Patent Description:
The present invention relates generally to a methodology of wide-angle optical imaging of a retina and, more specifically, to a catadioptric afocal pupil relay system and an anamorphic afocal optical pupil relay system.

Various optical imaging systems continue to employ scanning reflectors and are therefore in need of imaging of one of such scanning reflector onto another (as part of the imaging process through the optical system).

In principle, a conventional unit-magnification afocal relay (configured as a telescope) can image one of the scanning mirrors on to the other. However, in order to achieve favorable image quality at finite light beam apertures, the refracting lenses used in such a telescopic arrangement typically end up being rather long (which complicates their use) and intricate from the design point of view. In commercial x-y galvanometer scanning mirrors (an example of which is produced by Cambridge Technology, Inc. ), for instance, there exists an operationally-necessary physical separation between the mirrors scanning the light beam in x- and y-directions (referred to as x- and y-scanning mirrors, respectively) which prevents the mirrors from being optically conjugate with each other - they are not, in effect, optically superimposed on each other. If these mirrors, which are spatially-separated from one another, are optically relayed or imaged by means of an isotropic afocal telescope, the images of these mirrors still remain unconjugated with each other.

Such system configuration implies that the optical beams scanning in x- and y-directions at the output of the system (beams scanning horizontally and vertically), as viewed from the image plane, do not appear to originate from both of the scanning mirrors at the same time. Stated differently, at least one of such scanning output beams ends up being displaced relative to the ideal pupil position. This displacement presents a practical problem for an ultra-wide-angle system that has to effectuate optical imaging of an object through a small diameter pupil such as that of the undilated human eye (iris) - the scanning beams "wander" in the pupil across the field of view, which can cause vignetting at wide field angles, or loss of imaging of some parts of the field of view.

Furthermore, scan angles of a typical galvanometer mirror are usually limited to a full-angle of about <NUM> degrees (+/- <NUM> degrees). To increase the scan angle to that of the field of view (FOV) of the eye, a magnifying telescope may be required.

Related art such as <CIT> and <CIT> disclose the use of an ellipsoidal mirror (instead of an afocal relay) to image one scanning mirror onto the other. However, as is known to those skilled in the art, such an ellipsoidal mirror introduces significant aberrations at finite apertures. These aberrations either have to be compensated for by means of complicated dynamic optical elements during the scan, as described in <CIT>, or to be tolerated by keeping the aperture as small as possible (which, in turn, inevitably reduces diffraction-limited resolution). The additional practical disadvantage of this approach stems from the difficulty of manufacturing an ellipsoidal mirror to the required accuracy for precision scanning. Reference is also made to <CIT> which discloses the preamble of claim <NUM> and <CIT> in this regard.

Therefore, there remains a need to overcome the deficiencies of current state-of-the-art methodologies of producing an image on the retina when imaging involves the use of x- and y-beam-scanning systems.

According to the present invention, there is provided an optical system as recited in claim <NUM> below. The dependent claims define particular embodiments.

The invention will be more fully understood by referring to the following detailed description of specific embodiments in conjunction with the not-to scale drawings.

Generally, the sizes and relative scales of elements in the drawings may be set to be different from actual ones to appropriately facilitate simplicity, clarity, and understanding of the drawings. For the same reason, not all elements present in one drawing may necessarily be shown in another.

In the following explanation, in a case in which ophthalmic imaging device <NUM> is installed on a horizontal surface, the horizontal direction is referred to as the "X direction", a vertical direction relative to the horizontal direction is referred to as the "Y direction", and a direction facing the fundus from the anterior ocular segment of subject eye <NUM> via eyeball center O is referred to as the "Z direction". Accordingly, the "X direction" is perpendicular to both of the Y direction and the Z direction.

