as visible light source, a condenser lens 31, a color correction filter 32, a chart plate 33, a movable lens 34, a relay lens 35, reflection mirrors 36, 37, a relay lens 38, a reflection mirror 39, and an objective lens 40. In this embodiment, the chart plate 33 is illuminated by the tungsten lamp 30 through the condenser lens 31 and the color correction filter 32. The wavelength of the light emitted from the tungsten lamp 30 is selected by the color correction filter 32 and only visible light of the range from 400 nm to 700 nm is permitted to pass through the color correction filter 32. The chart plate 33 is formed with a chart 33a shown in Fig. 3 and the light passed through the chart 33a is guided to the movable lens 34 and the relay lens 38. The light guided to the relay lens 38 is shifted its optical path by the reflection mirrors 36, 37, 39, passes through the relay lens 38 and the objective lens 40, guided to the beam splitter 41 and projected toward the eye 6 under test through the beam splitter 20. The movable lens 34 is disposed in such a manner as to be movable in its optical axis. In objective measurement, the movable lens 34 is disposed in a position from where the eye 6 under test is far sighted or foggy sighted corresponding to refractive power of the eye 6 under test, so that the measurement can be carried out in the state that the accommodation of the eye 6 under test is removed. The anterior portion 7 of the eye 6 under test is illuminated by an illumination lump (not shown), and the image of the anterior portion 7 of the eye 6 under test is formed on the photosensitive surface 29a of the image pick-up apparatus 29 by the sighting optical system 5. Reflection bundle of ray reflected on the anterior portion 7 of the eye 6 under test is reflected by the beam splitters 20, 41 and a reflection mirror 42. The reflection bundle of ray reflected by the reflection mirror 42 passes through an imaging lens 43, the half mirror 27 and the image pick-up lens 28, guided onto the photosensitive surface 29a of the image pick-up apparatus 29, and an image of the anterior portion is formed on the photosensitive surface 29a of the image pick-up apparatus 29. The image pick-up apparatus 29 is connected to a television monitor 44, and 45 denotes a display surface. The display surface 45 displays a measuring target image formed on the photosensitive surface 29a as a visible image based on electrical signal from the image pick-up apparatus 29. In Fig. 1, 46 denotes a measuring target image formed by the imaging optical system 2, and 47 denotes an anterior portion image formed by the sighting optical system 5. In this embodiment, when the target image 46 displayed on the display surface 45 of the television monitor 44 is focused on the retina 8, the target image 46 is in agreement in the space ℓ₁ between a pair of target images 46a at its upper portion and the space ℓ₂ between a pair of target images 46b at its lower portion as shown in Fig. 4. For example, when the measuring target image is focused at a front portion of the retina 8, the space ℓ₁ is smaller than the space ℓ₂ as shown in Fig. 5. On the other hand, when the measuring target image is focused at a rear portion of the retina 8, the space ℓ₁ is larger than the space ℓ₂ as shown in Fig. 6. In measurement of the refractive power, the target plate 11 is moved in such a manner as to bring both the spaces ℓ₁, ℓ₂ of the measuring target image in alignment with respect to each other. The refractive power is obtained by moving quantity at that time. In this embodiment, the movable lens 25 is integrally actuated while maintaining the conjugate relation with the target plate 11. Next, a measurement circuit shown in Fig. 7 will be described. The electrical signal of the image pick-up apparatus 29 is partly inputted in the television monitor 44 to display the image of the anterior portion. The remaining part of the electrical signal is inputted in an electrical signal take-off circuit 52, so that the electrical signal regarding the measuring target image is taken off based on take-off instruction signal of a take-off instruction circuit 51. Such taken off electrical signal is inputted in a rectangular-shaped wave generation circuit 53, and the wave shape thereof is treated and converted to a predetermined rectangular-shaped wave. The rectangular-shaped wave is inputted in a level interpretation device 54 and a target image position detection circuit 55. The electrical signal level interpretation device 54 interprets luminous level of the rectangular-shaped wave. Due to the foregoing, light quantity level of the measuring target image 46 is detected. The target image position detection circuit 55 is adapted to detect signal space of the rectangular-shaped wave signal corresponding to the space between the measuring target image 46. In this embodiment, output signal outputted from the electrical signal level interpretation device 54 and the target image position detection circuit 55, or respective signals as will be described later is processed by CPU 50 as a micro computer. CPU 50 controls a measurement mode switch 56 for switching an auto-measurement and a manual measurement, an actuation switch 57 for moving the target plate 11 and the movable lens 25, a one meridian measurement finish switch 58 for emitting the instruction signal every time measurement of one meridian is finished, a measurement finish switch 59 for emitting the instruction signal when measurement of all meridians are finished, and an