Considering Hemostasis, Retinopexy and PRP
More expert opinion on the advantages and disadvantages of some common vitreoretinal surgical procedures.
Steve Charles, MD, FACS, FICS
|Steve Charles, MD, FACS, FICS, is clinical professor of ophthalmology at the University of Tennessee College of Medicine in Memphis. Dr. Charles reports significant financial interest in Alcon. He can be reached via e-mail at firstname.lastname@example.org.|
Hemostasis, retinopexy and panretinal photocoagulation are essential elements of our vitrectomy tool set. This column will attempt to address alternative approaches and surgical decision-making.
Although neovascularization is frequently encountered during diabetic vitrectomy, intraoperative bleeding is always manageable. The increased use of preoperative bevacizumab in proliferative retinopathies has significantly decreased the problem of intraoperative bleeding.
Endophotocoagulation is much better suited for hemostasis than diathermy because the energy is absorbed by the hemoglobin within the vessel lumen, which significantly reduces damage to the adjacent retina. Because bipolar diathermy can cause tissue shrinkage, retinal breaks, nerve fiber layer damage and optic atrophy, it should be reserved for large vessels that are to be transected or that actually bleed during surgery.
Disposable bipolar diathermy can be used, alternated with delamination with the vitreous cutter or with curved scissors. When extensive neovascularization is associated with epiretinal membrane, it is best to control bleeding during the dissection by using transient elevation of the intraocular pressure, either by raising the infusion bottle or preferably by using console-based alternative infusion pressure, such as that available on the Constellation Vision System (Alcon).
Vascular attachment points identified after delamination are best treated with endophotocoagulation, not diathermy. Meticulous hemostasis is crucial because blood can form a substrate and stimulus for postoperative glial proliferation. Despite the use of preoperative bevacizumab and meticulous attention to surgical hemostasis, postoperative hemorrhage after diabetic vitrectomy is quite common. It is fortunate that postoperative hemorrhage in the post-vitrectomy eye usually clears within a few weeks.
Diode-pumped 532- or 577-nm lasers are ideal for all operating room and office photocoagulation procedures. They have all the advantages of near infrared diode lasers but use optimal wavelengths for hemoglobin absorption and xanthophyll avoidance, as well as retinopexy.
Laser endophotocoagulation (Figure 1) is ideal for the treatment of bleeding from surface neovascularization, retinopexy and PRP. Endophotocoagulation should be used for surface bleeding from specific sites, usually identified after scissors delamination of ERMs. When using the endophotocoagulator, the endoilluminator is usually held in the opposite hand to provide diffuse illumination.
Figure 1. Laser photocoagulation is ideal for the treatment of bleeding from surface neovascularization, retinopexy, and PRP.
When there is acute bleeding, the soft-tip cannula or vitreous cutter should be alternated with the laser probe to remove blood and facilitate precise coagulation. Flexible or articulated laser probes are ideal for avoiding inadvertent lens contact, as well as for reducing obliquity resulting in elliptical spots: hot on the near side and cold on the far side, when treating peripheral retinal breaks.
Illuminated laser probes reduce inadvertent lens contact during phakic retinal detachment repair caused by endoilluminator contact with the lens. The straight laser probe is better for PRP than curved probes. Endo-PRP results in decreased VEGF and therefore reduces the incidence of neovascular glaucoma, anterior vitreous cortex fibrovascular proliferation and recurrent flat neovascularization, leading to postop bleeding.
Figure 2. Cryopexy disperses viable RPE cells, causing greater proliferation than laser.
Endophotocoagulation lesions are 600-800 µm in diameter, depending on the distance from the tip of the probe to the retinal surface, the beam divergence, and the power setting. If the retina is detached, endophotocoagulation must be preceded by fluidair exchange and internal drainage of SRF or the use of perfluorocarbon liquids, which bring the retina and retinal pigment endothelium into contact to permit bilayer energy absorption.
For focal treatment of retinal breaks, the continuous mode is used to treat in a confluent manner (“painting”) around the breaks. This technique minimizes the possibility of under-treatment or overtreatment, which is intrinsic to the placement of discrete photocoagulation spots in rows. Periodically during treatment, small amounts of subretinal fluid will shift posteriorly, making repeated internal drainage necessary to permit retinopexy. The endophotocoagulator should never be used in air (gas) if there is blood on its tip; thermal damage to the probe, and structural alteration may result. PRP under air to areas of retina that had been detached before surgery is a common cause of fibrin syndrome because of overtreatment due to persistent subretinal fluid and the thermal insulation properties of air.
I first reported endocyclophotocoagulation but am concerned that it is significantly overused by cataract surgeons in conjunction with phacoemulsification. Many glaucoma experts share this concern based on the observation that the apparent benefits are short term, and postop cystoid macular edema increases.
LASER INDIRECT OPHTHALMOSCOPE
The laser indirect ophthalmoscope (LIO) is ideal for performing retinopexy on the contralateral eye in the operating room after vitrectomy repair of retinal detachment. The LIO is ideal for retinopexy to peripheral retinal breaks in the office, especially when scleral depression is required. Panretinal photocoagulation in the office is best performed with the slit lamp and contact lens unless the patient has kyphoscoliosis, morbid obesity or another medical condition that prevents sitting at the slit lamp.
Endophotocoagulation is a far better method for performing PRP and retinopexy than LIO during vitrectomy. Although some surgeons use only LIO during vitrectomy, this method has no known advantages and many disadvantages. Iris damage is not uncommon with LIO use, especially when there is a small pupil. Light scattering from cataracts can potentially damage the macula, and inadvertent treatment of the macula can occur.
Small pupils, residual lens cortex and posterior capsular opacification all cause problems with LIO delivery during vitrectomy. Cervical and lumbar spine ergonomic issues for the surgeon, as well as significant prolongation of the operating time, are significant issues as well.
All retinal breaks, except macular holes, peripapillary breaks and retinotomies for submacular surgery, should be treated with confluent laser retinopexy. This strategy is necessary because of the impossibility of predicting which retinal break will result in detachment, and it is justified because of the relative safety of retinopexy. Retinopexy should be used only after vitrectomy, surgical dissection, internal drainage of SRF, fluid-air exchange, and completion of SRF drainage or liquid perfluorocarbon have reattached the retina.
Post-reattachment retinopexy will ensure better visualization, so that all breaks can be identified, and iatrogenic breaks can be treated. Completion of internal fluid-gas exchange and internal drainage of SRF will confine any RPE cells mobilized by retinopexy to the area of the break and possibly decrease the incidence of posterior vitreoretinopathy.
Trans-scleral cryopexy in vitrectomy has long been virtually replaced by laser endophotocoagulation. Cryopexy disperses viable RPE and glial cells and causes more inflammation and PVR than laser (Figure 2).
This column was written in part to emphasize the advantages of laser endophotocoagulation for hemostasis, the many disadvantages of LIO use during vitrectomy, and the needs for confluent retinopexy, rather than spot arrays. RP