New technologies bring opportunity for improving outcomes in cataract surgery. Yet, surgical success still hinges on adherence to core principles for planning the case, performing the procedure, and following the patient postoperatively.
Proper planning is the foundation for safe and efficient surgery, even in what seem to be routine cases, and it is of paramount importance when operating on eyes representing more complex situations. A comprehensive diagnostic evaluation allows surgeons to prepare for a smooth procedure and helps to minimize the risk of complications. Intraoperatively, advanced features found on modern phacoemulsification equipment enhance surgical safety. Regardless of the technology, however, no machine can prevent all complications. Achieving good outcomes still depends on surgeon skill and expertise (Figure 1).
Figure 1. Surgeon-related factors for optimizing cataract surgery outcomes
Conducting a thorough examination to identify pathologies that can complicate the surgery or limit the outcome, managing treatable conditions, and obtaining precise biometric measurements for use in IOL calculations are essential for achieving desired refractive and visual outcomes. These steps require use of proper diagnostic equipment.
In recent years there has been growing appreciation for the importance of detecting and managing ocular surface disease to optimize outcomes after cataract surgery. Because the cornea accounts for two-thirds of the refractive power of the eye, assessment of its optical quality is paramount to success, especially for refractive lens surgery. Current tomographic corneal topography systems providing this kind of assessment (including analysis of both the anterior and posterior surfaces), have become an essential tool in selecting the best IOL type for a particular patient.
Functional outcomes can also be affected by macular pathology. Because the cataractous lens can impede visualization of the posterior segment at the slit-lamp, there has been discussion about making macular optical coherence tomography (OCT) routine in the preoperative evaluation. The newest generations of biometers might also help surgeons in their daily routine. For example, with its integrated swept-source OCT technology, the ZEISS IOLMaster 700 allows surgeons a fixation check showing a small scan of the macula.
Zonular insufficiency is another issue to look for in a meticulous preoperative evaluation because it significantly increases the risk of anterior chamber instability and intraoperative complications, and it also can affect the IOL decision. In eyes with loose zonules or that are at risk for developing zonular laxity, selecting an IOL with tolerance to decentration is important for providing patients with good image quality in the long term.
A small pupil is also a risk factor for intraoperative complications, but the likelihood of adverse events can be reduced by proper planning. Preoperatively, therefore, surgeons should evaluate how well the pupil responds to dilating drops and elicit whether the patient has any risk factors for intraoperative floppy iris syndrome (IFIS) or intraoperative miosis.
Grading of the cataract is another important step in the preoperative evaluation because knowledge of the lens characteristics allows surgeons to choose an appropriate surgical technique and phacoemulsification machine settings that will favor surgical efficiency and safety. The Lens Opacities Classification System (LOCS) III is most commonly cited for this purpose although seldom applied in its full detail in clinical practice. Moreover, it does not encompass the more advanced cataracts that pose the greatest surgical challenge. For that reason, we created the BCN10 system, a simple classification that focuses on nucleus hardness, which has the greatest value for predicting surgical difficulty.1 While the role of BCN10 globally remains to be established, we have shown that it has good intra- and interobserver repeatability, high reliability, and good correlation with effective phacoemulsification time and phacoemulsification energy.1
Intraoperative considerations for avoiding complications (Figure 2)
Loss of anterior chamber stability is one of the most common causes for complications during cataract surgery, and it has several potential causes. Anterior chamber collapse can occur because of performance limitations of the phacoemulsification machine’s fluidics system, but also as the result of surgeon-related factors. Rushing through the procedure, choosing excessively high parameters for vacuum and/or aspiration, and maneuvering instruments in ways that distort the main incision or second instrument entry site can compromise anterior chamber stability and should be avoided.
Figure 2. Common causes of intraoperative complications
Achieving success in cataract surgery requires attention to constructing an incision that is self-sealing (I personally prefer a two-plane incision) and appropriately sized for the phaco handpiece. An incision that is too wide compromises anterior chamber stability because it allows leaking, while an incision that is too narrow also compromises anterior chamber stability by constricting the infusion sleeve. A simple geometry rule shows that as circumference is equal to ~3.14 (pi) times diameter and a knife creates two tissue surfaces of its width (W), the diameter of the incision tunnel will be about 2W/3.14 (i.e., a 2.2 mm keratome will create a 1.4 mm tunnel, not counting tissue stretch).
Other factors that can help with maintaining chamber stability include choosing an ophthalmic viscosurgical device (OVD) that has appropriate properties, repeating OVD instillation as needed during the procedure, and using a newer phacoemulsification machine with an advanced fluidics system. Regarding the latter, I found the new ZEISS QUATERA 700, which is built with the novel and innovative QUATTRO Pump, provides excellent chamber stability.
Keeping the phacoemulsification tip in the “safe zone”, i.e., the center of the anterior chamber at the pupillary plane, away from the posterior capsule, iris, and corneal endothelium, is important for avoiding complications such as capsular tears, intraoperative miosis, and damage to the corneal endothelium. This depends on surgeon technique, but also on the phacoemulsification machine’s effects on followability and anterior chamber stability. Please refer to the section titled “Anterior chamber stability and safe cataract surgery” by Dr Sri Ganesh for more information on this topic.
Providing patients with excellent outcomes after cataract surgery also depends on choosing an appropriately powered high quality IOL. As discussed in following sections, new implants along with new technology that supports IOL calculations, surgical planning, accurate data transfer, and postoperative IOL constant optimization help to achieve this goal.
1. Barraquer RI, Pinilla Cortés L, Allende MJ, et al. Validation of the nuclear cataract grading system BCN 10. Ophthalmic Res. 2017;57(4):247-251.
Part 2: Anterior chamber stability and safe cataract surgery