auto-measurement start switch 60 for starting auto-measurement, respectively. In addition, CPU 50 controls an actuation control portion 61. The actuation control portion 61 comprises a first actuation control portion 62 for moving the target plate 11 and the movable lens 25 along the optical axis, a second actuation control portion 63 for rotating the image rotator 18 about the optical axis, and a third actuation control portion 64 for moving the movable lens 34 of the chart projection system 4 along the optical axis. CPU 50 runs a predetermined auto-measurement program 65 or a manual measurement program 66 which are built therein beforehand. Respective measurement results are recorded by a printer 67 in order. Next, operation of the eye refractive power measuring apparatus of this constitution will be described with reference to a flow chart of Fig. 8. First of all, when calculative operation of CPU 50 is started upon charging of an electric power source, etc., a switch-over state of the mode switch 56 is interpreted in STEP 100. In the case the mode switch 56 is switched over to the auto-measurement side, CPU 50 calls the auto-measurement program 65, and the following measurement is carried out based on the foregoing. First, upon setting of an initial value in STEP 101, the target plate 11 is brought to "zero diopter position" by the first actuation control portion 62, the image rotater 18 is brought to "zero degree" position by the second actuation control portion 63, and the movable lens 34 is moved to "zero diopter" position by the third actuation control portion 64. Next, a light quantity level of the measuring target image 46 is checked by the electrical signal level interpretation device 54 based on electrical signal of the image pick-up device 29 in STEP 102. When the light quantity level of the measuring target image is interpreted that it does not reach the predetermined level yet here, the mode switch 56 is automatically switched to the manual measurement mode side according to the instruction of CPU 50. On the other hand, in the case the light quantity level exceeds the predetermined level, the spaces ℓ₁, ℓ₂ of the measuring target image are detected based on output of the target image position detection circuit 55 (STEP 103). When the spaces ℓ₁, ℓ₂ are detected, CPU 50 calculates the difference of the spaces ℓ₁ - ℓ₂ and the target plate 11 and the movable lens 25 is integrally moved along the optical path until the difference of the spaces ℓ₁ - ℓ₂ becomes "zero", that is, until the measuring target image 46 is brought to the focussing position onto the retina 8. In association with the foregoing movement, the movable lens 34 of the chart projection system 4 is moved. (STEPS 103 through 106), so that the foggy state of the eye 6 under test is maintained. And, when the difference of the spaces ℓ₁ - ℓ₂ becomes "zero", the position moved of the target plate 11 is read in (STEP 107), and the refractive power of the "zero degree" meridian direction is obtained based on the moved position. Next, the image rotator 18 is rotated, for example, 15 times per every "six powers" in the meridian direction to be measured with the position of the target plate 11 held stationary, and the differences of the spaces ℓ₁ - ℓ₂ corresponding to the respective rotating position are read in (STEPS 108 through 110). The refractive power "Dϑ" in the "ϑ" direction can be obtained by calculating the sum of the diopter value corresponding to the stop position of the target plate 11 and the diopter value corresponding to the value of the difference of the spaces ℓ₁ - ℓ₂. And, there is a relation as shown by the following formula (1) among spherical power A, astigmatism power B and astigmatism axis α. Dϑ = A + B cos (ϑ - α) (1) Accordingly, based on the refractive powers "Dϑ₁ through Dϑ₁₅" obtained in the respective meridian directions (15 meridian directions), the spherical power A, astigmatism power B and astigmatism axis α are calculated respectively based on the method for least squares (STEPS 111, 112). Next, such obtained calculation result is compared with the measurement value and checking is made whether irregularities of the respective measurement values are within a predetermined range (STEP 113). When the irregularities of the measurement values are found to exceed the predetermined range by the foregoing checking, the mode switch 56 is automatically switched over to the manual measurement mode according to the instruction of CPU 50. On the contrary, the irregularities are within the predetermined range, the measurement values are displayed on the television monitor 44 and at the same time the measurement values are printed by the printer 67 (STEPS 114, 115), and the processing of the auto-measurement program is terminated. According to this apparatus, since the display surface 45 of the television monitor 44 is displayed both the anterior portion image 47 and the measuring target image 46, the tester can observe the state in Which the measurement is being carried out. Next, there will be described on a case where the mode switch 56 was switched over to the manual measurement mode side either manually or automatically. In this case, CPU 50 runs the manual measurement program. First, in STEP 116, an initial setting like STEP 101 of the aforementioned auto-measurement mode is effected. Next, the tester turns on the actuation switch 57 until both the spaces ℓ₁, ℓ₂ of the measuring target image as shown in Fig. 4 and integrally moves the target plate 11 and