Article

Managing glaucoma and its comorbidities

Knowing the impact that cataract and ocular surface disease can have on treatment is crucial.

In North America alone, more than 3.3 million people ages 40 to 80 years old live with glaucoma, a number that is expected to grow significantly during the next 20 years.1 If you’re an anterior segment surgeon like myself, chances are you have either diagnosed or interacted with a glaucoma patient within the past week.

Now, think about how many of those patients had another condition, either pre-existing or diagnosed at the time of your exam. Whether systemic or ocular, patients with glaucoma frequently have other health issues, and many of these can impact the success of our treatment strategies.

In this article, I review the prevalence and impact of cataract and ocular surface disease (OSD), two of the more common ocular comorbidities, and present data on the importance of a comprehensive treatment approach.

GLAUCOMA AND CATARACT

Glaucoma and cataract are two of the leading causes of visual disability around the world, and the prevalence of both conditions tends to increase with age. It should come as no surprise, then, that a number of patients may suffer from both conditions. In a cross-sectional study of glaucoma patients, nearly a quarter of them (23%) had at least one visually significant cataract.2 The presence of a mildly visually significant cataract may seem innocuous to the unassuming observer but can have significant impact for the patient and the provider alike. As an example, consider the case of “Mrs. H.” She is a 67-year-old female who has been treated for glaucoma for the past 20 years but has been noticing her vision decrease only during the past year. Her visual acuity is 20/30 and IOP has remained stable at 19 mm Hg on three-bottle topical therapy. She is naive to ocular surgery and has the visual field shown in Figure 1. Certainly, Mrs. H has a glaucomatous visual field defect and it appears that there may be progression, but she also has a 2+ nuclear cataract and 1+ cortical change in that left eye. Where do we go from here, and how does the presence of cataract now affect our treatment plan?

Figure 1. Left eye visual fields of example patient. The present field is shown on the right and the prior field on the left, demonstrating progression of superior nasal defect and worsening mean deviation.

This is likely a familiar scenario that illustrates a few important issues in the management of patients with both cataract and glaucoma. From the patient’s perspective, a cataract can significantly impact quality of life. Both a visually significant cataract as well as reduced visual field index are directly related to worse quality-of-life scores among patients with glaucoma.2 In the case of Mrs. H, both factors are present, suggesting that intervention is likely warranted. From the provider’s perspective, it may be challenging to discern what, if any, of the visual field change is attributable to cataract development. Previous studies have shown that the cataract or lens opacity itself can lead to poor visual field testing or interpretation.3 This can result in underestimation or overestimation of visual field progression.4

Once the etiology of visual field change is determined, then comes the question of management strategy: cataract surgery alone, glaucoma surgery alone or a combined procedure? This is where it can get tricky. Cataract surgery alone is (or at least should be) considered a glaucoma procedure itself. In a recent Cochrane review, cataract surgery alone reduced IOP at one year by 1.0 to 5.8 mm Hg across available randomized trials,5 suggesting cataract surgery alone in our patient may not be unreasonable.

However, given the stage of glaucoma and possibility of progression, I would likely consider glaucoma surgery a priority. If the cataract was deemed not visually significant, glaucoma surgery alone could be considered. While this may also be a reasonable strategy for our patient, recent evidence has suggested that 50% of patients undergoing filtration or shunting procedures will progress to visually significant cataract within five years. What’s more, phacoemulsification following filtration surgery increases risk of bleb failure.6

Thus, in the case of Mrs. H, our 67-year-old patient, it may behoove us to consider cataract surgery at the time of surgical glaucoma intervention. We will discuss combined cataract and glaucoma surgery after we consider another common glaucoma comorbidity, which happens to be Mrs. H’s third problem.

GLAUCOMA AND OSD

In a recent survey aiming to evaluate the presence of OSD among glaucoma patients, dry eye was found in 16.5% of patients with glaucoma, compared with 5.6% of controls.7 Topical treatments of glaucoma (eg, prostaglandin analogues, beta blockers) likely have a leading role in this difference. Not only do patients on topical therapy report greater prevalence of OSD, but the intensity of their topical therapy (ie, drops/week x duration of treatment) correlates significantly with severity of OSD.8 Much of this effect has been attributed to toxicity of preservatives used in medication formulation, such as benzalkonium chloride (BAK), which can cause corneal and conjunctival epithelial disease along with corneal neurotoxicity.9 Though progress has been made regarding alternate preservatives and preservative-free options, this remains a major issue in the management of glaucoma.

