Cataracts:
From One Medical Student to Another
page 6
Surgery
If you are going to rotate through ophthalmology, you will likely see a cataract surgery. While the ability to spot a cataract will get your observation check list marked, being able to speak knowledgably will be noticed. Below is a list of the steps involved.
1. Creation of a paracentesis using a blade while stabilizing the eye with a fixation ring
2. Instillation of topical lidocaine into the anterior chamber of the eye
3. Placement of an ophthalmic viscoelastic device (OVD) in the anterior chamber. This "gel" is thicker than the aqueous of the anterior chamber it is replacing. It serves two purposes. One is to maintain the shape of the anterior portion of the eye allowing the surgeon room to maneuver. The other is to protect the inside of the cornea from the ultrasound energy emitted by phacoemulsification. The gel coats the tender inner surface of corneal endothelial cells protecting them from ultrasound energy.
4. Creation of the main wound. This wound is usually started in the clear portion of the cornea, but it can also be started more posterior (from the limbus) or even more posterior (from the sclera). Each area has its advantages or disadvantages based on ease, possible deformation of the cornea, ability to convert to a different surgical technique if needed and rate of post surgical infection.
5. Capsulorhexis. A hole is created in the capsule so that the surgeon can access and remove the nucleus and cortex of the lens. If you recall the previous M&M® analogy, this could be described as "peeling off the front of the candy shell to remove the chocolate and nut inside". The purpose of this step is to create access for removal of the lens fibers while still maintaining the integrity of the rest of the capsule, so it can hold the prosthetic lens. Here you will see the ophthalmologist perform a continuous curvilinear capsulorhexis (CCC) by creating a tag of capsule and then carefully maneuvering it to peel away a circular opening to the lens fibers. This is a technically challenging aspect of cataract surgery that takes years to master. Another technique is called "The Can Opener" technique. As you can imagine, it is not nearly as elegant, but can still be necessary in some cases.
6. Hydrodissection. The cortex of the lens is attached to the capsule. The capsule needs to remain so it can be used to hold the IOL. To separate the two, a balanced salt solution is injected between these two layers to cleave them away from one another. After this procedure, the lens should be freely mobile within the lens capsule. You will see the surgeon rotate the lens like a record on a turntable toward the end of this technique to ensure that the lens is mobile.
7. Phacoemulsification. This tool uses ultrasound energy to break down or emulsify the nucleus of the lens. A vacuum is attached to the ultrasound probe in order to suck away freed pieces as they are disassembled. Techniques with names such as the "Stop n' Chop" and "Divide and Conquer" are used to safely fragment the nucleus into manageable pieces for emulsification and removal.
8. Cortical Aspiration. Aspiration is used to grab the cortex and peel it away from the inside of the capsule. This is the most likely time to cause a tear in the capsule, which can allow the vitreous entry into the anterior chamber (a bad thing). Referring back to our analogy, the chocolate is removed in this step leaving an empty shell (the capsule) to be filled later with the intraocular lens (IOL).
9. Filling the bag with OVD. Just as before in the anterior chamber, the OVD is used to maintain the structure of an evacuated space allowing for increased maneuverability and safety.
10. Placement of intraocular lens (IOL), which has 2 parts: 1) an optic and 2) two arms or haptics branching from the side to hold the entire structure in place within the capsular bag. To fit the optic and the haptics into the small incision, the IOL is folded and injected through a cylindrical tube into the eye. In the video example, a single piece acrylic IOL is used and the haptics are placed centrally on top of the optic. Then the optic is rolled around the haptics in a soft shell taco formation (I know, enough with the food analogies). This "taco lens" is then pushed through a cartridge into the capsular bag where the haptics unfold and the optic is adjusted so that the haptics are at a 90 degree angle to the wound. If the optic is right side up, the haptics will look like a backwards "S". If the optic is upside down, the haptics will take on the appearance of the letter "S", which alerts the surgeon to "STOP!" and reposition the lens.
11. Removal of OVD from the capsular bag and anterior chamber.
12. Hydration of the corneal incision to "close" the wound. Water causes the cells of the cornea to expand and press against one another, sealing the wound shut without sutures.
13. Application of antibiotic drops
