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J Res Med Sci 2023,  28:34

Designing a tool for measuring determinants of eye self-care and evaluating its psychometric properties

1 Department of Health Education and Promotion Student Research Committee, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Biostatistics and Epidemiology, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran
3 Department of Health Education and Promotion, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran
4 Department of Ophthalmology, School of Medicine and Eye Research Center, Isfahan University of Medical Sciences, Isfahan, Iran
5 Department of Health Education and Promotionn, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Submission22-May-2022
Date of Decision13-Sep-2022
Date of Acceptance09-Nov-2022
Date of Web Publication20-Apr-2023

Correspondence Address:
Dr. Maryam Amidi Mazaheri
Department of Health Education and Promotion, School of Health, Isfahan University of Medical Sciences, Isfahan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jrms.jrms_368_22

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Background: Eye care is crucial for maintaining healthy vision. This study aimed to design a determinants assessment instrument related to eye self-care in the student community and evaluate its psychometric properties. Materials and Methods: The present mixed-method cross-sectional study was conducted in two sections using Creswell and Plano Clark methods for instrument development. The study was conducted in Isfahan, Iran, in 2021. The first section (textual analysis and qualitative research) explained and developed the instrument's fundamental items. This section included in-depth, semi-structured interviews with 21 students and eight experts. In the second, the psychometric properties of the designed instrument have been evaluated. Twenty students assessed the instrument's qualitative and quantitative face validity. The instrument's content was measured by computing the content validity ratio and content validity index. In addition, exploratory factor analysis (performed on 251 students) was used to establish construct validity. Internal and test–retest reliability was determined using Cronbach's alpha and intraclass correlation coefficients (ICC), respectively. Results: During face and content validity assessment, a 39-item questionnaire was finalized. Exploratory factor analysis led to the extraction of seven factors, including “perceived self-efficacy and self-regulation,” “outcome expectation,” “perceived barriers,” “motivation,” “perceived susceptibility,” “normative beliefs,” and “perceived severity.” The seven extracted factors explained 48.6% of the total variance. Cronbach's alpha was obtained to be 0.780, indicating good internal consistency, and the ICC for the total score of the questionnaire was 0.892 (95% confidence interval: 0.822–0.944), indicating excellent test–retest reliability. Conclusion: Our developed questionnaire was a valid and reliable instrument for assessing eye care determinants among students, a vulnerable population afflicted with eye defects and disorders.

Keywords: Eyes, psychometrics, reliability, students, validity

How to cite this article:
Chatripour R, Feizi A, Zamani-Alavijeh F, Beni AN, Mazaheri MA. Designing a tool for measuring determinants of eye self-care and evaluating its psychometric properties. J Res Med Sci 2023;28:34

How to cite this URL:
Chatripour R, Feizi A, Zamani-Alavijeh F, Beni AN, Mazaheri MA. Designing a tool for measuring determinants of eye self-care and evaluating its psychometric properties. J Res Med Sci [serial online] 2023 [cited 2023 Jun 4];28:34. Available from: https://www.jmsjournal.net/text.asp?2023/28/1/34/374399

  Introduction Top

Eye care is crucial for preventing age-related eye diseases, as age-related eye diseases, including diabetic retinopathy, age-related cataracts, open-angle glaucoma, and visual impairment, are a challenge worldwide.[1] Globally, there are approximately 36 million blind individuals and 217 million with moderate or severe visual impairment. Approximately 80% of moderate-to-severe cases of blindness and visual impairment are preventable.[2] This prevalence of eye problems affects the quality of life, the cost of resources, and the availability of health services.[3] Because self-care at a young age reduces the risk of developing eye problems, attention should be paid to preventing and reducing the incidence of eye problems from a young age.[4]

Eye care is an essential part of maintaining an individual's health and preventing and treating relevant diseases.[5] The literature demonstrates that self-care is crucial to eye health.[6] Therefore, it is necessary to assess and quantify the condition of eye care, and identifying the factors related to eye self-care at a young age is crucial.

