Orbital implant and method

An orbital implant is provided with a passageway extending from the anterior surface inwardly to receive a peg prior to implantation in the patient. The peg is made of non microporous material so that surrounding tissue will encapsulate the peg without adhering to it. This provides for later coupling of the ocular prosthesis to the implant without the necessity of a second operative procedure, and also allows the peg to be easily removed surgically if deemed necessary by the surgeon. The implant itself can be of any suitable material, but the implant is preferably made of biodegradable material having a matrix with random voids throughout to enhance tissue ingrowth into the implant. The matrix can be created by foaming or molding a suitable material, or the matrix can be formed from microporous thread of an inert material that is knitted, crocheted or otherwise formed into the desired size and shape.

BACKGROUND OF THE INVENTION 
The invention relates to eye replacement implants. If an eye has become 
damaged due to trauma or disease, the damaged eye may have to be 
eviscerated in which all of the inner contents of the eye are removed, or 
an enucleation may be performed in which the entire eyeball is removed 
after severing it from the eye muscles and the optic nerve. Following 
either of these procedures, it is common practice to fill the resulting 
void with an orbital implant and subsequently fit to the implant an ocular 
prosthesis that closely resembles the eye. When properly placed within the 
orbit, the orbital implant replaces the volume lost when the eye was 
removed and helps to maintain the normal structure of the eyelids and 
eyebrows. When the ocular prosthesis is properly matched to the other eye 
and coupled to the implant to move with it, substantially normal 
appearance of the patient is restored. 
A variety of orbital implants have been used and are known and available, 
usually taking the form of a sphere or globe of suitable inert material. 
When the implant has been inserted following enucleation or evisceration 
of the eye, tissues will heal over the implant after which the ocular 
prosthesis is placed on the tissues that have formed over the implant. 
However, over a period of time, migration and extrusion of the implant can 
occur. In the integrated implants first used in the 1950s, the primary 
cause of implant migration or extrusion was that when the ocular 
prosthesis was coupled to the orbital implant, it was necessary to expose 
a portion of the implant to the outside environment, thereby allowing 
bacteria to enter and infect the implant. Another cause of implant 
migration and extrusion is the lack of tissue supposedly covering the 
implant thereby allowing possible infection to enter through any opening 
where the implant is not covered by tissue. Also, sometimes the tissues 
which have previously covered the implant become pressured and necrose, 
thus allowing bacteria to enter and cause infection. This can occur years 
after the implant is made. 
A number of attempts have been made to overcome these and other problems of 
implant migration and extrusion. Perry, U.S. Pat. No. 4,976,731 teaches 
the use of an orbital implant made of low density hydroxyapatite, and 
following implantation of the implant and during the healing process, 
tissue penetrates the porous structure of the implant as the scleral sac 
or other covering is absorbed into the system. Perry teaches that after 
sufficient healing has occurred, the implant can be drilled to provide a 
passageway that allows the ocular prosthesis to be attached to the implant 
by insertion of a peg protruding from and forming a part of the 
prosthesis. Perry asserts that this will resolve the concern of migration 
or extrusion of the implant because tissue will also grow into and provide 
a lining for the drilled passageway. However, even using the Perry 
recommended material for the implant, a second surgical procedure is 
required with the normal risks of such procedures, including infection of 
the tissue around the peg implant. 
Vachet, U.S. Pat. No. 5,089,021, teaches the use of a spherical core over 
which there is bonded a layer of material made from a micro-porous, 
bio-compatible synthetic substance such as polytetrafluorethylene (EPTFE). 
Vachet claims that with this implant construction, the coating layer will 
be invaded by fibroblasts and blood vessels which will gradually transfer 
the coating layer into a tissue and vascular shell and thus minimize the 
risk of migration and extrusion of the implant. Vachet then asserts that 
following healing, the patient can be fitted with an ocular prosthesis by 
carefully molding the prosthesis over the tissues covering the implant. 
