US20080151190A1

US20080151190A1 - Corneal measurment apparatus and a method of using the same

Info

Publication number: US20080151190A1
Application number: US11/614,518
Authority: US
Inventors: Joseph R. Bentley; Ming Lai
Original assignee: Individual
Current assignee: Bausch and Lomb Inc
Priority date: 2006-12-21
Filing date: 2006-12-21
Publication date: 2008-06-26
Also published as: US7648241B2; US20080212030A1; EP2101631A1; EP2101631B1; ES2547278T3; PL2101631T3; WO2008079766A1

Abstract

A corneal measurement apparatus for measuring a subject's cornea, comprising (A.) an illumination projection subsystem comprising a light source (B.) a mask subsystem disposed in a path of light from the light source, comprising (i) a first slit mask defining a plurality of apertures, (ii) a second slit mask defining a selection aperture, (iii) a translation apparatus adapted to translate the second mask, the translation apparatus and the second slit mask being configured and arranged such that by translating the selection slit, portions of the light can be selectively transmitted through each of the plurality of apertures toward the cornea, (C.) an imaging element configured and arranged to image the plurality of apertures onto the cornea, and (D.) an image capture subsystem arranged to capture images of the portions of light after the light impinges on the cornea.

Description

FIELD OF INVENTION

The present invention relates to corneal measurement apparatus, and a method of corneal measurement, and more particularly to an apparatus and method for projecting a plurality of slits of light for performing corneal measurements.

BACKGROUND OF THE INVENTION

Ophthalmologists and optometrists would like to have an accurate representation of subjects' eye. Such representations include, for example, one or more of a representation of a subject's corneal anterior surface, posterior surface, and corneal thickness and density, as well as anterior chamber profiles. This information may be used to prescribe contact lenses and eye glasses, and to reshape the cornea by surgical procedures or to perform other surgical procedures. Since it is not comfortable to measure these data with physical contact, remote sensing techniques are preferably used to perform the measurements. A device that measures only the front surface of a cornea is commonly referred to as corneal topographer, a device that measures the front and back surfaces, and the stroma of the eye is referred to as a corneal profiler, and a device that measures anterior chamber profiles is called an anterior chamber analyzer.
One common technique for obtaining corneal measurement information includes projecting narrow bands of light (commonly referred to as slits or slit beams) onto a patient's cornea at multiple locations across a cornea. For each of the slits, after the light in the slit has been scattered by the cornea, an image of the light is obtained.
To project a slit of light, an aperture of appropriate shape and size, and a lens are placed in the path of light from a light source such that the light passing through the aperture forms a slit of light on a subject's cornea. Typically, to project slits at each of multiple locations across the cornea, a single aperture is translated such that the light passing through the aperture at selected times forms the multiple slits. One example of such a corneal measurement apparatus is presented in U.S. Pat. No. 5,512,966 to Snook.
A problem with such apparatus is that it is difficult to accurately position an aperture to form each of the slits, and over time (after many patients) it is difficult to know the position of the slits accurately so that an accurate recreation of a cornea can be obtained.

