Cataract tips from the teachers
Practice makes perfect: But how in the wet lab?

Sherleen Chen, M.D.

Assistant professor of ophthalmology Harvard Medical School Director of Cataract and Comprehensive Ophthalmology Massachusetts Eye and Ear Infirmary

Roberto Pineda, M.D.

Assistant professor of ophthalmology Harvard Medical School Director of Refractive Surgery Massachusetts Eye and Ear Infirmary
Wet lab rehearsal is an essential component in preparing for intraocular surgery. One difficulty in practicing for phacoemulsification is to find models and conditions that accurately simulate the tissue response, anatomic constraints, and atmosphere of operating on the human eye. We've asked three experienced cataract surgery instructors for their best ideas and tips on practicing the steps of phacoemulsification and preparing for surgery in the wet lab setting.

Sherleen Chen, M.D., and Roberto Pineda, M.D.

Joel Reisman, M.D.

Assistant professor of ophthalmology and director of Resident Wet Lab Tufts University School of Medicine, Boston

My goals for residents in the wet lab are: 1) Learn the basic steps in phacoemulsification;
2) Learn how to use an operating microscope;
3) Know the parameters and settings of the phaco machine; and 4) Become familiar with the names and uses of instruments.
We then give residents the unique skills to coordinate all the different aspects of phaco surgery—left foot microscope pedal, right foot phaco pedal, sideport hand, phaco hand, and phaco sounds—all into a smooth dance. This multitasking is the key to good eye surgery.
I teach using positive reinforcement, praising each small step in the learning process.
When demonstrating the use of the operating microscope, I recommend residents begin and stay with the lowest magnification because the greater depth of field makes it easier to operate. I also encourage them to refocus the microscope often during the procedure.
I usually ask the company representative to go over the phaco machine in depth in order for the residents to learn all the parameters and settings for both phaco and anterior vitrectomy.
In order to initially build a little confidence and minimize frustration in learning capsulorhexis, I begin using artificial eyes then move on to pig eyes.
I have tried making cataracts on the pig eyes using the microwave and formaldehyde/alcohol injections but do not find it to have much teaching value.
The pig eyes are held securely with a vacuum holder. The names and functions of the instruments are learned along with the best way to hold them. Because pig eyes have thick capsules and shallower chambers I modify the techniques. The corneal incisions are made more corneal and the capsular tears redirected to avoid them swinging out.
I encourage residents to work slowly and deliberately and to stop or slow down when they get into trouble. All too often there is a tendency to speed up when having problems.
When using the phaco handpiece, I want them to picture the lens as a sphere so that when learning to groove, they sculpt while knowing where the capsule lies. I try to have them coordinate the physical and visual sculpting with the position of the pedal and the sounds of the machine. Our microscope has a video camera so that we can teach as a group. The best way of learning and remembering is to teach, and therefore I have the residents instruct the medical student in each step of the surgery the same way that the other attending and I taught them.

A. Tim Johnson, M.D., Ph.D.
Professor of clinical ophthalmology and service director, Comprehensive Ophthalmology Clinic University of Iowa, Iowa City

Over the course of each year, I have the opportunity to interact with nearly 300 residents from all over the country. I enjoy the enthusiasm and energy the residents bring to improving their skills in the wet lab. I learn something each time I teach in the lab.
I have worked with various systems, but have by far the most teaching experience with the pig eye. Success with the pig eye is dependent on maintaining a clear cornea. A fresh source of eyes is critical. Corneal clarity can also be maintained by applying a 15% dextran (Swinger-Kornmehl) solution.1 Performing a capsulorhexis in a pig eye is challenging and is distinctly different from performing the procedure on an adult human eye. The pig capsule is significantly thicker and more elastic. The capsule can be modified by adding fixative to make it behave more like the human capsule. I use an equal mixture of formalin and viscoelastic, plus a little bit of trypan blue to make the capsule more visible. This solution can be applied to the capsule either under an air bubble or under viscoelastic (after creating an aqueous layer over the capsular surface with balanced salt solution). Using the cannula to paint the solution on the surface of the capsule helps ensure even distribution. Be careful not to use too much solution, as the fixative can contribute to clouding of the cornea. The nucleus can be hardened by microwaving the eye for 6-7 seconds or by injecting fixatives directly into it. The pupil is normally way too large to be useful for practicing advanced techniques, but a properly sized capsulorhexis can be used as a pupil for the purpose of practicing placement of a Malyugin ring (MST, Redmond, Wash.) and even suture fixation of a three-piece lens.
I have tried several artificial systems, and the one I find most useful is the Kitaro surgical training system (Frontier Vision, Japan). One nice feature of this system is its modular nature. The eye is assembled from various components, which are switched out after each procedure. Virtually every step of the procedure, including incision, capsulorhexis, and phacoemulsification, can be practiced with this system. There is a roll of capsular material for endless practice with the capsulorhexis. There are nuclei of varying hardnesses to practice lens disassembly techniques. The cost of the system is nominal for a training institution.

