JPH02295533A - Instrument for measuring axial length of eye - Google Patents

Abstract

PURPOSE:To obtain interference stripes having satisfactory contrust by providing an optical member for luminous quantity adjustment in the projecting optical path of a luminous flux lighting the eye of an organ so that the quantity of light or reflected luminous flux from an eyeground is almost the same as that from the cornea. CONSTITUTION:A parallel luminous flux P2 reflected by a reflecting surface 24' and a parallel luminous flux P1 passing through a beam splitter 24 are guided through a beam splitter 25 to the eye 29 of the organ. The parallel luminous flux P1 is converged through a cornea 32 and a crystal body 33 to an eyeground 34 in the eye 29 of the organ. Then, the parallel luminous flux goes to be an eyeground reflected luminous flux. On the other hand, the parallel luminous flux P2 is reflected on the cornea 32 and goes to be a divergent cornea reflected luminous flux. In the projecting luminous flux of the luminous flux lighting the eye 29 of the organ, namely, in the projecting optical path of the luminous flux lighting the eye 29 between the beam splitters 23 and 24, a concentration varying filter 30 is provided as the optical member for light quantity adjustment so that the quantity of light can be almost same as these eyeground reflected luminous flux and cornea reflected luminous flux.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in a free axis length measuring device that non-contactly measures the axial length from the cornea to the fundus of a living eye by observing interference fringes. ．． <<Prior art>> In recent years, axial length measurement devices have been proposed that measure the axial length of the eye in a non-contact manner by observing interference fringes. FIG. 3 shows an eyelid length measuring device that measures the eye axial length in a non-contact manner. F. Ferchar et al. (OPT
ICS LETTER VOL. 13 N0.3 PP
．． 186-1138 (March 1988) Op.
tical Society of America)
This is the technology described in . The axial length measuring device shown in FIG.
, a collimating lens 2, two plane parallel plates 3 and 4, a beam splitter 5, a condensing lens 6, and an imaging camera. A laser beam as an illumination beam emitted from a semiconductor laser 1 is made into a parallel beam by a collimating lens 2 and guided to two parallel plane plates 3 and 4.
The parallel light flux (referred to as the light flux ■) passing through the two parallel plane plates 3 and 4 is transmitted to the living body 111i18 via the beam splitter 5.
The light is projected as convergent light onto the fundus 9 of the eye, is reflected by the fundus 9, is emitted from the living eye 8 as a substantially parallel light beam (plane wave), and is reflected by the reflective surface 10 of the beam splitter 5 in the direction of the condenser lens 6. The light is focused by a condensing lens 6 and guided to an imaging camera 7. Also, a part of the parallel light flux that has passed through the parallel plane plate 3 is reflected by the parallel plane plate 4, and the reflected light flux (referred to as a light flux ■) returns to the parallel plane plate 3, and is reflected again by this parallel plane plate 3 to become a parallel light beam. It passes through the face plate 4, passes through the beam splitter 5, and reaches the corner Illi of the living limit 8.
The light is projected onto the ll. The reflected light beam reflected by the cornea 11 is guided to the beam splitter 5 as diverging light (spherical wave), is reflected by the reflecting surface 10 in the direction of the condenser lens 6, and is condensed by the condenser lens 6. and guided to camera 7. In addition, in FIG. 3, 12 is a light receiving sensor for monitoring the light amount of the semiconductor laser 1. In this conventional device, the distance between the parallel plane plate 3 and the parallel plane plate 4 is made variable, and the distance between the parallel plane plate 3 and the parallel plane plate 4 is made variable.
The refractive index of the substance existing between the two is n, and the refractive index of the intraocular material is N. The axial length (angle WA
Assuming that the distance Ill) from point In of l1 to the fundus 9 is X, the plane parallel plate 3 and the plane parallel plate 4 are arranged so as to satisfy the equation nl = NX.
