Compliance with Medical Management in Glaucoma

I Goldberg
Sydney Eye Hospital and Save Sight Institute
Sydney, Australia

Non-compliance with medical therapy has long been recognised as an important limiting factor in the medical management of many chronic diseases.^1,2 Patients with glaucoma who have lower rates of compliance are presumed to be at greater risk of developing progressive visual loss³ and van Buskirk suggests that the problem of non-compliance is "a leading cause of glaucoma blindness".⁴

Medical therapy is a cost-effective strategy that can reduce the need for surgery.⁵ However, poor compliance can adversely affect an individual's response to therapy since erratic dosing intervals can diminish the effect of a drug or increase adverse effects.⁶ Rates of compliance with therapeutic regimens for chronic disease may be as low as 50% and non-compliance has been associated with an increase in hospital admissions, length of stay, and health care costs.⁷

Non-compliance may be minimised through an understanding of the reasons patients have for failing to adhere to therapy.⁸ Compliance may vary depending on the type of illness and treatment, or even on a daily basis for a single individual. Patients may misunderstand the instructions, become confused about medications, or simply make inadvertent errors when trying to follow the schedule. Complex treatment regimens are associated with non-compliance;⁵ since the risk of chronic disease often increases with advancing age, compliance in older patients may be further complicated by additional therapies for concomitant illness.

Factors Affecting Compliance

In recent years, many studies, both in general medicine and ophthalmology, have been performed to assess the impact of non-compliance on disease progression. While non-compliance is recognised as being difficult to determine with any certainty, Weintraub estimates that 10% to 25% of patients take none of their prescribed medication, some of whom do not even fill their prescriptions.⁹ Approximately 25% to 35% of patients comply almost 100% with therapy, while a few people may even take more than the prescribed dose. The largest group are the partial compliers, who establish their own schedules.

Not surprisingly, the compliance rate is lower with suppressive or preventive medication than with treatment for acute symptomatic illness.⁶ Compliance also seems to depend more on a given situation than on individual tendencies. The reasons most frequently given for non-compliance include feeling better, carelessness, insufficient money to fill the prescription, misunderstanding of directions, not feeling better, or side effects.

In addition, compliance studies have correlated non-compliance with psychiatric illness, complex therapeutic regimens, side effects, missed appointments, inappropriate health beliefs, increased waiting times in outpatient clinics, unfavourable impression of the doctor, and family instability.

Measurement of compliance is difficult and may not always be correct. For example, a patient history may not always be accurate, drug serum concentrations may suggest regular medication use when the drug is only taken shortly before the test, and pill counts show only the total pills taken but not the dosing interval.⁷ The Medication Event Monitoring System (MEMS; Aprex Corp., Fremont, CA, USA) enables compliance studies to register accurately the pill-taking habits of individual patients in terms of the number of daily doses taken and how closely the prescribed schedule is followed.

Table 1. Overall Compliance rate with anti-epileptic drug use by dosing regimen⁷

Using MEMS containers, Cramer et al. were able to observe the compliance of 24 anti-epileptic drug users. 5599 of 7413 drug doses (76%) were taken as prescribed, with the compliance rate declining with increasing dosing frequency (table 1).⁷ The average pill count was 92%, with a range of 59% to 108%, indicating that some patients took more doses on some days and fewer on others. Five patients had at least one seizure associated with missed doses. These researchers concluded that despite the "medically dangerous consequences", patients with epilepsy took only 76% of their medication as prescribed.

Compliance in Glaucoma

If left untreated, glaucoma may result in increasing damage to the optic nerve, causing a reduction in visual field and, eventually, blindness,⁵ yet a major barrier to the successful treatment of glaucoma is poor patient compliance with the treatment regimen.¹⁰ Since glaucoma produces few symptomatic signs, there is little desire for patients to continue treatment, particularly when, prior to late complications such as visual field loss, the only symptoms may be the side effects of the medication.⁶ The aim of therapy for glaucoma is to preserve vision with minimal side effects and inconvenience.¹¹

A major determinant of compliance with glaucoma medication is a patient's awareness of having glaucoma and the potential for blindness the more serious their visual loss, the more likely it is that patients will take medication as prescribed.⁶ In addition, patients who miss follow-up appointments are more likely to misuse their medication. Non-compliance is further hindered by the physical inability of patients to use eye drops adequately, with difficulty aiming the drop, expelling the drop and blinking on insertion frequently being reported.¹² Technical difficulties are termed 'dyscompliance'.

Judgements about patient compliance, and therefore alternative treatments, are often based on clinical assessments and measurements of intraocular pressure (IOP), pupillary diameter and reactivity to light, weight of eye drops used from a bottle, patients' reports, and the physician's subjective impression of the patient.³ However, IOP and pupillary diameter have a low correlation with compliance with glaucoma treatment and pupillary response to light has a modest correlation. Similarly, non-compliant patients are not identified reliably by daily treatment records, questionnaire, or measuring the weight of the eye drops used. In addition, there is only a modest correlation between the physician's predictions about patient's compliance and the results of monitoring. Since none of these measures accurately indicates patients' compliance, an eye drop monitor is required for identification of patients who default from therapy.

Table 2. Summary of compliance by eye drop monitor and by patient report¹³

Figure 1. Distribution of compliance with topical pilocarpine treatment as reported by the patients and recorded by the eyedrop monitor.

Using an unobtrusive eye drop monitor as an objective measure, Kass et al. found considerable over-reporting of compliance with glaucoma medication in an interview situation (table 2).¹³ Patients administered a mean of 76% of the prescribed dose, with 6% of patients taking less than one quarter of their prescribed medication, and 15.2% taking less than half. However, when interviewed, the patients reported taking a mean of 97.1% of the prescribed dose (figure 1). This result suggests that patients are either unaware of their poor compliance or may fear a reprimand if they admit to taking medication incorrectly.