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Original article
Validation of a short version of the glaucoma medication self-efficacy questionnaire
  1. Betsy Sleath1,2,
  2. Susan J Blalock2,
  3. Jennifer L Stone3,
  4. Asheley Cockrell Skinner4,
  5. David Covert5,
  6. Kelly Muir6,
  7. Alan L Robin7,8,9
  1. 1Cecil G. Sheps Center for Health Services Research, Chapel Hill, North Carolina, USA
  2. 2Division of Pharmaceutical Outcomes and Policy, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina, USA
  3. 3Glaucoma Specialists, Baltimore, Maryland, USA
  4. 4Department of Pediatrics, University of North Carolina, Chapel Hill, North Carolina, USA
  5. 5Alcon Research, Ltd, Fort Worth, Texas, USA
  6. 6Department of Ophthalmology, School of Medicine, Duke University, Durham, North Carolina, USA
  7. 7Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA
  8. 8Department of Ophthalmology, School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA
  9. 9University of Maryland School of Medicine, Baltimore, Maryland, USA
  1. Correspondence to Dr Betsy Sleath, Cecil G. Sheps Center for Health Services Research, Division of Pharmaceutical Outcomes and Policy, Eshelman School of Pharmacy, University of North Carolina, CB # 7590, Chapel Hill, NC 27599-7590, USA; betsy_sleath{at}unc.edu

Abstract

Aims The aims of this study were: (1) to examine whether the original glaucoma medication adherence and eye drop technique self-efficacy scales could be shortened for easier use in practice settings; and (2) to validate these scales against objective medication adherence measures.

Methods Prospective study conducted at a single private practice site. We measured subjects' adherence to glaucoma medications through Medication Event Monitoring System (MEMS) devices and assessed eye drop instillation technique by video-recording. Principal components factor analysis and logistic and linear regression were used to analyse the data.

Results Our results yielded a 10-item Glaucoma Medication Adherence Self-Efficacy Scale that was strongly associated with subject adherence measured using MEMS (β coefficient 8.52, 95% CI 1.94 to 15.1). In addition, the six-item Eye Drop Technique Self-Efficacy Scale was strongly associated with video-recorded subject eye drop installation technique (OR 10.47, 95% CI 1.78 to 61.63).

Conclusions Eye care providers and researchers could use these shorter scales to identify subjects with either poor glaucoma medication adherence and/or eye drop instillation technique. This could help to identify those who may benefit most from education and training on both adherence and eye drop instillation.

  • Glaucoma
  • adherence
  • eye drop technique
  • self-efficacy
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Background

Between 9% and 12% of all blindness in the USA is attributed to glaucoma.1 2 Proper use of glaucoma medications can lower intraocular pressure and reduce the progression of glaucoma.3–5 However, despite the availability of effective monotherapy medications taken once a day, patients' non-adherence to treatment regimens is a significant problem.6 Approximately half of all subjects started on glaucoma medications will discontinue treatment within 6 months.7 8

Beyond simply remembering to take their drops and being properly motivated to do so, subjects may not be using their eye drops correctly.9 A study of 324 glaucoma subjects revealed that 20% of subjects reported that no one had shown them how to use their glaucoma medications.10 11 Another study of 140 experienced glaucoma subjects who all claimed they instilled their own eye drops found that 18% of subjects missed their eye when administering their drops, only 60% instilled the correct number of drops, and 65% of subjects contaminated the bottle by allowing it to touch the eye.9

We have developed a glaucoma medication self-efficacy questionnaire to examine subject self-confidence in using eye drops correctly and adhering to their glaucoma medications.12 Self-efficacy is defined as individuals' personal beliefs regarding their capabilities to carry out a specific task to achieve a desired outcome.13 14 Our original scale included a 21-item self-efficacy scale about overcoming barriers to the use of glaucoma medications and a 14-item self-efficacy scale about carrying out specific tasks required to use eye drops correctly.12 These scales were initially validated against two self-reported measures of glaucoma medication adherence.12

The purpose of the present study was: (1) to examine whether the original glaucoma medication adherence and eye drop technique self-efficacy scales that comprise the glaucoma medication self-efficacy questionnaire could be shortened for easier use in practice settings; and (2) to validate these scales against an objective medication adherence measure, namely data derived from the Medication Event Monitoring System (MEMS) and video-recordings of patients' eye drop instillation techniques.

Methods

Design

This study was conducted at a single private practice site and used a prospective open-label design.

