Cataract and glaucoma
Optimised fluidics key to safe and uncomplicated surgery in glaucomatous eyes
The fluidics of the phacoemulsification system in cataract patients with glaucoma should be optimised to ensure a stable, low-pressure anterior chamber during surgery and prevent damage to the optic nerve, Roberto Bellucci MD, Verona, Italy, told the 36th Congress of the ESCRS in Vienna.
“Better understanding of phaco fluidics improves the safety of cataract surgery especially in glaucomatous eyes,” he emphasised.
Microincision cataract surgery (MICS) is the best option in glaucomatous eyes because it has gentler fluidics than standard incision surgery, whether using a Venturi or peristaltic pump settings. Femtosecond laser-assisted cataract surgery is indicated in glaucoma eyes with shallow anterior chambers, pseudoexfoliation and low endothelial cell counts, he said.
But what is most important is the optimisation of fluidics to avoid IOP elevation and anterior chamber oscillation, which can further damage the already compromised optic nerve, Dr Bellucci stressed.
Using a high bottle height is a poor solution. Raising the bottle height one metre above the eye will increase the pressure within the anterior chamber to 70 mmHg. If the bottle is raised to 1.3m the pressure will rise to 100 mmHg. Raising the bottle in this way will not only increase the patient’s pain but will also increase the oscillation of the anterior chamber depth. That, in turn increases the difficulty of the surgery and raises the risk of complications and damage to the optic nerve head. The potential complications include posterior capsule rupture and cystoid macular oedema.
luidics optimisation can instead be achieved by reducing the aspiration ports and system hysteresis, separate control of aspiration and ultrasound, avoiding occlusion, allowing some leakage and varying infusion pressure according to the pressure in the anterior chamber, Dr Bellucci summarised.
In MICS procedures, rigid low hysteresis tubing must be used, together with low hysteresis pumps possessing small ports and pressure sensors and double venting systems.
Separate control of aspiration and ultrasound allows the activation of ultrasound power at any vacuum level and also avoids excessive pressure within the anterior chamber and resulting hydration of the vitreous. Venturi pumps and peristaltic pumps perform equally well in separately controlled aspiration and ultrasound systems, provided that they are properly adjusted.
The use of micro-pulse ultrasound delivery and small phaco tips will generate very small fragments, thereby avoiding occlusion of the aspiration line. Phaco tips with transverse/rotational needle movement appear to work very effectively when used with a peristaltic pump, Dr Bellucci said.
He added that some incision leakage during surgery can be helpful. It avoids excessive pressure and deepening of the anterior chamber. Furthermore, leakage provides a reservoir of fluid, which helps in avoiding chamber collapse when aspiration increases abruptly. It also maintains some fluid stream within the anterior chamber during occlusion or clogging.
The latest evolution in phaco fluidics control are irrigation systems that use feedback from sensors that detect the anterior chamber pressure. The result is better and more delicate fluidics control. The increase of vacuum that the system allows and the small tip improve fragment hold-ability, and the reduced flow improves fragment follow-ability.
“What is nice is that you can select the IOP you want; I use 25mmHg, which corresponds to a bottle height of 40mmHg. Nobody was using such low bottle heights before these machines came along,” Dr Bellucci said.
The choice of IOL also requires special consideration in cataract patients with glaucoma. For example, “soft” hydrophilic IOLs with weak haptics are contraindicated in eyes with weak zonules, as in eyes with pseudoexfoliative glaucoma, because they will not resist capsular bag contraction.
IOLs that decrease contrast sensitivity like multifocal IOLs are also contraindicated in patients with glaucoma. On the other hand, aspheric IOLs that enhance contrast sensitivity are beneficial in such cases.
At the conclusion of surgery, thorough viscoelastic removal is essential to avoid post-op IOP spikes. IOP should be brought under control the same day, with attention to possible aqueous misdirection syndrome, he advised.