Similar to the comorbidity of cataract with glaucoma, OSD in patients with glaucoma also negatively impacts quality-of-life scores and may be related to how often patients need to instill topical drops.10 Patients with more advanced glaucoma, and those requiring greater amounts of topical glaucoma therapy for adequate pressure control, have worse OSD and significantly worse quality-of-life scores.11

OSD in the setting of glaucoma isn’t just a patient’s problem, either. Like cataract, the presence of OSD alone can impact the reliability and results of visual field testing,12 further clouding the clinical decision-making process.

When it comes to surgical glaucoma management, OSD can play a major role in determining the success of therapy. Glaucoma filtering procedures dependent on bleb formation may be compromised by excessive conjunctival inflammation from OSD,13 and there is evidence that a bleb may worsen OSD.14,15 The mere presence of OSD may exacerbate glaucoma.16 However, reports surveying glaucoma specialists have found that fewer than half of us consider pre-operative OSD treatment as “necessary” before glaucoma surgery,17 and additional studies may be necessary to develop consensus on management strategy.

Now, let’s revisit the case of Mrs. H and her moderate-to-severe glaucoma. She has undergone topical treatment of her glaucoma for 20 years and has developed significant OSD and conjunctival injection secondary to chronic topical therapy (Figure 2). Circling back to our previously outlined treatment decisions for Mrs. H’s glaucoma and cataract, does the presence of moderate OSD impact our surgical strategy? Regardless of surgical approach, I think that ocular surface optimization is important for surgical success of not only the glaucoma intervention but also the cataract surgery. Addressing instability in the tear film, abnormality in tear osmolarity or staining of the ocular surface should be considered before planning surgery. Trabeculectomy with phacoemulsification could be considered in this case, given the severity of the disease and the likely necessity of achieving low IOP. However, if her surface inflammation is a risk factor for scarring, and the trabeculectomy may exacerbate her OSD, a bleb-based procedure may not be the best initial route. Instead, this may be an ideal time to consider a minimally invasive glaucoma surgical (MIGS) procedure.

Figure 2. Left eye slit lamp image of example patient. Notice the dense epitheliopathy present near the pupil center and erythematous lid margin.

WHY MIGS MAY BE IDEAL IN OSD

MIGS procedures vary widely in cost, effectiveness and safety. While a full discussion of the MIGS arena is beyond the scope of this article, one thing that unites this class of procedures is the ability to combine the procedures with cataract surgery with little additional risk. Because most of these options are angle based, they can be performed via the same cataract incision and do not create a bleb (this statement excludes Allergan’s Xen, an ab-interno bleb-based procedure that many consider a MIGS).

Another pertinent factor is that, while these procedures may not pack the same IOP-lowering punch as a filtering surgery, most demonstrate moderate efficacy in IOP control, reduce topical glaucoma medications18 and do not limit our ability to perform bleb-based surgery in the future. The ability to reduce glaucoma drop burden in Mrs. H’s case is extremely appealing.

When I discuss glaucoma management options with patients like Mrs. H, I try to stay unbiased and involve patients in the decision-making process, explaining risks and benefits to each procedure and managing expectations. For any patient I am considering as a MIGS candidate, I explain that the goal is better IOP control and maintenance of vision and that, while it’s possible we may stop one or more drops after surgery, I usually consider that a bonus.

In a patient like Mrs. H, I might also combine one or more MIGS procedures (ie, target the trabecular meshwork with one and Schlemm’s canal and collector channel dilation with another) in an attempt to increase our odds of reducing medication burden. Lastly, it is also important to discuss cost with patients. We, as surgeons, should make an effort to help them understand what their insurance may or may not cover.

SUMMARY

As if glaucoma management was not complex enough, ocular comorbidities like cataract and OSD may compound the challenges of management for patients and providers alike.

As we have learned more about the interplay of glaucoma’s common comorbidities and their impact on our patients, we understand the necessity of a comprehensive approach to glaucoma management, which should involve consideration of new techniques and technologies. OM

REFERENCES

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