Source: https://patents.google.com/patent/US6467907B1/en
Timestamp: 2019-12-07 14:38:48
Document Index: 405753389

Matched Legal Cases: ['art 53', 'art 53', 'art 52', 'art 14', 'art 14', 'art 14', 'art 50', 'art 54', 'art 50', 'art 53']

US6467907B1 - Apparatus for determining an amount of corneal ablation and surgical apparatus for a cornea - Google Patents
Apparatus for determining an amount of corneal ablation and surgical apparatus for a cornea Download PDF
US6467907B1
US6467907B1 US09/744,909 US74490901A US6467907B1 US 6467907 B1 US6467907 B1 US 6467907B1 US 74490901 A US74490901 A US 74490901A US 6467907 B1 US6467907 B1 US 6467907B1
US09/744,909
Yokinobu Ban
Masahiro Oyaizu
1999-10-21 Priority to JP11-300148 priority Critical
1999-10-21 Priority to JP30014899 priority
2000-08-03 Application filed by Nidek Co Ltd filed Critical Nidek Co Ltd
2000-08-03 Priority to PCT/JP2000/005250 priority patent/WO2001028479A1/en
2001-01-31 Assigned to NIDEK CO., LTD. reassignment NIDEK CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BAN, YUKINOBU, OYAIZU, MASAHIRO, FUJIEDA, MASANAO
2002-10-22 Publication of US6467907B1 publication Critical patent/US6467907B1/en
238000002679 ablation Methods 0 abstract claims description title 185
210000004087 Cornea Anatomy 0 abstract claims description title 57
206010038264 Refraction diseases Diseases 0 abstract claims description 16
230000004430 ametropia Effects 0 abstract claims description 16
230000036040 emmetropia Effects 0 claims description 30
201000000766 irregular astigmatism Diseases 0 description 11
102100003423 CCNB1IP1 Human genes 0 description 2
101700047187 CIP1 family Proteins 0 description 2
101700042838 HEI10 family Proteins 0 description 2
The purpose of the present invention is to provide an apparatus for determining an amount of corneal ablation, which can calculates an amount of corneal ablation in order to perform an operation for correcting ametropia adequately, based on a corneal shape and/or an eye refractive power. Another object of the present invention is to provide a surgical apparatus for a cornea, by which the surgical operation can be performed efficiently based on the obtained amount of corneal ablation. The apparatus for determining an amount of corneal ablation, based on which surgical operation for correcting ametropia is performed, the apparatus comprises a first input unit (53) for inputting data of a pre-operative corneal shape of a patient's eye; a second input unit (52, 53, 54) for inputting data of a post-operative corneal shape of the eye, to be estimated (to be a target for correcting); an ablation amount calculating unit (54) for calculating data of a corneal ablation amount of the eye, in a manner of calculating data of an ablation amount in a symmetric component and data of an ablation amount in an asymmetric component separately and respectively, based on the data inputted by the first input unit and the second input unit; and an output unit (56, 59 a, 59 b) for outputting results calculated by the ablation amount calculating unit.
The present invention relates to an apparatus for determining an amount of corneal ablation and a surgical apparatus for a cornea, and more particularly, to the apparatus utilized for correcting ametropia in a manner of ablating a corneal surface and varying its shape.
It is known for surgery operation, by which ametropia of an eye is corrected by a process of ablating a corneal surface (corneal stroma and the like) with a laser beam then varying its shape. In the surgical operation, both of a corneal shape (a corneal surface shape) and a refractive power of the eye to be operated (a patient's eye) are obtained, based on which, an amount of corneal ablation necessary for correction is calculated and found. In the past, procedures for calculating an amount of corneal ablation is conducted as following.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention comprises below mentioned construction.
FIG. 1 is a view showing a schematic configuration of an optical system in the apparatus for determining an amount of corneal ablation of the preferred embodiment of the present invention;
A detailed description of one preferred embodiment of the present invention will now be given referring to the accompanying drawings. FIG. 1 is a view showing a schematic configuration of an optical system in the apparatus for determining an amount of corneal ablation of the preferred embodiment of the present invention. The optical system is roughly divided into an eye refractive power measuring optical system, a fixation target projecting optical system and a corneal radius of curvature measuring optical system.
A corneal shape calculating part 53 detects an edge of an image of ring patterns by processing an image photographed by the camera 38. Then, the calculating part 53 calculates a corneal radius of curvature by obtaining each edge position relative to a vertex of the cornea Ec at intervals of a given angle (1°).