Procedures

During the initial visit, subjects completed a demographic questionnaire and then their typical eye drop instillation technique was video-recorded. All subjects instilled artificial tears. Subjects were issued with an activated MEMS cap device and medication phial for each bottle of eye drops used. The MEMS cap records the date and time for each instance that the ophthalmic medication is accessed by the subject. This method of assessing adherence has been successfully used in prior research.15 During a subsequent 1-month follow-up visit, subjects were given a glaucoma medication self-efficacy questionnaire to complete. Subjects returned all MEMS caps at the 3-month visit and any subject without a current visual field test result underwent testing at that time.

Study population

We included all consecutive subjects with a diagnosis of glaucoma who were using one or more topical hypotensive medications in one or both eyes. Subjects were only excluded if they did not instil their own medications, if they could not come to all follow-up study visits, or if they had a known hypersensitivity to over-the-counter artificial tears. Subjects were required to have had a complete ophthalmic examination within the preceding 6 months.

Measurement

Self-reported race was originally measured as a categorical variable and then was dichotomised for the multivariable analyses (ie, white, non-white). The number of glaucoma medications a subject was taking was measured as a continuous variable.

Visual field defects were classified as mild (mean deviation ≥−6 dB), moderate (mean deviation <−6 but >−12 dB) or severe (mean deviation ≤−12 dB) according to Hodopp–Parrish-Anderson criteria.16 One visual field was used in this study, only the most recent (within 9 months of enrolment) was allowed and testing strategies varied based on what was appropriate for the patient's severity of defect (24–2 or 10–2) or history of reliability (SITA Standard vs SITA-Fast). Only SITA strategies were used. If a recent (9 months) visual field result was not available, the patient then completed testing during study enrolment. The reliability parameters of <20% errors were used.

The eye drop technique of each subject was video-recorded. Prior to analysis of the recordings, a comprehensive list of items associated with eye drop instillation technique was developed, based on prior research.9 One researcher (AS) who was unfamiliar with the subjects was trained by the another author9 (JS) to code and review all recordings in accordance with previous studies.

The original glaucoma medication self-efficacy questionnaire included 35 items.12 The questionnaire had two subscales: a 21-item self-efficacy in overcoming barriers that might interfere with the use of glaucoma medications scale (or more simply referred to as the Glaucoma Medication Adherence Self-Efficacy Scale); and a 14-item self-efficacy in carrying out specific tasks required to use eye drops correctly scale (or more simply referred to as the Eye Drop Technique Self-Efficacy Scale). There were four possible response choices for the self-efficacy items: not at all confident, somewhat confident, very confident, and does not apply. In previous research, the self-efficacy scales both correlated significantly with two subject self-reported measures of glaucoma medication adherence, which demonstrates concurrent validity.12 For the current study, we added an item ‘How confident are you that you will not touch your eye with the eye drop bottle?’ to the Eye Drop Technique Self-Efficacy Scale.

Medication adherence over a 3-month period was evaluated via electronic data from the MEMS caps system.15 Adherence using MEMS caps was measured using the following formula: adherence = (number of doses used during the past 3 months divided by the number of prescribed doses) multiplied by 100. Adherence was measured as a continuous variable. If a patient was on more than one medication, an average adherence score was calculated and used in the analyses.

Analysis

Two separate principal components factor analyses with varimax rotation were performed.17 18 In the factor analyses, the mean score was substituted for items with missing values. The maximum number of missing items for a variable was five. Factor loadings, eigen values and scree plots were examined to determine the number of factors to extract. Factor loadings indicate the correlation of an item with an underlying factor. Correlations greater than 0.30 or 0.40 are generally considered meaningful, but since our goal was a shorter questionnaire we only retained items with loadings greater than 0.60.17 18 Once the number of factors was identified, scale scores were computed by summing the unweighted responses across items. Reliability of the resulting scales was assessed using Cronbach's α.

We performed three sets of multivariable analyses. First, we conducted multivariable linear regressions to examine the relationship between patient characteristics and (1) the Glaucoma Medication Adherence Self-Efficacy Scale and (2) the Eye Drop Technique Self-Efficacy Scale. Second, we used multivariable linear regression to examine the relationship between the two self-efficacy scales and medication adherence. Finally, we used logistic regression to examine to examine the relationship between the two self-efficacy scales and each of the four criteria used to assess eye drop technique: (1) drop lands in eye on first attempt; (2) subject instils a single drop; (3) subject touches any part of eye or eyelid with eye drop bottle; and (4) subject touches face with eye drop bottle. In this final set of analyses, length of time with glaucoma and always administers own eye drops were not included as control variables because they were not associated with eye drop technique in the bivariate analyses.

