Cataract surgery in the glaucoma population tends to be more difficult than conventional cataract surgery in many cases. There is a higher incidence of patients with small pupils. There are more patients with shallow anterior chambers. There is a higher rate of patients with small hyperopic eyes. Mature lenses are also frequently encountered. Pseudoexfoliation is present in glaucoma patients at a higher rate than in the non-glaucoma population. Problems with zonular integrity occur more frequently in this group, along with poor pupil dilation.

Many glaucoma patients have had prior surgery — either glaucoma or otherwise. Patients with prior intraocular surgery tend to have lower corneal endothelial cell counts, and patients who have undergone prior filtering surgery often have relatively high levels of astigmatism.

Traditional cataract surgery alone has a number of limitations in efficacy and safety, which can impact surgeon confidence. Complications in cataract surgery are currently 10 times that of LASIK, and predictability of visual outcomes is only half that of LASIK. Endothelial cell loss, vitreous loss, cystoid macular edema, endophthalmitis, and retinal detachment are risks associated with surgery. Also, improvements are needed in astigmatic correction, predictability of effective lens position, and presbyopic correction.^1,2

Benefits and Considerations

In laser-assisted cataract surgery, the phaco machine is still used to remove the lens, but studies³ show the laser can facilitate the procedure when used to make the capsulorhexis, corneal incisions, arcuate incisions, and can soften the nucleus.

The technology that makes femtosecond laser-assisted cataract surgery possible is the real-time OCT imaging of the anterior segment of the eye. The laser systems provide an image of the cornea, iris, and lens. This imaging allows for accurate placement of the laser incisions and provides information about anatomical placement not previously available in cataract surgery.⁴

Laser cataract surgery provides some significant advantages over traditional phacoemulsification techniques. Studies⁵ have shown that the anterior capsulotomy can be up to 10 times more precise than one created manually. The laser fragments the lens and softens the nucleus, which can significantly reduce the amount of ultrasound energy needed to remove the nucleus. Arcuate incisions for astigmatism correction can be very accurate and provide for very precise control of the depth, location, and length of the incisions. It is also possible to create intrastromal incisions.⁶

The corneal incisions used for the phacoemulsification portion of the case can be created with the laser in a very efficient manner. Because these incisions can be configured in real time in terms of location, length, and multiple dimensions, the end result can be better architecture and reproducibility compared with manually created incisions. Because the tissue planes are cleaner, the incisions may seal better as well.

In terms of economics, patients usually pay for a cataract procedure in which a femtosecond laser is used. Cost safe harbors are those situations in which a refractive IOL is used, as the more precise capsulorhexis can aid in IOL positioning. The other scenario that justifies the use of the laser is the presence of astigmatism, which supports a need for astigmatic incisions.

Another general concern is that of the incomplete capsulorhexis, though newer software decreases this risk compared with earlier versions. At the beginning of the phacoemulsification portion of the case, the surgeon should evaluate the continuous capsulorhexis edge and use a cystotome or forceps to confirm completion. The surgeon should not hydrodissect until confirmed complete or a radial tear may develop. If incomplete, the capsulorhexis can be completed with forceps or cystotome.

Another risk in laser-assisted cases is capsular block syndrome. This is more likely due to perfectly round capsulotomy, which results in no specific point for fluid to escape. “Fluffed-up” cortex at the capsulotomy edge may block fluid egress. Bubbles in the capsular bag already create intralenticular pressure and, as a result, excessive hydrodissection should be avoided.⁷

In eyes with small pupils due to pseudoexfoliation or other pathology, several considerations should be taken into account. Maximal preoperative dilation should be achieved. For example, 10% phenylephrine should be used for poorly dilating pupils. Preoperative NSAIDs may help to maintain dilation during the laser and phacoemulsification portions of the procedure.

During the laser portion of the case, the capsule diameter should be adjusted down to avoid coming within 0.5 mm of the iris, because laser application near the iris can cause further papillary constriction. The time lapse between the laser and phacoemulsification portions of the case should be minimized. Intraoperative Omidria (Omeros) should be considered to maintain and possibly dilate the pupil further.

Glaucomatous eyes that have undergone prior surgery present a challenge to using the femtosecond laser. There are concerns that preexisting filtering blebs can be traumatized by the suction and contact with the laser system. Remarkably, this does not seem to occur and blebs are left intact after the femtosecond laser phase of the procedure. The more common problem is in the context of large, overhanging filtering blebs that can interfere with achieving suction of the laser onto the cornea. The laser system can compress the bleb enough to achieve suction and fixation, but it is not uncommon to need extra manipulations to proceed.

Another issue that pertains to filtering surgery is the incidence of subconjunctival hemorrhage after the laser portion of the case. There are theoretical concerns that the conjunctival hemorrhage may result in trauma to the conjunctiva and buttonholes if filtering surgery is performed at the same time; however, this seems to be a low occurrence event. The hemorrhage may affect the amount of blood at the time of filtering surgery, but does not seem to impact the performance of the case or outcomes after surgery.

Subconjunctival hemorrhage does not appear to be an issue when performing a glaucoma drainage device tube procedure at the same time as the laser-assisted portion of the case. There may be more inflammation of the conjunctiva at the time of surgery, but there is no alteration in the integrity of the conjunctiva.

