Treatment of severe glaucoma requires focus on IOP, visual field
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In the United States, we are now required by the ICD-10 system of coding to provide a seven-digit code when billing for glaucoma.
The seventh digit describes the severity of the glaucoma as unspecified (0), mild (1), moderate (2), severe (3) or indeterminate (4). It is no longer good enough to simply describe the glaucoma as open-angle glaucoma unilateral or bilateral, as we did in the ICD-9 era. We must also code the severity to get properly reimbursed and justify our diagnostic and therapeutic recommendations as well as our frequency of patient examinations.
There are many classification systems for glaucoma severity, and fellowship-trained glaucoma specialists can and do argue at length about which is most useful. However, there is only one system that is accepted by payers in the U.S. and Europe, and that is the International Classification of Diseases (ICD) staging of glaucoma. In the ICD glaucoma staging system, visual field findings are primary, along with some examination of the optic nerve. OCT testing is not required nor considered. In addition, other risk factors we clinicians consider significant, including IOP level, patient age, patient race, family history, comorbidities such as diabetes, hypertension and hypotension, prior ocular surgery, corneal thickness, and a host of others, are not considered.
Using ICD-10 staging, mild glaucoma has optic nerve changes consistent with glaucoma but no visual field defect on a standard white-on-white automated perimetry. In moderate glaucoma, the visual field demonstrates a defect in one hemifield not within 5° of fixation. This is usually the classical nasal step or Bjerrum arcuate scotoma in one hemifield only. In severe glaucoma, we have a visual field defect in both hemifields or a visual field defect in one hemifield along with a visual field defect within 5° of fixation. Every eye care professional must understand this classification system as it applies to every form of glaucoma because it is required for proper billing and reimbursement and to justify our choice of diagnostic or therapeutic options and appropriate IOP level targets.
The accompanying cover story is focused on severe glaucoma. A few personal thoughts. In severe glaucoma, the measured IOP and visual field become the most important measurable variables to follow. At the severe glaucoma stage, optic nerve damage is advanced enough that OCT is often no longer useful to detect progression. Because central visual field findings become more important in severe glaucoma, a 10-2 visual field test may be more informative in some patients.
In general, patients with severe glaucoma require a lower target IOP. While every mm Hg of IOP reduction matters in glaucoma, I think of IOP targets in 3 mm Hg increments, as this represents one standard deviation of IOP. With 15 mm Hg approximating the mean IOP in an American patient, I like to use IOP targets of 7 mm Hg to 9 mm Hg, 10 mm Hg to 12 mm Hg, and 13 mm Hg to 15 mm Hg in patients with severe glaucoma.
Achieving this low level of IOP with medical therapy nearly always requires multiple topical medications. I find compliance is related to the number of bottles and eye drops required per day, not the number of active pharmaceutical ingredients (APIs) utilized. I am also an advocate of reducing preservative toxicity as much as possible. Because I am comfortable with compounded eye drops from a quality 503B specialty manufacturer, I can provide five APIs in two bottles, one non-preserved. The first bottle, available from Imprimis, contains non-preserved timolol, brimonidine and dorzolamide and is used twice daily. The second bottle, available from Aerie/Alcon, contains netarsudil combined with latanoprost (Rocklatan) and is used once at night. This two-bottle, three-drop-a-day regimen with five effective APIs represents my maximum topical medical therapy and is manageable for most patients. Unfortunately, medical therapy is often incapable of achieving the target IOPs required to stop progression in patients with severe glaucoma, and surgery is often required.
As I reflect on my decades treating patients with severe glaucoma, I believe my patients benefited most from two actions. First, early referral to an experienced, fellowship-trained glaucoma specialist. Second, early surgery, occasionally minimally invasive but often the more invasive trabeculectomy, tube shunt or even cyclodestructive procedure alone or in combination. Patients with severe glaucoma are difficult to manage by even the most experienced clinician and often progress despite aggressive therapy. These patients deserve and require our best effort.
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