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Cataract surgery in patients with diabetes poses challenges
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Diabetes mellitus affects 285 million people worldwide, and the number of people afflicted is expected to double in 10 years. The majority, 90%, have type 2 adult-onset diabetes mellitus, which is secondary to insulin resistance exacerbated by our Western diet and more sedentary lifestyle. Type 1, or juvenile-onset diabetes mellitus, is caused by a lack of insulin and generally represents a more severe disease. A small number of cases occur during pregnancy or are associated with medication side effects and the like. The long-term effects of diabetes mellitus, especially in the face of poor glucose control, are manifest in damage to the capillary vascular structure, resulting in fluid and protein leakage and ischemia. Thus, the hallmark renal and retinal findings.
In the early stages of diabetic retinopathy, visual symptoms are absent. It is estimated that more than 50% of patients with diabetic retinopathy are unaware of its presence. Thus, the importance of an annual eye examination in every diabetic patient to screen for diabetic retinopathy.
The symptoms of diabetic macular edema, which significantly affects vision, overlap significantly with those of cataract. DME, much like cataract, results in painless, progressive loss of vision, blurring and occasionally diplopia. Metamorphopsia is more unique to macular pathology, but one cannot differentiate loss of vision from cataract or DME based on symptoms.
The treatment of cataract in the diabetic patient presents today an interesting combination of new challenges and new opportunities. First, we cataract surgeons must be sure to diagnose pre-existing DME, as it is almost always, at least initially, made worse by cataract surgery. Careful fundus examination is critical, but subtle DME is easily missed.
Through the years, many adjunct tests have been developed to help measure the “macular visual potential,” including simple devices such as super pinholes and macular photostress testing, to the more sophisticated potential acuity meters and laser interferometers. Unfortunately, all of these tests, including fundus examination by the most expert, can miss subtle DME, which can be diffuse or discrete, as well as central or paracentral.
For me, optical coherence tomography is the answer. Fluorescein angiography is also an alternative, but I find OCT to be the answer for screening the cataract patient for DME. The fact is, it is getting harder and harder for the anterior segment surgeon who treats cataract and glaucoma to practice without OCT.
In the cataract patient with diabetes mellitus and no evidence of DME, there is significant risk of inducing it by surgery. Counseling and prophylactic treatment make sense, but knowledge is lacking regarding the ideal therapeutic approach. Good evidence is accumulating, including outcomes from one prospective randomized clinical study in Europe to support preoperative and postoperative topical steroid and NSAID drops in the patient with cataract and diabetes mellitus to reduce the incidence of DME.
There is no definitive evidence to support any specific length of preoperative or postoperative therapy. I start 1 week preoperative in high-risk patients and monitor with postoperative OCT to help me determine duration of therapy, which for me extends at least 4 weeks, and usually 6 to 8 weeks. Others use intraoperative subconjunctival or even intravitreal steroids and some intravitreal anti-VEGF drugs routinely. We need more evidence to help guide our therapy in this area. In the cataract patient in whom preoperative OCT demonstrates evidence of DME, I engage a retina specialist in his or her care before and after surgery.
As discussed in the cover story in this issue, treatment approaches are evolving, but in our city, intravitreal anti-VEGF before surgery with the goal of operating with a dry macula is favored. Then, preoperative and, in most cases, prolonged potent postoperative topical steroids and NSAID drops with careful monitoring. Additional intravitreal anti-VEGF, steroid or focal laser is applied as indicated by the retina specialist. More frequent follow-up, monitoring for steroid-induced glaucoma and the higher potential for a poor outcome make the patient with cataract and diabetes mellitus a challenge. Better diagnostics, especially OCT, and many new potential therapies are improving outcomes, but we have much to learn regarding the ideal therapeutic plan. For me, close collaboration with a retina specialist is extremely helpful.