A total of 224 respondents took part in the analysis of the English version of the National Eye Institute Visual Functioning Questionnaire while another 204 participated in the Malay version.
The mean age of these patients was 66.8 years of age and 64.3 years of age for those involved in the English version and Bahasa Malaysia version respectively (Not In Table). The respondents were made up of 52.5% males in the English version and 49.8% males in the Bahasa Malaysia version. The main ethnic groups in the English version database comprised of Malays (56.1%) followed by Chinese (29.8%) and the Indians (14.1%) while the Bahasa Malaysia version database consisted of Malays (53.7%) followed by Chinese (31.2%) and the Indians (15.1%).
A total of 19 items each from the English version and Bahasa Malaysia version of the questionnaire were identified to be suitable for the component factor analysis.
As illustrated in Table 1, Kaiser-Meyer-Olkin’s measure of sampling adequacy indicated excellent compactness with regards to the pattern of correlations with values of 0.923 for the English questionnaire and 0.927 for the Bahasa Malaysia questionnaire (P value < 0.05 for Bartlett’s Test). These results allowed us to proceed with factor analysis.
We performed extraction of components followed by the use of all rotation types possible. Bearing in mind that items are independent of each other, we utilized Varimax rotation followed by Equamax rotation and finally ending with Quartimax rotation. We finally settled for the use of Equamax rotation as this rotation produces the least discrepancies in percentage of variance among the various components produced with Eigenvalue of more than one.
As shown in Table 2, a total of three components have eigenvalues of more than one with cumulative percentage of 60.7% for the English version of the questionnaire. Components one, two and three contributed 23.8%, 22.2% and 14.6% towards the total variance, respectively. As for the Bahasa Malaysia version of the questionnaire, similarly a total of three components presented with eigenvalues of one and above (Table 2). These three components accounted24.2%, 23.6% and 18.6% respectively towards the total variance and together contributed a cumulative variance of 66.5% which was approximately 5.8% higher that the cumulative variance seen in the English version of the questionnaire.
In the English version of the questionnaire, nine items loaded strongly onto component one, six items were loaded onto component two and a further three items onto component three (Table 3). As for the Bahasa Malaysia version of the questionnaire, we observed loadings of 10 items, seven items and one item respectively onto components one, two and three respectively (Table 4).
The loading process in component one (defined here as “Difficulty in Activity of Daily Living”) revealed nine similar items for both English and Bahasa Malaysia versions of the questionnaire (Table 3 and Table 4).
As for component two (defined here as “Dependency on others due to poor eyesight”), the loading revealed six similar items for both English and Bahasa Malaysia versions of the questionnaire (Table 3 and Table 4).
The English version of the National Eye Institute Visual Functioning Questionnaire comprises of three components:
1) Component one: “Difficulty with activities”, which accounted for 23.8% of the total variance. This component contained nine items and reflected perception of the difficulty in activity of daily living. The highest loading items were as follows – “Because of your eyesight, how much difficulty do you have noticing objects off to the side while you are walking along?” (factor loading of 0.73); “Because of your eyesight, how much difficulty do you have seeing how people react to things you say?” (factor loading of 0.84); “How much difficulty do you have reading street signs or the names of stores?” (factor loading of 0.69).
2) Component two: “Responses to vision problems”, which comprised of 22.2% of the total variance. Six items were included within this component which reflected perception on dependency on others due to poor eyesight. We noted the highest loading items as follows – "Because of my eyesight, I have to rely too much on what other people tell me." (factor loading of 0.77); "I worry about doing things that will embarrass myself or others, because of my eyesight." (factor loading of 0.76); "I need a lot of help from others because of my eyesight." (factor loading of 0.74).
3) Component three: “General health and vision”, which contributed 14.6% of the total variance. This component comprised of three items which portrayed poor perception of respondents on status of eyesight. The following items were loaded highest as follows –
"At the present time, would you say your eyesight using both eyes (with glasses or contact lenses, if you wear them) is excellent, good, fair, poor, or very poor or are you completely blind?" (factor loading of 0.60); "How much of the time do you worry about your eyesight?" (factor loading of 0.57); "How much difficulty do you have reading ordinary print in newspapers?" (factor loading of 0.42).
The final Bahasa Malaysia version of the National Eye Institute Visual Functioning Questionnaire constitutes the following three components:
1) Component one: “Difficulty with activities”, contributing towards 23.6% of the total variance. A total of ten items were loaded which reflected perception of the difficulty in activity of daily living. The highest loading items were as follows – "How much difficulty do you have reading ordinary print in newspapers?" (factor loading of 0.78); "How much difficulty do you have reading street signs or the names of stores?" (factor loading of 0.76); "Because of your eyesight, how much difficulty do you have going down steps, stairs, or curbs in dim light or at night?" (factor loading of 0.71).
2) Component two: “Responses to vision problems”, comprising of 24.2% of the total variance. We observed seven items that were included within this component which reflected perception on dependency on others due to poor eyesight. The highest loading items were as follows –
"Because of my eyesight, I have to rely too much on what other people tell me." (factor loading of 0.83); "I have much less control over what I do, because of my eyesight." (factor loading of 0.76); "I feel frustrated a lot of the time because of my eyesight." (factor loading of 0.73).
3) Component three: “Poor perception of status of eyesight”, accounting for 18.6% of the total variance. There was only one item loaded into the component which portrayed poor perception of respondents on status of eyesight. The lone item loaded was noted as follows –
"Do you accomplish less than you would like because of your vision?" (factor loading of -0.77).
Reliability – Internal Consistency
After construct validation was computed, Cronbach’s alpha was computed for the revised questionnaire and we obtained Cronbach alpha values of 0.904, 0.898 and 0.608 for the three components of the English version of the questionnaire – difficulty with activities, responses to vision problems and general health and vision. As for the Bahasa Malaysia version, computation of Cronbach’s alpha revealed values of 0.921, 0.927 for the first two components - difficulty with activities, responses to vision problems. Cronbach’s alpha was not done on Component 3 (general health and vision) of the Bahasa Malaysia version as Component 3 has only one item.