Simulated diseased eye lens and methd of making the same

A simulated cataractous lens and method of making the same are disclosed. The simulated lens is comprised of a proteinaceous material, such as natural animal lens material which is selectively hardened and which has the hardness and transparency thereof altered by predetermined amounts so as to correspond to different stages of cataract afflicted lenses.

BACKGROUND OF THE INVENTION 
The present invention relates generally to simulated eye lenses and, more 
particularly, to simulated diseased lenses and processes of making the 
same. 
Microsurgical operations are highly successful, but they require the 
surgeon to exercise a great degree of control over the surgical handpiece 
and yet provide a minimum degree of bodily invasiveness. In 
ophthalmological microsurgery one known technique for removing cataracts 
is phacoemulsification. The phacoemulsification technique typically 
involves the use of a microsurgical handpiece that includes an 
ultrasonically operative tip that is typically inserted through an 
incision in the eye; which incision is in the order of about 3 mm. Extreme 
care must be taken during such surgery to avoid unnecessary damage to 
other parts of the eye. Phacoemulsification is a procedure that is very 
demanding of the surgeon in terms of both surgical skill and 
intraoperative vigilance. In this regard, a surgeon performing such an 
operation must receive instructions regarding the technique. 
It is important that surgeons have the ability to learn and practice the 
phacoemulsification technique. The surgeon must be able to repeatedly 
practice the motor coordination skills required to manipulate and emulsify 
a lens. Towards this end there have been several approaches. One includes 
using animal eyes (e.g., geese, rabbits, cows and pigs). A shortcoming of 
this approach is that animal eyes have not developed cataracts. 
Accordingly, these untreated animal eye lenses are generally inadequate. 
Thus, the simulation desired for practicing and demonstrating the 
simulation desired for the emulsification techniques is not as good as is 
otherwise desired. 
Other approaches designed for improving simulation are described in U.S. 
Pat. Nos. 4,762,495 and 4,762,496 to Maloney et al. Basically, these 
patents describe the formation of a simulated human ocular system 
employing an artificial lens phantom. The lens phantom is constructed so 
as to resemble human cataracts both in terms of hardness and lens 
translucency. The overall simulated ocular system includes the use of a 
number of man-made elements that are fitted together such as, for example, 
a unitary corneal cap and an encapsulated lens and iris. The encapsulated 
lens includes a wall made of a vinyl film, which is cataract phantom 
composed of a water-soluble composition designed to be similar to that 
found in the natural occurring cataract. To retain the same emulsification 
characteristics a permanent hydrogel material is provided using a 
cross-linked gelatin. The material is hydrated or provided with proper 
water sensitivity by the incorporation of a water soluble polymer. The 
hardness of the artificial cataract is controlled by the addition of 
fillers of micron-sized glass beads. It is appreciated that the foregoing 
approach is expensive and time consuming. Further, the degree of 
simulation is less than entirely satisfactory given the large number of 
artificial components. 
The present invention is directed to improving upon heretofore known 
techniques for producing simulated diseased lenses, especially cataractous 
lenses, having degrees of hardness and loss of transparency so that they 
resemble the various degrees or stages of cataract affliction. Heretofore, 
none of the known approaches utilize natural animal eyes or other suitably 
hardened proteinaceous material with the desired hardness and loss of 
transparency which correspond to various stages of diseased cataract 
lenses. 
SUMMARY OF THE INVENTION 
The present invention overcomes the disadvantages of the prior art by 
providing vastly improved simulated diseased lenses, especially those 
which ideally correspond to various stages of cataractous afflicted human 
eyes and which are both simple and economical to manufacture. 
In accordance with this invention, there is provided a method of hardening 
a proteinaceous material so as to simulate the hardness of a cataractous 
lens. The method comprises a step of selecting proteinaceous material 
which is shaped similar to a human eyes lens; the step of selectively 
opening preselected portions of the proteinaceous material; the step of 
applying, to at least the partially opened lens portions a treating 
solution which includes a preselected strength of protein hardening agent; 
and the step of subjecting the immersed lens to a predetermined 
temperature for a preselected time period for effecting a predetermined 
hardening of the lens. 
