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Cataract surgery training using pig eyes filled with chestnuts of various hardness

Mekada, Atsushi MD, PhDa,*; Nakajima, Junko MD, PhDa; Nakamura, Jiro MD, PhDa; Hirata, Hirohumi MDa; Kishi, Takashi MDa; Kani, Kazutaka MD, PhDa

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Journal of Cataract & Refractive Surgery: May 1999 - Volume 25 - Issue 5 - p 622-625
doi: 10.1016/S0886-3350(99)00003-6
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Abstract

Many inexperienced cataract surgeons are being required to safely perform phacoemulsification and aspiration. Postmortem pig or rabbit eyes have generally been used for training in cataract surgery; however, because of the softness of their lenses, it is impossible to practice phacoemulsification dividing techniques before performing human cataract surgery.

We found that cooked chestnuts are an excellent material to simulate the various degrees of hardness of the cataractous lens nucleus. Three different hardnesses of cooked chestnuts were used: roasted, roasted and boiled, and cooked in a sweet syrup. The consistency is similar to that of human cataract lens nuclei. We designed a cataract surgery training method using pig eyes filled with these chestnuts to teach dividing techniques of phacoemulsification and aspiration to inexperienced surgeons.

Surgical Technique

Figure 1, A shows the 3 hardnesses of the cooked chestnuts. All pseudonuclei are about 10.0 mm in diameter and 2.5 mm thick at the center. The hardest pseudonuclei are chestnuts that are roasted and then shelled and trimmed to lens size using a 10 mm leather punch and a knife (Figure 1, B). Medium-hard pseudonuclei are chestnuts that are roasted, shelled, trimmed, and then boiled for 10 minutes. The soft pseudonuclei are commercially prepared chestnuts that are cooked in a syrup of sugar and water (Figure 1, C).

Figure 1.
Figure 1.:
(Mekada) A: The chestnuts were prepared to simulate the varying degrees of hardness of the human lens nucleus. B: The chestnuts were then trimmed to lens size. C: The soft pseudonuclei were commercially prepared chestnuts that had been cooked in a sweet syrup of sugar and water and trimmed to lens size.

Two side ports are made in the pig cornea, and viscoelastic material is injected through the ports. Then, a continuous curvilinear capsulorhexis with viscoelastic material and a self-sealing straight incision of about 14 mm are made. The complete lens cortex is expressed using high-pressure hydrodissection. Viscoelastic material is again injected into the capsular bag and the chestnut inserted. The incision is closed with a shoelace suture.

Results

Experienced surgeons initially performed the preparatory procedures. Therefore, various techniques including phaco chop, divide and conquer, and nondividing phacoemulsification could be practiced on the pseudonuclei by inexperienced surgeons. After practicing several times, the inexperienced surgeons could perform the preparatory procedures and then the entire phacoemulsification technique.

Nondividing and dividing phacoemulsification techniques could easily be performed by inexperienced surgeons on the soft chestnuts, with a consistency of nuclear sclerosis grade 1 to 2 (Figure 2, A, B). The medium-hard chestnuts, with a consistency similar to a nuclear sclerosis of grade 2 to 4, could be used to practice phacoemulsification, aspiration, and dividing techniques, especially phaco chop (Figure 2, C). Phacoemulsification was difficult on the hard pseudonuclei for both experienced and inexperienced surgeons. These nuclei had a hardness similar to a nuclear sclerosis grade of 4 to 5 (Figures 2, D, E). (Figure 3, D, E).

Figure 2.
Figure 2.:
(Mekada) A, B: Nondividing and dividing phacoemulsification could easily be performed by inexperienced surgeons on the soft chestnuts, whose consistency is similar to nuclear sclerosis of grade 1 to 2. C: The medium-hard chestnuts, with a consistency similar to nuclear sclerosis of grade 2 to 4, could be used to practice phacoemulsification and dividing techniques, especially phaco chop. D, E: Phacoemulsification was difficult for both experienced and inexperienced surgeons on the hard pseudonuclei, with a consistency similar to nuclear sclerosis of grade 4 to 5.

Using these methods, inexperienced surgeons at our institution gradually attained the skills of phacoemulsification and dividing techniques before performing surgery in humans, including gaining experience in handling capsular rupture and tissue damage. Although at first it was difficult for the inexperienced surgeons to make a self-sealing incision wide enough to insert the chestnut, this procedure was gradually mastered.

Discussion

The consistency of the soft, medium-hard, and hard chestnuts was similar, respectively, to nuclear sclerosis of grades 1 to 2, 2 to 4, and 4 to 5. Human cataract lens nuclei of varying degrees of hardness could be simulated using chestnuts of various hardnesses.

Soft chestnuts were useful for practicing nondividing and dividing phacoemulsification techniques. The medium-hard ones were suitable for practicing dividing phacoemulsification techniques such as phaco chop and divide and conquer. The hard chestnuts were difficult for inexperienced surgeons to handle successfully because they demand a higher skill level. The different hardnesses of pseudonuclei required the inexperienced surgeons to use various techniques, as is the case in cataract surgery; that is, they could practice techniques suitable for different human cataract lens nucleus hardness without the complications of actual surgery.

With the hard pseudonuclei, phacoemulsification and aspiration was difficult for even the experienced surgeons. Therefore, they can be used by all surgeons to attain a higher level of skill. These methods also make it possible to practice planned extracapsular cataract extraction.

One study reported a system that uses a rabbit eye filled with a human cataract lens nucleus removed in its capsule.1 Another described a cataract training system using synthetic cataract materials with 3 hardnesses similar to ours2; however, the consistency of those materials was different from that of a human lens. In 1 study, a rapid and easy method of inducing cataracts in pig eye lenses using microwaves was described.3 Although the goal of the study was to provide practice in such techniques as central sculpting, divide and conquer, and chopping, the induced cataract was white, like a mature cataract, making capsulorhexis more difficult.

Pig eyes filled with chestnuts are suitable for all surgeons to practice dividing and nondividing phacoemulsification techniques.

References

1. Tolentino FI, Liu H-S. A laboratory animal model for phacoemulsification practice. Am J Ophthalmol 1975; 80:545-546
2. Maloney WF, Hall D, Parkinson DB. Synthetic cataract teaching system for phacoemulsification. J Cataract Refract Surg 1988; 14:218-221
3. van Vreeswijk H, Pameyer JH. Inducing cataract in postmortem pig eyes for cataract surgery training purposes. J Cataract Refract Surg 1998; 24:17-18
© 1999 by Lippincott Williams & Wilkins, Inc.