SUMMARY

Aspects of the present invention are directed to an apparatus for measuring a subject's cornea, comprising (A.) an illumination projection subsystem comprising a light source, (B.) a mask subsystem disposed in a path of light from the light source, comprising (i) a first slit mask defining a plurality of apertures, (ii) a second slit mask defining a selection aperture, (iii) a translation apparatus adapted to translate the second slit mask, the translation apparatus and the second slit mask being configured and arranged such that by translating the selection aperture, portions of the light can be selectively transmitted through ones of the plurality of apertures toward the cornea, sequentially, (C.) an imaging element configured and arranged to image the plurality of apertures onto the cornea, and (D.) an image capture subsystem arranged to capture images of the portions of light after the light impinges on the cornea.
In some embodiments, the corneal measurement apparatus, further comprises (E.) a second illumination projection subsystem comprising a second light source, (F.) a second mask subsystem disposed in a path of second light from the second light source, comprising (i) a third slit mask defining a second plurality of apertures, (ii) a fourth slit mask defining a second selection aperture, (iii) a second translation apparatus adapted to translate the fourth slit mask, the second translation apparatus and the fourth slit mask being configured and arranged such that by translating the second selection aperture, portions of the second light can be selectively transmitted through each of the second plurality of apertures toward the cornea, and (G.) a second imaging element configured and arranged to image the second plurality of apertures onto the cornea, the image capture subsystem arranged to capture images of the portions of second light after the light impinges on the cornea.
In some embodiments, the second slit mask is disposed upstream of the first slit mask. In other embodiments, the illumination projection subsystem is configured and arranged to project light from the light source through each of the plurality of apertures defined in first slit mask without moving the illumination projection subsystem. The light source may comprise at least one LED arranged to project light in the path of light. 14. In some embodiments, the light source comprises at least one LED. And in some embodiments, the light source consists of only a single LED (e.g., a high power LED).
In some embodiments, the corneal measurement apparatus further comprises a condenser lens configured and arranged to gather light from the light source and project the light in the path of light. The imaging element and condenser lens may configured and arranged to operate as a condenser-projector system. The imaging element and the first slit mask may be disposed in a Scheimflug arrangement to obtain a plane of slit images at the cornea.
In some embodiments, the plurality of apertures is disposed in a single plane. The plurality of apertures may be formed on a single substrate. The plurality of apertures may be defined by openings in an opaque layer deposited on the substrate.
The corneal measurement apparatus may further comprise an image processing subsystem coupled to the image capture subsystem, the image processing subsystem being adapted to convert the images into a single representation of the cornea. The corneal measurement apparatus may further comprise a subject positioning apparatus adapted to maintain the subject's cornea in a location.
Another aspect of the invention is directed to a method of facilitating measurement of a subject's cornea, comprising (A.) providing a plurality of apertures, (B.) projecting light toward the plurality of apertures, (C.) translating a selection aperture while maintaining the plurality of apertures in fixed locations to selectively transmit a portion of the light toward the cornea, the portion of the light passing through the selection aperture and a selected one of the plurality of apertures and (D.) imaging the portions of light after the light impinges on the cornea.
In some embodiments, the light passes through the selection aperture prior to passing through any of the plurality of apertures. In some embodiments, the step of projecting light comprises projecting light from at least one LED. The method may further comprise processing the images to convert the images into a single representation of the cornea.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which the same reference number is used to designate the same or similar components in different figures, and in which:

FIG. 1 is a schematic plan view of an example of a corneal measurement apparatus according to aspects of the present invention;

FIG. 2 is an expanded plan view showing further details of one arm of the corneal measurement apparatus of FIG. 1;

FIG. 3 is an illustration of an example of an embodiment of a first slit mask defining a plurality of apertures viewed along line 3-3 of FIG. 2; and