In one illustrated embodiment the proteinaceous material is selected from 
animal eye lenses having physiological similarities to a human eye lens. 
In another illustrated embodiment the hardening agent is an organic 
hardening compound. In still another embodiment the organic hardening 
agent is an aldehyde fixative; such as glutaraldehyde. 
In still another embodiment the hardening agent reduces the translucency of 
the animal eye lens. 
In another illustrated embodiment, the degree of lens hardness is 
proportional to the duration of immersion time in the treating solution. 
Among the other objects and features of the present invention are the 
provision of an improved simulated cataractous lens; the provision of an 
improved simulated cataractous lens having various degrees of hardness 
which correspond to the different hardness stages of cataracts; the 
provision of an improved lens of the last noted type in which the 
transparency thereof is selectively diminished so as to simulate the 
various stages of cataract affliction; the provision of an improved method 
of providing an animal eye lens with sufficient hardness to simulate a 
cataract lens; the provision of an improved method of providing an animal 
lens with diminished transparency so as to simulate a cataractous lens; 
and the provision of an improved method of forming proteinaceous material 
into a simulated cataractous eye lens. 
Still other objects and further scope of applicability of the present 
invention will become apparent from the detailed description to follow. 
DETAILED DESCRIPTION 
The present embodiment is directed to the end of providing simulated 
cataract lenses having varying degrees of hardness and reduced 
transparency. This is significant because cataract lenses vary in hardness 
depending on the different stages of the disease. Also, the transparency 
thereof is diminished so as to simulate the transparency of a cataract 
lens. 
In this invention, proteinaceous material is selected as the base material 
for use in making simulated cataract lenses. In a preferred embodiment, 
the proteinaceous material selected, is in the form of animal lenses which 
possess physiological characteristics similar to a human eye. Thus, the 
animal lenses, when suitably hardened, will particularly lend themselves 
to simulated cataract surgery. In this embodiment, the animal lenses can, 
for example, be from pigs, rabbits, cows, etc. These lenses can include 
the intact lens capsules. 
To harden preselected areas of the animal lens, which may include the lens 
capsules, the animal eye is suitably punctured, split or otherwise opened 
in the desired vicinity of the intended tissue to be hardened. The lens 
capsules are suitably punctured by appropriate tools, such as a knife or 
the like so as to allow the application of a treating solution to the 
intended tissue. In this manner, the solution can evenly mix and react 
with the selected portions of the eye tissue. Thus, as will be described 
hereafter, the treating solution effects increased hardness and diminishes 
tissue transparency. 
Each animal lens, which is to be treated, is placed in a suitable holder so 
as to be immersed in the treating solution. The treating solution includes 
a protein hardening or fixative agent having a strength needed to effect 
the desired degree of hardness. Immersion occurs at a preselected 
temperature and for predetermined time periods so as to achieve the 
desired degree of hardness and diminished transparency. Lenses can also be 
injected internally by means of a syringe with the treating solution to 
effect hardening from within. 
The present invention discloses the use of protein or body tissue hardening 
or fixative agents. These fixatives cross-link the protein tissue so as to 
preserve its structure with the least possible alteration thereof. Both 
organic and inorganic hardeners are contemplated for the formation of 
stable cross-links in the proteinaceous material. Organic hardeners, such 
as aldehyde hardeners can be used. In this preferred embodiment, the 
tissue fixative used is glutaraldehyde which is particularly useful in 
preserving sections of cells and tissues cf animals. In addition, 
glutaraldehyde is a good anti-bacterial agent which serves to prevent 
possible destruction of the tissue. Examples of other hardening agents 
which can be used are as follows: osmium tetroxide, formaldehyde and 
acrylic aldehyde. 
Of course, the hardening agent selected determines the concentration which 
should be used in the treating solution to achieve the desired hardening. 
Additionally, the hardening agent selected should, preferably, react with 
the lens tissue so as to effect a diminished transparency thereof to a 
degree which simulates the range of diminished transparency of cataract 
lenses. 