the movable lens 25 along the optical axis while observing the measuring target image on the display surface 45 of the television monitor 44 (STEP 117). Upon finish of this movement, the tester turns on the 1 meridian measurement finish switch 58 to cause CPU 50 to read in the moving position of the target plate 11. The moving position corresponds to the refractive power in the "zero degree" meridian direction same as in the case of the auto-measurement. In this case, when the 1 meridian finish switch 58 is turned on (STEP 118), a piece of * mark, for example, indicating the number of measurement is displayed on the television monitor 44 (STEP 119), the position of the target plate 11 is read in (STEP 120), and at the same time, the image rotator 18 is rotated by a predetermined angle (STEP 121). Next, the tester turns on the actuation switch 57 to move the target plate 11 while observing the measuring target image displayed on the television monitor 44 and operation such as reading-in of the moving position is repeated as in the same manner as the above mentioned STEP. At this time, every time one measuring operation is finished, one piece of * mark is displayed on the television monitor 44. And, when at least three measuring operations are effected, the measurement finish switch 59 is turned on to finish the measuring operation (STEP 122). The number of measurement is decided in advance without providing the measurement finish switch 59, so that the measurement will be automatically finished after the predetermined number of measurement is finished. According to the three times measuring operation, the refractive power in the 3 meridian directions can be obtained (STEP 123), the spherical power A, astigmatism power B and astigmatism α are obtained respectively based on the aforementioned formular (1) according to the method for least squares (STEP 124). And, the measuring results of the spherical power A, astigmatism power B and astigmatism axis α are displayed on the television monitor and at the same time, they are printed out by the printer 67 (STEPS 125, 126).

Claims: An automatic eye refractive power measuring apparatus for automatically measuring the refractive power of an eye under test by measuring objectively the focusing state of a measurement target projected onto the retina of the eye under test, comprising: a target image projection system (1) for projecting with invisible light the image of a measuring target (11) onto the retina of the eye under test; an imaging optical system (2) for imaging at an imaging position a reflection image of the measuring target image reflected by the retina; an opto-electric detector (29) having a photosensitive surface (29a) disposed at said imaging position and arranged to output an electrical signal corresponding to the reflection image of the measuring target image formed on the photosensitive surface; display means (44) for converting the reflection image of the measuring target image to a visible image (46) in accordance with said electrical signal and for displaying the converted visible image; and computer means (50) for calculating the refractive power of the eye under test in accordance with said electrical signal; characterised by the computer means being arranged to be selectively operable in either an automatic measurement mode or a manual measurement mode, where in said automatic measurement mode the focusing state of the measuring target image projected onto the retina is determined in accordance with said electrical signal and the refractive power of the eye under test is automatically calculated based on said focusing state, and where in said manual measurement mode a manual measurement means (66) is activated for measuring the refractive power of the eye under test by an operator directly observing the focusing state of the measurement target image on said display means and manually activating said computer means to calculate the refractive power of the eye under test in accordance with said electrical signal describing the observed focusing state of the measurement target image; and by measurement mode switching means (56), for selectively activating said automatic measurement mode and said manual measurement mode, the switching means being automatically selectively activated by said computer means depending on the light intensity of the reflection image of the measuring target image detected by the opto-electric detector. An automatic eye refractive power measuring apparatus according to claim 1, characterised by the computer means automatically activating said measurement mode switching means to switch to the manual measurement mode when the detected light intensity of the reflection image of the measuring target image is less than a predetermined value. An automatic eye refractive power measuring apparatus according to claim 1 or 2, characterised by a measurement finish switch (58, 59) for storing the measured focusing state at a first predetermined meridian in the computer means when said switch is activated during the manual measurement mode; and means (62, 63) for rotating said measuring target (11) relative to the eye under test to measure the focusing state of the measuring target image along a second predetermined meridian.

Inventors: HORIGUCHI KIWAMI, KATO YASUO, KITAO IKUO, WADA SHINJI, HORIGUCHI, KIWAMI, KATO, YASUO, KITAO,  IKUO, WADA, SHINJI, KITAO, IKUO
Applicants: TOPCON CORP, KABUSHIKI KAISHA TOPCON
Application year: 1986
Main classification: A61B3
IPC codes: A61B3