Ophthalmic imaging device <NUM> according to the present embodiment has two functions that exemplify the main functions that can be realized by ophthalmic imaging device <NUM>. The first function is a function whereby ophthalmic imaging device <NUM> is operated as a Scanning Laser Ophthalmoscope (SLO), and imaging is performed by the SLO (hereinafter, referred to as an "SLO imaging function"). The second function is a function whereby ophthalmic imaging device <NUM> is operated according to Optical Coherence Tomography (OCT), and imaging is performed by OCT (hereinafter, referred to as an "OCT imaging function").

The SLO imaging function is realized, from among the components of ophthalmic imaging device <NUM>, by control device <NUM>, SLO unit <NUM>, and scanning device <NUM>, which includes X-Y scanner unit <NUM> and objective lens unit <NUM>. SLO unit <NUM> includes, for example, a light source and a detection element, and is capable of capturing an image of the fundus of subject eye <NUM>. That is, by operating ophthalmic imaging device <NUM> according to the SLO imaging function, an image of the fundus of subject eye <NUM> (for example, imageable region 12A) is captured as the imaging target. Specifically, light from SLO unit <NUM> (hereinafter, referred to as "SLO light") is scanned by scanning device <NUM> with respect to imageable region 12A via the pupil of subject eye <NUM>, by X-Y scanner unit <NUM> in the Y direction (vertical direction) and in the X direction (horizontal direction), and an image is acquired at SLO unit <NUM> from the reflected light. Detailed explanation is omitted as the SLO imaging function is a well-known function.

The OCT imaging function is realized by control device <NUM>, OCT unit <NUM>, and scanning device <NUM>, which includes X-Y scanner unit <NUM> and objective lens unit <NUM>. OCT unit <NUM> includes, for example, a light source, a spectroscope, a sensor and a reference optical system, and is capable of capturing images of plural tomographic regions in a film thickness direction of the fundus. That is, by operating ophthalmic imaging device <NUM> according to the OCT imaging function, images are captured of tomographic regions, which are regions in a film thickness direction of the fundus (for example, imageable region 12A). Specifically, light from OCT unit <NUM> (hereinafter, referred to as "measurement light") is scanned by scanning device <NUM> with respect to imageable region 12A via the pupil of subject eye <NUM>, by X-Y scanner unit <NUM> in the Y direction (vertical direction) and in the X direction (horizontal direction), and interference light is produced using reflected light of the measurement light and fundus. That is, by operating ophthalmic imaging device <NUM> according to the OCT imaging function, images are captured of tomographic regions, which are regions in a film thickness direction of the fundus (for example, imageable region 12A). Specifically, light from OCT unit <NUM> (hereinafter, referred to as "measurement light") is scanned by scanning device <NUM> with respect to imageable region 12A via the pupil of subject eye <NUM>, by X-Y scanner unit <NUM> in the Y direction (vertical direction) and in the X direction (horizontal direction), and interference light is produced using reflected light of the measurement light and reference light. OCT unit <NUM> detects each spectral component of the interference light and, using the detection results, control device <NUM> acquires a physical quantity (for example, a tomographic image) showing the tomographic regions. Detailed explanation is omitted as the OCT imaging function is a well-known function.

In the following explanation, since the SLO light and the measurement light are both light that is scanned two-dimensionally in the X direction and the Y direction, the SLO light and the measurement light are referred to together as "scanning light" when there is no need to provide explanation that distinguishes between the SLO light and the measurement light.

The operational problem(s) caused by the use of an optical imaging system that employs two reflectors that are axially-separated from one another (each of which is configured to contribute to the process of imaging of the object, but in different planes that are transverse to each other) is solved by complementing the optical imaging system with a magnifying anamorphic afocal optical relay system configured to image both of these reflectors onto a single plane of the optical pupil with a substantially high angular magnification. In a case in which each of the two reflectors, which are axially-separated from one another, is configured to scan, within a certain limited scan angle, the beam of light incident thereon in a respectively corresponding plane, the use of such a magnifying anamorphic afocal optical pupil relay also overcomes the numerical limitation of the scan angles by increasing the scan angles of the resulting combined optical imaging system.