It has been determined that the longer the immersion time the harder the 
lens. If the immersion time is too long, the lens will become unacceptably 
hard. If the immersion time is too short, the lens will be insufficiently 
hard to simulate a cataract lens. The time period selected should be such 
as to promote the degree of fixing or cross-linking reaction necessary to 
generally uniformly harden the tissue intended to be hardened. The 
hardening or immersion time varies based on the proteinaceous material 
being used, the temperature range, and the strength of hardening agent in 
the treating solution. Increased hardness, in general, is proportional to 
increased immersion time. Generally, the temperatures selected should fall 
into a range from about 4.degree. C. to 50.degree. C. The temperature 
range is selected because it provides convenience and allows fairly 
uniform penetration and diffusion of the hardening agent into the lenses. 
Temperatures outside this range can lead to tissue destruction by freezing 
or heat denaturation, and result in uneven hardening. 
As noted, the preferred proteinaceous material for simulating the lens is 
an animal eye. These animal eyes can be selected from animals such as 
pigs, geese, cows, etc. For accessing the tissue to be treated, the lens 
is split or punctured through utilization of a knife, surgical blade, or 
other suitable instrument. In this embodiment, the animal lens capsule is 
split with a 3 mm knife and placed in the holder for purposes of immersion 
in a treating solution contained on a Petri dish or the like. For example, 
a porcine eye is selected and the lens with the intact capsules is 
removed. It should be noted that the lens capsules can be removed if 
desired. The reason for removing the capsule is for even more uniform 
treating of the lens. The punctured lens allows the hardening solution to 
intimately mix with the desired tissue. 
The treating solution includes a balanced saline solution (BSS), such as 
the type commercially available from Alcon Surgical, Inc. of Ft. Worth, 
Tex. The balanced saline solution has a pH value of about 7.7, but the pH 
ranges can vary from about 7.0 to 7.8 for use with the hardening agent of 
this embodiment. If the pH value is outside the noted range, there is the 
possibility of affecting the reactivity of the crosslinking agent or 
causing lens tissue damage. The treating solution besides including the 
balanced saline solution, includes a concentration of 2.5% glutaraldehyde 
which material is commercially available. Other concentrations of the 
glutaraldehyde are contemplated, for example, ranging from 1% to 5% of the 
solution. Concentrations of glutaraldehyde outside this range would lead 
to poor penetration or inadequate hardening. Alternatively, application of 
the treating solution can be achieved through the use of a syringe. 
The present concentration range quickly preserves or hardens the protein 
molecules forming the animal lens tissue. Glutaraldehyde is preferred 
because it diminishes the transparency of the porcine lens so as to 
simulate that found in human cataractous lenses. With glutaraldehyde the 
color of the lens becomes slightly yellow and the yellow color intensifies 
as the immersion duration increases. Other protein fixatives selected 
preferably should not only cause hardening, but also develop the degree of 
opacity desired to simulate that found in the human cataractous lens. 
Additionally, glutaraldehyde is a good anti-bacterial agent which serves 
to prevent possible destruction of the tissue. 
In accordance with this invention, hardness for a given material increases 
independently as a function of increasing immersion time, increasing 
processing temperatures and increasing concentrations of the hardening 
agent. Stated differently, other variables being constant, the higher the 
temperature, the quicker the eye hardens; the higher the concentration of 
hardening agent, the quicker the eye hardens, and the longer the immersion 
time, the harder the lens becomes. The foregoing parameters can be varied 
to accommodate a great variety of needs. For instance, immersion times can 
vary from about two (2) minutes to twenty-four (24) hours or more; the 
treating temperatures can be in a range of from about 4.degree. C. to 
50.degree. C., and the concentrations of the glutaraldehyde, for example, 
can vary from about 1% to 5%. Referring back to the immersion step, it can 
be conducted for time periods ranging from, for example, about two (2) 
minutes to twenty-four (24) hours or more with the preferred time 
durations being indicated in the Tables below. 
Whatever combinations of temperature, time and concentration are selected, 
however, they should be for achieving uniform hardness and decreasing 
transparency. The more uniform the hardening, the more uniform the loss of 
transparency, and the harder the lens, the greater the opacity of the 
lens. Loss of transparency is also a function of the hardening agent, lens 
material and concentration of the hardening agent.

