Article

IOL selection in the glaucoma patient

We must take the patient’s disease state into account prior to cataract surgery.

Worldwide, cataract (51%) and glaucoma (8%) are the leading causes of blindness.1 In the United States, about 2% of the population over 40 years old has glaucoma.2 As a result, ophthalmologists often perform cataract surgery in patients, primarily the elderly, who have glaucoma or are glaucoma suspects.

However, glaucoma presents a challenge for the surgeon who needs to decide which intraocular lens technology to offer the patient. Although IOLs continue to improve in their ability to allow patients to achieve many uncorrected vision goals postoperatively, these lenses sometimes require optical compromises, such as reduced contrast sensitivity, that are ill-suited for glaucoma patients. Of course, glaucoma itself causes loss of contrast sensitivity, often early in the disease.3,4 This loss appears before a decline in high-contrast Snellen visual acuity but is clinically and functionally significant.5,6

Patients with glaucoma rely on the surgeon to take their disease status into account, so we have a medical and ethical obligation to make recommendations that are in their best interest.

Here I discuss the IOL options for glaucoma patients undergoing cataract surgery.

TORIC IOLS

Monofocal toric IOLs do not reduce contrast sensitivity, so I believe they are appropriate for almost all patients, including those with glaucoma. One exception would be a patient who will have a combined phaco-trabeculectomy because of the unpredictable change in cylinder induced by the glaucoma surgery.7,8 However, if a patient already had a trabeculectomy and is phakic, then using a toric IOL to correct the resulting astigmatism is certainly fine. Patients with extremely advanced glaucoma also might not appreciate the benefit of astigmatism correction. Fortunately, this is a rare situation that essentially applies to glaucoma that has already affected central vision.

Pseudoexfoliation presents a potential problem because zonulopathy can affect success of a toric IOL in two ways. First, it can complicate the surgery itself, making it impossible to place a toric IOL safely. Second, a late IOL dislocation would obviously degrade the visual performance of any IOL.

During my preoperative conversation with patients with pseudoexfoliation, I discuss both of these issues and mention that we might not be able to place the originally intended lens if there are problems during the surgery or if I think the zonules are too weak. If a toric IOL cannot be placed successfully, the patient still has the option of laser vision correction as a secondary procedure.

CRYSTALENS/TRULIGN

Because the Crystalens/Trulign (Bausch + Lomb) is not designed with diffractive optics, it does not diminish contrast sensitivity as much as other presbyopia-correcting IOLs.9 That means that it could be an option for patients with mild, well-controlled glaucoma who are highly motivated to decrease their use of glasses, although I use this platform very infrequently.

The floppy haptic-optic junction makes this IOL susceptible to Z syndrome even in normal eyes.10 For that reason, I would not use this platform in a patient with zonular issues such as pseudoexfoliation because I worry about the potential for phimosis, decentration and tilt.11,12 Unfortunately, I have seen multiple cases in which a CTR failed to counteract the centripetal forces that destabilized a Crystalens.13

MULTIFOCAL IOLS

My general approach in evaluating a preoperative cataract patient is to look for reasons not to implant a multifocal IOL. Only after a patient has “qualified” with reasonable astigmatism, few higher-order aberrations (especially coma), normal-appearing zonules, a perfect macula and a normal optic nerve would I suggest a diffractive multifocal like the Restor (Alcon) or Tecnis (Johnson & Johnson Vision).

I do not recommend using a multifocal IOL for patients with definite glaucoma, no matter how early or well-controlled. The additional loss in contrast sensitivity caused by the lens optics makes the risk of poor quality vision and patient dissatisfaction too high for me.14-17 Furthermore, multifocal IOLs may affect the ability to monitor and treat glaucoma because they change visual field testing even in healthy eyes.18

EDOF (SYMFONY) LENS

In my experience, the Symfony (Johnson & Johnson Vision) lens provides more consistent range of vision than the Crystalens/Trulign, with the trade-off being more night vision symptoms. Although its modulation transfer function with a 5-mm pupil is the same as the Tecnis monofocal IOL, the Symfony IOL shows a loss in contrast sensitivity with the more physiologic 3-mm pupil. The Symfony attempts to improve contrast by correcting chromatic aberration.19

I generally feel comfortable using the Symfony in patients who are glaucoma suspects or who have ocular hypertension. If a patient has very early glaucoma that is well-controlled and documented to be stable, I might consider the Symfony if that person is extremely motivated for spectacle independence.

Although I feel very comfortable with doing an IOL exchange, I worry about problems with quality of vision and contrast sensitivity later on if the glaucoma progresses. By this point, the patient may have already had YAG capsulotomy, which totally alters the risk-benefit calculation of a IOL exchange. If considering a Symfony, I would discuss the potential issues with quality of vision and contrast sensitivity at length preoperatively.

Again, I am careful about this lens in someone with pseudoexfoliation or other zonulopathies. Although the Symfony is more forgiving than a multifocal IOL, decentration still can lead to visual symptoms, and the high amount of negative spherical aberration in the Tecnis IOL will induce higher-order aberrations if the IOL is not well centered.

Minimally invasive glaucoma surgery (MIGS)

I currently use the Kahook dual blade (New World Medical) and iStent (Glaukos). I offer a MIGS procedure to almost every patient undergoing cataract surgery who is a candidate (on pressure drops with mild to moderate open-angle glaucoma without a prior trab or tube). This includes performing MIGS on patients who receive a toric IOL.

MONOVISION

If a patient has been happy with monovision, I almost always maintain it after cataract surgery. This is an excellent option for patients with glaucoma because it does not result in any reduction in contrast sensitivity or night vision problems.20 However, I only recommend monovision if a patient has already tried and liked it.

If the glaucoma progresses, then the resulting larger visual field defect may reduce the effectiveness of monovision. Of course, if that happens, correction with glasses or contacts can always get both eyes working together for distance and near.

CONCLUSION

Counseling patients with glaucoma before cataract surgery requires the ophthalmologist to balance multiple goals. First, of course, is safety, meaning that we should avoid strategies that provide unacceptable risk of patient dissatisfaction. At the same time, patients should not be deprived of reasonable options for best postoperative uncorrected vision simply because they have glaucoma.

As IOL technology continues to improve, we will hopefully be able to offer even more range of vision without having to make optical trade-offs. OM

IOL REFERENCES

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  19. Tecnis Symfony Extended Range of Vision IOL Directions for Use. 2016.
  20. de Silva SR, Evans JR, Kirthi V, et al. Multifocal versus monofocal intraocular lenses after cataract extraction. Cochrane Database Syst Rev 2016 Dec 12.

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