By adjusting the distance 9 between the light beam and the light beam ■, the light beam ■ and the light beam ■ have equal optical path lengths, and the camera 7 observes interference fringes. Therefore, by obtaining the parallel plane root snow as a measurement value when this interference fringe is observed, the axial length X can be determined. (Problem to be Solved by the Invention) By the way, the contrast of interference fringes is best when the light intensity ratio of mutually interfered light beams is one to one, but there are individual differences in living eyes. Since the transmittance of the crystalline lens and vitreous body differs depending on the living eye, the reflected light flux from the fundus is not always constant, and if the amount of light reflected from the fundus and the amount of light reflected from the cornea are significantly different, The problem is that the contrast of the interference fringes decreases. The present invention has been made in view of the above circumstances, and its purpose is to provide an axial length measuring device that can obtain interference fringes with good contrast. (Means for Solving the Problems) In order to achieve the above object, the axial length measuring device according to the present invention is configured so that the amount of light reflected from the fundus of the eye and the amount of light reflected from the cornea are almost the same. In this case, an optical member for adjusting the light m is provided in the light path of the illumination light beam to the living eye. (Function) According to the axial length measuring device of the present invention, when the contrast of interference fringes is not good, the optical member for adjusting the amount of light is used to adjust the reflection from the fundus so that the contrast of interference fringes is fine. Adjust the light intensity of the light beam and the light intensity of the light beam reflected from the cornea. (Example) In FIG. 1, 20 is a semiconductor laser, 2l is a collimating lens, 22 is an optical path length changing member, and n, 24, and 25 are beam splitters. The laser beam as the illumination beam emitted from the semiconductor laser 20 is made into a parallel beam by the collimating lens 21. The parallel light beam is split by the reflecting surface 26 of the beam splitter 23 as a light beam splitting member into a parallel light beam P1 guided to the beam splitter 24 and a parallel light flux P2 guided to the optical path length changing member 22. Here, the beam splitter 23 is configured such that the amount of laser light reflected by the reflective surface 26 of the beam splitter 23 is smaller than the amount of transmitted laser light passing through the reflective surface 26 of the beam splitter 23. The reflectance of the reflective surface 26 is designed. A variable drift filter 30 as an optical member for adjusting the amount of light is provided in the projection optical path of the illumination light beam between the beam splitter 23 and the beam splitter 24.
is provided. As shown in FIG. 2, this variable density filter 30 has a structure in which the amount of transmitted light changes continuously in the direction of the arrow around its axis 31. The optical path length changing member 22 has a reflective surface 28 in front. This forward path length changing member 22 is moved in the direction of the arrow and has the function of changing the optical path length of the parallel light beam P2. When the optical path length changing member 22 is moved in the direction of the arrow to change the optical path length by ΔL/2 (here, equal to the mechanical movement distance of the optical path length changing member 25), the optical path length of the parallel light beam pt changes by the amount Δ
Only L changes. The beam splitter 24 has a reflective surface 24'
It functions as an optical path combining member. The parallel light beam P2 reflected by the reflecting surface 24' and the parallel light beam P+ passing through the beam splitter 24 are guided to the living eye 2g via the beam splitter 25. Parallel light flux P1
is converged on the fundus 34 of the living eye 29 via the corneal feathers and the crystalline lens 33, and is reflected by the fundus 34 to become a fundus reflected light beam. This light flux line reflected from the fundus passes through the crystalline cornea 32 again, becomes a parallel light flux, and is guided to the beam splitter 25.
On the other hand, the parallel light beam P2 is reflected by the cornea 32 to become a diverging corneal-reflected light beam, and is guided to the beam splitter 25. The lI bottom-reflected light beam and the corneal-reflected light beam are reflected by the reflecting surface 35 of the beam splitter 25 and deflected in the direction in which the condenser lens 36 is located. The corneal reflected light flux and the fundus reflected light flux are condensed by a condenser lens 36 and guided to a COD camera 37. The COD camera 37 is connected to a television monitor 38 and a high-pass filter 39. High bass filter 3
9 has a function of passing high frequency components among the interference signal components output from the CCD camera 37.