FIG. 4 is an illustration of an example of an embodiment of a second slit mask defining a selection aperture viewed along line 4-4 of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic plan view of an embodiment of a corneal measurement apparatus 10 according to aspects of the present invention. The corneal measurement apparatus is adapted to measure a subject's cornea C. The corneal measurement apparatus comprises two illumination projection systems 13 a, 13 b (including light sources 12 a and 12 b, respectively), two mask subsystems 100 a, 100 b, and an image capture subsystem 50. Mask subsystems 100 a and 100 b are disposed in the paths of light from illumination projection systems 13 a and 13 b, respectively.
Illumination projection system 13 a and mask subsystem 100 a are in a first arm 75 a of the corneal measurement apparatus and illumination projection system 13 b and mask subsystem 100 b are in a second arm 75 b of the corneal measurement apparatus. In the illustrated embodiment, the first arm projects slits of light onto one half of the cornea, and the second arm projects slits of light onto the other half of the cornea. For example, the path of the projects slits of light may be at a forty-five degree angle to the visual axis of the subject's eye. Although the illustrated embodiment of a measurement apparatus has two arms, in other embodiments, a measurement apparatus may only have a single arm.
Referring to FIG. 2, further details of one arm of the corneal measurement apparatus 10 are shown. The arm comprises a first slit mask 130 defining a plurality of apertures 132 ₁and a second slit mask 120 defining a selection aperture 122. The arm also comprises a translation apparatus 110 adapted to translate the second mask. Second slit mask 120 is configured and arranged such that, by appropriately positioning the second slit mask using the translation apparatus, selection slit 122 selectively transmits portions of the light from source 12 a such that light traveling through a selected one of the plurality of apertures 132 ₁impinges on cornea C. Ray R demonstrates that the selection aperture 122 transmits light to cornea C from a selected one 132, of the plurality of apertures, when selection aperture 122 is appropriately aligned with the selected one 132 ₁of the plurality of apertures. Subsequently, by translating second slit mask 122, the selection aperture can be positioned such that light from another of the plurality of apertures 132 _ncan be transmitted to cornea C. Such positioning of the selection aperture can be repeated such that light from each of the plurality of apertures or light from any suitable ones of the plurality of apertures 132 can be transmitted to cornea C. It will be appreciated that, on portions of the first slit mask and the second slit mask that are outside of the apertures disposed thereon, the slit masks are opaque or substantially opaque to light from source 12 a.
It is to be appreciated that although, in the illustrated embodiment, the second slit mask 120 (i.e., the mask including the selection aperture)is disposed upstream (i.e., closer to source 12 a along the optical path) from first slit mask 130, in other embodiments, the first slit mask (i.e., the mask including the plurality of apertures) can be disposed upstream of the second slit mask.
Referring again to FIG. 1, light sources 12 a and 12 b generate the light in which a corresponding mask subsystem is disposed. In some embodiments, the illumination projection system projects light from the light sources in a cone of light L to permit light to be projected through each of the apertures defined in first slit mask 130 without moving the source or any other component in the illumination projection system. That is to say that, in some embodiments, only the second slit mask 120 is moved. The movement occurs to expose a given one of the plurality of apertures on the second mask to light from a light source. It will be appreciated that, in such embodiments, the plurality of apertures 132 that provide the slits of light can remain fixed in a given location during the acquisition of the plurality of slit images used to produce a representation of a subject's eye. An advantage over prior art measurement apparatus, in which an aperture is moved, is that slits of light are produced with positions that are more accurately known, thereby providing more accurate representations of subjects' eyes.
In some embodiments, it is advantageous if the source is monochromatic and suitably bright. For example, an LED or a plurality of LEDs may be used to generate the light. In some embodiments, a high power LED has been found useful. In some embodiments, a superluminescent LED is used. An aspect of the invention is directed to a single high power LED configured and arranged to be capable of illuminating the plurality of apertures 132 as the selection aperture is moved.
In some embodiments, it is advantageous that the projection subsystem include a conventional condenser-projector system. In FIG. 1, condenser lenses 14 a, 14 b gather light from sources 12 a and 12 b respectively, and projector lenses 18 a, 18 b are configured and arranged such that the condenser lenses images sources 12 a and 12 b onto the projector lenses 18 a, 18 b, respectively. The projector lenses are also configured and arranged to image the apertures 132 onto cornea C. It is typically preferable that the slits of light are not convergent or divergent between the first slit mask and the cornea. However, some convergence or divergence may be present. Although in the illustrated embodiment the projectors 18 a, 18 b are lenses, any suitable imaging element may be used (e.g., a mirror, holographic element).
Although in the illustrated embodiment the condenser lenses 14 a, 14 b are illustrated as lenses, any suitable imaging element may be used (e.g., a mirror, holographic element). In some embodiments, the condenser lens may be omitted. The projection system components and first slit mask 130 may be disposed in a Scheimflug arrangement to obtain a plane of slit images at cornea C. Also, one or more folding mirrors 16 a and 16 b may be included to direct light onto the cornea, and to achieve an appropriate package shape for a housing (not shown) of the apparatus.
