Surgical Technique
Topical anesthesia with an intracameral supplement is appropriate if the patient is able to cooperate and the PIOL can be inserted through a small incision. If the patient cannot cooperate for the use of topical anesthesia or if a large incision is required, peribulbar or general anesthesia is preferable. Retrobulbar anesthesia should be used with caution in patients whose eyes have a high axial length because of the increased risk of globe perforation.
A peripheral iridotomy is recommended for all currently FDA-approved PIOLs to reduce the risk of pupillary block and angle closure; however, this recommendation may soon change, and iridotomy is not required for angle-supported PIOLs. One or more laser iridotomies can be performed before the PIOL surgery, or an iridectomy can be performed as part of the implant procedure. Viscoelastic material should be meticulously removed at the conclusion of surgery to prevent postoperative elevation of IOP.
Iris-fixated phakic intraocular lens
Most surgeons induce pupillary miosis before they initiate iris-fixated PIOL implantation, both to protect the crystalline lens and to make the iris easier to manipulate. The lens is generally inserted through a superior limbal incision but can be implanted with the wound placed at the steep meridian to minimize postoperative astigmatism. The long axis of the PIOL is ultimately oriented perpendicular to the axis of the incision. A side port incision is made approximately 2–3 clock-hours on either side of the center of the incision; thus, a 12 o’clock incision requires side port incisions near the 10 and 2 o’clock meridians. The “claw” haptics are fixated to the iris in a process called enclavation. After the PIOL has been carefully centered over the pupil, it is stabilized with forceps while a specially designed enclavation needle is introduced through one of the side port incisions, and a small amount of iris is brought up into the claw haptic. This procedure is repeated on the other side. If adjustment of the PIOL position becomes necessary after fixation, the iris must be released before the PIOL is moved. Careful wound closure helps minimize surgically induced astigmatism. PMMA PIOLs require a 6-mm wound and thus generally require sutures for proper closure, whereas iris-fixated PIOLs made of flexible materials can be inserted through a small, self-sealing wound of approximately 3 mm. Video 8-1 demonstrates implantation of an iris-fixated IOL.
VIDEO 8-1 Implantation of an iris-fixated phakic IOL.
Courtesy of David R. Hardten, MD. Access all Section 13 videos at
www.aao.org/bcscvideo_section13.
Sizing the iris-fixated phakic intraocular lens
Because this PIOL is fixated to the midperipheral iris, not the angle or sulcus, it has the advantage of having a “one-size-fits-all” length. It is 8.5 mm in length, with a 5.0- or 6.0-mm PMMA optic (Fig 8-1).
Posterior chamber phakic intraocular lens
Posterior chamber PIOLs require pupillary dilation prior to implantation. These PIOLs are made of a flexible collamer material and are implanted through a small wound approximately 3 mm in length (Fig 8-2). The optic of the PIOL is vaulted to avoid contact with the crystalline lens and to allow aqueous to flow over the crystalline lens. This vaulting can be viewed at the slit lamp as well as with ultrasound biomicroscopy or Scheimpflug imaging (Fig 8-3). The lens manufacturers suggest that an acceptable amount of vaulting of the lens optic over the crystalline lens is 1.0 ± 0.5 corneal thicknesses. Using the appropriate vault is crucial for reducing complications (discussed later in the chapter).
For lens implantation, following pupil dilation, a 3.0- to 3.2-mm temporal clear corneal incision is made, and 1–2 additional paracentesis incisions are created, usually superiorly and inferiorly, to facilitate lens positioning. The lens is inserted using a cohesive viscoelastic material; after the lens unfolds, the footplates are positioned under the iris (Fig 8-4). The leading footplate is marked for identification and must be confirmed to be in the correct location once the lens exits the injector in order to ensure the lens is oriented with the correct side facing anteriorly. The surgeon should avoid contact with the central 6.0 mm of the lens, as any contact might damage the thin lens optic. Care should be taken to avoid touching the crystalline lens with the PIOL to minimize the risk of cataract formation. Positioning instruments should be inserted through the paracenteses and should be kept peripheral to this central area. The pupil is then constricted. It is crucial to remove all viscoelastic material at the conclusion of the procedure to reduce the risk of a postoperative spike in intraocular pressure (IOP). Video 8-2 demonstrates implantation of a posterior chamber PIOL.
VIDEO 8-2 Implantation of a posterior chamber phakic IOL.
Courtesy of George O. Waring IV, MD.
Sizing the posterior chamber phakic intraocular lens
The correct IOL length is selected by using the white-to-white measurement between the 3 and 9 o’clock meridians or by direct sulcus measurements made by a variety of techniques, including high-frequency ultrasound, anterior segment OCT, slit-beam or Scheimpflug imaging, and laser interferometry. Although the FDA-approved technique for measurement remains white-to-white measurement, there is growing evidence that direct sulcus measurement using any of these methods is superior and minimizes the risk of incorrect PIOL sizing. For more information on PIOLs, please refer to the FDA website.
Angle-supported phakic intraocular lens
No angle-supported PIOLs are currently approved by the FDA. Outside the United States, several commercial angle-supported PIOLs are available. The most widely used lens is made of flexible acrylic material and can be inserted through a small incision without the need for pupil dilation.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.