Note: Descriptions are shown in the official language in which they were submitted.
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Interface Unit for Positioning an Irradiation Object rela-
tive to a Radiation Source
The invention relates to an interface unit for positioning
an object to be irradiated in relation to a radiation
source, the interface unit having at least one first posi-
tioning surface for positioning the interface unit in rela-
tion to the radiation source, and a second positioning
surface for bearing on the object to be irradiated, the in-
terface unit providing a path which passes through the sec-
ond positioning surface for the radiation from the radiation
source.
Such an interface unit may, for example, be used for laser
surgical cutting operations on the human eye. The interface
unit, which in the case of a human object to be irradiated
may also be referred to as a patient interface, is used in
this case to establish positionally fixed coupling between
the patient's eye and the laser system which provides the
laser radiation, usually between the eye and a focusing ob-
jective of laser system. Fixed coupling is necessary in or-
der to maintain a constant distance between the focusing
objective and the patient's eye, so that the cut can be made
with the desired high precision in the eye's tissue portion
to be processed, for example the cornea.
For cutting operations not only eye tissue but also other
biological tissue, as well as dead material, it is known per
se to use so-called laser-induced optical breakdown. By ap-
plying focused laser radiation, such breakdown is created in
the focal region when there is a sufficient spatial and tem-
poral energy density of the pulses, lying above the break-
down threshold. Optical breakdown causes substantially
athermic local destruction of the tissue being treated. This
effect is referred to as photodisruption. By sequencing such
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photodisruptions, virtually any desired three-dimensional
cutting pattern can be produced in the tissue being proc-
essed. Typically, laser systems having laser radiation pulse
durations in the femtosecond range are nowadays used for
cutting operations. For these ultrashort pulse durations,
the breakdown threshold is comparatively low, which is con-
ducive to low radiation exposure of the tissue being
treated. The size of the photodisruption is essentially lim-
ited to the extent of the radiation focus. The cutting pre-
cision therefore depends crucially on the spatial adjustment
accuracy of the focus.
It is possible to reference the eye's front surface in rela-
tion to the coordinate system of the laser system by using
an interface unit of the type considered here. However,
manufacturing tolerances of the interface unit, which can be
manifested as tolerances of the optical properties of the
interface unit, cause corresponding deviations of the focal
position in the tissue being treated. The cutting precision
therefore depends crucially on the manufacturing precision
of the interface unit. A high manufacturing accuracy of the
interface unit is therefore extremely desirable.
The interface unit may for example have a sleeve-like spacer
piece and an optical window arranged on one end, in which
case the laser radiation travels along the sleeve axis
through the inner region of the spacer piece, passes through
the window and then emerges from the interface unit. The
outer side of the window is used for the object to be
treated to bear on, for example the eye to be treated. The
laser radiation therefore enters the material to be treated
directly from the window. Correspondingly, the outer side of
the window forms a positioning surface for positioning the
object to be irradiated. On the other end of the sleeve from
the window, the interface unit is furthermore equipped with
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suitable positioning structures for axial positioning of the
interface unit in relation to the laser system. The spacer
piece may for example be configured in the shape of a cylin-
drical sleeve; solutions in which a conical sleeve shape is
selected for the spacer piece are known in the prior art,
the window being provided at the narrow end of the cone. In
these solutions, the spacer piece may be referred to as a
spacer cone; it is to be understood that a conical shape for
the spacer piece is in no way compulsory in the scope of the
invention.
One way of manufacturing an interface unit configured in the
above manner, with a spacer piece and a window for the ra-
diation to pass through, consists in making the spacer piece
from a metallic material, for example aluminium, and, for
the window, fitting a glass plate which satisfies the opti-
cal requirements into a frame in the spacer piece and adhe-
sively bonding it therein. Such a manufacturing method,
however, places stringent requirements on compliance with
permissible tolerances, because the individual manufacturing
tolerances of the spacer piece and the glass plate can add
together, and the adhesive bonding process can furthermore
be another source of inaccuracies.