Further details of first slit mask 130 are now given with reference to FIG. 3. Slit mask 130 includes a plurality of apertures 132 ₁-132 _n. Typically, the slits are of a same width W and length L and are evenly spaced apart; however, aspects of the invention are not so limited.
For example, twenty apertures may be provided on the slit mask in first arm 75 a (shown in FIG. 1) so that twenty slits of light are projected onto a subject's cornea and twenty images are obtained using light from the first arm 75 a of the measurement apparatus 10 (shown in FIG. 1). Accordingly, when combined with twenty images from second arm 75 b (shown in FIG. 1) a total of 40 slit images of a subject's eye are obtained. It will be appreciated that any suitable number of apertures may be provided on the first slit mask in each of mask subsystems 100 a, 100 b (shown in FIG. 1).
For example, first slit mask 130 may be formed on a substrate 135 of soda lime glass or BK7 glass. An opaque layer may be deposited on a surface of the substrate. For example, an opaque metal layer may be deposited on the substrate, and the apertures may be subsequently formed by etching a portion of the metal layer to expose the substrate. Each of the apertures is sized and shaped such that in a given measurement apparatus a slit of light is projected onto a cornea in a conventional manner. Typically, the apertures are rectangular in shape. However, any suitable shape may be employed. In some embodiments, it may be desirable to apply and antireflective coating to one or both of the surfaces of a substrate. Although the plurality of apertures 132 are shown as being formed on a single substrate (and in a single plane) any suitable construction may be used in which the apertures are formed at fixed locations relative to one another.
Further details of the second slit mask 120 are now given with reference to FIG. 4. Slit mask 120 includes a single selection aperture formed on a substrate 125. The selection aperture is sized to permit light to pass from one of the plurality of apertures to cornea C (shown in FIG. 1). Typically, the size of the selection aperture is larger in width and length than any of the plurality of apertures. The selection aperture is also typically small enough such that light is only permitted to pass through a single one of the plurality of apertures and onto cornea C.
In the illustrated embodiment of the second slit mask, an aperture portion 124 (typically half the length of the selection aperture) is also provided. The aperture portion is used for alignment of the measurement apparatus relative to a subject's cornea on whom a corneal measurement is to be made. The aperture portion is aligned with one of the plurality of apertures on the first slit mask, such that light is projected though only a portion of the one of the plurality of apertures and a portion of a slit of light is projected onto the middle of a subject's eye by the first arm 75 a (shown in FIG. 1) (e.g., an upper half of a slit is formed at the middle of the subject's eye by the first arm).
Another, second slit mask 120 also having an aperture portion is disposed in the other arm 75 b (shown in FIG. 1). Similar, to the aperture portion in the first arm, the aperture portion in the second arm is aligned with one of the plurality of apertures on the first slit mask of the second arm. Again, the aperture is arranged to project light onto the middle of the subject's cornea (e.g., a lower half of an aperture is formed at the middle of the subject's eye). In a conventional manner, the subject's cornea is aligned with the measurement apparatus, by positioning either the subject or the machine such that the two portions of the slits of light align to form a single, full-length slit of light (e.g., the upper half of the slit of light from the first arm aligns with the lower half of the slit of light from the second arm) to form a single, full slit of light. The second slit masks 120 (in the first and second arm) may be formed in a manner similar to that described above for the first slit mask 130.
Referring again to FIG. 1, the image capture subsystem 50 is arranged to be able to capture an image of light projected for each of the plurality of apertures after the light impinges on the cornea. It will be appreciated that, to capture of the images to obtain a representation of a cornea, each of the plurality of apertures is selected sequentially by appropriately aligning each aperture with the selection aperture as described above. Image capture subsystem 50 may be any suitable conventional imaging device, such as a CCD camera.
Translation apparatus 110 may comprise any suitable mechanism for translating the second mask 120 to project slits of light form the plurality of apertures 132 on the first slit mask 130 to cornea C. For example, the translation apparatus may comprise a linear translation motor capable of the moving the second slit mask in a direction perpendicular to the length L of the plurality of apertures 132.
Corneal measurement apparatus 10 also includes an image processing subsystem to convert the images into a single representation of the cornea. Techniques for reconstructing a representation of a subject's cornea once the slit images are obtained are well known and are not described further here. Projection systems as described herein may be used with cornea topographers, cornea profiler apparatus and anterior chamber analyzers.
Corneal measurement apparatus 10 includes a subject positioning apparatus 60 adapted to maintain a subject's cornea in a location. For example, the apparatus may be provided with a chin rest and/or a forehead rest which will fix the location of the subject's head.
Having thus described the inventive concepts and a number of exemplary embodiments, it will be apparent to those skilled in the art that the invention may be implemented in various ways, and that modifications and improvements will readily occur to such persons. Thus, the embodiments are not intended to be limiting and presented by way of example only. The invention is limited only as required by the following claims and equivalents thereto.