Results

One hundred and two subjects participated and their demographics are presented in table 1. Eleven out of 21 items were deleted from the scale because they loaded <0.60. The 11 deleted items included: (1) when you are busy at home; (2) when there is no one to remind you; (3) when you worry about using them the rest of your life; (4) when they cause some side effects; (5) when they cost a lot of money; (6) when you come home late from work or some other activity; (7) when you are afraid they make your eye red; (8) when the time to use them is between your meals; (9) when you feel you do not need them; (10) when you have other medications to take; and (11) when you feel well. A principal components analysis conducted on the remaining 10 items yielded one interpretable factor explaining 56.95% of the total variance. Table 2 presents the factor loadings for this one factor solution. All items loaded at 0.60 or higher. The resulting 10-item factor had a Cronbach's α reliability of 0.91. Mean scores on the items ranged from 1.10 to 3.0 (mean 2.76±0.37).

Table 1

Subject characteristics (n=102)

Table 2

Results of principal components analysis with varimax rotation for the Glaucoma Medication Self-Efficacy Scale (n=102)

We deleted nine out of 14 items from the scale because they loaded <0.60. The nine deleted items were: (1) using your eye drops without having someone help you; (2) getting refills before you run out; (3) cashing in your glaucoma prescriptions whatever the cost; (4) making your glaucoma medications part of your routine; (5) always remembering to use your glaucoma medications; (6) using your glaucoma medications for the rest of your life; (7) opening the eye drop bottle; (8) getting the plastic seal off a new eye drop bottle; and (9) using your eye drops with someone helping you. The item that was added to the scale ‘not touch your eye with the eye drop bottle’ loaded at >0.60. A principal components analysis with a varimax rotation yielded a six-item factor explaining 54.11% of the total variance. Table 3 presents the factor loadings for the one-factor solution. Item mean scores ranged from 1.33 to 3.0 (mean 2.72±0.37).

Table 3

Results of principal components analysis with varimax rotation for Eye Drop Technique Self-Efficacy (n=102)

Table 4 presents the multiple linear regression results assessing the relationship between subject characteristics and (1) glaucoma medication adherence self-efficacy and (2) eye drop technique self-efficacy. Female subjects (β coefficient 0.17, 95% CI 0.03 to 0.31) and subjects with milder visual field defects (β coefficient −0.13, 95% CI −0.23 to −0.03) had significantly higher glaucoma medication adherence self-efficacy scores than men and those subjects with more severe visual field defects. Subjects with a longer period since glaucoma diagnosis had significantly higher glaucoma medication adherence (β coefficient 0.13, 95% CI 0.03 to 0.23) and eye drop technique (β coefficient 0.12, 95% CI 0.2 to 0.22) self-efficacy scores. Subjects who administered their own eye drops all of the time had significantly higher glaucoma medication adherence (β coefficient 0.28, 95% CI 0.06 to 0.50) and eye drop technique (β coefficient 0.23, 95% CI 0.01 to 0.45) self-efficacy scores than subjects who administered their own drops most of the time.

Table 4

Linear regression predicting mean scores on the glaucoma medication adherence and eye drop technique self-efficacy scales (n=102)

Table 5 presents the linear regression results predicting adherence. Patient adherence ranged from 31.4% to 100% (mean 93.5±11.9%). Subjects with higher glaucoma medication adherence self-efficacy were significantly more adherent (β coefficient 9.14, 95% CI 2.70 to 15.58). Patients who always administered their own drops were significantly more adherent (β coefficient 8.52, 95% CI 1.94 to 15.1). The Eye Drop Technique Self-Efficacy Scale was not significantly associated with medication adherence.

