JP3112108B2 - Corneal thickness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corneal thickness measuring apparatus for optically measuring the thickness of a cornea.

[0002]

2. Description of the Related Art Conventionally, as a corneal thickness measuring device for optically measuring the thickness of a cornea, slit illumination light P is incident along an optical axis O ₁ of an eye 1 to be examined as shown in FIG. The pre-parallel 3 is rotated while observing the cornea 2 from the direction of the predetermined angle θ so that the image 2b and the image 2f ′ overlap as shown in FIG. 2, and the thickness of the cornea is determined based on the rotation angle φ of the pre-parallel 3. A corneal thickness measuring device for measuring the thickness is known.

[0003]

However, in this conventional corneal thickness measuring apparatus, a measurer measures the thickness of the cornea 2 by matching the image 2b and the image 2f 'while observing the cornea 2. Therefore, measurement errors due to individual differences and time differences occur, and it is difficult to match the image 2b and the image 2f ′.
There is a drawback that the measurer and the subject are likely to cause fatigue.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a corneal thickness measuring apparatus capable of eliminating measurement errors due to individual differences and improving measurement accuracy.

[0005]

A corneal thickness according to claim 1.
The measuring device includes an illumination optical system that irradiates illumination light toward the cornea from an oblique direction with respect to the optical axis of the eye to be examined, a reflected light flux reflected from the surface of the cornea and a reflected light flux reflected from the back surface of the cornea. And an optical axis of the illumination optical system and an optical axis of the light receiving optical system are arranged at substantially left-right symmetrical positions with respect to an optical axis of the eye to be inspected. A photoelectric conversion element capable of detecting an image forming position of each of the reflected light beams is provided, and the photoelectric conversion element is connected via an amplifier circuit.
Corresponding to the reflected light flux reflected from the surface of the cornea
To the electrical conversion signal and the reflected light flux reflected from the back of the cornea.
Measures the thickness of the cornea based on the corresponding photoelectric conversion signal
Measuring circuit, the measuring circuit
Differentiation circuit for detecting rising and falling parts of signal
And has a path for preventing reflected light flux reflected from the surface of the cornea.
Between the corresponding rising edge of the photoelectric conversion signal and the back of the cornea
Rise of the photoelectric conversion signal corresponding to the reflected light flux
Distance from the bulge and reflected from the surface of the cornea
The falling part of the photoelectric conversion signal corresponding to the reflected light flux and the
Photoelectric conversion corresponding to the reflected light beam reflected from the back of the cornea
The thickness of the cornea based on the distance between the falling edge of the signal
It is characterized by measuring the height .

[0006]

According to the corneal thickness measuring apparatus according to the present invention, the illumination light beam is emitted toward the cornea obliquely with respect to the optical axis of the subject's eye. The illuminating light flux is reflected mainly on the front surface of the cornea and the back surface of the cornea, which are the boundary surfaces. The light quantity of the reflected light flux reflected on the surface of the cornea and the light quantity of the reflected light flux reflected on the back surface of the cornea are the reflected light flux when the illumination light flux is directed toward the cornea along the optical axis of the eye to be examined. It is large compared to the amount of light. The light receiving optical system receives the reflected light beam reflected on the surface of the cornea and the reflected light beam reflected on the back surface of the cornea. The photoelectric conversion element outputs a photoelectric conversion signal corresponding to a light beam reflected from the surface of the cornea and a photoelectric conversion signal corresponding to a light beam reflected from the back surface of the cornea. The measurement circuit measures the thickness of the cornea based on the photoelectric conversion signal corresponding to the light beam reflected from the front surface of the cornea and the photoelectric conversion signal corresponding to the light beam reflected from the back surface of the cornea.

[0007]

Next, an embodiment of a corneal thickness measuring apparatus according to the present invention will be described with reference to FIGS.