The Tables below illustrate that for a given temperature and concentration, 
that by increasing the immersion time, the hardness and the color changes 
are increased proportional to the increased immersion time. 
It is pointed out that the softer the lens the earlier the stage of 
cataract affliction. Less hard cataract lenses are indicative of cataract 
diseased lenses at an earlier stage of the disease's development. 
Table I indicates one example. 
The materials used in the reduction to practice of a preferred embodiment 
are shown in Table I: 
2.5% Glutaraldehyde in BSS (pH 7.4) (GSS); 
BSS Solution (Balanced Saline Solution); 
Porcine (pigs) eyes; holder; Petri dishes; 
surgical blades; 1 cc syringes with 22 g needle, and a 3 mm knife. 
TABLE I 
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(IN VITRO LENS FIXATION) 
LENS # FIXATION TIME, MINS. 
RESULT 
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1 2 slightly yellow, quite 
soft, increasing 
2 5 yellow color 
3 7 " 
4 10 " 
5 15 " 
6 20 " 
7 25 " 
8 30 " increasing hardness 
9 45 " increasing hardness 
10 1 hr " increasing hardness 
11 2 hrs. " increasing hardness 
12 3 hrs. " (medium/hard) 
______________________________________ 
The examples of Table I are performed at 4.degree. C. 
Examples have shown that an even greater fixation time (e.g. 4 or 5 hours), 
if performed at room temperature, would lead to lenses which are too hard 
for simulation purposes. From Table I, it will be noted that at reduced 
temperatures, such as 4.degree. C., longer fixation times lead to good 
simulation results. Also, if for example, syringes were used to apply the 
hardening agent locally to the center of the lens, there was limited 
localized hardening in the center, but not the desired overall hardening 
effect. Thus, immersion is preferred. Following immersion for the noted 
times, the eyes are rinsed in a BSS solution. 
Table I indicates a series of lenses tested, wherein each tested lends 
becomes increasingly opaque as the immersion time increases; since the 
degree of yellow darkens and the lens becomes brown in color. Thus, the 
loss of transparency of the lens increases proportionally to increased 
immersion time. 
The following Table II gives results with different concentrations of 
glutaraldehyde solution and longer immersion times. The procedure used in 
like that used in Table I including the use of the same temperature. 
TABLE II 
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LENS # [GSS] % FIXATION TIME, HRS. 
RESULT 
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1 2.5 3 Good, 
slightly 
hard softer 
center 
2 2.5 4.5 Too hard 
3 2.5 6 " 
4 2.5 " 
5 2.5 " 
6 2.5 " 
7 5.0 " 
8 5.0 3 Good, 
slightly 
hard, soft 
center 
9 5.0 4.5 Too hard 
10 5.0 6 " 
11 5.0 60 " 
12 5.0 120 " 
______________________________________ 
It will be appreciated that this example is subject to the variables as 
discussed above with respect to time, temperature and concentration. 
Although the above examples indicated that immersion times of four (4) to 
five (5) hours can lead to unacceptable results, the invention 
contemplates immersion times up to, for example, twenty-four (24) hours. 
However, to achieve the longer immersion times, for example, the 
temperature or concentration of fixative can be suitably decreased. 
It will be appreciated that the foregoing procedures yield an economical 
and highly efficient approach for providing simulated cataractous lenses 
having varying degrees of hardness and loss of transparency with animal 
lenses so as to correspond to the various stages of a cataract lens 
disease. 
Although the above embodiments disclose the procedure of natural lens 
material in conjunction with glutaraldehyde, it will be appreciated that 
other protein materials such as collagen and gelatin may be used in lieu 
of the animal lenses. Of course, the collagen and gelatin can be shaped 
into lenses having a transparency similar to animal eye lenses. 
According to the present invention, it will be recognized that certain 
changes ma be made in the above described simulated lens and method of 
making the same without departing from the scope of the present invention 
herein involved. It is maintained that all matter contained in this 
description shall be interpreted as illustrative and not in a limiting 
sense.