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Slide 1 |
The authors have no financial interest in products mentioned in this article.
The authors received no public or private financial support pertaining to the information published in this article.
The presence of vitreous gel in the anterior chamber is associated with an increased risk of serious intraoperative and postoperative complications. It is fortunate that the incidence of many vision-threatening complications associated with vitreous loss can be reduced by meticulous vitreous clean-up.1 However, vitreous clean-up can be challenging even to experienced surgeons because of the transparency of vitreous gel under the operating microscope. Even in cases in which vitreous is known to be present, surgeons must use indirect clues to determine the extent and location of vitreous gel in the anterior segment.
Triamcinolone acetonide has been injected into the vitreous cavity by vitreoretinal surgeons since it was first described by Tano, Chandler, and Machemer in 1980.2 Triamcinolone suspension has been found to be nontoxic3-5 and it is currently being injected directly into the vitreous cavity for the treatment of a variety of vitreoretinal diseases. In 2000, Peyman and colleagues described the use of triamcinolone suspension for localizing cortical vitreous, enabling a more thorough vitrectomy.6 By adapting this technique for use in the anterior segment, we have developed a technique for making vitreous visible to the anterior segment surgeon.7
Removal of the preservative was accomplished by preparing the triamcinolone suspension as follows. A tuberculin syringe was used to withdraw 0.2 mL of well-shaken 40 mg/mL triamcinolone acetonide (Kenalog-40 Bristol-Myers Squibb). The needle was removed and replaced with a 5-micron syringe filter (Sherwood Medical). The plunger was then depressed forcing the suspension into the 5-micron filter, which allowed the vehicle to pass through, yet stopped the triamcinolone particles. The filter was then transferred to a 6-mL syringe containing 2 mL of balanced salt solution (BSS). The plunger was depressed causing the BSS to rinse through the filter and the triamcinolone. Without removing the filter from the syringe, a 22-gauge needle was then placed on the distal end of the filter and approximately 5 mL of BSS was drawn into the syringe, resuspending the triamcinolone. The syringe was inverted several times to ensure thorough resuspension and washing of the triamcinolone particles. The plunger was then depressed expressing all of the fluid through the same 5-micron filter, which stopped the triamcinolone particles. Finally, 2 mL of BSS was drawn into the syringe through the filter to resuspend the triamcinolone particles. The filter was removed and the washed triamcinolone suspension was transferred to a sterile 3-mL syringe, which was inverted several times before using to ensure thorough suspension. The washed triamcinolone suspension was injected into the anterior chamber through a 27-gauge cannula.
Although this technique provides triamcinolone particles that are "well washed" from the preservative containing vehicle, it is somewhat cumbersome. Another method involves allowing the triamcinolone particles to settle in the original vial for 30 minutes followed by decanting the clear upper solution and mixing with BSS.8 Alternatively, some surgeons have used triamcinolone directly from the bottle diluted with BSS to the appropriate concentration (M. Packer, MD, oral communications, 2003). Finally, preservative-free triamcinolone can be purchased from commercial pharmaceutical compounding centers. Currently, there is no clear evidence that preservative-free, versus washed, versus diluted triamcinolone for anterior vitrectomy results in a clinical difference, and further studies in this area are needed.
Our initial experimentation involved six fresh human cadaver eyes. Vitreous prolapse into the anterior chamber was induced by creating a zonular dialysis or by creating a rent in the posterior capsule after phacoemulsification. Triamcinolone suspension was injected directly into the anterior chamber where the triamcinolone particles tended to become entrapped in the vitreous gel. The trapped triamcinolone particles made the vitreous gel plainly apparent.
Our ability to visualize vitreous provided us with the opportunity to examine the behavior of the vitreous gel in an experimental setting. One common misconception is that irrigating fluid in the presence of vitreous prolapse "hydrates" the vitreous, which results in more vitreous prolapse. Because the vitreous consists of 98% to 99% water, it seemed improbable that the vitreous gel could expand by absorbing more water from BSS. Triamcinolone injection allowed us to observe the vitreous dynamics and thereby explore this concept in cadaver eyes.
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As expected, irrigation in the anterior chamber neither increased the vitreous volume nor resulted in vitreous prolapse. However, when the triamcinolone suspension was injected directly within the substance of the vitreous gel there was obvious expansion of fluid pockets (Slide 1) and the amount of expansion was dependent upon the volume injected. Thus, it seems likely that the concept of vitreous "hydration" has been used to describe this phenomenon of expanding fluid pockets in vitreous gel. More importantly, it was noted that injection of triamcinolone suspension directly into the substance of the vitreous gel enhanced its capture by the gel. Rather than primarily clinging to the superficial vitreous gel, the triamcinolone was impregnated throughout the prolapsed vitreous.