FIG. 3 is a plan view showing the corneal thickness measuring apparatus. In FIG. 3, reference numeral 10 denotes an anterior segment observation optical system for observing the anterior segment of the eye E to be examined. The anterior ocular segment observation optical system 10 includes a half mirror 11, an objective lens 12, an optical path switching mirror 13, and an area CCD 14.
O ₂ is the optical axis. The anterior segment of the eye E is illuminated by an anterior segment illumination light source (not shown). Half mirror 11
Constitutes a part of the alignment optical system 12 '. The optical path switching mirror 13 is retracted from the optical path of the anterior ocular segment observation optical system 10 before the alignment is completed. The alignment optical system 12 'includes an alignment light source 13',
It is roughly composed of a projection lens 14 '. The alignment index light beam from the alignment optical system 12 'is projected onto the cornea 15 of the eye E to be inspected. The alignment index light beam reflected by the cornea 15 is formed on the area CCD 14 via the half mirror 11 and the objective lens 12 together with the image of the anterior segment of the eye E to be inspected. The area CCD 14 is scanned and processed by the drive processing circuit 15, and the anterior eye image and the alignment index image are displayed on the monitor 16. The observer observes the alignment index image while fixing the fixation target (not shown) to align the apparatus optical system with the eye E to be inspected. The optical path switching mirror 13 is inserted into the optical path of the anterior ocular segment observation optical system 10 when the alignment is completed.

An illumination optical system 17 is provided on one side of the optical axis O ₂ of the anterior ocular segment observation optical system 10. Illumination optical system 1
7 serves to the slit illumination light from an oblique direction with respect to the optical axis O ₂ of the eye E to irradiate the cornea 15. The illumination optical system 17 includes an illumination light source 18, a condenser lens 19, a slit 20, and a projection lens 21, and O ₄ is the optical axis. The optical axis O ₄ has an inclination of θ with respect to the optical axis O ₂ .

A light receiving optical system 22 is provided on the other side of the optical axis O ₂ of the anterior eye observation optical system 10. Receiving optical system 2
2 is an objective lens 23, a half mirror 24, a field stop 2
5, a total reflection mirror 26 and an imaging lens 27. The optical axis O ₅ of the light receiving optical system 22 is the anterior ocular segment observation optical system 1
It is arranged almost symmetrically with respect to the optical axis O ₄ with respect to the optical axis O _{2 of} zero. At the time of completion of the alignment, the optical axis O ₄ of the illumination optical system 17
And the optical axis O ₅ of the light receiving optical system 22 is substantially symmetric with respect to the optical axis O _{2 of the} eye E. The slit illumination light flux reflected by the cornea 15 passes through the objective lens 23 and the half mirror 24
Is led to. The half mirror 24 reflects a part of the reflected light beam toward the one-dimensional line sensor 28 as a photoelectric conversion element, and transmits the rest. The reflected light beam transmitted through the half mirror 24 is once imaged at the position of the field stop 25,
The light is reflected by the total reflection mirror 26 toward the imaging lens 27, is formed on the area CCD 14 via the imaging lens 27 and the optical path switching mirror 13, and the endothelial image of the cornea 15 is displayed on the monitor 16. The one-dimensional line sensor 28 and the field stop 25 are substantially conjugate with respect to the endothelial position of the cornea 15 in a state where the alignment is completed.

The one-dimensional line sensor 28 receives a slit reflected light beam P ₁ from the front surface 30 of the cornea 15 and a slit reflected light beam P ₂ from the back surface 31 of the cornea 15 as shown in FIG. In FIG. 4, P ₁₁ is slit 20
An illumination light beam is defined by the end edge 20a, P ₁₂
Is the illumination light beam that is defined by the edge 20b of the slit 20, P ₁₃ is the reflected light beam of an optical beam P ₁₁ reflected at the surface 30 of the cornea 15, P ₁₄ is reflected at the rear surface 31 of the cornea 15 a reflected light beam of an optical beam P _11. Also, P ₁₅ is the reflected light beam of an optical beam P ₁₂ reflected at the surface 30 of the cornea 15, P ₁₆ is the reflected light beam of an optical beam P ₁₂ reflected at the rear surface 31 of the cornea 15. Further, the illumination light flux K ₁ indicated by a solid line is a main light flux passing through the center of the slit 20, K ₂ is a reflected main light flux reflected on the surface 30 of the cornea 15, and K ₃ is reflected on the back face 31 of the cornea 15. 3 shows a reflected main luminous flux.