Another concern is whether a prior tube changes the effect of the laser. The femtosecond laser appears capable of working through a tube that is slightly long. If the tube is directly on top of the lens capsule, the capsulorhexis may be incomplete, and manual completion may be required.

In patients in whom a glaucoma procedure is to be performed at the same time as cataract surgery, the impact of that procedure on the refractive outcome must be considered. MIGS devices, such as the iStent (Glaukos) or CyPass (Alcon), appear to cause minimal changes on the astigmatism correction calculations. This holds true for related procedures, such as angle procedures (e.g., goniotomy), ab interno canaloplasty, or endoscopic cyclophotocoagulation. The latter group of procedures can cause some bleeding, inflammation, or corneal edema that may slightly delay optimal visual recovery.

More aggressive IOP-lowering procedures, such as filtering procedures using the Ex-Press (Alcon) shunt or a trabeculectomy, are more likely to induce refractive changes and cylinder than the MIGs procedures. Any glaucoma procedures that require suturing near the limbus induce the change of cylinder being introduced. Therefore, minimal suturing techniques are preferred in astigmatism-reduction cases.

The same holds true for cases with early IOP lowering. Certain procedures, such as trabeculectomy, are more likely to result in low IOP early in the post-op course. As a result, there may be a hyperopic shift that occurs in the refractive error. If there is anterior segment shallowing with a shift in IOL position, there may be a myopic shift in refraction.

Careful Planning

If the IOP is expected to be much lower after surgery, the effect of significant IOP lowering should be taken into account in the preoperative calculations. For this reason, MIGS procedures or MIGS-like procedures that create dramatic IOP changes are preferred, if possible. An advantage of the laser-created capsulorhexis in this situation is that the IOL is less likely to shift out of its position in the capsular bag, due to the preciseness of the opening created. The more stable refractive positioning may be a reason to consider laser-assisted cataract surgery in these cases.

Laser-assisted cataract surgery also requires additional planning if the procedure is to be performed in combination with angle-based surgery. The presence of arcuate incisions can alter the view of the angle when gonioscopy is performed. Arcuate placement planning should be done to move the incision away from the temporal aspect of the cornea so the view is compromised the least. This may mean that a larger nasal arcuate incision is placed versus two separate temporal and nasal arcuate incisions.

Care must be taken in planning the placement of temporal clear corneal incisions if angle surgery is to be done, as well. The laser-assisted incisions tend to seal a bit tighter than manual incisions and may result in a bit more local edema around the incision. These incisions can, at times, be more anterior in location than a manual incision. Therefore, careful pre-op planning should be done to ensure that the temporal incision does not significantly alter the view of the angle with the gonioscopy lens.

If it does appear that the incision created with the laser may be anterior or tight, consider performing the angle-based glaucoma procedure before the phacoemulsification portion of the case. This way, the view may be better and the MIGS procedure may be performed more easily. There does not seem to be any adverse effect on either portion of the procedures if the angle based surgery is performed first. The only drawback may be that the view of the angle isn't as open as it would be after the cataract is removed.

The other factor than can affect visualization is the presence of air bubbles created from the laser portion of the case. Use of viscoelastic to push the bubbles aside is important but in some instances, additional bubbles rise into the anterior chamber from the lens. If the gonioscopic procedure is performed first, then additional viscoelastic may be needed if more bubbles come to rest on the cornea during manipulation.

Evolving Technology

Femtosecond laser-assisted cataract surgery is an established but evolving technology that provides image-guided laser cataract surgery. It is computer-controlled and provides laser accurate incisions for the treatment of astigmatism. This technology can create improved capsulotomies in difficult eyes. Using the laser results in reduced phacoemulsification time and energy. It can be advantageous in many glaucoma patients who need cataract surgery.

At the same time, there are special considerations when performing laser-assisted cataract surgery on glaucoma patients undergoing combined operations. The impact of the laser portion of the case on angle viewing is most important. The impact of IOP lowering on refractive outcome must be considered, and the role of suturing in the glaucoma portion of the case must be taken into account in the calculation of astigmatism reduction.

As the glaucoma surgery landscape changes, more patients will be candidates for premium cataract surgery. This presents opportunities and challenges. Laser-assisted cataract surgery can provide excellent refractive results, but these may be more variable than those seen in patients who have not undergone previous glaucoma interventions. GP

References

1. Pereira AC, et al. J Cataract Refract Surg. 2006;32(10):1661-1666.
2. Park JH, et al. Ophthalmic Surg Lasers Imaging. 2010;41(2):236-241.
3. Grewal DS, et al. Surv Ophthalmol. 2016;61(2):103-131.
4. Palanker DV, et al. Sci Transl Med. 2010;2(58):58ra85.
5. Kránitz K, et al. J Refract Surg. 2011;27(8):558-5563.
6. Edwards KH, et al. Invest Ophthalmol Vis Sci. 2010;51(13):5394.
7. Roberts TV, et al. J Cataract Refract Surg. 2011;37(11):2068-2070.

Dr. Noecker specializes in the medical, laser, and surgical management of glaucoma and cataracts at Ophthalmic Consultants of Connecticut.