It is an object of the invention to be able to produce an
interface unit of the type referred to in the introduction
with high accuracy. In order to achieve this object, the
invention proposes that the interface unit should comprise
an integrally produced interface body which forms both the
at least one first positioning surface and the second posi-
tioning surface. In this way it is possible to avoid assem-
bly inaccuracies, of which there would otherwise be a risk
if the at least one first positioning surface is provided on
a first sub-body and the second positioning surface is pro-
vided on a second, separately manufactured sub-body, and the
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two sub-bodies need to be adhesively bonded together or
firmly connected in another way. The tolerance chain to be
taken into account when producing the interface unit from
separate sub-bodies, made up of the manufacturing accuracy
of each one of the sub-bodies and the assembly accuracy when
connecting the sub-bodies, can be reduced by the solution
according to the invention to any manufacturing inaccuracies
of the monobloc interface body. Addition of a plurality of
individual tolerances can be avoided. This applies not only
to the geometrical dimensions of the interface unit, but
also to its optical properties (optical path lengths).
The at least one first positioning surface defines a refer-
ence surface of the interface unit on the radiation input
side, while the second positioning surface defines a refer-
ence surface on the radiation output side. The path provided
for the radiation by the interface unit extends in the di-
rection from the radiation input reference surface to the
radiation output reference surface. Along this path, the
radiation travels through at least two mediums with differ-
ent optical densities, and in a simple and expedient con-
figuration one of the mediums is air and the other medium
may be the material of a radiation-transparent window ele-
ment forming the second positioning surface.
In a preferred configuration, the interface body is made of
a material which is suitable for an injection moulding
method, preferably an injection compression moulding method,
this material preferably being a plastic material. The plas-
tic material may for example comprise a cyclo-olefin copoly-
mer, a cyclo-olefin polymer, polycarbonate or polymethyl
methacrylate. It is to be understood that these mentions of
materials are purely exemplary, and other injection-
mouldable, in particular biocompatible plastic materials are
possible.
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Preferably, at least a part of the interface body is trans-
parent in the visible wavelength range. Such transparency of
the interface body is expedient in particular for a part of
the interface body which forms a spacer piece enclosing the
radiation path. The transparency makes it possible to avoid
partial shadowing of the light from a light source used to
illuminate the operation field. It is then even possible,
when configuring the interface unit with a cylindrical or
conical spacer piece, to make its circumferential surface
continuous i.e. free from any openings.
According to one configuration, the entire interface body
may consist of the same material. According to an alterna-
tive configuration, the interface body may have various re-
gions which respectively consist of different material. Even
in this alternative configuration, however, the interface
body is produced as one piece. When there are different re-
gions of the interface body, which consist of different ma-
terials, integral production of the interface body is
possible, for example, by injection moulding the various
regions in the same production step in an injection mould.
Modern multi-component injection moulding apparatus are ca-
pable of injection moulding components made of different
materials. The scope of the invention furthermore does not
exclude at least one sub-piece of the interface body being
prefabricated and the other regions of the interface body
then being injection moulded onto the prefabricated sub-
piece, so as to create a material-fit connection. For exam-
ple, it is feasible to use a prefabricated suction ring com-
ponent, place it into an injection mould and then injection
mould the remaining regions of the interface body onto the
suction ring component. Preferably, at least one continuous
section of the interface body, comprising the two position-
ing surfaces, in any event consists of the same material.
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In a preferred configuration, the interface body has a
spacer cone enclosing the path for the radiation, and a con-
tact element provided on the narrow end of the spacer cone
for bearing on the object to be irradiated. The contact ele-
ment forms the said window for the radiation output. It may
have a contact surface, facing towards the eye, which is
configured to be plane, concave or convex or has rounded
edge regions. On its other side facing towards the radiation
source (i.e. on the side facing away from the eye), the con-
tact element may on the other hand be configured to be plane
or with a freeform surface. A biplanar contact plate may for
example be employed as the contact element, or a planocon-
cave or planoconvex contact element may be used on which the
contact surface facing towards the eye is respectively con-
cave or convex, and the opposite side facing away from the
eye is configured to be plane. By configuring the contact
element's side facing away from the eye as a freeform sur-
face, when there is a non-planar configuration of the con-
tact surface, it is possible to compensate for a focal
degradation due to edge distortion (spherical aberrations).
