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7/29/2019 Lens Management for Vitrectomy
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Article Date: 7/1/2012
S U RGI C AL P REC I S I O N
Lens Management for Vitrectomy
Th e ro le of pa rs pl an a lensect om y in a pha co- vi t w or ld .
Steve Charles, MD, F ACS, FI CS
There is a common misconception that cataracts invariably follow pars plana vitrectomy. In fact,clear lenses rarely develop cataracts after PPV. There are two separate mechanisms involved in
cataracts after PPV: one for nuclear sclerosis progression and another for posterior subcapsular
cataracts.
Some surgeons believe that an age threshold of 40 years old, or some say 50, determineswhether nuclear sclerosis will develop after PPV; in fact, the presence or absence of nuclear
sclerosis is the real issue. Rapid de novo nuclear sclerosis is highly unusual.
Dr. Nancy Holekamp has shown that partial pressure of oxygen in the vitreous cavity is
permanently elevated after PPV by about 10 mm Hg. Nuclear sclerosis biochemistry is well
understood to be an oxidative reaction. Ascorbate levels are nine times higher in the vitreous
cavity than in the serum, and ascorbate is an anti-oxidant; ascorbate levels are much lower
after PPV.
Of interest is that patients with proliferative diabetic retinopathy are much less likely than
nondiabetic patients to develop progression of nuclear sclerosis after PPV, probably because of
oxygen consumption by a retina rendered ischemic due to retinal capillary loss.
Steve Charles, MD, FACS, FICS, is clinical professor of ophthalmology at the University ofTennessee College of Medicine in Memphis. Dr. Charles reports significant financial interest in
Alcon. He can be reached via e-mail at [email protected].
Posterior subcapsular cataracts can occur immediately after PPV secondary to a metabolic insult
to the lens epithelial cells (LECs), typically due to gas bubble contact with the posterior or,
occasionally, the anterior surface of the lens if gas gains access to the anterior chamber.
Simply stated, the LECs, like the corneal endothelium, drink aqueous. Poor-quality infusion
fluid, such as lactated Ringers, and inappropriate additives, such as dextrose or bicarbonate, can
damage LECs, causing posterior subcapsular cataracts. Adding dextrose to the infusion fluid was
appropriate before rapid serum glucose monitoring became available; dextrose 5% in water(D5W) intravenous infusion during vitrectomy, which is used to prevent hypoglycemia, resulted
in greatly elevated serum glucose, making dextrose additive necessary on an osmotic basis.
Today's diabetic patients are euglycemic during PPV; adding dextrose is inappropriate. Balancesalt solution and, even better, BSS Plus, eliminate the need to add bicarbonate to the infusion
fluid. There is no need to add epinephrine or antibiotics; mixing errors can occur, as well as
toxicity.
COMBI NED VI TRECTOMY AND P HACOEMULSI FI CATI ON
The m ost significant advantage of combined phacoemulsification and vitrectomy (phaco-vit) is
the elimination of a second procedure. In addition, phaco-vit eliminates the issue of inadvertent
lens contact during peripheral vitrectomy, especially during PPV for retinal detachment.
Although phaco-vit is convenient for the patient and reduces cost, there are a number ofdisadvantages. For one, visualization can become an issue if phaco is performed first. The pupil
typically becomes smaller during phaco; if miosis occurs, iris hooks must be placed, which can
increase the surgical complexity and cost, as well as result in postoperative inflammation.
Corneal edema and striate keratopathy, as well as ophthalmic viscosurgical devices in the
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anterior chamber, can interfere with visualization, which can be a real issue with ILM peeling.
If phaco is performed after PPV, the cataract may limit the view, potentially interfering with ILM
peeling as well.
Refractive outcomes are less predictable with phaco-vit than with phaco performed by a
high-volume refractive cataract surgeon as a separate procedure on another day. This is because
effective lens position is less predictable after PPV. Vitreoretinal surgeons rarely perform enough
cataract surgery to be proficient in the use of toric intraocular lenses and femtosecond laser-
assisted cataract surgery, which are rapidly becoming the standard of care.
A-scan ultrasound axial length errors are significant in the presence of epimacular membrane,macular hole, or vitreomacular membrane syndrome because the A-scan cannot calculate the
axial position of the fovea after vitreomacular traction or after tangential traction is removed.