R=(2 D/H) mh′
It is also possible to adapt a method of calculating a corneal radius of curvature as following. The corneal radius of curvature of the region where the j-th ring is projected onto the cornea is defined as Rj. The proportional constant which is determined by the height of the j-th ring, the distance up to the eye E and the photographing magnification, is defined as Kj. The image height on the photographing plane is defined as hj. Under the definition, the relationship expression as identified above is given by following expression:
Where, if a plurality of model eyes having known different corneal radius of curvature which cover the measurement range is measured in advance, then the proportional constant Kj is obtained as an intrinsic value for the apparatus. Therefore, if the constant Kj is read out and utilized for calculation at the time of measuring, then the distribution of the corneal radius of curvature is obtained in extremely short time. (The details of this calculation, see U.S. Pat. No. 5,500,697 corresponding to the Japanese Patent Publication Laid-Open No. HEI 7(1995)-124113, or the like.) The obtained distribution data of the corneal radius of curvature is stored in a memory 55 b.
A surgical apparatus for a cornea is used on the assumption that a pupil center is defined as an origin position of an eye, but, in general, a corneal vertex disagrees with a pupil center, so the positional relationship between a corneal shape (a corneal center or the like) and a pupil center should be found in advance. In view of this point, based on the anterior portion image photographed by the camera 38, a pupil center is defined as an intersecting point defined by following first and second lines: the first line is passing through a center between two points and extending in a perpendicular direction (the two points are respectively on opposite edges of a pupil, the points on edges are the intersecting points with a horizontal line passing through approximately a center of an pupil) and the second line is passing through a center between two points and extending in a horizontal direction (the two points are respectively on opposite edges of a pupil, the points on edges are intersecting points with a perpendicular line passing through approximately a center of a pupil). The method for definition of a pupil center is not limited thereto, another method may satisfactorily adopted. For example, a pupil center may satisfactorily be defined based on a gravity of a pupil. The obtained pupil position relative to a corneal shape is also stored in the memory 55 b.
On the contrary, in the case of measuring an eye refractive power (it is referred to as “an objective eye refractive power” hereinbelow), the operator changes the mode to the mode for measuring an eye refractive power (in the case of the continuous measurement mode, it is automatically changed to the mode for measuring an eye refractive power), then the measurement is performed by the measuring optical system 100. The refractive power calculating part 52 obtains distribution of an objective eye refractive power, based on each phase difference of each output signal from each photo-detector of the photo-receiving part 14. More specifically, firstly, the preliminary measurement is performed by a similar method of measuring a refractive power in the prior art, such as a phase difference method. Based on its result, the eye E is fogged by moving the lens 33. Thereafter, the center of each photo-detector 15 a-15 f is determined in a meridian direction where the photo-detectors 15 a-15 f are placed. This determination is based on each signal outputted from the photo-detectors 15 g and 15 h, the signals varying in accordance with movement of a slit-light (a slit-image) on the photo-receiving part 14. Next, based on a phase difference between each signal outputted from each photo-detector 15 a-15 f relative to the center of each photo-detector 15 a-15 f , each refractive power at each corneal part corresponding to each photo-detector is calculated. If this calculation is performed in order to obtain each refractive power per every meridian of each axial step under the condition that the projecting optical system 1 and the photo-receiving part 14 are made to be rotated 180° around the optical axis at a given angle, such as 1°, then the distribution of refractive power varying in a meridian direction can be obtained (in details, see Japanese Patent Publications Laid-Open No. HEI10(1998)-108836 and No. HEI10(1998)-108837 corresponding to U.S. Pat. No. 5,907,388). Where, the value of the refractive power is expressed as a vertex power (the apparatus can also output or convert a value of a refractive power as a spectacles power which is based on a position where a pair of spectacles is worn). The obtained distribution data of the objective eye refractive power is stored in a HDD 55 a or the memory 55 b.
If respective measured data including a corneal radius of curvature and an objective eye refractive power are obtained as above described, then the operator operates a keyboard 58 and/or a mouse 57 in accordance with an instruction displayed on a color display 56, connected to a control part 50, thereby causing analysis to start. The analysis part 54 provided for the control part 50 converts the corneal radius of curvature into a corneal refractive power, then executing an analysis program in order to obtain relationship between the converted corneal refractive power and the corresponding objective eye refractive power.
D=(ne−1)/r,
where, r is defined as a corneal radius of curvature, ne is an equivalent refractive rate (in general, ne=1.3375).
N sin i=N′ sini′,
where, each refractive index at each medium of a refraction plane is defined as N and N′, an angle formed by an incident light beam and a normal line is defined as i, and an angle formed by a refracted light beam and a normal line is defined as i′.
