Supplements Managed Care Issues in Glaucoma: Emerging Trends and Treatment
Current Management of Glaucoma and the Need for Complete Therapy
Glaucoma is a long-term ocular neuropathy defined by optic disc or retinal nerve fiber structural abnormalities and visual field abnormality. Primary open-angle glaucoma is the most common type of glaucoma. Currently available treatments, initiated in a stepwise process, focus on intraocular pressure (IOP) reduction, and initially include topical drug therapy (single then multidrug combinations), followed by laser then surgical treatment. Topical prostaglandin analogues or beta-adrenergic receptor blockers are first used, followed by alpha-agonists or topical carbonic anhydrase inhibitors, and infrequently, cholinergic agonists and oral therapy. Limitations to existing topical IOP-reducing medications include continued disease progression in glaucoma patients with normal IOP, treatment failure, and low rates of compliance and persistence. Therapeutic agents under investigation include neuroprotectants, which target the disease process manifested by death of retinal ganglion cells, axonal loss, and irreversible loss of vision. Neuroprotectants may be used alone or in combination with IOPreducing therapy (a treatment strategy called complete therapy). Memantine, an N-methyl-D-aspartate receptor blocker currently approved for dementia, is the neuroprotectant farthest along in the process seeking regulatory approval for glaucoma treatment and has a favorable safety profile because of its selective mechanism of action. Several other neuroprotectants are in early stage investigation. Complete therapy provides hope for improved outcomes by reducing the significant morbidity and economic consequences that occur as a result of neurodegeneration and disease progression.
(Am J Manag Care. 2008;14:S20-S27)The definition and management of glaucoma have changed substantially over the past 3 decades, but several evolving treatment paradigms have not yet moved into clinical practice.1 These include a widespread recognition that glaucoma is a neuropathy of the optic nerve rather than a disease of elevated intraocular pressure (IOP) as well as a diminishing reliance on a minimum IOP as the primary treatment goal.2 Advances in the study of glaucoma neuroprotectants have made these issues more clinically relevant.
Significance of Glaucoma to Managed Care
About one half of the 2.2 million Americans with open-angle glaucoma are unaware of their disease, since they do not have ocular or systemic symptoms.3-5 The visual impairment resulting from progressive glaucoma is irreversible.6 Loss of peripheral vision, depth perception, and contrast sensitivity associated with this optic neuropathy can have a major effect on an individual’s life.7-12 For example, injuries from automobile accidents and falls because of visual impairments are greater in patients with glaucoma.13-15 End-stage glaucoma is associated with appreciable resource utilization and costs because of the need for both vision rehabilitation and ophthalmology care.16 Glaucoma patients may also be at increased risk for depression.17 These factors may lead to increased costs of care for managing glaucoma as well as for concomitant morbidities.
Despite abundant evidence that early detection and optimal management of glaucoma are the best ways of preserving sight and reducing economic consequences,18,19 the National Committee for Quality Assurance (NCQA) reports that approximately 40% of Medicare beneficiaries enrolled by participating plans do not undergo screening for glaucoma.20 Moreover, as agents used to treat ocular conditions constitute a relatively small proportion of overall pharmaceutical spending, ocular conditions and ophthalmic products remain one of the least managed areas of pharmaceutical care.21
To address these disparities, several health policy and quality-ofcare initiatives have recently been implemented. These include the 2005 Health Plan Employer Data and Information Set measure for glaucoma screening22; expanded glaucoma-specific preventive benefits for Medicare beneficiaries23; and specific glaucoma prevention, detection, and management objectives in Healthy People 2010.24 Glaucoma is primarily a disease of aging,6 and this population is increasingly being covered under managed care plans as a result of the advent of the Medicare Modernization Act of 2003 (known as Medicare Part D). Therefore, managed care decision- makers are reprioritizing glaucoma as a disease that is being actively managed for their covered population.
This article will review the current treatment options for the most common type of glaucoma, known as primary open-angle glaucoma (POAG), explore the rationale for new therapies directed at preventing vision loss (neuroprotectants), and describe a new paradigm in managing POAG using complete therapy directed at the full pathophysiology of the disease.