One solution stems from the realization that the catadioptric afocal relay may be judiciously configured to avoid the shortcomings of the existing solutions - both those utilizing the ellipsoidal re-imaging optical elements and those utilizing purely dioptric reimaging elements.

X-Y scanner unit <NUM> is explained in detail.

<FIG> shows a cross-section through a relay <NUM> that is configured as a Dyson-type relay to image the mirror <NUM> (which is disposed to scan the light beam, incident onto this mirror, in one plane; for example, the yz-plane) onto the mirror <NUM> (configured to scan the light beam, incident onto this mirror, in another plane that is transverse to the plane of scanning of the mirror <NUM>; for example the xz-plane). The relay <NUM> may be a part of another, selected, optical system. The propagation of light through the relay <NUM> includes the propagation of light reflected off of the mirror <NUM> through the first element of the relay (shown as <NUM>) towards the reflector <NUM> and then back to and through the third element of the relay (the role of which is played by the same element <NUM>) and towards the mirror <NUM>. The term transverse, unless specifically defined herein otherwise, is used to identify a situation in which one of the elements referred to as being transverse with respect to another is lying or extending across the other element or in a cross direction, and is not parallel to the other element.

Notably, and in stark contradistinction with conventional Dyson systems employed in the related art in a finite-conjugate imaging system, in the Dyson-type system of the present invention the roles of pupil and image are reversed and the relay <NUM> is configured as a unit magnification afocal relay. Positions across a reflector <NUM>, indicated with numerals "<NUM>", "<NUM>", "<NUM>", and so on, show the locations of the input light beam <NUM> that has been y-scanned by the reflector <NUM> (and which enters the optical imaging system and strikes vertically-scanning mirror <NUM> from the bottom as shown) at the surface of the reflector <NUM>. <FIG> shows a perspective view of the embodiment <NUM> of <FIG>, where the light beam <NUM> enters the system <NUM> from the bottom, and the beam <NUM>, which has been scanned in two transverse planes by the mirrors <NUM>, <NUM>, appears to emerge from the top scan mirror. The reflector <NUM> (in a specific implementation, a spherical reflector) can have a circular aperture (as viewed along its optical axis). Alternatively, the reflector <NUM> can be truncated to a narrow rectangular ("strip") aperture, which would be all that is used in practice in one embodiment during the scanning of the input beam <NUM>. The alternative embodiment of the relay system of the invention in which the area and clear aperture of the reflector is reduced to that of the reflecting "strip" is shown in the same <FIG>; here, the boundaries of the alternative implementation of the strip-shaped reflector are indicated with the lines 420A, 420B. As shown in <FIG>, the effective reflection region between lines 420A and 420B is elongated along the scanning direction by the vertically scanning mirror <NUM>. Because the embodiment of the system operates at unit magnification, the optical distortion is infinitesimal, if present at all.

Further, <FIG> shows X-Y scanner unit <NUM>, which relates to a light beam scanned by Y-scanning mirror <NUM>, and <FIG> shows X-Y scanner unit <NUM>, which relates to a lightbeam scanned by X-scanning mirror <NUM>. Reflector <NUM> includes a reflector that reflects a width region corresponding to the beam diameter of a light beam irradiated along a scanning path in X-Y scanner unit <NUM>. Further, the width of the effective reflection region at the reflector surface can be any integer multiple of the scanning beam diameter (for example, <NUM>), preferably a multiple of approximately <NUM> to <NUM> is effective, and <NUM> is preferable in terms of practical application. In order to maintain the surface accuracy of the reflective surface and support the reflector within the device, the shape of the reflector itself may be circular, a rectangle inscribed within the circle, or an ellipse, and the shape of the reflective region may be a narrow rectangle as described above.