However, since the only traction between the prosthesis and the implant is 
from the tissues forming the posterior aspect of the socket, this 
technique may produce less than satisfactory motility. 
In all of the prior art teachings, references are made to the use of a 
variety of different materials for the orbital implant which materials are 
all preferably inert. Also, the prior art teaches the use of materials 
which are microporous so that the surrounding tissue will eventually 
penetrate the implant to hold it in place and thereby minimize the 
possibility of extrusion of the implant. Perry, U.S. Pat. No. 4,976,731, 
referred to above is an example of this teaching. The prior art also 
teaches the use of different synthetic materials that are used by oral and 
orthopedic surgeons to replace voids created in bone structures. Brekke 
U.S. Pat. No. 4,186,448 is an example of such a teaching in which bone 
voids created by fracture, surgery, etc. are treated by filling the voids 
with a material that is bio-degradable and which has randomly positioned 
voids throughout substantially all of the its volume. Brekke also teaches 
the use of a wetting agent incorporated in the material to promote the 
filling of the voids in the material with blood vessels so as to form 
tissue that will fill the voids. Eventually, this material becomes 
absorbed. 
However, prior art materials that are currently known and used for some eye 
implants are quite expensive, and those that are not microporous, 
occasionally require additional surgical procedures to minimize migration 
and extrusion. In addition, the known structures and techniques for 
integrating the ocular prosthesis with the orbital implant are not 
entirely satisfactory. Some such techniques require post-surgical drilling 
of the implant after healing has occurred adding to the cost and patient 
trauma and always with risk of infection. 
There is therefore a need for an improved orbital implant that will reduce 
the surgical procedures and time involved and thus lower the cost of the 
overall implant process as well as provide for improved integration of the 
implant with the ocular prosthesis. There is furthermore a need for the 
use of improved materials for the orbital implant which materials will 
reduce greatly the likelihood of migration or extrusion of the implant. 
SUMMARY OF THE INVENTION 
One aspect of the invention provides an orbital implant of any suitable 
material which is pre-drilled or pre-formed with a passageway extending 
inwardly from the anterior surface for receipt of an implant peg of a 
non-microporous material. The orbital implant with the peg in place is 
then surgically inserted following either enucleation or evisceration. 
Since the peg is of a non-microporous material, a fibrous capsule will 
form around it but not adhere to it, which allows the surgeon to later 
remove the peg implant easily from the orbital implant if deemed 
necessary. Moreover, the peg implant provides a means for direct 
integration with the ocular prosthesis for improved motility. 
Another aspect of the invention provides for the use of microporous threads 
formed into a sphere by knitting, crocheting or any other procedure so as 
to form an orbital implant of the desired size and shape containing a 
plurality of continuous voids to facilitate tissue invasion. A further 
aspect of the use of microporous threads is to form the orbital implant 
into a sphere using any suitable material and then cover either the 
anterior surface only or the entire surface of the sphere with a thin 
sheet of soft material formed of a microporous material. Materials 
suitable for this aspect of the invention are polyproplyene, polyesthers 
(Mercilene, Dacron) and ePTFE, which is expanded polytetrafluoroethylene. 
Another aspect of the invention is to form the orbital implant from an 
absorbable, bio-degradable material such as polylactic acid (PLLA), 
polyglycolic acid (PLA) or absorbable coral or any other absorbable 
material. 