Particularly with an injection moulding method, any desired
configurations of such a freeform surface may be produced
per se, so that the freeform surface can be configured opti-
mally with a view to compensation for any aberrations which
may be induced by a non-planar configuration of the contact
surface.
Instead of a biplanar contact plate, it is possible to use a
contact element configured application-specifically in an-
other way, for example a planoconcave or planoconvex contact
element and/or one with rounded edge surfaces. Instead of
plane, the side of the contact plate facing towards the ob-
ject to be irradiated may for example also be convex or
rounded at the edge.
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The contact element may be provided with a reflection-
reducing coating on its side facing towards the eye and/or
its side facing away from the eye, in order to reduce any
reflection losses of the material of the interface body at
the wavelength of the radiation being used.
It is known to use interface units with the functionality
considered here, at least for ophthalmological operations,
in conjunction with a suction ring which is first placed on
the eye and then fixed there by suction force. The interface
unit is subsequently brought close to the suction ring and
made it to engage with it. In this way, not only is the eye
fixed by the suction ring, but the interface unit is also
positioned in relation to the suction ring, and in particu-
lar centred. In one configuration of the invention, it is
now feasible to configure the interface body with integrally
formed structures which can fulfil the functionality of such
a suction ring. Correspondingly, the interface unit may have
at least one evacuation space which is at least partially
open towards the object to be irradiated, for fixating the
interface body by suction on the object to be irradiated.
The use of a separate suction ring can then be obviated.
It has already been explained that the interface body may
have various regions which respectively consist of different
material. In an interface body which is equipped with the
formations that a fulfil the function of a conventional suc-
tion ring, this concept may be used to form a continuous
first section of the interface body, comprising the two po-
sitioning surfaces, from a different material than a second
section of the interface body which forms such suction ring
formations (for example an evacuation space). For example,
the second section may consist of Macrolon or another plas-
tic. The possibility that the second section consists of the
metallic material is not in fact excluded.
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According to a further aspect, the invention relates to a
method for producing an interface unit of the type described
above. The interface body is in this case produced by an
injection compression moulding method. In injection compres-
s sion moulding, the plastic melt is injected into the not yet
fully closed injection moulding tool. The tool is not closed
completely until during the solidification process. The clo-
sure pressure thereby built up ensures the definitive shap-
ing of the moulded part. To that extent, it has a combined
injection moulding-compression moulding method. It has been
found that with an injection compression moulding method,
plastic interface bodies can be produced in large batch num-
bers with the requisite optical quality at a comparatively
economical cost, and above all with extraordinarily high
manufacturing accuracy.
The invention will be further explained below with the aid
of the appended drawings, in which:
Figure 1 represents an interface unit according to an em-
bodiment in a partially cut-away perspective view,
Figure 2 represents the interface unit of Figure 1 together
with a suction ring unit placed on a human eye and
Figure 3 schematically represents an interface unit accord-
ing to another embodiment.
Reference will first be made to Figures 1 and 2. They show
an interface unit denoted overall by 10, which is used for
coupling to a laser system (not represented in detail) and
makes it possible to position and reference a human eye 12
to be treated in relation to the laser system. The interface
unit 10 comprises the spacer cone 14 having a cone axis 16.
The conical side surface of the spacer cone 14 has a plural-
ity of openings 18 in the exemplary case shown; it is to be
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understood that the conical side surface may alternatively
be configured as a side surface consisting of solid mate-
rial.
When a spacer cone is referred to here, it is to be under-
stood that neither the internal nor external circumferential
surface of the cone necessarily has to form a conical sur-
face exactly in the mathematical sense. Instead, when pro-
gressing in the axial direction, the conical side surface
may readily have a plurality of notches, steps or bends.
Overall, however, the spacer cone exhibits a conical general
configuration by becoming increasingly wide, starting from
one of its axial ends, in the direction of the other axial
end.
It is to be understood that, in a variant, a cylindrical or
differently shaped, internally hollow spacer body may be
used instead of the spacer cone 14.