Claims

1. an apparatus for measuring a subject's cornea, comprising:

(A.) an illumination projection subsystem comprising a light source;

(B.) a mask subsystem disposed in a path of light from the light source, comprising

(i) a first slit mask defining a plurality of apertures,

(ii) a second slit mask defining a selection aperture,

(iii) a translation apparatus adapted to translate the second slit mask, the translation apparatus and the second slit mask being configured and arranged such that by translating the selection aperture, portions of the light can be selectively transmitted through ones of the plurality of apertures toward the cornea, sequentially;

(C.) an imaging element configured and arranged to image the plurality of apertures onto the cornea; and

(D.) an image capture subsystem arranged to capture images of the portions of light after the light impinges on the cornea.

2. The apparatus in claim 1, further comprising

(E.) a second illumination projection subsystem comprising a second light source;

(F.) a second mask subsystem disposed in a path of second light from the second light source, comprising

(i) a third slit mask defining a second plurality of apertures,

(ii) a fourth slit mask defining a second selection aperture,

(iii) a second translation apparatus adapted to translate the fourth slit mask, the second translation apparatus and the fourth slit mask being configured and arranged such that by translating the second selection aperture, portions of the second light can be selectively transmitted through each of the second plurality of apertures toward the cornea; and

(G.) a second imaging element configured and arranged to image the second plurality of apertures onto the cornea,

the image capture subsystem arranged to capture images of the portions of second light after the light impinges on the cornea.

3. The apparatus in claim 1, wherein the second slit mask is disposed upstream of the first slit mask.

4. The apparatus in claim 1, wherein the illumination projection subsystem is configured and arranged to project light from the light source through each of the plurality of apertures defined in first slit mask without moving the illumination projection subsystem.

5. The apparatus in claim 1, wherein the light source comprises at least one LED arranged to project light in the path of light.

6. The apparatus in claim 1, further comprising a condenser lens configured and arranged to gather light from the light source and project the light in the path of light.

7. The apparatus in claim 6, wherein the imaging element and condenser lens are configured and arranged to operate as a condenser-projector system.

8. The apparatus in claim 1, wherein the imaging element and the first slit mask are disposed in a Scheimflug arrangement to obtain a plane of slit images the cornea.

9. The apparatus in claim 1, wherein the plurality of apertures are disposed in a single plane.

10. The apparatus in claim 1, wherein the plurality of apertures are formed on a single substrate.

11. The apparatus in claim 10, wherein the plurality of apertures is defined by openings in an opaque layer deposited on the substrate.

12. The apparatus in claim 1, further comprising an image processing subsystem coupled to the image capture subsystem, the image processing subsystem being adapted to convert the images into a single representation of the cornea.

13. The apparatus in claim 1, further comprising a subject positioning apparatus adapted to maintain the subject's cornea in a location.

14. The apparatus in claim 5, wherein the light source comprises at least one high power LED.

15. The apparatus in claim 5, wherein the light source consists of a single LED.

16. A method of facilitating measurement of a subject's cornea, comprising:

(A.) providing a plurality of apertures;

(B.) projecting light toward the plurality of apertures;

(C.) translating a selection aperture while maintaining the plurality of apertures in fixed locations to selectively transmit a portion of the light toward the cornea, the portion of the light passing through the selection aperture and a selected one of the plurality of apertures; and

(D.) imaging the portions of light after the light impinges on the cornea.

17. The method of claim 16, wherein the light passes through the selection aperture prior to passing through any of the plurality of apertures.

18. The method of claim 16, wherein the step of projecting light comprises projecting light from at least one LED.

19. The method of claim 16, wherein the step of imaging produces images, and the method further comprises processing the images to convert the images into a single representation of the cornea.