COMPARISON AMONG SEQUENTIAL PHACO AND VITRECTOMY, COMBINED PHACO-VITRECTOMY, AND PARS PLANA LENSECTOMY/CAPSULECTOMY
Combined Phacoemulsification Vitrectomy Procedures
Combined Phacoemulsification Vitrectomy Procedures
Many surgeons now combine phacoemulsification with vitrectomy for a variety of reasons. This approach adds significant complexity but is indicated in certain situations. There is a widespread but incorrect notion that vitrectomy inevitably leads to cataract. It is widely appreciated that vitrectomy leads to progression of preexisting nuclear sclerosis, likely due to ascorbic acid depletion and resultant permanent increase in the partial pressure of oxygen in the vitreous cavity by 7 to 12 mm Hg (Holekamp, Chang, Steffanson). BSS Plus (Alcon) has been available for three decades (Edelhauser) and has eliminated the development of posterior subcapsular cataract during the procedure, yet many surgeons use BSS or, even worse, lactated Ringer’s solution. Other surgeons choose inappropriately to add a variety of compounds including bicarbonate, dextrose, antibiotics, and epinephrine, all of which can lead to posterior subcapsular cataract, especially if infrequent mixing errors do not occur. Bicarbonate is unnecessary and inappropriate to use with BSS Plus because it is correctly buffered without additives. Dextrose was added three decades ago when diabetic patients were often markedly hyperglycemic during surgery, but the widespread availability of serum glucose monitoring during surgery has eliminated this issue. Contact of the posterior lens with a gas bubble over a period of several days leads to posterior subcapsular cataract; this occurs only if the patient does not maintain the correct position and when there is discontinuity in the anterior vitreous cortex. Patient education is very important. Some of what is described as poor compliance by the patient should be attributed to poor patient education. The vast majority of younger patients with a clear lens undergoing vitrectomy will retain a clear lens for decades if BSS Plus without additives is used and gas bubble contact with the lens is avoided. In short, cataract is not inevitable after vitrectomy.
Optimal visualization is essential for vitrectomy, especially if epiretinal or internal limiting membrane (ILM) dissection, drainage of subretinal fluid through retina breaks, or retinopexy is required. Posterior subcapsular cataracts interfere with visualization more than nuclear sclerotic cataracts. If the surgery is elective, as is typically the case with macular surgery, cataract surgery can be performed 1 month before vitrectomy if the cataract is likely to interfere with visualization during vitrectomy. A potential problem with pre-pars plana vitrectomy (pre-PPV) cataract surgery is the accurate determination of axial length. The Zeiss IOL Master uses the retinal pigment epithelium (RPE) for measurement in contrast to A-scan ultrasound that uses the ILM. Measurement from the RPE is not a problem with epimacular membranes (EMMs) or vitreomacular traction syndrome; however, the A-scan ultrasound axial length may be reduced when these conditions are present or increased when macular holes are present. Fixation is an additional issue with macular disease; it may be difficult to determine if the axial length is measured in the fovea or an extramacular region with either technology.
Cataract surgery performed as a separate procedure after PPV permits more accurate axial length measurement. The procedure can be performed before or shortly after PPV if cataract interferes with examination of the retina and a retinal detachment (RD) is present. For this scenario, the options are phaco-vit or pars plana lensectomy with complete removal of the posterior capsule. Although endocapsular lensectomy with retention of the anterior capsule followed by intraocular lens (IOL) implantation in the ciliary sulcus is possible, this typically results in severe capsular opacification. Therefore, the anterior capsule could not be utilized as a barrier for silicone oil posterior retention. The lensectomy, complete removal of the capsule with forceps and inferior iridectomy, approach has been advocated for these cases, but phaco-vit approach is now favored because it enables the preservation of a silicone oil barrier and optimal correction of aphakia.
SILICONE OIL ISSUES
Silicone oil has a different index of refraction than vitreous. Because the posterior surface of most IOLs is convex, instead of plano, the usual IOL power calculations cannot be used. Although many surgeons think silicone oil must be removed after a certain number of months, this is simply not true. The incidence of silicone oil-related glaucoma is approximately 11% (1), silicone oil is not toxic to the retina, and corneal complications are even less common. A not uncommon scenario is PPV plus silicone oil to accomplish reattachment, removal in several months followed immediately by redetachment, and reoperation with replacement of the silicone oil. There is simply no need to remove oil contained behind a posterior chamber lens; the refractive effect is approximately four diopters (D), and contrary to popular belief, oil does not cause decreased vision. If there is a full fill behind a posterior chamber intraocular lens (PCL), change in focus with changing head position as well as emulsification is minimized. IOL calculations must anticipate the ultimate retention or removal of oil. There is a greater impetus to removal of oil in younger patients.