On the narrow end of the spacer cone 14, the interface unit
10 has a contact plate 20, here configured in a plane-
parallel fashion, which forms a contact surface 22 for bear-
ing on the surface of the eye 12 to be treated. The contact
plate 20 is oriented orthogonally to the cone axis 16 and,
owing to the planarity of its contact surface 22, is usually
referred to in technical terminology as an applanation
plate; it makes it possible to flatten the cornea of the eye
12.
The side of the contact plate 20 opposite to the contact
surface 22 (i.e. the side facing away from the eye) is des-
ignated 23.
On the wide end of the spacer cone 14, the interface unit 10
is furthermore configured with a mounting flange 24, which
extends annularly around the spacer cone 14 and protrudes
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radially from the spacer cone 14. Over a part of its circum-
ferential extent, the mounting flange 24 is widened to form
a gripping plate 26, which allows a user to grip the inter-
face unit 10 and insert it radially into a slot (not repre-
sented in detail) of the laser system. The radial insertion
depth may be limited by a projection 28, which is formed on
the gripping plate 26 and interacts with a radial bearing
flange (not represented in detail) of the laser system. In
the slot, the interface unit 10 is fixed axially in relation
to the laser system; suitable clamping elements, by means of
which the mounting flange 24 can be clamped firmly in the
slot, may be provided on the laser system if so desired.
On the upper side of the mounting flange 24, a total of
three positioning projections 30 are provided, these being
distributed at approximately equal angular spacings along
the cone circumference and respectively forming an axially
oriented positioning surface 32 on their upper side. When
the interface unit 10 is being installed, the positioning
surfaces 32 of the projections 30 enter into axially posi-
tioning engagement with an axial bearing surface of the la-
ser system, so that fixed axial positioning of the interface
unit 10 in relation to the laser system is provided by the
mutual bearing of the positioning projections 30 on this
bearing surface.
The interface unit 10 provides an access path for the laser
radiation of the laser system 10, extending along the cone
axis 16, as indicated by a focal ray bundle 34 in Fig. 1.
The access path for the laser radiation extends through the
contact plate 20. The positioning surfaces 32 of the posi-
tioning projections 30 respectively form a first positioning
surface in the sense of the invention, whereas the contact
surface 22 of the contact plate 20 forms a second position-
ing surface in the sense of the invention.
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Because the interface unit 10 is often a disposable article
for reasons of hygiene, particularly in the case of use for
eye surgery treatments, users require a stock of interface
units in order to be able to use a new interface unit for
each operation. Replacement of the interface unit should not
of course lead to the laser system having to be readjusted,
i.e. the z position of the beam focus having to be re-
referenced. This places correspondingly stringent require-
ments on the manufacturing accuracy of the interface unit
10, and above all on the axial (geometrical) distance of the
positioning surfaces 32 from the contact surface 22 and on
the thickness of the contact plate 20. Both the geometrical
distance of the positioning surface 32 from the contact sur-
face 22 and the axial thickness of the contact plate 20 in-
fluence the effective optical path lengths of the interface
unit 10 when the bundle of rays 34 passes through the inter-
face unit 10.
For high manufacturing precision, and correspondingly for
high precision of the optical properties of the interface
unit 10, in the exemplary case shown it is configured as a
monobloc interface body, i.e. the spacer cone 14 is produced
in one piece together with the contact plate 20 and the
mounting flange 24. Owing to the transparency requirement
for the contact plate 20, the material of this monobloc in-
terface body is a material which is transparent to the laser
radiation. The material of the interface body preferably
also has a high, colour-neutral transparency in the visible
wavelength range, in order to provide a sufficiently bright
true-colour operation field for the doctor. A plastic injec-
tion moulding method is suitable for producing a compara-
tively complexly shaped structure such as the interface unit
10 in one piece, and the stringent accuracy requirements of
the interface unit 10 can be fulfilled in particular by an
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injection compression moulding method. Here, injection com-
pression moulding is intended to mean a method in which the
plastic melt is injected into an enlarged cavity and com-
pressed by mobile tool elements in the subsequent compres-
sion phase. Using the injection compression moulding
technique, components can be produced with an optical qual-
ity which satisfies even the stringent requirements of laser
systems for ophthalmological applications.