Firstly, as shown in FIG. 5, the angle θ is given by following expression: θ = sin - 1  ( X R a ) ( 1 )
Next, the angle γ is given by following expression based on the Snell's law: γ = sin - 1  ( X R a × n ) ( 2 )
Based on the expressions (1) and (2), an angle α (an angle formed by a segment hP and a segment Pf), a distance Rr, and a segment hf are given by following expressions:
α=90−θ+γ
R r = X cos   ( α )   hf _ = R r 2 - X 2 ( 3 )
In addition, a distance of a segment Th is given by following expression:
{overscore (Th)}=R a −{square root over (Ra 2 −X 2)} (4)
Accordingly, a distance from the corneal vertex T to the point f is given by following expression:
{overscore (Tf)}={overscore (Th)}+{overscore (hf)}=R a −{square root over (Ra 2 − X 2)}+ {square root over (Rr 2 −X 2)} (5)
A refractive power DC in a cornea is given by following expression: Dc = 1 Tf _ = 1 R a - R a 2 - X 2 + R r 2 - X 2 ( 6 )
In contrast, a refractive power D in air is given by following expression under definition that a refractive index is n (=1.376): D = n × Dc = n R a - R a 2 - X 2 + R r 2 - X 2 ( 7 )
If the calculation by using the above identified expressions (1) to (7) is performed with respect to all measuring region, then the corneal refractive power is calculated. Alternatively, the calculation may satisfactorily be performed by the corneal shape calculating part 53.
Next, the objective eye refractive power is then converted to a refractive power equivalent to a corneal surface with respect to the corneal refractive power calculated as described above. The converted value results in the form of a corneal refractive power necessary for causing the eye E to be emmetropia (in this specification, this is referred to as “an equivalent emmetropia corneal refractive power”).
Accordingly, in the region where the objective eye refractive power is measured, a corneal refractive power which causes the eye to be emmetropia is calculated in a manner of adding the measured objective eye refractive power including a sign to the corneal refractive power obtained from the corneal shape measurement. The calculated value proves to be the equivalent emmetropia corneal refractive power, given by following expression: Equivalent   emmetropia corneal   refractive   power = Corneal refractive   power + Objective   eye refractive   power
In addition, the equivalent emmetropia corneal refractive power can be converted into the corneal radius of curvature, based on the Snell's law. This conversion can be performed by using the below identified two expressions found by the same way as shown in FIG. 5: R r = R a 1 - ( X n × R a ) 2 - 1 n  1 - ( X R a ) 2   R r 2 - X 2 + R a - R a 2 - X 2 - n D = 0 ( 8 )
Where, D is defined as the equivalent emmetropia corneal refractive power; Ra is the solved corneal radius of curvature.
Prior to calculate the data of an ablation amount in a cylindrical component, an axial direction angle A is defined following below mentioned procedures. Firstly, distribution data of a corneal radius of curvature at each coordinate position is established by using a shape of the data of a total ablation amount 72. Then, the flattest curvature direction is found among the established data and is defined as the axial angle direction A. In FIG. 8(a), the axial angle direction A is defined as 0°.
In the case of correcting myopia on a spherical (non-spherical) surface based on the data of an ablation amount in a spherical (non-spherical) component, a laser beam is limited by the circular aperture 109 a , then a plane mirror 105 is caused to move in turn so that the laser beam may move to the Gaussian distribution direction. Every time when the laser beam finishes moving on one surface (one scan), then the image rotator 107 rotates and causes the laser beam to change its moving direction (for example, three directions at intervals of 120°). Then, the region limited by the circular aperture 109 a is ablated by the laser beam approximately uniformly. If this ablation is performed every time when changing an opening region of the circular aperture 109 a in turn, then the ablation can be performed with respect to a spherical (non-spherical) component so that the center part of a cornea may be ablated deeply and the periphery part of a cornea may be ablated slightly.
As described above, according to the present invention, even in the case of an irregular astigmatism or the like, an appropriate amount of corneal ablation can be determined in accordance with a corneal shape and/or a refractive power of the eye to be operated, for the purpose of performing surgical operation for correcting ametropia adequately.
1. An apparatus for determining an amount of corneal ablation, based on which surgical operation for correcting ametropia is performed, the apparatus comprising:
a first input unit for inputting data of a pre-operative corneal shape of a patient's eye;
a second input unit for inputting data of a post-operative corneal shape of the eye, to be estimated;
an ablation amount calculating unit for calculating data of a corneal ablation amount of the eye, in a manner of calculating data of an ablation amount in a symmetric component and data of an ablation amount in an a symmetric component separately and respectively, based on the data inputted by the first input unit and the second input unit; and
an output unit for outputting results calculated by the ablation amount calculating unit.
2. The apparatus according to claim 1, wherein the output unit comprises a display unit for displaying the results calculated by the ablation amount calculating unit, graphically.
a corneal shape measuring unit for measuring distribution data of a corneal radius of curvature of the eye;
an eye refractive power measuring unit for measuring distribution data of an eye refractive power of the eye;
a corneal shape calculating unit for calculating distribution data of an equivalent emmetropia corneal refractive power of the eye based on pre-operative distribution data measured by the corneal shape measuring unit and pre-operative distribution data measured by the eye refractive power measuring unit, subsequently, calculating distribution data of a post-operative corneal radius of curvature of the eye, to be estimated, based on the obtained distribution data of the equivalent emmetropia corneal refractive power; wherein the first input unit inputs the results measured by the corneal shape measuring unit into the ablation amount calculating unit, and the second input unit inputs the results obtained by the corneal shape calculating unit into the ablation amount calculating unit.