A row of minute photoelectric elements of the one-dimensional line sensor 28 is driven and scanned by a driving circuit 33. Drive circuit 3
3 outputs a clock pulse C at a constant period as shown in FIG. Photoelectric conversion signal shown in FIG. 5 (b) based on the reflected light beam P ₁ from the one-dimensional line sensor 28 and the reflected light flux P ₂ is output. In FIG.
₁ is a photoelectric conversion signal corresponding to the reflected light flux P ₁ ,
₂ is a photoelectric conversion signals corresponding to the reflected light beam P _2. The rising portion S ₁₁ in the photoelectric conversion signals S ₁ corresponds to the reflected light beam P ₁₃ reflected at the surface 30 of the cornea 15, the falling section S ₁₂ corresponding to the reflected light beam P ₁₅ reflected at the surface 30 of the cornea 15 doing. Also, the photoelectric conversion signal S
Backside 31 of the rising portion S ₂₁ is the cornea 15 at ₂
Corresponding to the reflected light beam P ₁₄ reflected at the falling portion S ₂₂ corresponds to the reflected light beam P ₁₆ reflected at the rear surface 31 of the cornea 15. Flat portion F ₁ of the photoelectric conversion signals S ₁ are due to the reflected light beam between the reflected light beams P ₁₃ and the reflected light beam P _15, the flat portion F ₂ of the photoelectric conversion signal S ₂ is reflected beams P ₁₄ and the reflected light beam P _This is due to the reflected light flux between the _16th and _16th . The output between the photoelectric conversion signals S ₁ and the photoelectric conversion signal S ₂ is slightly low, because the reflected light beam from the corneal stroma is small compared to the boundary surface.

The photoelectric conversion output from the one-dimensional line sensor 28 is amplified by an amplifier circuit 34 and input to a measurement circuit 35. The measuring circuit 35 has a differentiating circuit 36 as shown in FIG. The differentiating circuit 36 outputs the differential outputs B ₁ , B ₂ , B based on the photoelectric conversion signals S ₁ , S ₂ as shown in FIG.
_3, and outputs the B _4. The differential output B ₁ is a signal based on the rising portion S ₁₁ , the differential output B ₂ is a signal based on the falling portion S ₁₂ , the differential output B ₃ is a signal based on the rising portion S ₂₁ , and the differential output B ₄ is a signal based on the edge portion S ₂₂ standing.

The differential outputs B ₁ and B ₃ are input to a peak detector 37. The differential outputs B ₂ and B ₄ are inverted by an inverting circuit 38 and input to a peak detector 39. Peak detector 3
7 outputs clock pulses CL ₁ and CL ₂ shown in FIG. 5D based on the differential outputs B ₁ and B ₃ , and outputs a peak detector 39.
Outputs clock pulses CL ₃ and CL ₄ shown in FIG. 5E based on the differential outputs B ₂ and B ₄ . Clock pulse C
L ₁ and CL ₂ are input to the frequency divider 40 and the clock pulse C
L ₃ and CL ₄ are input to the frequency divider 41. Divider 40 becomes high by the clock pulses CL _1, becomes low by the clock pulses CL _2. Divider 41 becomes high by the clock pulse CL _3, the low by the clock pulse CL _4.

The output of the frequency divider 40 is input to one input terminal of an AND circuit 42, and the reference clock signal of the clock signal generator 43 is input to the other input terminal of the AND circuit 42. The output of the frequency divider 41 is input to one input terminal of the AND circuit 44, and the reference clock signal is input to the other input terminal of the AND circuit 44. The AND circuit 42 includes the frequency divider 4
While 0 is high, the reference clock signal SC shown in FIG.
L, and the AND circuit 44 passes the reference clock signal SCL ′ shown in FIG. 5G while the frequency divider 41 is high. The output of the AND circuit 42 is input to a counter 45, and the output of the AND circuit 44 is input to a counter 46. The counter 45 counts the number of reference clock signals SCL, and the counter 46 counts the number of reference clock signals SCL ′. The count information of the counter 45 and the count information of the counter 46 are input to the arithmetic circuit 47.