One of the best times to focus on eye health and prevention is during studenthood.[7] In light of the fact that computer use increases the risk of developing eye problems. Computers play a significant role in students' daily lives, who are susceptible to computer vision syndrome.[8],[9],[10],[11] Changing behaviors during the academic year is deemed a relatively suitable time, according to research.[9],[10] The behavioral change was beneficial for eye health, preventing and managing eye problems.[12],[13]

To the best of the authors' knowledge, limited research exists on eye care for students, and this topic warrants further study. For self-care education, measuring the factors in the youth age group is essential, and a valid and dependable instrument is the starting point for conducting research.[12]

The authors could not identify appropriate tools for evaluating eye care determinants in this regard. Therefore, the purpose of the present study was to design an eye care determinants assessment instrument and evaluate its psychometric properties.

  Methods Top

Study design

The current cross-sectional mixed-method methodological study was carried out in Iran during October 2020–May 2021, among Persian-speaking students at Isfahan University of Medical Sciences. The Creswell and Plano Clark tool design methods were used to create the study.[13]

Phase 1: Design of an eye care tool

Based on a qualitative study, the following items were designed and explored for the current instrument: (a) Reviewing scientific texts; (b) Obtaining expert (ophthalmologist, optometrist) and participant (students and experts) opinions; (c) Combining the results of reviewing texts with the opinions of experts and participants.

In-depth semi-structured interviews were conducted with 21 students (8 face-to-face and 13 telephone interviews) and eight experts for the present qualitative study.

Phase 2: Psychometric properties of the eye care tool

Face validity

The questionnaire was communicated to 20 students with varying levels of education to evaluate its face validity, and they were asked to comment on the clarity and readability of each item.

Quantitative face validity assessment

On a 5-point Likert scale ranging from “not important at all” (score 1) to “very important” (score 5), the same 20 individuals were asked to rate the significance of each item. Consequently, the item impact score was calculated for each item. The impact score for each item was calculated using the following formula, “Impact score = Frequency (%) × Importance.” “Frequency” in the formula was the number of patients rated the item 4 or 5, while “Importance” was the mean score of the item on the 1–5 rating scale. An item impact score of more than 1.5 was considered an acceptable criterion for the quantitative face validity of the questionnaire's items.[14]

Content validity

To evaluate the content validity using the qualitative method, the initial questionnaire was distributed among 10 specialists, including seven specialists in health education and promotion, one ophthalmologist, and two optometrists, who were asked to provide their corrective opinions regarding the use of appropriate words, adherence to Persian grammar, the suitable placement of items, and appropriate scoring.

Quantitative content validity assessment

The content validity ratio (CVR) and content validity index (CVI) of the instrument were calculated to evaluate the content validity of the quantitative method or the compatibility between the instrument's content and the study objectives.

Content validity ratio

Ten experts were given a 44-item questionnaire to determine the CVR. The panel of experts was then asked to provide their opinions on each item alongside the other items in the form of three options: “essential,” “useful but not essential,” and “not essential.” CVR was computed for each item using the formula CVR = [Ne-(N/2)]/(N/2), where Ne represented the number of panelists who indicated “essential” and N represented the total number of panelists.[15] The items exceeding 0.62 were subsequently retained as per the Lawshe table.[15]

Content validity index

On a 4-point Likert scale, the same ten experts were asked to comment on each item separately for three criteria: (a) simplicity, (b) specificity, and (c) clarity for calculating the CVI. Based on the formula, CVI was then calculated (the number of professionals who answered 3 and 4, divided by the total number of professionals). An item was retained and considered acceptable if its CVI value was >0.79; it was questionable and required correction if the CVI value fell between 0.79 and 0.7, and it was considered unacceptable and removed if the value fell below 0.7.[15]

Finally, the necessity and relevance of the questions were determined by examining the validity of the content using qualitative and quantitative techniques. Per the experts' recommendations, the questions that required editing (simplicity and clarity) were revised.