7. The apparatus according to claim 6, wherein the corneal shape calculating unit calculates distribution data of a corneal refractive power based on the distribution data of the corneal radius of curvature measured by the corneal shape measuring unit, subsequently, calculating the distribution data of the equivalent emmetropia corneal refractive power based on the obtained distribution data of the corneal refractive power an d the distribution data of the eye refractive power measured by the eye refractive power measuring unit; and the output unit includes a display unit for displaying graphically at least one distribution data selected from the group consisting of the distribution data of the corneal refractive power, the distribution data of the eye refractive power and the distribution data of the equivalent emmetropia corneal refractive power.
a correcting-refractive power input unit for inputting data of a correcting-refractive power of the eye; and
a corneal shape calculating unit for calculating the data of a post-operative corneal shape, to be estimated, based on the inputted data of the correcting-refractive power; wherein the second input unit inputs the results calculated by the corneal shape calculating unit into the ablation amount calculating unit.
9. The apparatus according to claim 1, wherein at least one between the first input unit and the second input unit comprises an input unit with which an operator inputs data.
a first input unit for inputting data of a pre-operative corneal shape of the eye;
an ablation amount calculating unit for calculating data of a corneal ablation amount of the eye, in a manner of calculating data of an ablation amount in a symmetric component and data of an ablation amount in an a symmetric component separately and respectively, based on the data inputted by the first input unit and the second input unit;
a first ablation unit for ablating the cornea, based on the obtained data of the ablation amount in the symmetric component; and
a second ablation unit for ablating the cornea, based on the obtained data of the ablation amount in the asymmetric component.
11. The surgical apparatus for a cornea, according to claim 10, wherein the first ablation unit comprises an irradiating optical system for irradiating the cornea with the laser beam from a laser source; and the second ablation unit shares the irradiating optical system with the first ablation unit.
a corneal shape measuring unit for measuring distribution data of a corneal radius of curvature of a patient's eye;
a corneal shape calculating unit for calculating distribution data of an equivalent emmetropia corneal refractive power of the eye based on pre-operative distribution data measured by the corneal shape measuring unit and pre-operative distribution data measured by the eye refractive power measuring unit, subsequently, calculating distribution data of a post-operative corneal radius of curvature of the eye, to be estimated, based on the obtained distribution data of the equivalent emmetropia corneal refractive power;
an ablation amount calculating unit for calculating data of a corneal ablation amount of the eye, in a manner of calculating data of an ablation amount in a symmetric component and data of an ablation amount in an asymmetric component separately and respectively, based on the results measured by the corneal shape measuring unit and the results calculated by the corneal shape calculating unit; and
14. The apparatus according to claim 13, wherein the corneal shape calculating unit calculates distribution data of a corneal refractive power based on the distribution data of the corneal radius of curvature measured by the corneal shape measuring unit, subsequently, calculating the distribution data of the equivalent emmetropia corneal refractive power based on the obtained distribution data of the corneal refractive power and the distribution data of the eye refractive power measured by the eye refractive power measuring unit; and the output unit includes a display unit for displaying graphically at least one data selected from the group consisting of the distribution data of the corneal refractive power, the distribution data of the eye refractive power, the distribution data of the equivalent emmetropia corneal refractive power, data of a total ablation amount, data of the ablation amount in the symmetric component and data of the ablation amount in the asymmetric component.
US09/744,909 1999-10-21 2000-08-03 Apparatus for determining an amount of corneal ablation and surgical apparatus for a cornea Active US6467907B1 (en)
JP11-300148 1999-10-21
JP30014899 1999-10-21
PCT/JP2000/005250 WO2001028479A1 (en) 1999-10-21 2000-08-03 Amount-of-cornea-to-be-excised determining device and cornea surgery device
US6467907B1 true US6467907B1 (en) 2002-10-22
ID=17881332
US09/744,909 Active US6467907B1 (en) 1999-10-21 2000-08-03 Apparatus for determining an amount of corneal ablation and surgical apparatus for a cornea
US (1) US6467907B1 (en)
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WO (1) WO2001028479A1 (en)
ZA (1) ZA200104760B (en)
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WO2001028479A1 (en) 2001-04-26
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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FUJIEDA, MASANAO;BAN, YUKINOBU;OYAIZU, MASAHIRO;REEL/FRAME:011545/0766;SIGNING DATES FROM 20001218 TO 20001221