If significant media opacity is present, the Humphrey IOLMaster 500 or the Haag Streit LENSTAR
LS900 cannot be used because they both measure axial length from the RPE using
low-coherence optical technology.
Vitreomacular surgery is a relative contraindication for phaco-vit because high visual and
refractive expectations driven by modern-day refractive cataract surgery cannot be reliably
achieved with this surgical approach. Phaco-vit is indicated if there is a cataract sufficient to limit
visualization during non elective PPV, and it is typically indicated for diabetic tractional retinaldetachments, posterior vitreoretinopathy, or giant breaks.
Posterior synechia are more common if gas bubbles are used, even with intermittent use ofmydriatic agents. On occasion, gas may pass through the zonules into the anterior chamber,especially if the infusion cannula tip is allowed to tip anteriorly as fluid-air exchange is initiated.
PA RS PLANA LENSECTOMY
Pars plana lensectomy is underutilized today because of the growth of phaco-vit. A
one-compartment eye is essential for severe uveitis, phakic endophthalmitis, a traumaticcataract with a nonintact capsule plus retinal detachment, intraocular foreign bodies, or vitreous
hemorrhage. A highly inflamed one-compartment eye with all of the lens capsule removed is
much less likely to develop a cyclitic membrane, hypotony, or phthisis than a two-compartment
eye or an aphakic eye with a capsule.
Highly myopic eyes with vitreomacular traction syndrome, macular schisis, or retinal
detachment with PVR or giant breaks are ideal cases for pars plana lensectomy (PPL); these are
often best left aphakic. Large refractive errors are common if phaco-vit and IOL implantation
are utilized in these cases because of posterior staphyloma and calculation complexity.
Traditionally, the first step in PPL was to insert the MVR blade through the equator of the lens
into the nucleus a very bad idea. Many years ago, I adapted the techniques used in phaco to
PPL. The first step in what I call endocapsular lensectomy is to perform an anterior vitrectomy
and capsulorhexis with the vitreous cutter (Figure 1 ). This can be followed by hydrodissectionperformed through the posterior capsule rhexis (Figure 2).
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Figure 1. Posterior capsulorhexis is performed with the vitreous cutter after anterior
vitrectomy to prevent engagement of vitreous in the fragmenter.
Figure 2. Cortical cleaving hydrodissection is performed with a blunt 27-g cannula
attached to a 3- to 5-mL syringe via a short length of tubing.
The fragmenter should be used at full power with continuous aspiration and sonification because
aspiration without sonification causes plugging, and sonification without aspiration rapidly causes
scleral burns. The fragmenter tip should be positioned in the equatorial plane of the lens, staying
away from anterior and posterior capsule. Drilling into the lens and then pulling back whilesonification is activated will allow lens material to be aspirated without plugging.
Remove all of the lens capsule with end-gripping forceps with serrated teeth by zonulorhexis if
there is florid neovascularization, severe inflammation, or a scleral laceration nears the pars
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plicata (Figure 3 ). Removal of all of the capsule is not possible using the vitreous cutter; the
forceps method is safer and more effective. Removal of the entire capsule reduces cyclitic
membrane formation, hypotony, phthisis, concave iris secondary to iris-capsule synechia, and
capsule-anterior adherence leading to vitreous base traction.
Figure 3. Zonulorhexis is performed in a circular fashion with the I LM or end-grasping
forceps.
Capsule retention is indicated if there is no inflammation, infection, or neovascularization and
the intent is to perform IOL implantation, either at time of surgery or at a later date. Although
the intact capsule can retain silicone oil in the vitreous cavity, rapid and marked fibrous
proliferation invariably occurs, rendering the capsule opaque.
This technique can buy time until the oil can be removed, but often fibrous PCO is so marked
that the retina can be visualized, and B-scan ultrasonic imaging is ineffective with silicone oil in
the vitreous cavity.
SUMMARY
PPL is a powerful technique that must be part of the vitreoretinal surgeon's armamentarium.
Use of phaco-like techniques for lensectomy is superior to traditional methods. Phaco-vit is a
crucial technique for vitreoretinal surgeons but is often overutilized because of the false belief
that PPV always causes cataracts. Phaco-vit simply does not provide the refractive outcomes
patients expect and deserve. RP
Retinal Physician, Volume: 9 , Issue: July 2012, page(s): 62 - 65
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