This is because it is desirable to use a high-frequency component in order to control the contrast of interference fringes, which will be described later.
This high bass filter 39 is the contrast judgment circuit 4.
Connected to 0. The contrast determination circuit 40 determines whether or not the contrast of the interference fringes is higher than a predetermined level, and functions as a collar drive means that automatically adjusts and drives the variable density filter 30 so that the contrast of the interference fringes becomes higher. ．． Measurement using this axial length measuring device is performed as follows. Let the known reference axial length be Xs. This standard axial length Xs
The average axial length of living body II29《22ml~24m
II1》 is used. Here, suppose that when the optical path length changing member 22 is moved in the direction of the arrow, interference fringes are projected on the television monitor 38 at a predetermined position of the optical path length changing member 22 in the direction of the arrow. At this time, the parallel light flux P with respect to the parallel light flux P+! The optical path difference is defined as the reference optical path difference L●. Now, the optical path length of the parallel light beam P+ from point K+ to point K2 is K+K
*, and the optical path length from when the parallel light beam P2 is reflected at point K1 to point K2 via the optical path length changing member 22 is K +
If K s + K s Ka + Ka Ka Ka, then the reference optical path difference ● is Ls=+:K+K*+KsKa+K4K*-KtKa. However, K + K s, K a Ke is the optical path length of the parallel light beam P2 in the air, and KsKa is the optical path length changing member 22
The optical path length is taken to include the refractive index of . Between the reference optical path difference L● and the reference axial length X●, there is a difference between the living eye 2
If the average refractive index of 9 is N, the optical path difference based on the reference axial length X● is N-X●, so L●=N-X-...
...■ The relational expression holds true. Next, a living body 8129 with an unknown axial length X is set. Assume that no interference fringes are displayed on the television monitor 38 at this time. Therefore, the optical path length changing member 22 is moved in the direction of the arrow. When the optical path length changing member 22 is moved by (ΔL/2) from the reference position, the TV monitor 38
Suppose that interference fringes are projected on . The optical path length based on the axial length X is N-X, which is the reference optical path difference L. Since interference fringes are obtained when it is equal to the sum of the amount of deviation and the amount of deviation ΔL, N-X = L● + ΔL ...■ Therefore, the unknown axial length X can be transformed by substituting the formula ■ into the formula ■. By doing so, it can be found as X=x●+(ΔL/N). When the contrast of the interference fringes is lower than a predetermined level,
The contrast determination circuit 40 rotates the variable density filter 30 and automatically adjusts the variable density filter 30 so that the light intensity of the fundus reflected light beam and the corneal reflected light beam become almost the same. (Effects) As explained above, the in-vivo anteroposterior diameter distance measuring device according to the present invention makes the amount of light reflected from the cornea and the amount of light reflected from the fundus almost the same, so interference fringes are prevented. The contrast can be improved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the optical system of the axial length measuring device according to the present invention, Fig. 2 is a plan view of the optical member for adjusting the light amount in Fig. 1, and Fig. 3 is a diagram showing the optical system of the conventional axial length measuring device. This is a diagram showing the system.

Claims (2)

[Claims] (1) An axial length measurement device that projects an illumination light beam onto a living eye and measures the axial length from the cornea to the fundus based on the interference between the light flux reflected from the cornea of the living eye and the light flux reflected from the fundus. In this method, an optical member for adjusting the light amount is provided in the light path of projecting the illumination light beam to the living eye so that the light amount of the reflected light beam from the fundus of the eye and the light amount of the reflected light beam from the cornea are almost the same. An axial length measuring device characterized by: (2) A driving means is provided for automatically adjusting and driving the light amount adjusting optical member so that the amount of light reflected from the fundus of the eye and the amount of light reflected from the cornea are the same. The axial length measuring device described in .