March 2012

 

NEWS & OPINION

 

Complicated cataract cases

Cataract surgery in the setting of prior pars plana vitrectomy: Surgical pearls


by Arup Chakrabarti, M.S.

 

Kevin Miller, M.D.

Cataract development is a common complication of pars plana vitrectomy. Children and young adults usually develop posterior subcapsular cataracts. Older adults usually experience progressive nuclear sclerosis. As the indications for pars plana vitrectomy expand and the number of procedures performed increases, the volume of post-vitrectomy cataracts will increase in lock step.

Cataract surgery in the post-vitrectomy eye is usually straightforward, especially if the anterior cortical gel and vitreous face were spared. However, it can also be very challenging, especially if more than one vitrectomy was performed or silicone oil was injected into the eye. Unique features of post-vitrectomy eyes may include conjunctival scarring, small pupils, increased nuclear density, zonular laxity, trampolining of the iris-lens diaphragm, and the presence of posterior capsule plaques. Many of these problems are further aggravated if a scleral buckle is also present.

The visual potential of eyes that have undergone a vitrectomy is often reduced and patients' expectations for visual improvement need to be managed appropriately. Epiretinal membranes and cystoid macular edema are especially prevalent in this population.

In his article, Dr. Chakrabarti discusses pre-op considerations, IOL selection, patient counseling, intraoperative considerations for each step of cataract surgery, post-op management, and post-op complications. Although experience comes with practice, those who are early in their careers and those who do not encounter post-vitrectomy eyes frequently will find many useful pearls in this article.

Kevin Miller, M.D., Complicated cataract cases editor

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Introduction

Conjunctival scarring

Figure 1. Conjunctival scarring in a vitrectomized eye

Emulsified silicone oil

Figure 2. Emulsified silicone oil in the anterior chamber Source (all): Arup Chakrabarti, M.S.

Use of microrhexis scissors Figure 3A. Use of microrhexis scissors in excising a fibrotic anterior capsular rent

Use of microrhexis forceps Figure 3B. Use of microrhexis forceps in completing the rhexis in the presence of anterior capsular fibrosis

Central posterior capsular plaque Figure 4A. Central posterior capsular plaque in a post-vitrectomy cataract

after posterior capsular rhexis Figure 4B. View after posterior capsular rhexis that includes the capsular plaque

Post-op migration of silicone oil Figure 5. Post-op migration of silicone oil bubble in the anterior chamber

Post-op anterior capsular phimosis Figure 6. Post-op anterior capsular phimosis

Source (all): Arup Chakrabarti, M.S.

Cataract development is one of the most common complications after vitrectomy; it develops in 12.5-80% of eyes.1,2 The risk factors for the development and progression of cataract are older age, degree of pre-op nuclear sclerosis, intraoperative lens touch, diabetic retinopathy, and silicone oil injection.3,4 The indications for pars plana vitrectomy are fast expanding, and the number of patients undergoing this procedure is increasing because of the improved surgical results. Therefore, there is a significant increase in the volume of vitrectomized patients, who in their vitrectomized state pose a challenge to the cataract surgeon.

Risks in vitrectomized eyes

The vitrectomized eyes are at a higher risk of developing intraoperative and post-op complications due to the following factors: 1. The eyes harbor sequelae of previous surgery and inflammation. 2. They have associated comorbid conditions.

3. Nuclear brunesence (denser cataracts) is common.

4. They lack the support of vitreous gel.

The following factors need to be taken care of while dealing with post-vitrectomy cataracts: 1. Conjunctival scarring (Figure 1) 2. Compromised corneal endothelium (Figure 2) 3. Poor pupillary dilatation 4. Zonular weakness and pre-existing posterior capsular rent 5. Low scleral rigidity 6. Cystoid macular edema 7. Diabetic retinopathy 8. Increased lens-iris diaphragm retropulsion

Pre-op considerations

A thorough pre-op evaluation taking into account the patient's compromised ocular health, structural changes resulting from the trauma of the earlier surgical procedure, and the poor visual potential is necessary in formulating a definite surgical plan. Pre-op examination should make note of the following important findings: The presence of conjunctival and episcleral scarring, endothelial cell count, deep anterior chamber and presence of emulsified silicone oil bubbles in it, presence of iridophacodonesis indicating a compromised zonule, pupillary status, and detailed examination of the retinal status, especially to assess the integrity of the macula, and the presence of open breaks. In eyes with advanced cataract, assessment is made using a B-scan. B-scan in the presence of silicone oil, however, gives very few relevant details and has limited utility.