The clock pulse CL ₁ and the clock pulse C
Spacing D ₁ of the and L ₂ corresponds to the distance L ₁ shown in FIG. 4, the distance D ₂ between the clock pulses CL ₃ and the clock pulses CL ₄ corresponds to the distance L ₂ shown in FIG. The average value D of the distance D ₁ and the distance D ₂ corresponds to the distance L shown in FIG.
Between the outline thickness d'distance L of the cornea 15, the length from the point A on the surface 30 of the cornea 15 of the illumination main beam K ₁ to the point A'of the back surface 31 of the cornea 15 of the illumination main beam K ₁ Assuming that W is W, according to the formula of trigonometric function, L = Wcos (90 ° −2θ) d ′ = Wcosθ, d ′ = Lcosθ / cos (90 ° −2θ) Here, if the angle θ is set to 30 ° D ′ = L That is, the approximate thickness d ′ of the cornea 15 is represented by the distance L.

The approximate thickness d 'of the cornea 15 obtained here is a value calculated by ignoring the difference between the refractive index of air and the cornea and the curvature of the cornea. Can be accurately determined. For example, the thickness d of the cornea 15 is corrected by adding the length from the corneal vertex H to the point H '.

These calculations are performed by the calculation unit 47, and the calculation results are output to the monitor 15 or the printer 48.

[0019]

Corneal thickness measuring apparatus according to the present invention, the following
As described above, the corneal membrane having a curved surface shape
Since the measurement can be accurately performed even when the thickness is large, measurement errors due to individual differences can be eliminated and the measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system of a conventional corneal thickness measuring apparatus.

FIG. 2 is an explanatory diagram for explaining a measuring method of a conventional corneal thickness measuring apparatus.

FIG. 3 is a plan view showing an embodiment of an optical system of the corneal thickness measuring apparatus according to the present invention.

FIG. 4 is an explanatory diagram of a reflection state of an illumination light beam by an optical system of the corneal thickness measuring apparatus according to the present invention.

FIG. 5 is a timing chart of a measurement circuit according to the present invention.

FIG. 6 is a block diagram showing a detailed configuration of a measurement circuit according to the present invention.

[Explanation of symbols]

15 ... cornea 17 ... illumination optical system 22 ... light-receiving optical system 28 ... one-dimensional line sensor (photoelectric conversion element) 30 ... surface 31 ... rear surface 35 ... measurement circuit E ... subject eye O ₁ ~ O ₅ ... optical axis

Continuation of the front page (56) References JP-A-58-192507 (JP, A) JP-A-2-311704 (JP, A) JP-A-58-28601 (JP, U) (58) Fields investigated (Int) .Cl. ⁷ , DB name) A61B 3/00-3/16 G01B 11/00-11/30

Claims (1)

(57) [Claims] 1. Illumination from an oblique direction with respect to an optical axis of an eye to be examined.
An illumination optical system for irradiating light toward the cornea; and a table of the cornea.
Reflected light from the surface and reflected from the back of the cornea
And a light receiving optical system for receiving the reflected light flux, The optical axis of the illumination optical system and the optical axis of the light receiving optical system are
It is arranged in a substantially symmetrical position with respect to the optical axis of the eye to be examined,
The imaging position of each reflected light beam can be detected by the light receiving optical system.
Photoelectric conversion element is provided, and the photoelectric conversion element
The reflected luminous flux reflected from the surface of the cornea through the road.
The corresponding photoelectric conversion signal and the reflected light reflected from the back of the cornea
The thickness of the cornea based on the photoelectric conversion signal corresponding to the emitted light flux
Is connected to a measurement circuit for measuring the
Detect rising and falling parts of photoelectric conversion signal
Having a differentiating circuit for reflecting light reflected from the surface of the cornea.
Rising part of the photoelectric conversion signal corresponding to the light flux and the cornea
Photoelectric conversion signal corresponding to the reflected light beam reflected from the back surface of
Distance from the rising part of the corneal surface and from the surface of the cornea.
Fall of the photoelectric conversion signal corresponding to the emitted reflected light beam
Corresponding to the light flux reflected from the part and the back of the cornea
Based on the distance between the falling portion of the photoelectric conversion signal and the
Corneal thickness measuring device for measuring corneal thickness
Place.