Table 5

Linear regression predicting Medication Event Monitoring System (MEMS) adherence (n=102)

Table 6 presents the logistic regression results predicting eye drop technique. Eighty per cent of subjects successfully instilled a drop in their eye on the first attempt as graded in the video recordings. Subjects with higher eye drop technique self-efficacy scores were significantly more likely to have a drop land in their eye on the first attempt (OR 10.47, 95% CI 1.78 to 61.63). Seventy per cent of subjects instilled only a single drop. Subjects with higher eye drop technique self-efficacy were significantly more likely to instil one drop (OR 7.95, 95% CI 1.86 to 33.92). Thirty-four per cent of subjects touched their eye or eyelash with the eye drop bottle and 52% of subjects touched their face with the eye drop bottle. Subjects with higher eye drop technique self-efficacy were significantly less likely to touch their face (OR 0.03, 95% CI 0.0004 to 0.23) or eye or eyelash with the eye drop bottle (OR 0.13, 95% CI 0.03 to 0.55). Subject scores on the Glaucoma Medication Adherence Self-Efficacy Scale were not significantly associated with any of the eye drop technique measures.

Table 6

Logistic regression results predicting eye drop technique (n=102)

Discussion

Currently there is no objective way for a clinician a priori to assess whether his or her patients with glaucoma are either adherent or able to correctly instil their own eye drops. Prior research has shown that patients are not accurate in assessing their own eye drop technique abilities.9 In addition, physicians are often not able to tell which patients are adherent with medications.19

The Glaucoma Medication Adherence Self-Efficacy Scale was shortened from 21 to 11 items and the Eye Drop Technique Self-Efficacy Scale was shortened from 14 to five items with one new item being added to the scale for a total of six items. We found the Glaucoma Medication Adherence Self-Efficacy Scale to be significantly associated with the objective electronic measure of adherence but not with the subjects' eye drop technique. The Eye Drop Technique Self-Efficacy Scale was significantly associated with subjects' eye drop technique but not with the objective electronic measure of adherence. These findings are important because they demonstrate the scales are measuring different aspects of glaucoma medication use, and are specific to the tasks specified.

Subjects who had glaucoma longer, and those who administered their own medications, scored higher on both the Glaucoma Medication Adherence and Eye Drop Technique Self-Efficacy Scales. Providers need to educate subjects who do not administer their own drops all the time with strategies to improve self-confidence in taking their glaucoma medications. Alternatively, providers should ensure that patients have adequate social support when using their drops. Subjects who had more severe visual field defects actually scored higher on the Glaucoma Medication Adherence Self-Efficacy Scale, suggesting that subjects with worse defect severity might be more motivated to take their medications to prevent further vision loss.

The Glaucoma Medication Adherence Self-Efficacy Scale can be used by eye care providers to detect subjects who do not feel confident taking their glaucoma medications under certain circumstances. Providers could pinpoint the problem based on patients' responses and help address the specific challenge. In addition, since the Glaucoma Medication Adherence Self-Efficacy Scale was significantly associated with medication adherence, the scale may help providers detect subjects who are more likely to be non-adherent with their medication regimen. The lower a patient's score on the Glaucoma Medication Adherence Self-Efficacy Scale, the more likely the patient is non-adherent.

The Eye Drop Technique Self-Efficacy Scale may be used by eye care providers to screen for patients reporting a lack of confidence with certain aspects of using their eye drops. Providers could use these results to identify patients who need additional teaching and modelling on how to correctly use their eye drops.

These validated and simple self-efficacy scales could also be used in glaucoma research. The scales could be administered to large groups of patients to examine how self-efficacy or self-confidence in using eye drops is related to intraocular pressure control and glaucoma progression. In addition, intervention studies could be conducted to educate patients to improve their adherence and eye drop technique. These scales could be administered before and after intervention to allow researchers to examine the impact of the interventions on self-efficacy.

This study has several limitations. First, although most subjects were willing to participate, we did not track the characteristics of those subjects who did not respond to the questionnaire, which introduces bias. Second, the study was conducted at a single site and this may limit broad applications of these findings. Further studies are needed to both replicate this study and to apply it in both clinical and research settings. Future studies should also make sure to ask patients if they have been educated on how to instil their eye drops and by whom, and if they have been educated about why it is important to adhere to their glaucoma medications. Eye care providers and researchers could use these scales to identify patients who may be struggling to instil their eye drops and those who are having trouble adhering to their prescribed glaucoma medication regimens.

References

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Footnotes

  • Funding Funding was provided by Alcon Research, Ltd. BS was also supported by grant EY018400 from the National Eye Institute and by grant UL 1RR02574 7 from the National Center of Research Resources, NIH.

  • Competing interests None to declare.

  • Patient consent Obtained.

  • Ethics approval This study was conducted with the approval of the Southwest Independent Institutional Review Board.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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