Anytime we perform cataract surgery in an eye with prior ocular surgery, there are additional challenges. In eyes with prior keratorefractive surgery such as LASIK, the IOL power calculations are affected. In eyes with prior vitreo-retinal surgery, there is less lens support due to absence of the anterior hyaloid face. And in eyes with prior glaucoma surgery, such as this eye with a prior trabeculectomy, there can be challenges with fluidic balance. In addition, we must protect the functioning bleb to ensure continued control of the intra-ocular pressure in the post-operative period.
This patient was referred by a glaucoma specialist who has been controlling the progression of the disease for two decades. There is an avascular, functioning bleb from a trabeculectomy surgery that was done years prior (figure 1). This referring doctor has two requests for you: (1) ensure that the IOL stays in the capsular bag even if the anterior chamber shallows in the post-op period, and (2) ensure the integrity and function of the bleb.
When making the phaco incisions, our usual instrumentation like the fixation ring may not be the best choices since the small spikes could damage the delicate bleb. We can use a weck-cel sponge or cotton tip to brace the eye as we make the paracentesis, then we can place the chopper in this side port incision to fixate the eye as we make the main phaco incision (figure 2). Note that we want to make an incision with a sufficiently long tunnel length so that it seals well even if the eye is hypotonus in the post-op period. If there is any doubt as to the incision sealing, a single 10-0 nylon suture can be used to further secure the wound.
The capsulorhexis in this eye should be on the smaller side so that the IOL is securely held in position even if the anterior chamber shallows in the healing period. Aiming for a centered 4.5 mm diameter capsulorhexis will ensure that the 6 mm optic will not prolapse out of the capsular bag even if the anterior chamber becomes flat.
The trabeculectomy site is an additional outflow path for the irrigating balanced salt solution that we will use during phacoemulsification surgery. The sole source of inflow is from the infusion fluid coming through the phaco probe. There are now three points of fluidic outflow: the active aspiration through the phaco tip, leakage from the incisions, and outflow through the trabeculectomy site. At the beginning of the case, we can inject viscoelastic to help form a barrier and decrease fluidic outflow into the bleb. This temporizing measure will help to maintain the fluidic balance, but we should still adjust our phaco parameters by decreasing our aspiration flow rate by at least 25%. During cataract surgery, any fluidic bounce or anterior chamber instability should be adjusted on the fly by decreasing the aspiration flow rate even more.
We also want to control the infusion pressure that we are using during cataract surgery. These glaucoma patients have nerves which are more susceptible to damage from increased pressure, which can be many times higher than physiologic during phaco. Limiting the infusion pressure or bottle height and being more efficient during nucleus removal can help minimize the effect of barotrauma.
Once the IOL is implanted in the capsular bag, the viscoelastic can be fully aspirated from the anterior segment. We can place the aspiration port of the IA hand-piece close to the trabeculectomy site to ensure complete removal of the viscoelastic. Decreasing the infusion pressure and the aspiration flow rate will help ensure that excess fluid is not pushed through the trabeculectomy site which would distend and overinflate the bleb.
A small aliquot of preservative-free triamcinolone acetonide suspension is injected in the anterior chamber at the end of the case (Figure 3). This will allow us to visualize the fluid outflow through the trabeculectomy site to ensure functioning of the bleb. If there is resistance to outflow, balanced salt solution can be injected using a 3cc syringe and a 27g blunt cannula to power wash the angle near the trabeculectomy.
Once adequate bleb function is confirmed, the incisions are sealed with focal corneal stromal hydration. If an incision is leaking, the best course of action is often placement of a 10-0 nylon suture to ensure watertight sealing. Finally, the bleb site is checked with fluorescein dye to make sure that the conjunctiva is sealed and without defects.
In the post-op period, this patient may experience increased or decreased filtration from the bleb site. More filtration will result in a shallower anterior chamber and lower pressure, whereas lower filtration will result in a rise in the intra-ocular pressure which may require additional medications or procedures. These patients may also be more susceptible to steroid-induced pressure spikes, so a shorter course of topic corticosteroids may be advisable.
With these guidelines, patients with prior trabeculectomy glaucoma surgery can have a successful cataract surgery with great visual results. This video shows the complete surgery, start to finish, at double speed so that you can learn these important surgical pearls in just 5 minutes.
click to learn these pearls about phaco in eyes with a prior trabeculectomy: