Untreated glaucoma is a chronic, progressive condition leading to visual field loss and risk of blindness. The majority of glaucoma damage is preventable with appropriate therapy [1–3] and the mainstay of treatment is eye drops to reduce intraocular pressure (IOP) . Non-adherence to therapeutic regimens is associated with a reduction in treatment benefit  resulting in additional health service costs through changes to prescribed medication requiring additional follow-up of efficacy, wastage of unfinished pharmaceutical supplies, or the costs of surgery that may have been avoidable . If surgical treatment is required, there is also the increased risk of associated adverse effects.
Patient non-adherence with anti-glaucoma therapy is poorly understood with reported rates between 5% and 80% . Historically, non-adherence has been categorised as intentional or unintentional, but the ultimate behaviour is often an amalgam of these factors . Unintentional non-adherence is a passive process that prevents use of medication as intended by the prescriber, such as forgetfulness, poor comprehension of dosing regimen or physical inability to self-administer medication. Intentional non-adherence is a deliberate decision by the patient to deviate from the prescribed recommendations by not taking medication, reducing the dosing frequency or premature discontinuation.
According to UK national guidance , a typical care pathway involves referral to a specialist glaucoma clinic for diagnosis by standard glaucoma examination, followed by long-term monitoring, with treatment if indicated, according to risk of disease progression. Provision of information for patients, carers and family members is usually offered by the diagnosing clinician.
Poor glaucoma education has been cited as an explanation for non-adherence to therapy [9–17] however, the magnitude and nature of any association is not consistent. A semi-structured educational session reported by Sheppard et al.  identified an improvement in participant knowledge but no significant difference in adherence between intervention and control groups. Sheppard’s findings may, in part, be attributable to the small sample size (n = 73), short follow-up (12 weeks) and failure to ascertain the fidelity of intervention delivery by nurses.
Studies related to oral anti-hypertensives have found that education alone is ineffective in improving adherence [18, 19] and similar outcomes have been reported with glaucoma. Three studies using education alongside an individualised care planning programme have demonstrated an improvement in adherence [11, 16, 17].
A study of a 30 minute education and tailoring program (n=73) reported by Norell et al. , detected a positive, significant improvement in adherence. Norell’s educational component was similar to other reported studies, however, the additional ‘one to one’ tailoring program allowed the patient to consider and discuss strategies for incorporating the medication administration into daily activities; the study findings were limited by a short follow-up (20 days), no estimate of sustainability of intervention effect and no estimate of intervention cost.
One method to overcome the issue of assuring fidelity is to use standardised information. A web-based glaucoma education and support intervention study , used links to information on the internet for participants to access independently. Whilst information provision was standardised, participants controlled how much and what information they chose to access based upon personal requirements. The study failed to significantly improve adherence  which may partly be attributable to the absence of direct contact with healthcare team members, as non-adherent participants are more likely to feel that insufficient time is devoted to them by their healthcare team .
It appears that the influence of both intentional and unintentional factors and complexities of non-adherent behaviour may explain the failure of purely educational interventions to achieve significant adherence improvement. A Cochrane review of adherence interventions  concluded that effective adherence interventions were complex in nature which may explain the success of the Norell et al. education and tailoring program [11, 22] relative to simple educational interventions. The Norell et al. approach of using glaucoma assistants rather than written or IT based techniques is also supported by research which has demonstrated that interventions using personal contact are more effective . It seems appropriate, therefore, to conduct a larger scale trial adopting a similar approach to Norell et al. with longer follow-up, and detailed reporting of research methodology to demonstrate research rigour.
A further appropriate enhancement for future interventions would involve considering all factors known to affect adherence. The Theory of Planned Behaviour suggests that the best predictor of behaviour is intention which is determined by the attitude towards the behaviour formed from beliefs about the likely outcomes of behaviour and the value of that outcome . Similarly, Social Cognitive Theory considers the key constructs of a particular behaviour to be patient belief in their capability to perform the required behaviour (self-efficacy) and their perception that the behaviour will have a positive effect on the health condition (outcome expectation) . When patients express ambivalence to adhering to their prescribed regimen, Motivational Interviewing (MI) and more recently Behaviour Change Counselling (BCC) have been developed in order to identify ambivalence and guide patients in adopting behavioural change .