Regardless of the use of the particular material for the orbital implant, 
the implant may be pre-drilled or pre-formed to receive a peg of 
non-microporous material. The anterior surface of the ball peg or flat peg 
could be lined, if desired, with a microporous inert biomaterial such as 
ePTFE, etc. The ingrowth of tissue that occurs will decrease the 
possibility of exposure of the peg and prevent having to remove the peg to 
replace it.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 illustrates a known implant and technique in which the orbital 
implant 10 is in place and attached to the eye muscles 12 to provide for 
motility. The implant 10 has a longitudinal passageway formed in it 
extending inwardly from its anterior surface. The present teaching is that 
the passageway 14 is drilled into the implant after the implantation 
procedure has been completed and after a period of healing of a few 
months. At this time, the ocular prosthesis 16 that is formed with an 
integral peg 18 is attached to the implant 10 by insertion of the peg 18 
into the passageway 14 of the implant 10. However, if bacteria enter the 
space between the tissue and the peg 18, or if the implant 10 is not 
ingrown, exposure of the implant 10 may occur. The infection results from 
exposure of the implant 10 to the outside environment after the drilling 
procedure necessary to attach the ocular prosthesis 16. 
In the first aspect of the invention, the orbital implant 10 is formed with 
a passageway 14a in it. The passageway 14a extends from the interior 
surface of the implant 10 inwardly along a radial line, and is either 
formed at the time the implant 10 is produced, such as by molding, or the 
passageway 14a can be drilled into the implant 10 prior to sterilization 
and implantation. Also prior to sterilization and implantation, the 
implant 10 is provided with a peg 20 of a non-microporous material such as 
an elastomeric material like silicone. The peg 20 is formed in the shape 
of a flat peg with no head or a ball peg having a head 22. The head 22 may 
be spherical as illustrated in FIG. 4 or it may be elongated in one 
direction as illustrated by the head 22a also shown in FIG. 4 which is a 
front view of the orbital implant 10. The main body 24 of the peg 20 may 
be provided with a ridge or screw as illustrated in FIG. 3 to allow tissue 
to fill the voids and prevent the peg 20 from moving freely in the 
passageway 14a. 
Since the peg 20 is formed of a non-microporous material, once the implant 
10 containing the peg 20 is implanted in tissue, a fibrous capsule will 
form around the peg 20, and the capsule will not adhere to the elastomeric 
material. This allows the surgeon to later remove the peg 20 from the 
implant 10 if deemed necessary. If the peg 20 is made of elastomeric 
material, it will stretch and can be easily extracted. 
The use of the ball peg 22 provides for direct integration of the implant 
10 with any suitable ocular prosthesis. If the elongated ball 22a is 
utilized, undesirable rotation of the ocular prosthesis will be decreased. 
Of course, if the flat peg 20 is used, there will be no direct integration 
with the prosthesis, and if improved motility is desired at a later date, 
a small portion of the conjunctiva and the tenon can be incised allowing 
extraction of the flat peg 20 and insertion of any other peg including the 
commonly known and used sleeved peg. 
By pre-forming the passageway 14a in the orbital implant 10, the secondary 
procedure for drilling the implant 10, after implantation and healing, is 
eliminated. If after implantation the ball peg 20 of the invention should 
become exposed due to pressure necrosis, for example, it will always be 
possible to extract the peg 20 and replace it with the commonly known and 
used sleeved peg. However, the anterior surface of the ball peg or flat 
peg can be lined, if desired, with a microporous inert biomaterial such as 
ePTFE, etc. The ingrowth of tissue that occurs will decrease the 
possibility of exposure of the peg and prevent having to remove the peg to 
replace it. 
The peg 20 can be made of any suitable type of material which generates 
encapsulation and to which tissues will not readily adhere. The material 
for the implant 10 can also be of any suitable known material, since any 
of the materials suitable for the orbital implant 10 can be easily formed 
with the passageway 14a. Suitable materials include nylon, 
polyvinylfluoridene, etc. However, another aspect of the invention is to 
produce the implant 10 from a microporous or braided thread of a suitable 
material such as polyproplyene, polyester (Mercilene, Dacron) or expanded 
polytetrafluorethylene (ePTFE). These materials are suitable because of 
their inertness in the body as well as being microporous and therefore 
providing some tissue invasion after the implantation procedure. The 
braided or monofilament threads are formed into the desired spherical 
shape, and when so formed, the implant 10 will contain a plurality of 
voids or matrix that will encourage tissue ingrowth and decrease the 
possibility of migration. 