Since the x-scan mirror <NUM> is optically conjugate (with 1x magnification via the relay <NUM>) with the y-scan mirror <NUM>, these scanning mirrors are re-imaged exactly and precisely to another, auxiliary, pupil position by means of any isotropic afocal relay or F-theta lens system. Two points are considered to be optically-conjugate with one another when the image of the object placed at one of the points is located at another of the points. This provides a practical solution to operational problems persistently experienced by the users of ultra-wide-angle scanning systems that have to form optical images through a small-diameter pupil, such as that of an undilated eye. Advantages of the proposed configuration include: (i) well-corrected aperture aberrations; (ii) lack of angular distortion; and (iii) simple and compact design due to the presence of only spherical surfaces, and the operational limitation of this design comes from limited angular magnification, which necessarily limits the linear and, therefore, solid or spatial, angle(s) over which the retinal surface can be scanned with the use of an optical system complemented with such a catadioptric afocal relay unit. Notably, the embodiment of the system contains only one, single, reflector (the reflector <NUM>).

Referring again to <FIG>, and in further reference to Table <NUM>, optical elements interacting with light propagating through the relay <NUM> on its way from the reflector <NUM> to the reflector <NUM> and forming an image on the reflector <NUM> are sequentially tabulated and numbered as elements <NUM> through <NUM>. The entrance surface of the relay (surface 40A of the lens <NUM>) - which, at the same time, represents the exit surface (surface 406B) of the relay - is an aspheric surface, the parameters of which are summarized in Table <NUM>. Table <NUM> discusses the decentering constants used in the design of the system <NUM>.

Table <NUM> summarizes the results of the analysis of the wave front of light propagating through the embodiment <NUM> in the spectral range from <NUM> to <NUM>, for several values of the field height (in the range from <NUM> degrees, considered to be a field height of <NUM>, to -<NUM> degrees, considered to be a field height of -<NUM>). It is readily observed that, with respect to the best individual focus, the Strehl ratio characterizing the imaging is higher than <NUM> anywhere across the field range both with respect to the best individual focus and with respect to the best composite focus. Accordingly, the operation of the embodiment of the invention in light at wavelengths within a spectral range from <NUM> to <NUM> is characterized by a first Strehl ratio at a central wavelength of the range (such as <NUM>, for example) and a second Strehl ratio at any wavelength of said range, with both the first and second Strehl ratios exceeding <NUM>.

<FIG> and <FIG> complement the description of the design of the relay <NUM> by illustrating the values of ray aberrations, for each of the three chosen wavelengths within the spectral range considered for this design, at the same values of field heights as those summarized in Table <NUM>. Characteristically, it will be appreciated by a skilled artisan that the absolute values of ray aberrations of the Y-fan of rays do not exceed about <NUM> milliradians for any field height, while the absolute values of ray aberrations of the X-fan of rays are substantially smaller and do not exceed approximately <NUM> milliradian. The optical path difference, illustrated for light at wavelengths of <NUM>, <NUM>, and <NUM> through the relay <NUM>, does not exceed about <NUM> waves for any field height (for the Y-fan of rays) and is smaller than <NUM> waves for the X-fan of rays.

The value of the optical path difference of about <NUM> waves, as is appreciated by a skilled artisan, is thought of as evidencing a substantially "diffraction-limited" system (which historically goes back to the Rayleigh criterion for defocus). Accordingly, in the present implementation, the imaging provided by the system is almost perfect in the X-fan or rays, but greater than <NUM> waves in the Y-fan. The residual chromatic aberrations can be corrected in / by an anisotropic relay lens to the eye, added as a follow-up to the embodiment of the invention. Alternatively, the residual chromatic aberrations may be considered operably acceptable in some cases. An embodiment of the invention can be used by itself, or be complemented with an isotropic relay.

Disclosed aspects, or portions of these aspects, may be combined in ways not listed above. Accordingly, the invention should not be viewed as being limited to the disclosed embodiment(s).

