Intraocular lens with threadably locked retention loops

An optical section of an intraocular lens has a pair of spaced apart threaded recesses which are threadingly locked to threaded shank sections of an iris retention loop. The shank sections are integrally joined to such loop so each shank section acts as an anchor preventing a screwing movement of the other shank relative to the optical section. A method is described of expanding a shank section of a lens retention member in situ within a threaded or other undercut recess of an optical section of an intraocular lens.

BACKGROUND 
U.S. Pat. No. 3,996,626 schematically shows how a typical intraocular lens 
is surgically implanted within the eye. An optical section fits against 
one face of the iris (often the anterior) and two or more retention loops 
fit against an opposite face of the iris (often the posterior). Each iris 
retention loop has a pair of shank sections which are secured to the 
optical section to provide a space for receiving the iris. It is important 
to firmly lock the shank sections to the optical section to prevent any 
change in the length of the shank section. 
The above patent describes a process wherein the shank sections are 
positioned in passages of the optical section so that a portion of the 
shank sections protrude beyond a forward surface of the optical sections. 
Enlarged bulbular portions are formed on such protrusions. The bulbular 
portions are then driven into the passages of the optical section with a 
vibrating punch to cause the lens to distort outwardly within a central 
portion of the passage to "cold flow" and form a pocket for the bulbular 
portion. Such "cold flow" could stress the optical section and change its 
optical properties. 
Another approach to maintaining a precise length of the shank sections for 
receiving the iris is described in U.S. Pat. No. 3,991,426. Here a series 
of small individual screws are secured to the optical section and pointed 
heads of the screw pierce the iris. A separate snap-on ring fits over the 
protruding heads of the screws to act as a retainer and thereby replace 
the conventional iris loops that are integral with their shank sections. 
In addition to requiring complicated special tools for use during the 
steps of piercing the iris and assembling the snap ring, the individual 
screws could possibly twist within the snap ring to loosen and increase 
the space in which the iris fits. 
Retention loops of a special material, such as Supramid (a Nylon type 
material), have been heated and forced into a conical recess in the 
optical section in U.S. Pat. No. 3,994,027. The optical section of an 
intraocular lens is usually made of polymethylmethacrylate (PMMA). The 
machined conical recess of this patent would have some surface roughness 
formed during the machining step which would have a slight clinging effect 
on the Supramid shank section. In practice, such design has limited 
holding power and the shank section could be pulled out of this conical 
recess with a small force. Because of the dissimilarity of materials, 
there is litte, if any, fusion bond between the shank section and the 
optical section, particularly since the optical section is not heated to 
its softening point. Such high temperature heating would alter the optical 
properties of previously ground or molded and polished optical sections. 
SUMMARY OF THE INVENTION 
The present invention overcomes the problems of the above prior art by 
providing a pair of spaced threaded recesses in the optical section into 
each of which is inserted a generally cylindrical nonthreaded shank 
section of an iris loop. Energy, such as heat and/or pressure, applied to 
the shank section causes a thread to form in situ and lock to the optical 
section of the lens. Thus, no threading or twisting motion is needed on 
the shank sections to assemble them to the optical section. Also, because 
there are two shank sections integrally joined to the loop forming a 
unitary one-piece construction, each shank section acts as a locking 
anchor preventing the other shank section from unscrewing. A method is 
described in which a rod-like shank section is moved into a recess of the 
optical section which has an undercut recess (such as a thread) and such 
shank section is expanded in situ.

DETAILED DESCRIPTION 
The rear prospective view of FIG. 1 shows an intraocular lens with an 
optical section shown generally as 1. To this optical section is attached 
iris retention loops 2 and 3 that are secured to the optical section by 
shank sections 4, 5, 6, and 7. The intraocular lens of FIG. 1 is intended 
to be representative of many types of lenses, including different rod-like 
iris retention means. 
In FIG. 2, the intraocular lens is secured to an iris 8 of an eye. 
Typically, the optical section 1 is in an anterior section of the eye and 
rests against a forward or anterior face of the iris 8. The iris retention 
loops 2 and 3 fit against a rear or posterior face of iris 8. It can be 
seen that shank sections 4 and 7 are very critical in controlling the 
spacing into which the iris 8 fits. 
In FIG. 3, the optical section 1 has a drilled recess 9 that can be of a 
diameter of 0.004 to 0.020 inch (0.10 to 0.51 mm) . A hole diameter of 
0.008 inch (0.20 mm) extending completely through the optical section has 
worked very well. This hole is then tapped with microthreads. A tap of 
0.30 UNM (Unified National Minature) size can be used. Different thread 
pitches could be used in the range of 100 to 300 threads/inch (3.9 to 12 
threads/mm) with 200 threads/inch (7.9 threads/mm) working very well. It 
is understood that the diameter, thread pitch, and thread depth could be 
varied without departing from the spirit and scope of the invention. Also, 
other forms of specially formed undercuts could be used besides threads in 
the method of practicing this invention. Threads, however, are the most 
convenient to form. 
In FIG. 3, the shank section 7 is formed and placed in proper jigging to 
insure a precisely controlled length of a tip section 11 that protrudes 
from a forward face 12 of the optical section of the lens. When properly 
jigged to the position shown in FIG. 3, energy in the form of heat and/or 
pressure is applied to the shank section to laterally expand a portion of 
shank section 7 within the threaded bore 9 of the optical section. A tool 
for applying such energy is schematically shown at 13 and has a face 
generally following the contour of the optical section's front surface. It 
is understood that heat can be applied in many forms, such as conductive, 
ultrasonic, etc., with the important aspect being to soften the shank 
section so it expands. Some forms of heat application may not require the 
schematically shown tool 13. 
Because of the precisely controlled protruding length 11 of shank 7 and the 
expansion of a locking portion 14 of shank section 7, the protruding 
portion 11 disappears after the expansion step as shown in FIG. 4. This 
provides a very smooth forward surface 12 at the inner face between shank 
section 7 and ocular section 1. This smooth forward section is important 
for intraocular lenses that fit within the eye. 
The method of the present invention is much simpler than previous methods 
of attaching iris retention loops to optical sections of intraocular 
lenses. The forming in situ process avoids the problem of manually 
screwing a threaded member in too far or not far enough to change the 
spacing between the optical section and iris loops. This process also 
eliminates the requirement for adhesives or other extraneous materials. 
Also, in the preferred version of the invention, two shanks are integrally 
connected to a loop section, and each shank acts as an anchor preventing 
the twisting unscrewing motion of the other shank. 
The intraocular lens structure and method of this invention work very well 
when the optical section is of a polymethylmethacrylate (PMMA) and the 
iris loops and integral shank sections are of an inert thermoplastic 
material, such as polypropylene. In the past, it has been extremely 
difficult to adhesively bond or otherwise firmly secure the polypropylene 
shank to an optical section. This is because of the slipperiness and 
nonadhering characteristics of polypropylene. However, polypropylene is 
desired for intraocular lens retention loops because of its inertness, 
biocompatibility, and stiffness. It is preferred over the previous metal 
loops of platinum-iridium wire. 
In the foregoing specification, a specific example has been used to 
describe the invention. However, it is understood that certain 
modifications can be made to this example by those skilled in the art 
without departing from the spirit and scope of the invention.