Cynthia Chiu, M.D.
Associate professor and director, Comprehensive Ophthalmology & Optometry University of California, San Francisco

Practicing cataract surgery in the wet lab poses several challenges. First and foremost is finding a substitute for the human eye with: 1) anatomic similarity, 2) realistic tissue "feel," 3) clear view through the cornea and anterior chamber, and 4) reasonable cost. There is no perfect system, but five options are worth discussing. Human cadaveric eyes are ideal in size and dimensions, as well as tissue feel. However, the cost ($200 each) prohibits sequential practice. Visibility through the cornea can be problematic. It is important to request phakic cadaveric eyes to avoid receiving pseudophakic or aphakic eyes by accident. Pig eyes are much less expensive ($3 each), though freshness is essential as the cornea clouds with tissue decay. Difficulties with pig eyes are twofold: 1) the much larger size and dimensions create difficulty in reaching across the anterior chamber with standard phaco instruments, and 2) the capsule is extremely elastic, and it is nearly impossible to prevent a capsulorhexis from running away unless the capsule is pretreated (see below). Lens size and capsular thickness in rabbits is similar to that of humans, although the rabbit lens occupies disproportionately more space within the anterior chamber, and proximity to the cornea makes manipulation of instruments difficult. Additionally, practice on (or explanting lenses from) live animals has significant cost, both financial and ethical. Computerized simulators such as the VRmagic Eyesi (VRmagic, Mannheim, Germany) allow unlimited practice and repetition without actual tissue, instruments, or lab space. Although feedback sensation may not be perfectly realistic, the cerebellar training through reiterated movements is beneficial. My preferred system is the synthetic eye model from Phillips Studio in the U.K. Each eye costs about $20, but the dimensions are perfect, the cornea is always clear, the lens capsule is realistic, and the nucleus can be made to a density that feels like true senile cataract, receptive to sculpting and chopping.
Once an eye model system is selected, there are a few tricks to assist in phaco practice. Cloudy corneas can be treated with glycerine and the epithelium can be scraped to improve visibility. Soft globes can be inflated with saline. I recommend staining pig capsules with trypan blue to improve visibility and decrease elasticity. The capsulorhexis can also be practiced on boiled tomatoes. Pig eyes can be microwaved or injected with alcohol to increase lens hardness and opacification. Practicing nuclear fragmentation (cracking and chopping) is best done with an actual phaco machine and surgeon settings. However, many critical steps in phaco surgery (wound construction, capsulorhexis, and hydrodissection) can be practiced without a machine. In my opinion, a large component of the learning needed in phaco surgery is cerebellar—and therefore repetition is key. Repetition in seemingly artificial environments (e.g., rhexis on a tomato or a simulator) still leads to increased comfort and agility during real surgery. Lastly, the value of having an experienced phaco teacher watch and proctor surgical practice cannot be underestimated. An hour or two of supervised practice can set the foundation of good technique that will translate to improved patient outcomes.

References

1. Ophthalmic Surg. (1985) 16:182-184.

Contact information

Chiu: chiuc@vision.ucsf.edu
Johnson: a-tim-johnson@uiowa.edu
Reisman: jreisman@tuftsmedicalcenter.org