While advantages of the proposed configuration include: (i) well-corrected aperture aberrations; (ii) lack of angular distortion; and (iii) simple and compact design due to the presence of only one spherical mirror surface, the operational limitation of this design comes from limited angular magnification, which necessarily limits the linear and, therefore, solid or spatial, angle(s) over which the retinal surface can be scanned with the use of an optical system complemented with such a catadioptric afocal relay unit.

As mentioned above, catadioptric solutions to the construction of anamorphic afocal relays, while possessing some operational advantages, are limited in terms of angular magnification, and practical use may require yet another additional magnifying telescope.

The following embodiments not part of the present invention, therefore, address dioptric solutions. <FIG> shows a diagram representing a yz-cross section through a dioptric afocal relay (telescope) <NUM>. For convenience, rays are traced from the eye pupil <NUM> (entrance pupil, EP, of the eye) on the left of <FIG> to a plane <NUM> in which the scan mirror of the external optical imaging system is situated. The external optical imaging system contains two scanning mirrors as discussed above, and is not shown, for simplicity of illustration. In practice, the relay <NUM> is employed with such a system. The plane <NUM> is optically-conjugate with the eye pupil <NUM>. The yz-plane in this case corresponds to the horizontal section, in which the human eye has a full-angle field of view of about <NUM> degrees (+/- <NUM> dg. ) (see, for example, "<NPL>). The afocal system reduces this field angle by a factor of 4x to about <NUM> degrees (+/- <NUM> degrees) for the scanning mirror. In other words, as far as light propagating in the opposite direction (from the scanning mirror located in the plane <NUM> towards the EP <NUM>) is concerned, the scan angle is magnified by 4x to match the angular value of the FOV of the eye in the yz-plane.

The field lens element <NUM> to the right of the intermediate image plane <NUM> of the system <NUM> has one optical surface 514A that is anamorphic; that is, it has a different radius of curvature in the yz- and xz-planes, causing, therefore, the lens element <NUM> to be an anamorphic lens element. The field lens element <NUM> images the eye pupil in the yz-plane to a plane that is located at about <NUM> from the last element of the telescope, on the right of <FIG>, as schematically indicated by arrows 520A, 520B. This is where the horizontal scan mirror of the external optical imaging system (not shown) is located.

<FIG> shows the same system <NUM> in the cross-section produced by the xz-plane, which corresponds to the vertical section in which the field of view of the eye is smaller than that in the horizontal cross-section, or about <NUM> degrees (+/- <NUM> degrees). In this cross-section, the anamorphic lens <NUM> with a single anamorphic lens surface 514A images the eye pupil <NUM> to another plane located at about <NUM> distance from the last element of the telescope on the right of <FIG> (as indicated with the arrows 520A, 530B). This is where the vertical scan mirror of the external optical imaging system is located, which is separated, in this example, by about <NUM> from the horizontal scan mirror as viewed along the optical axis of the external optical imaging system. The magnification of such imaging provided by the field lens <NUM> is, again, approximately 4x. Generally, the measures or coefficients of magnification provided by the field lens in the two transverse planes (in this example, in vertical and horizontal cross-sectional planes of the relay <NUM>) are not required to be exactly the same, because in practice the values of scan angles of the external optical imaging system can be somewhat adjusted to match the exact magnification value.

As is well understood in the art, and unless expressly specified otherwise, the term "anamorphic" applied to the optical lens refers to, and defines, a lens that is configured to form a version of an image that is compressed (or, alternatively, expanded) along one of the dimensions with respect to another. Stated differently, and unless expressly defined otherwise herein, an optical system is referred to as anamorphic when it has, or provides for, different magnification in its meridional and sagittal sections or planes. The term "afocal" defines an optical element or system pertaining to or having no finite focal point.