A revised questionnaire based on the face and content validity stage was sent to 38 students to determine the instrument's reliability. The participants were then instructed to complete each questionnaire item carefully. The Cronbach's alpha coefficient was calculated to determine the instrument's internal reliability. Cronbach's alpha values >0.70 were considered acceptable.[16]

The test–retest reliability was determined by calculating the intraclass correlation coefficient (ICC). Thus, the questionnaire was sent to the same individuals 14 days later for a retest. The two-way mixed method was utilized to calculate the ICC (along with a 95% confidence interval for ICC). An ICC coefficient >0.70 was considered highly stable item.[16]

Construct validity assessment

Exploratory factor analysis was performed on 251 students to determine construct validity. In this regard, a cross-sectional study was conducted. Multi-stage cluster random sampling was adopted for student selection from faculties as first-level clusters and classes in each faculty as the second-stage clusters. The study's objectives were explained to the participants before participating in our study. All participants gave their informed consent to take part in the current research. Electronic data entry was utilized to complete the questionnaire (sending the online questionnaire link to them through media and online tools).

The Kaiser–Meyer–Olkin (KMO) index was used to evaluate the adequacy of the sample size. The KMO value >0.6 indicated an adequate sample size.[16] Bartlett's test of sphericity was utilized to ensure the correlation between the questionnaire or to evaluate factorability. The number of factors was then determined using the slope of the Scree plot diagram and eigenvalues (eigenvalues more than 1 was considered), and the Varimax rotation method was used to enhance factor interpretability [Figure 1].
Figure 1: Scree plot of the exploratory factor analysis

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Criterion validity

The criterion validity was determined by analyzing the correlation between each item and the corresponding and noncorresponding factor constructs. Each item with a correlation of more than 0.3 with corresponding constructs and a correlation lower than 0.3 with a noncorresponding construct indicates the establishment of criterion validity.[17]

Other variables and statistical analysis

Age, gender, level of education, place of residence, level of education of parents, marital status, economic status, and refractive error status were also collected. This paper's qualitative and quantitative variables were expressed as frequency (percentage) and mean (standard deviation [SD]), respectively. SPSS-25 (IBM Corp., Armonk, N. Y., USA) was employed for data analysis.

Ethical considerations

Isfahan University of Medical Sciences approved this study's design (IR.MUI.RESEARCH.REC.1399.544) per its ethical guidelines. All participants were informed of the study's objectives and then invited to participate.

The names of the students were initially encoded. The data were stored in a secure location protected by a username and password.

  Results Top

Content and face validity

Only a few items in the first version of the literature-based questionnaire design were modified during qualitative face and content validity. Finally, a 39-item questionnaire was subjected to quantitative validity and reliability analysis. The item impact score was determined for each item for evaluating face validity quantitatively. As a result, all questionnaire items with a score greater than 1.5 were retained. The panel of experts also evaluated each questionnaire item's necessity, simplicity, relevance, and clarity. Therefore, according to the Lawshe table, all items with a CVR score >0.62 were retained. CVI was determined for each item and all items had acceptable value, i.e., more than 0.79. Three items had a CVI of 0.8, while the remaining items had a CVI >0.8.