MI is defined as ‘a client-centred, directive method for enhancing intrinsic motivation to change by exploring and resolving ambivalence’ and has been successfully applied to improving medication adherence [27–30]. MI in its original format consisted of multiple sessions, each of 30–60 minutes. However, in a medical setting, patient encounters usually range from 10–15 minutes and patients often do not see the same clinician throughout follow-up, limiting the use of MI. Additionally, in medical and public health settings, there is often a multi-component approach to care such as the provision of educational materials and information communication . Thus, Behaviour Change Counselling (BCC), an adaption of MI suitable for brief consultations, was developed for use in healthcare. Whereas MI uses open questions and reflective listening , BCC can additionally be used to exchange information. BCC can be of brief duration or extended to a longer time if required, typically 5–30 minutes .
There are a multitude of adaptations to the original form of MI used in randomised controlled trials (RCTs). However, RCTs rarely report precise intervention details and there is often no evidence of any skill assessment of the practitioners delivering the intervention or measures of patient-centeredness . A number of instruments measure patient-centeredness  but these are not specific to health behaviour change techniques. The Motivational Interviewing Skill Code (MISC)  and Behavioural Change Counselling Index (BECCI)  are specific measures of fidelity to MI and BCC respectively. MISC applies three phases of analysis by means of direct observation of a recorded clinical encounter. MISC scores from each phase are computed to produce an overall summary score which can be compared to the benchmarks depicting proficiency in MI techniques . Despite revision in 2008 to a more streamlined process , MISC still includes a number of subsections that are not essential for users of BCC .
BECCI was developed to evaluate practitioner competence in using BCC in controlled trials. BECCI focuses on the practitioner consulting behaviour, rather than patient response, in a single-phase analysis using Likert-type scales to indicate either frequency or strength of practitioner behaviour over 11 items to produce an overall mean score .
There are numerous approaches to measuring adherence, each with merits. Patient self-report, using questionnaires, diaries and/or interviews are cheap and easy to administer but in comparison with objective measures, can yield higher adherence estimates . This discrepancy is attributed to both the social desirability to be adherent resulting in reporting bias and memory bias. Prescription refill databases can provide adherence estimates based on how many prescriptions have been ordered over a period of time, which may show intention to use medication, but does not ensure administration .
In diseases where medication adherence correlates with therapeutic outcome, objective observations are possible. However, with glaucoma, adherence does not easily correlate with immediate clinical benefit and ideally both adherence and clinical endpoints should be assessed . The chronic nature of glaucoma means that determination of the relationship between adherence magnitude and therapeutic efficacy requires long term follow-up with assessment of optic nerve damage and/or visual field loss. IOP may provide an alternative measure, however, there is considerable diurnal variation [40–42] and so there is no universal standard for using IOP as an adherence measure .
An 80% adherence rate is widely recognised as ‘acceptable’ for many systemic medications  but there is no such acceptance for ocular hypotensives. However, a recent cross-sectional glaucoma study in the USA found that participants with adherence rates < 80%, according to a medication event monitoring system (MEMS®), had worse visual field defects than those with adherence rates ≥ 80% .
Electronic drug monitoring is a more objective method to measure adherence and particularly appropriate with eye drops as ‘pill counting’ methods cannot be employed. Electronic monitors are, however, often expensive and cumbersome, limiting their use. The Alcon® Travatan dosing aid (TDA; Travalert®, Alcon, Fort Worth, TX) is designed for patients to easily reload their eye drop bottle into the device and electronically records every drop discharged . Whilst electronic monitoring devices have previously been criticised for modifying adherence and/or behaviour by emphasising the monitoring itself (the Hawthorne effect) , a pilot study has established that the TDA had no such demonstrable impact .