In another aspect of the invention, the implant 10 can be produced of any 
suitable material, including the braided thread construction, and then 
covered either partially or fully with a sheet of microporous material 
such as polyproplyene, polyester (Mercilene, Dacron), expanded PTFE 
(Teflon), etc. If a partial covering is made, only the anterior surface of 
the implant 10 is covered, with the covering either sutured or attached to 
the implant in with a suitable adhesive. 
In another aspect of the invention, the implant 10 can be formed using an 
absorbable, bio-material. Examples of such material are foamed polylactic 
acid (PLLA) or polyglycolic acid (PGA). Foam structures of these materials 
produce a matrix containing a plurality of continuous voids. Initially, 
the implant 10 fills the void created due to enucleation or evisceration. 
During the healing period following the surgical procedure, cellular 
ingrowth and fibro vascularization will attach to all the surrounding 
tissues and create a fibrous capsule to which the muscles previously 
sutured to the implant 10 will remain attached. After a period of months 
and after the healing process has slowed or stopped, the matrix of the 
implant will have entirely absorbed and the space previously occupied by 
the implant 10 will be filled by more tissue ingrowth. If a matrix of 
foamed polylactic acid is used, the material comprises only five percent 
of the total volume, the remaining being the air space of the voids. As 
the material is absorbed over time, some shrinkage may occur in the 
implant but this should be negligible. Since the matrix structure of the 
implant 10 is random, the fibrous tissue will grow in almost every 
direction to minimize contracture. Moreover, these new tissues can then be 
surgically altered as needed to practically eliminate the possibility of 
late migration or malposition. Extrusion will not occur after the material 
is absorbed. For example, if more orbital volume is needed, another 
implant of the desired size and shape can be implanted within these soft 
fibrous tissues. Also, if the posterior aspects of the ocular socket are 
unacceptable and cause a problem in fitting the ocular prosthesis, some of 
the soft tissues can be surgically altered with relative ease. Thus, the 
use of an absorbable material has tremendous potential for improved 
patient care. 
Use of a polylactic acid structure for the implant 10 also provides for 
attachment of the muscles by suturing, and the implant need not be wrapped 
or encased with any material. This eliminates the commonly used surgical 
technique of wrapping implants in sclera or fascia. 
In another aspect of the invention, caps formed of foamed polylactic acid 
can be placed in front of a spherical shaped implant 10. These curved caps 
are of a preferred thickness of 1 to 2 mm and during the implant procedure 
are positioned over the spherical implant before closing tenon's and 
conjunctiva. In this aspect of the invention, the space occupied by the 
foamed cap offers a matrix that will be invaded first by fibroblasts and 
then by vascular ingrowth. Over a period of time, this matrix will create 
an extra layer of tissue over the implant 10 and under tenon's and 
conjunctiva. This new tissue created on the anterior surface of the 
implant 10 will serve as a cushion between the implant 10 and the ocular 
prosthesis. 
From the foregoing description, it will be evident that the various aspects 
of the invention provide new and improved techniques for eye replacement 
implants. With the use of the materials described herein for the basic 
implant or for coverings for implants, and in selected cases preforming 
the implant with a passageway for receipt of a peg prior to implantation, 
the surgeon has available a number of new and improved materials and 
techniques that can be used in any particular case depending upon the 
judgment of the surgeon. By providing the surgeon with new and improved 
options, the eye replacement procedures can be performed at lower cost and 
with less trauma to the patient. 
Having thus described the invention in connection with certain preferred 
embodiments and aspects thereof, it will be evident to those skilled in 
the art that various provisions and modifications can be made to the 
preferred embodiments described herein without departing from the spirit 
and scope of the invention. It is my intention, however, that all such 
revisions and modifications that are obvious to those skilled in the art 
will be included in the scope of the following claims.