Pre-op considerations should also include IOL choice. Both the hydrophobic and hydrophilic acrylic IOLs have been associated with consistently satisfactory outcomes and have been well tolerated by the eye. A rigid PMMA IOL may also be considered. A silicone IOL should be avoided in an eye that has undergone prior vitrectomy. Also, one-piece plate haptic-design lenses and lenses with small and ovoid optics should be avoided. Silicone oil can interact with the posterior surface of the IOL in patients with a posterior capsular rent, impairing visual acuity as well as fundus visualization both intra- and post-operatively. Silicone oil adhesion to the IOL surface is maximized with the silicone IOL. However, it can also occur with hydrophobic acrylic, PMMA, and hydrophilic acrylic lenses in decreasing order. A surface modified heparin-coated IOL can reduce the post-op reaction. A lens with a 360-degree square edge design with a large optic diameter (6-6.5 mm), which gives a greater viewing area for fundus visualization, is preferred. A plano convex configuration of the implanted IOL with the plano surface facing posteriorly ensures minimal refractive surprises. Finally, pre-op patient counseling should be included in pre-op considerations. It is necessary to give the patient a realistic idea of his visual potential as well as to make him aware of the expected and unexpected intraoperative events that can complicate his surgery.

The benefit of the surgical intervention to the patient may provide an improved color perception, better peripheral vision, or only a better view of the fundus for the ophthalmologist. The patient may be bothered by diplopia, metamorphopsia, central scotoma, or anisometropia.

Surgical strategy for phacoemulsification in vitrectomized eyes

Long-acting cycloplegic and NSAIDs should be started at least 1 week prior to the surgery. This may help to maintain adequate mydriasis throughout the phacoemulsification procedure. It is important to decide on the type of anesthesia. Injection anesthesia is preferred by many surgeons, although the procedure can be safely performed under topical anesthesia. Injection anesthesia is preferred in patients with hard cataract and associated comorbid conditions like subluxated cataract, small pupils, etc. When performed under topical anesthesia, the patient may experience discomfort during maneuvers that stretch the zonular apparatus, when there is excessive movement of the lens-iris diaphragm. This undesirable sensation may be eliminated by intracameral non-preserved lidocaine. Enhanced posterior diffusion of the anesthetic drug through the zonule may cause transient blindness due to temporary retinal block.

Intraoperative problems and surgical technique

The intraoperative problems to be anticipated during phacoemulsification include: ocular hypotony, deep anterior chamber, disturbed vitreous dynamics, compromised zonule, poor pupillary dilatation, loose capsular bag, pre-existing posterior capsular rent, posterior capsular plaque, dropped nuclear fragments, and infusion deviation syndrome. Ocular hypotony can be countered by firming the globe with viscoelastics. An infusion cannula may be placed through an inferotemporal sclerotomy port and the flow used to firm the globe. To prevent excessive deepening of the anterior chamber, it is advisable to perform the surgery at a reasonably low infusion bottle height, and other phaco parameters are also adjusted appropriately. Another technique is to enter the anterior chamber with the phaco probe in a dry manner with prior elevation of the pupillary margin with a spatula working from the side-port. The microscope magnification (zoom) can also be adjusted at a low level to enhance the depth of focus.

1. Incision

A clear corneal incision is preferred to a scleral tunnel incision. Both the phaco and side-port incisions should be carefully fashioned to avoid fluid leakage since fluid dynamics become increasingly important in these eyes.

A scleral tunnel incision is preferred if the patient opts for a rigid IOL or in a very challenging case where the surgeon may have to convert to a large incision non-phaco technique. A fornix-based conjunctival flap (Figure 1) can be dissected, which may be difficult due to the scarring. The conjunctival flap should be anchored at the periphery at the conclusion of surgery.

2. Capsulorhexis

Capsulorhexis may be challenging in view of the increased prevalence of anterior capsular fibrosis in many eyes. The red fundal reflex may also be compromised due to the posterior segment pathology, advanced nature of the cataract at the time of presentation, and a lusterless cornea in some patients. Therefore, it is prudent to stain the anterior capsule with trypan blue dye to enhance its visibility. A sharp cystotome should be used for capsulorhexis. It is prudent to keep a pair of microrhexis forceps and scissors handy. One may need to incise the fibrotic areas with microrhexis scissors (Figures 3A and 3B). Every effort should be made not to deepen the anterior chamber excessively during injection of viscoelastic. A rhexis of about 5-5.5 mm should be fashioned. This facilitates nuclear emulsification, reduces the incidence of posterior capsular opacification and capsular phimosis, and promotes adequate fundus visualization during post-op follow-up.

3. Hydrodissection steps

Hydrodissection must be slow and gentle, keeping in mind the possibility of pre-existing posterior capsular rent. Slow and gentle hydrodissection followed by frequent decompression should be done to avoid a posterior capsular blowout. It is necessary to verify that adequate nuclear rotation has been achieved to prevent further stress on the compromised capsulozonular apparatus. In eyes presenting with mature white cataracts after vitrectomy, the possibility of lens touch and occult capsular rupture should be kept in mind. In these cases, instead of hydrodissection, a gentle hydrodelineation and/or hydro-free dissection may be performed prior to removal of the nucleus.

4. Nucleus management

A technique of nuclear emulsification that is least traumatic to the capsulozonular apparatus should be employed. A direct phaco chop technique is believed to be the least traumatic and is the author's technique of choice. However, the surgeon may employ any technique that he/she is comfortable with, and these may include the stop-and-chop or divide-and-conquer techniques. Post-pars plana vitrectomy cataracts are denser than the senile cataract, and therefore, more time has to be spent in emulsifying the nucleus. Care must be taken not to cause thermal burns to the cornea and not to apply excessive force on the lens while emulsifying it.

