The National Eye Institute Visual Functioning Questionnaire – 25 (NEI VFQ 25) has been designed to measure important areas of well-being and functioning among patients with eye diseases [14]. It has been further described as a valid and reliable tool in assessing vision-specific quality of life among patients with various eye diseases [15].
The ultimate aim of this study was to translate the National Eye Institute Visual Functioning Questionnaire-25 into Bahasa Malaysia and validate both versions (English and Bahasa Malaysia) on their capacity in measuring and assessing quality of life of people with cataracts. We assessed the reliability and validity of the English and Bahasa Malaysia version of the NEI VFQ-25 in ophthalmic patients with cataract diseases.
The original National Eye Institute Visual Functioning Questionnaire – 25 which was first developed by RAND [16] is comprised of three factors which touched upon general health and vision, difficulty with activities and responses to vision problem.
We observed both English and Bahasa Malaysia versions to have high reliability with Cronbach’s alpha values of 0.90 and above in factors on difficulty with activities and responses to vision problems which mirrored results seen in studies validating the questionnaire in Japanese [17], Italian [18], French [19], Spanish [20], Turkish [21] and German [22].
With regards to construct validity, exploratory factor analysis performed has revealed that the three-factor model fits the data well for the English version of the questionnaire. Extraction and rotation of the data produced a model that mirrored the original version with regards to production of a total of three factors – difficulty with activities (23.81% of variance), responses to vision problem (22.22% of variance) and general health and vision (14.68% of variance). The items were mostly similar between the model and the original questionnaire in these three factors– there were a total of nine identical items shared in the factor on difficulty with activities, six identical items shared in the factor on responses to vision problem and two similar items shared in the factor on general health and vision. The results supported a three-factor solution as per original version of the questionnaire, with the factors accounting for 60.72% of the variance.
However, there were a couple of items left out in the model. For instance, on difficulty with activities, two items which pertain to driving at night and driving in difficult conditions were omitted from the model. Similarly, a study by Lloyd et al noted that driving in difficult conditions or at night items merged out into a totally separate domain [23].
A further three items on accomplishment, limitation of work activities and pain discomfort were left out from the model in the factor on responses to vision problems.
As similarly seen in the English version, the Bahasa Malaysia version of the questionnaire produced three factors with two of the factors resembling the factors from the original version of the questionnaire - difficulty with activities (24.28% of variance) and responses to vision problem (23.66% of variance). In addition, there was higher cumulative variance in the Bahasa Malaysia version (66.56% Bahasa Malaysia version versus 60.72% English version) indicating stronger fit to the model for the Bahasa Malaysia version as compared to the English version. Altogether, there were a total of ten identical items shared in the factor on difficulty with activities and seven identical items shared in the factor on responses to vision problem between the Bahasa Malaysia and the original version of the questionnaire.
Factor analysis on the Brazilian version of the NEI VFQ-25 indicated that the tool could be utilized in the country to assess vision-related quality of life as the psychometrics properties are comparable to the original American version [24]. The Japanese version of the questionnaire also noted similar observation [17].
However, in comparison to these studies conducted in Brazil [24] and Japan [17] which focused on subscales derived from the optional questions rather than the main parts of the questionnaire, our research revealed three factor model – difficulty with activities, responses to vision problem and general health and vision which mirrored precisely with the main parts of the original NEI VFQ-25 questionnaire (Part 2, Part 3 and Part 1 respectively). In addition, as the population of Malaysia are well conversant in both the Malay and English languages, we were able to perform validation analyses for questionnaires in both languages and ultimately witness the high reliability and validity in these questionnaires in assessing the quality of life of people with cataract.
With good reliability and validity, the VFQ-25 has been utilized in surveys involving ophthalmic patients with diabetic retinopathy, primary open-angle glaucoma, cataract, low vision, optic neuritis, uveitis and others such as age-related macular degeneration and cytomegalovirus retinitis [9,25,26,27,28].
This study with good psychometric features could be used as a routine tool to assess visual function among patients especially among rural folks who predominantly understand Bahasa Malaysia which is the official language in Malaysia. In addition, this study validates the use of the English version of the questionnaire which may be utilized by those who prefer the use of the English language which is especially seen among the urban population of Malaysia.