The plastic used to produce the interface unit 10 is expedi-
ently biocompatible. Suitable plastics, which can receive
certification as biocompatible, are for example PMMA (poly-
methyl methacrylate), cyclo-olefin polymers, cyclo-olefin
copolymers and polycarbonates. Examples of commercially
available materials which are suitable for integral produc-
tion of the interface unit 10 by an injection compression
moulding method are Topas from Topas Advanced Polymers and
Zeonex8 from Zeon Chemicals. It is to be understood that no
restriction to one of these exemplary materials is intended;
any plastic materials which are compatible with an injection
compression moulding method and exhibit sufficient transmis-
sion at least at the wavelength of the laser radiation being
used, and are furthermore sufficiently radiation-stable, may
be used in principle.
In order to avoid reflection losses, it is recommendable to
provide the integrally produced interface body with a re-
flection-reducing coating on at least one or both plate
sides of the contact plate 20.
During use, in accordance with the representation of
Fig. 2, the interface unit 10 is brought axially close to a
suction ring unit 36 previously placed onto the eye 12 and
fixed there (in a manner not represented in detail) by suc-
tion force, as indicated by two direction arrows 38. The
=
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spacer cone 14 is then introduced into a receiving funnel 40
of the suction ring unit 36 and is thereby centred in rela-
tion to the suction ring unit 36. A suction chamber may be
delimited between the interface unit 10 and the suction ring
unit 36, the evacuation of which leads to suction of the
interface unit 10 onto the suction ring unit 36 and there-
fore to mutual fixing of these two components. In the course
of introduction of the interface unit 10 into the receiving
funnel 40 of the suction ring unit 36, the contact plate 20
can come to bear with its contact surface 22 on the surface
of the eye; as an alternative, it is feasible that the con-
tact plate 20 does not yet bear on the eye 12 when the in-
terface unit 10 is in the fully introduced state, and in
order to establish bearing contact between the eye 12 and
the contact plate 20 it is first necessary to evacuate the
space between them.
In the exemplary case shown, the suction ring unit 36 is
configured with two connection glands 42, 44, which are re-
spectively used for attachment to a tube line (not repre-
sented in detail) for connection to a pump system. Each of
the connection glands 42, 44 is connected via an internal
path system respectively to a suction chamber of the suction
ring unit 36 so that these two suction chambers can be
evacuated separately from one another.
In the embodiment shown in Fig. 3, components which are the
same or have the same effect are provided with the same ref-
erences as before, but suffixed by a lower-case letter. In
order to avoid unnecessary repetition, reference is made to
that stated above in connection with the explanation of Fig-
ures 1 and 2, unless otherwise indicated below.
The interface unit 10a according to the embodiment of
Fig. 3 is formed by an integrally produced interface body
- =
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which forms not only the spacer cone 14a, the contact plate
20a and the mounting flange 24a, but also a suction ring 46a
having a suction chamber 48a which is open towards the sur-
face of the eye and is used to suck the suction ring 46a
onto the eye 12a. The suction chamber 48a is configured here
as an annular chamber, which is open towards the surface of
the eye along its entire annular circumference and is con-
nected to an evacuation connection, schematically indicated
at 50a, to which a tube line (not represented in detail) can
be attached in order to connect the interface unit 10a to a
pump system. The interface unit 10a therefore combines the
functions of a suction ring for fixing the eye 12a, the ap-
planation of the cornea of the eye 12a and the axial posi-
tioning of the eye 12a in relation to the laser system. That
which was stated above applies to the production of the in-
terface unit 10a; it is produced from a transparent and bio-
compatible plastic material by an injection moulding method,
in particular by an injection compression moulding method.
In the scope of this injection moulding method, it is con-
ceivable to use a different material for the suction ring
46a than for the other parts of the interface unit 10a, in
particular the spacer cone 14a, the contact plate 20a and
the mounting flange 24a. In this way, it is possible to pro-
duce an interface body which is monobloc but nevertheless
has regions which respectively consist of different mate-
rial. As an alternative, it is of course possible to manu-
facture the entire interface unit 10a from the same
material.