In the present embodiment, as shown in <FIG> and <FIG>, relay system <NUM> is configured, in order from the side of eye pupil <NUM>, by first lens group G1 having positive refractive power and second lens group G2 having positive refractive power and being disposed at a significant interval from first lens group G1. Further, first lens group G1 has a positive meniscus lens having a concave surface facing the side of the eye, a positive lens having a surface with higher curvature facing the opposite side from the eye, a negative meniscus lens having a convex surface facing the opposite side from the eye, and the biconvex lens <NUM> discussed above that substantially functions as a field lens. Further, second lens group G2 is configured by a positive meniscus lens having a convex surface facing the side of the eye, which is disposed near conjugate points <NUM> and <NUM> of the eye pupil <NUM>. Eye fundus image <NUM> is formed, in first lens group G1, between the positive lens functioning as a field of view lens, and the negative meniscus lens.

<FIG> exemplifies a schematic diagram of X-Y scanner unit <NUM> and objective lens unit <NUM>. In <FIG>, objective lens unit <NUM> is configured by first lens group G1 and second lens group G2, which correspond to first lens group G1 and second lens group G2 in <FIG> and <FIG> described above. That is, objective lens unit <NUM> is an anamorphic afocal optical pupil relay system as shown in <FIG> and <FIG>, and forms two conjugate points of the pupil of subject eye <NUM> at the respective positions of Y-scanning mirror <NUM> and X-scanning mirror <NUM>, which are disposed at a remove therefrom. By this configuration, a laser beam from a light source not shown in the drawing is two-dimensionally scanned by X-scanning mirror <NUM> and Y-scanning mirror <NUM> at predetermined angles and guided to subject eye <NUM> through objective lens unit <NUM>. By this anamorphic afocal optical pupil relay system, the center point of scanning at predetermined angles by X-scanning mirror <NUM> and Y-scanning mirror <NUM>, which are disposed at positions removed from each other, is transferred to an identical point at the pupil surface of eye <NUM>, and the laser beam is two-dimensionally scanned at the fundus of eye <NUM>.

The dioptric afocal relay system shown in <FIG> and <FIG> functions as the objective lens unit <NUM> in <FIG> and forms an image of the retina of the eye in combination with the X-Y scanner unit <NUM> through the SLO unit <NUM> and/or OCT unit <NUM>. As shown in <FIG>, <FIG> and <FIG>, the first scanning reflector <NUM> scans, in operation, a beam of light incident thereon in a first plane (Y-Z plane), and the second scanning reflector <NUM> scans a beam of light incident thereon in a second plane (X-Z plane). The first and second planes are orthogonally transverse to one another; and the first scanning reflector <NUM> and the second scanning reflector <NUM> are axially separated from one another along the optical axis of the optical system. The afocal optical relay system <NUM> has an anamorphic surface 514A as an anamorphic element and forms a first pupil image of the eye onto the first scanning reflector <NUM> in the first plane and forms a second pupil image of the eye onto the second scanning reflector <NUM> in the second plane. The magnification of the first pupil image in the first plane and the magnification of the second pupil image in the second plane are both greater than unity. This means that the maximum angle of the light on the eye side (θ2) is larger than the maximum angle of the scanning mirror side (θ1); that is, the ratio (θ2)/ (θ1) is greater than <NUM>. Then, the scanning angles by both the first and second scanning reflectors <NUM> and <NUM> are enlarged at the position of the pupil of the eye. By the Lagrange Invariant, the diameter of the light beam entering the eye is smaller than the diameter of the beam at the scanning mirrors by the same ratio as the angular magnification. Such configuration of the optical system is greatly advantageous for the ultra-wide field view in OCT as well as SLO. <FIG>, similarly to <FIG> and <FIG>, shows a cross-sectional view of another embodiment of an anamorphic afocal optical pupil relay system that functions as objective lens unit <NUM>. In this relay system, too, the conjugate point of the eye pupil is formed at positions removed in the x and y directions; however, since the shapes of the lenses other than the anamorphic lens are identical, a cross-sectional view perpendicular to this drawing is omitted.