An additional vitreous behavior that we examined was the response to posterior pressure. In a closed system, even strong posterior pressure did not send vitreous into the anterior chamber. Posterior pressure caused the vitreous gel to bulge forward, but, in the absence of a wound leak, it rebounded to its original position when the pressure was relieved.
The physical force that moved the vitreous gel in every case was a pressure gradient. The vitreous gel always moved from an area of high pressure to an area of low pressure. As expected, vitreous gel streamed into the aspiration port of the irrigation/aspiration handpiece as soon as the aspiration was applied. Furthermore, if the vitreous was at or near an incision site, any fluid leak, even a small leak at a paracentesis, provided a pressure gradient that resulted in further vitreous prolapse, and entrapment in the wound.
Following our preliminary work in cadaver eyes, we have used washed triamcinolone suspension to assist the anterior vitrectomy in many eyes with zonular dialyses and in a few eyes with vitreous prolapse from other etiologies such as ruptured posterior capsule, and secondary lens implantation when the posterior capsule was absent.
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Subjectively, each surgeon felt that the ability to visualize the vitreous gel made vitrectomy easier. Triamcinolone particles in the vitreous allowed the surgeon to visualize the vitreous response to each surgical maneuver (Slide 2). As with the cadaver eyes, vitreous movement was driven by pressure gradients and it became clear that fluid egress at the wound or paracentesis tended to carry nearby vitreous with it. Thus, if the location of vitreous prolapse is known in advance, the surgeon can minimize vitreous prolapse and entrapment during the injection of triamcinolone by striving for excellent (watertight) wound construction and selecting a paracentesis site remote from the area of vitreous prolapse for the instillation of triamcinolone.
This technique also illustrated certain advantages of a pars plana approach for anterior vitrectomy. One of these advantages was that a pars plana approach obviated the need to place the vitrector through the clear corneal incision thereby limiting fluid egress that could draw vitreous to the wound. Another important advantage is that a pars plana approach tended to pull vitreous back into the vitreous cavity rather than forward into the anterior segment. While this may seem obvious, it is important to note that triamcinolone particles injected into the anterior chamber are trapped by the vitreous already present there and are not significantly trapped in more posterior vitreous. Thus as the surgeon watches the triamcinolone-laden vitreous being drawn backward into the vitrector it is improbable for additional clear vitreous to remain behind in the anterior chamber. On the contrary, when performing a vitrectomy from the anterior segment, as the last of the triamcinolone-impregnated vitreous is engulfed by the vitrector, the surgeon must be wary that he or she has not inadvertently drawn additional clear vitreous forward.
Additionally, as with the cadaver experiments, when triamcinolone is injected directly into vitreous gel, it is trapped efficiently. However, in cases with highly liquefied vitreous that presents only small strands of vitreous in the anterior chamber, the entrapment of triamcinolone particles is less intense. Although rarely necessary, additional triamcinolone can enhance entrapment in these vitreous wisps. Additional triamcinolone instillation following vitrectomy can also confirm removal of all vitreous strands especially if performing vitrectomy from an anterior approach rather than through the pars plana.
Ideally, triamcinolone-assisted vitrectomy is performed without viscoelastic in the eye. When there is viscoelastic in the eye, the surgeon should be aware that viscoelastics tend to occupy space and exclude triamcinolone from that space. Thus, viscoelastic can potentially hide vitreous strands from trapping triamcinolone particles.
To date, we have seen no complications such as glaucoma that were attributed to the intracameral use of triamcinolone suspension. On the contrary, postoperatively, these eyes have decreased postoperative inflammation and corneal edema.
Hanemoto presented a paper at the 2003 American Academy of Ophthalmology meeting entitled Triamcinolone-Assisted Vitrectomy for SIOL Implantation. In addition to the clear visualization of the vitreous afforded by triamcinolone injection, Hanemoto noted improved postoperative visual acuity in the eyes that had triamcinolone-assisted vitrectomy compared with the controls.8 The investigators attributed this to "luck" rather than triamcinolone. However, the difference bordered on statistical significance among the aphakic eyes (P=.05) and was highly statistically significant when comparing the severely subluxated lenses delivered by ICCE to matched controls (P<.0001). This suggests that triamcinolone-assisted vitrectomy may actually improve outcomes in selected patients. In addition to reducing inflammation and corneal edema, triamcinolone-assisted anterior vitrectomy allows a surgeon to perform the minimum amount of surgery necessary, which is less traumatic to the eye and thus likely to yield better functional results.9
Triamcinolone suspension when injected into the anterior chamber provides a surgeon a means for localizing and identifying vitreous gel. The clear visualization of the vitreous gel allows for thorough removal of the prolapsed vitreous and alerts the surgeon to residual strands of vitreous that may have gone otherwise unnoticed. It also allows for a surgeon to observe the vitreous behavior so that he or she may avoid maneuvers that increase vitreous traction or prolapse.
Triamcinolone-assisted vitrectomy promises to be a significant surgical adjunct for both planned and un-planned vitrectomies.