Construct validity

The cross-sectional study on a sample of 251 students revealed that 31% of the participants were male, and 69% were female. The mean age ± SD was 22.6 ± 4.1 years (ranging from 18 to 49 years). [Table 1] displays the study samples' basic demographic characteristics.
Table 1: Participants' characteristics

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The KMO index value of 0.78 indicated the adequacy of the sample size for exploratory factor analysis. Bartlett's test was also statistically significant (P < 0.0001). Thus, the data's factorability was approved. Using the Scree plot and an eigenvalue greater than one, the number of factors was determined to be seven [Figure 1] and [Table 2]. According to the concepts of items in each factor, the identified seven factors were named: “perceived self-efficacy and self-regulation,” “outcome expectation,” “perceived barriers,” “motivation,” “perceived susceptibility,” “normative beliefs,” and “perceived severity.” The seven extracted factors explained the total variance of 48.6% of the original variables. [Table 2] shows the variance explained by each factor.
Table 2: The factor loadings on 39 items obtained from exploratory factor analysis

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Criterion validity

The correlation of each item with the corresponding and noncorresponding factor constructs was evaluated to determine criterion validity. Each item correlated with the corresponding construct >0.3 but <0.3, indicating excellent criterion validity [Table 3].
Table 3: Corrected item-total correlation

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Reliability analysis's results

Cronbach's alpha was obtained to be 0.780, indicating good internal reliability. The ICC was reported separately for each item and extracted factors as well as the total score of the developed instrument [Table 4]. The obtained ICC values indicate excellent repeatability of each item, factor, and total score of the instrument.
Table 4: Test-retest reliability evaluated by intraclass correlation coefficients

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Methods of instrument's items scoring

All questionnaire items were scored using a 5-point Likert scale, and 30 items scored from “strongly agree” to “strongly disagree” (items 1 and 2 were scored from zero to four, while items 3–27 and 37–39 were scored reversely from four to zero). The scoring format for nine items (28–36) ranged from “never” to “always” (scoring from zero to four). With a minimum score of zero and a maximum score of four for each item, the maximum total score for the instrument was 156, and the minimum total score was zero [Table 5].
Table 5: Instrument's items scoring

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  Discussion Top

This research aimed to design a determinants assessment instrument related to eye self-care in the student community and evaluate its psychometric properties. Due to the passage from a scientific procedure, the seven factors and their related questions were the most significant determinants for eye self-care. The name determinants for eye self-care-39 (DES-39) was given to the present questionnaire by the research team due to its function of assessing eye self-care determinants. The DES-39 determined the status of the most significant eye self-care determinants. “Perceived self-efficacy and self-regulation” (10 items), “outcome expectation” (9 items), “perceived barriers” (6 items), “motivation” (4 items), “perceived susceptibility” (3 items), “normative beliefs” (3 items), and “perceived severity” (4 items).

The Cronbach's alpha coefficient of 0.78 for the DES-39 indicated that the questionnaire's internal consistency was comparable to instruments derived from other valid psychometric studies.[16] The ranges of ICC (95% confidence interval) for the questionnaire items and factors and the seven factors were 0.727–0.970 and 0.787–0.906, respectively, indicating the DES-39 questionnaire's good external reliability.[17] Each item correlated strongly with both the corresponding and non-corresponding factor constructs of the present questionnaire.

The percentage of the total variance explained by the questionnaire was 48.6%, ranging from 4.88% to 10.09% for the seven factors; therefore, the result was acceptable. The first factor, perceived self-efficacy, and self-regulation for eye care accounted for the greatest percentage of variance explained (10.09%).

The percentage of the total variance explanation of the questionnaire was 48.6%, ranging from 4.88% to 10.09% for the seven factors; hence, the result was appropriate. Among the factors, the first factor, the perceived self-efficacy and self-regulation for eye care, had the highest percentage of variance (10.09%).

Study properties

(a) The application of its psychometric stages to students of various disciplines and academic levels (age range of 18–49 years). (b) The present questionnaire items were designed based on the population's needs, culture, and other characteristics after qualitative research was conducted on the population.

  Conclusion Top

The questionnaire developed in this study was a valid and reliable instrument for assessing eye care determinants among students, a vulnerable population afflicted with eye defects and disorders. To this end, we recommend measuring eye care with the developed instrument. The questionnaire is self-reported, and its items are simple to comprehend. Moreover, the questionnaire requires approximately 20 min to complete.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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