<FIG> schematically illustrates a related embodiment <NUM> not part of the invention, specifically configured to provide for reduced lateral color aberration over a <NUM> to <NUM> micron wavelength band (which may be of importance for operation of an OCT system). In this diagram, and for the purposes of characterizing the quality of optical imaging, the eye <NUM> is schematically represented with its Navarro model. (The Navarro eye model is described in <NPL>).

Here, in comparison with the embodiment <NUM>, cemented doublets <NUM>, <NUM> are immediately adjacent to one another along the optical axis and are introduced to provide a longer eye relief distance (increased to about <NUM> or larger, as compared to the typical <NUM> relief of devices of the related art). The increased eye relief, in turn, allows for advantageous increase of the diameters of the eyepiece-lenses (elements <NUM>, <NUM>, <NUM>, and <NUM>). One of the doublets <NUM>, <NUM> (specifically, the doublet <NUM>) is configured as a field lens that, in a specific case, can include an anamorphic aspheric surface (for example, surface S9) to image separated X, Y scanning mirrors onto the eye pupil (as discussed in reference to <FIG> and <FIG> above).

The specific lens configuration of the embodiment shown in <FIG> is explained. Similarly to the lens configuration shown in <FIG> and <FIG>, basically, the configuration has first lens group G1 having positive refractive power disposed at the side of eye <NUM> and second lens group G2 having positive refractive power disposed at the side of the conjugate point of eye <NUM>. First lens group G1 includes, in order from the side of eye <NUM>, positive meniscus lens <NUM> having a concave surface facing the side of the eye, positive meniscus lens <NUM> also having a concave surface facing the side of the eye, doublet lens <NUM>, described above, formed by joining biconvex lens <NUM> and biconcave lens <NUM>, and doublet lens <NUM>, described above, which substantially functions as a field lens, having positive refractive power, and is formed by joining negative lens <NUM>, having a surface with higher curvature facing the opposite side from the eye, and biconvex lens <NUM>. Further, second lens group G2, which is disposed at a significant distance therefrom and near the conjugate position of the eye pupil, is configured by positive meniscus lens <NUM> having a convex surface facing the side of the eye. The eye fundus image is formed between the two doublet lenses <NUM>, <NUM>.

It is appreciated, therefore, that the embodiments of the anamorphic afocal pupil relay, when used in conjunction with an external optical system having two scanning reflectors (referred to as x- and y-scan mirrors, each of which is configured to scan a beam of light, incident thereon, in a plane that is transverse to the plane in which another reflector scans the beam of light), provides a remarkable operational advantage over the known solutions of the related art. Specifically, in such a situation, both x-scan mirror and y-scan mirror are re-imaged simultaneously and precisely to the same location, in which another optical pupil can be placed. This advantage is important for ultra-wide-angle scanning systems that have to image through a small pupil, such as that of an undilated eye. In the proposed solution, aperture aberrations are well corrected. The use of the proposed solution does not require any manufacture of complicated ellipsoidal mirrors for use in the external optical imaging system that otherwise, according to the related art, are often used in an attempt to achieve the same results in re-imaging of the two scan mirrors to the same location. The proposed solution can find its use in, for example, scanning laser ophthalmoscopes and/or retinal OCT (Optical Coherence Tomography) systems.

Claim 1:
An optical system (<NUM>) configured for retinal imaging, the optical system having an optical axis and comprising:
first and second scanners (<NUM>, <NUM>), the first scanner being configured to scan a beam of light incident thereon in a first plane, the second scanner being configured to scan a beam of light incident thereon in a second plane, and the first and second planes being transverse to one another; characterized in that the system further comprises
a catadioptric afocal relay system (<NUM>) disposed along the optical axis between the first and second scanners, said catadioptric afocal relay system being configured to image one of the first or second scanners onto another of the first or second scanners, in light propagating along the optical axis, with a unit magnification.