Notable fluctuation of anterior chamber depth may occur because of increased movement of the lens-iris diaphragm. Excessive fluctuations can be reduced by keeping the bottle height low and maintaining irrigation whenever the phaco probe or irrigation-aspiration probes are in the eye. These patients are prone to infusion deviation syndrome wherein the fluid migrates posteriorly through the weakened zonule. Raising the infusion bottle has the paradoxical effect of further shallowing the anterior chamber.

5. Cortical clean up

Cortical clean up should be thorough and performed using lower I/A parameters and circumferential stripping to reduce stress on the zonule. A bimanual irrigation-aspiration system is very efficient for safe and complete cortex removal. Gentle posterior capsular polishing should be performed to reduce the incidence of post-op posterior capsular opacification.

6. Small pupil strategy

As mentioned earlier, a long-acting cycloplegic and NSAIDs should be instilled in the post-op period. The surgeon should utilize a step-wise approach to small pupil management (posterior synechiolysis, viscomydriasis, pupillary membrane dissection, stretch pupilloplasty, and iris hooks). The Malyugin Ring (MST, Redmond, Wash.) is also a good option. Intraoperative manipulations and anterior chamber depth fluctuation should be minimized.

7. Dense posterior capsular plaques

Marked posterior capsular fibrosis or plaques are quite common in silicone oil-filled eyes. Centrally located plaques (Figures 4A and 4B) may be visually significant and need to be removed. Many plaques may be removed by capsular polishing or dissection with a 26-gauge needle. Once an edge is created it can be peeled off with Utrata forceps. Very dense plaques may be managed by including them in the primary posterior capsulorhexis.

8. IOL implantation

The IOL should be implanted in such a position so as to ensure long-term fixation and stability as well as to optimize visualization of the posterior segment. Regardless of the IOL design, placement must be gentle, avoiding excessive rotational maneuvers.

If there is zonular dialysis, use of a capsular tension ring ensures that the capsular bag is evenly distended and the IOL is placed with one haptic oriented in the direction of the dehiscence.

At the conclusion of surgery, hypotony should be avoided by reforming the anterior chamber and ensuring watertight closure. Altered scleral rigidity and perilimbal scarring may necessitate suture placement to close the phaco and side-port incisions.

Post-op management

Rigorous post-op management is necessary to prevent post-op inflammation, secondary glaucoma, posterior synechiae, and cystoid macular edema (CME). Use of topical steroid drops, nonsteroidal anti-inflammatory drops, and cycloplegics are absolutely necessary. Subconjunctival injection of steroids should be considered if the intraocular inflammation is not under control. Post-op fibrin may be managed by successful use of intracameral tPA. Vigilant management is necessary to detect and treat CME and worsening of diabetic retinopathy.

Complications

Early post-op complications include blepharoptosis, moderate to severe corneal edema, intraocular pressure spike, wound leak, moderate to severe post-op iritis, peaked pupil with vitreous in the wound, iris prolapse, incorrect IOL power, IOL decentration or dislocation, endophthalmitis, macular phototoxicity, retinal detachment, and vitreous hemorrhage. Silicone oil migration (Figure 5) to the anterior chamber may occur early as well as late in the post-op period. Late post-op complications that occur more than a week after surgery include blepharoptosis, moderate to severe corneal edema, pseudophakic bullous keratopathy, chronic iritis, irregular pupil, neovascularization of the iris, capsulorhexis contraction (Figure 6), IOL decentration, and posterior capsular opacification. Posterior segment complications include new or persistent macular edema, persistent recurrent choroidal neovascularized membrane, proliferative diabetic retinopathy, reopened macular hole, retinal detachment, visually significant epiretinal membrane, and vitreous hemorrhage.

Conclusion

By recognizing the differences in the physiologic state of the vitrectomized eye and keeping in mind the nature of the patient's previous vitreoretinal pathology, the modern cataract surgeon may readily adapt a small incisional phaco technique to this challenging patient population. The principles discussed in this article will hopefully minimize surgical difficulty and help reduce complications.

References

1. Blakenship GW, Machemer R, et al. Long-term diabetic vitrectomy results. Report of l0 year follow-up. Ophthalmology 1985; 92:503-6.

2. de Bustros S, Thompson JT, Michels R G, et al. Nuclear sclerosis after vitrectomy for epiretinal membranes. Am J Ophthalmology 1988; 105:160-4.

3. Thompson MA, Melberg NS, et al. Nuclear sclerotic cataract after vitrectomy for patients younger than 50 years of age. Ophthalmology 1995; 102:1466-1471. 4. Ogura Y, Takanash T, et al. Quantitative analysis of lens changes after vitrectomy by fluorophotometry. Am J Ophthalmol 1991; 111:179-83.

Editors' note: Dr. Chakrabarti has no financial interests related to this article.

Contact information

Chakrabarti: arupeye@gmail.com

Cataract surgery and surgical pearls Cataract surgery and surgical pearls
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