Clinical Controversy: Beyond IOP
POAG is a long-term ocular disease process that is generally bilateral and often asymmetric.2 It is defined by optic disc or retinal nerve fiber structural abnormalities and visual field abnormality as detected by optic disc examination and visual field testing.1,2 The most definitive evidence of glaucoma is documented, progressive change in optic disc appearance and reproducible worsening in automated visual field testing.1 Structural alterations of the optic nerve or nerve fiber layer more frequently occur prior to visual field abnormalities or visual defects, although the opposite may be seen.25
There is strong evidence that IOP plays an important role in the neuropathy of POAG,2,26-28 and it has been shown that a reduction in the level of IOP lessens the risk of visual field progression in open-angle glaucoma.29-32 Previously, an IOP of more than 21 mm Hg in adults was generally accepted as being significantly raised.33,34 In the Advanced Glaucoma Intervention Study associative analysis, patients with 100% of their visits with IOPs less than 18 mm Hg over 6 years had mean changes from baseline in visual field defect score close to zero during follow-up, whereas patients with less than 50% of visits with IOPs less than 18 mm Hg had an estimated worsening over follow-up of 0.63 unit of visual field defect score (P = .083).35 More recently, a minimum IOP target level has been replaced by the goal to lower IOP by a percentage reduction from baseline, typically 25% to 30%, or even greater when there is substantial damage already present in the visual field.36 Therefore, there is no IOP maximum level criterion used in the definition of open-angle glaucoma.2
The relationship between elevated IOP and glaucomatous optic neuropathy is highly variable,2 and there are unresolved questions regarding the relationship between IOP control and visual field damage. Up to 10% of patients with elevated IOP show signs of visual field loss,37 and up to 61% of patients with low IOP (≤21 mm Hg) show glaucomatous disc and vision field changes.26,37-39 Additionally, there is an ongoing controversy regarding which aspect of IOP is most important in progression: mean IOP over time, fluctuation (diurnal vs visit-to-visit) of IOP over time, or peak pressure over a designated level.29,35,40-43 Further challenging reliance on IOP levels is the fact that population-based screening for glaucoma using IOP measurement is not clinically or cost-effective because of low sensitivity and specificity of the test.44 About half of all individuals with POAG have IOP levels less than 22 mm Hg, the usual screening cutoff.45
However, the practice of glaucoma screening routinely combines direct examination with IOP measurement.2,46 A Netherlands-based Markov cost-effectiveness simulation model of patients aged at least 40 years visiting an ophthalmic practice (where all patients were subject to ophthalmoscopy, but tonometry was performed on (1) all initial patients, (2) high-risk patients only, or (3) no one) found it most cost-effective to routinely perform tonometry to all initial ophthalmic patients to prevent blindness as a result of glaucoma.47 Moreover, a US-based cost-effectiveness model of screening at-risk members demonstrated a positive return on investment for commercial and Medicare managed care populations.48 These cost-effectiveness data further support the rationale for the Medicare glaucoma screening benefit and the NCQA biannual requirement of glaucoma screening for Medicare members aged 65 years and older.22,46
Current Treatment Options
These clinical debates have led to a reassessment of the role of the current treatment options for glaucoma directed at lowering IOP as well as consideration of the need for glaucoma therapies that address the optic neurodegenerative disease processes. Clinical practice guidelines for POAG have been developed by the American Academy of Ophthalmology (AAO),2 although several recent studies have indicated low compliance with these guidelines in various practice sites.49,50 The treatment goals, according to the AAO practice guidelines (2005), include achieving stable optic nerve or retinal fiber layer status, controlled IOP, and stable visual fields while maintaining quality of life.2 Treatment plans are often difficult to implement because the disease is frequently asymptomatic, long term, and typically requires multiple medications.51
The AAO Preferred Practice Pattern notes that laser trabeculoplasty is an appropriate initial therapeutic alternative (Evidence A-I) to topical medications. 2 However, most clinicians initiate with medical therapy, followed by laser, filtering, and cyclodestructive surgery (alone or in combination), and the stepwise process reflects the safety and efficacy of the treatments for the individual patient.2,52
Conventional treatment within typical clinical practice usually begins with the use of topical antiglaucoma medications, with an initial trial in the eye with higher IOP. Pressure measurements are taken, and the clinician attempts to distinguish between therapeutic impact and normal IOP fluctuation. 53 Multiple drug classes may be used, generally added sequentially for their complementary contribution to IOP reduction.2 Examples of eyedrops for first-line therapy include topical cardioselective, beta1-adrenergic (eg, betaxolol) or noncardioselective beta-adrenergic (eg, timolol, levobunolol, metipranolol, carteolol) receptor blockers, or topical prostaglandin analogues (eg, latanoprost, bimatoprost, travoprost, unoprostone).2 Beta-blockers, which reduce IOP by decreasing aqueous humor formation in the eye, are used as first-line treatment because they have relatively few ocular adverse effects, can be used once or twice daily, and do not affect pupil size or accommodation. They may have ocular, respiratory, cardiac, and certain central nervous system side effects.53 Prostaglandin analogues are highly potent at reducing IOP by increasing aqueous humor outflow in the eye. They have few systemic side effects, can be used once daily while maintaining good 24-hour control, and do not affect pupil size or accommodation, although they do have certain adverse ocular effects (eg, iris pigmentation changes, eyelash hypertrichosis, and ocular inflammation). Prostaglandin analogues (specifically bimatoprost, latanoprost, and travoprost) have been shown to be superior, or at least as effective, in reducing IOP as timololol, the gold standard (2003).54-60 In addition, they are theoretically more effective for prevention of acute IOP spikes because of their mechanism for increasing aqueous humor outflow rather than suppressing production.61
Second-line treatments include alpha-agonists (eg, brimonidine) and topical carbonic anhydrase inhibitors (eg, dorzolamide, brinzolamide). They are typically administered 2 to 3 times daily and have few systemic side effects, but they may cause ocular irritation. Alpha-agonists work by increasing uveoscleral outflow of aqueous humor,61 and the newer, more specific alpha2 agonists (eg, brimonidine, apraclonidine) have fewer systemic hypotensive side effects than earlier alpha-adrenergic agonists. Brimonidine is used for long-term sustained therapy, whereas apraclonidine is most useful for short-term adjunctive use.61 Carbonic anhydrase inhibitors decrease aqueous humor production via enzymatic inhibition.61 These may replace or be added to beta-blocker or prostaglandin analogue therapy to further lower IOP.2,52 Combination drugs (eg, beta-blockers with a carbonic anhydrase inhibitor, alpha-agonists, or a prostaglandin analogue) may be used to improve compliance.62